Freshwater Fishes
of North-Eastern Australia
Freshwater Fishes
of North-Eastern Australia
Brad Pusey, Mark Kennard and Angela Arthington
Centre for Riverine Landscapes, Griffith University
Nathan, Qld 4111, Australia
Text © 2004 Brad Pusey, Mark Kennard, Angela Arthington and the Rainforest CRC
Illustrations © 2004 B.J. Pusey
All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any
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copyright owners. Contact CSIRO PUBLISHING for all permission requests.
National Library of Australia Cataloguing-in-Publication entry
Pusey, Bradley J.
Freshwater fishes of north-eastern Australia.
Bibliography.
Includes index.
ISBN 0 643 06966 6 (hardback).
ISBN 0 643 09208 0 (netLibrary eBook).
1. Freshwater fishes – Australia, North-eastern.
2. Freshwater fishes – Australia, North-eastern Identification. 3. Freshwater ecology – Australia,
North-eastern. I. Kennard, Mark J. II. Arthington, Angela H.
III. Title.
597.1760994
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Front cover
Hephaestus tulliensis (khaki grunter), photograph by G.R. Allen
Set in 9.5 Minion
Cover design by Jo Waide
Text design by James Kelly
Typeset by J & M Typesetting
Printed in Australia by Ligare
To my parents Pat and Jim (dec.) for fostering a love of natural history,
and to my family, Moira, Michael and Olivia for their support and tolerance
B.J.P.
To my loving partner Lorann and chiens lunatiques Saśa and Max,
for happy diversions and indulgences, and to my family, especially Jill and Colin,
for inspiration and encouragement
M.J.K.
To my New Zealand family and to Mark, Kirstie, Ayden, Huntley and Liveya,
for their enduring love and encouragement
A.H.A.
Foreword
This book is the end product of the authors’ extensive
research on the ecology and flow requirements of fishes in
Queensland rivers. Production of the book has been a
major initiative of the Co-operative Research Centre for
Tropical Rainforest Ecology and Management (Rainforest
CRC) via its fundamental research on biodiversity in the
Wet Tropics region, and the CRC’s new Catchment to Reef
research program. The Rainforest CRC and the Centre for
Riverine Landscapes, Griffith University, have subsidised
production of the book and worked together with the
publishers, CSIRO Publishing, to achieve its high standard
of presentation.
North-eastern Australia contains over 130 native species of
freshwater fish which is approximately half of the freshwater fish fauna of the entire continent. This fauna is of great
interest for its diversity, scientific importance and value.
Many species occurring in this region also extend westward across much of northern Australia and southward
through coastal New South Wales, Victoria, South
Australia and Tasmania. This makes the book of singular
importance as the only text covering the freshwater fishes
of this vast region in the richness of detail presented here.
The value of this baseline work is potentially enormous.
Tropical Australia faces a number of serious problems
directly stressing the environment we value so highly.
There is increasing demand for water for agriculture and
for urban use and we are likely to see our water resources
further stressed by increasing climatic variability – one of
the likely results of global climate change. There is also
international concern about runoff from catchments causing a decline in the health of the Great Barrier Reef and its
feeder streams. Fish are important indicators of ecosystem
health and this book provides the sort of detailed information needed for a monitoring toolkit that can be used at
the stream level by community groups, farmers and scientists concerned with these issues. We continue to lead the
tropical world in these fields of science and application.
On behalf of the Rainforest CRC and Griffith University, I
congratulate the authors on their dedicated efforts in
producing this significant contribution to knowledge, and
commend the book as an indispensable compendium,
catalogue and baseline reference for anyone with a keen
interest in this fascinating component of Australia’s unique
biodiversity.
Nigel Stork
CEO, Rainforest CRC
Cairns, Queensland
February 2004
vii
Table of contents
Foreword
vii
Acknowledgements
xiii
Introduction
1
Origins, structure and classification of fishes
3
Key to the native and alien fishes of north-eastern Australia
14
Study area, data collection, analysis and presentation
26
Ceratodontidae
Neoceratodus forsteri – Queensland lungfish
49
Osteoglossidae
Scleropages leichardti – Saratoga
60
Megalopidae
Megalops cyprinoides – Tarpon
64
Anguillidae
Anguilla australis, Anguilla obscura, Anguilla reinhardtii – Eels
71
Clupeidae
Nematalosa erebi – Bony bream
92
Ariidae
Arius graeffei, Arius leptaspis, Arius midgleyi – Fork-tailed catfishes
102
Plotosidae
Neosilurus hyrtlii – Hyrtl’s tandan
Neosilurus ater – Black catfish
Neosilurus mollespiculum – Soft-spined catfish
Porochilus rendahli – Rendahl’s catfish
Tandanus tandanus – Eel-tailed catfish
112
121
129
133
137
Retropinnidae
Retropinna semoni – Australian smelt
152
Hemiramphidae
Arrhamphus sclerolepis – Snub-nosed garfish
161
Belonidae
Strongylura krefftii – Freshwater longtom
166
Atherinidae
Craterocephalus marjoriae – Marjorie’s hardyhead
Craterocephalus stercusmuscarum – Fly-specked hardyhead
171
180
Melanotaeniidae
Rhadinocentrus ornatus – Ornate rainbowfish
Cairnsichthys rhombosomoides – Cairns rainbowfish
Melanotaenia splendida – Eastern rainbowfish
Melanotaenia duboulayi – Duboulay’s rainbowfish
Melanotaenia eachamensis – Lake Eacham rainbowfish
197
205
211
221
231
ix
Melanotaenia utcheesis – Utchee Creek rainbowfish
Melanotaenia maccullochi – MacCulloch’s rainbowfish
237
242
Pseudomugilidae
Pseudomugil mellis – Honey blue-eye
Pseudomugil signifer – Pacific blue-eye
Pseudomugil gertrudae – Spotted blue-eye
247
254
269
Synbranchidae
Ophisternon gutturale, Ophisternon spp.? – One-gilled swamp eels
272
Scorpaenidae
Notesthes robusta – Bullrout
278
Chandidae
Ambassis agrammus – Sailfin glassfish
Ambassis agassizii – Agassiz’s glassfish
Ambassis macleayi – Macleay’s glassfish
Ambassis miops – Flag-tailed glassfish
Denariusa bandata – Pennyfish
284
292
302
306
309
Centropomidae
Lates calcarifer – Barramundi
313
Percichthyidae
Macquaria ambigua, Macquaria sp. B – Yellowbelly
Macquaria novemaculeata – Australian bass
Guyu wujalwujalensis – Bloomfield River cod
Maccullochella peelii mariensis – Mary River cod
Nannoperca oxleyana – Oxleyan pygmy perch
326
337
345
348
353
Terapontidae
Amniataba percoides – Barred grunter
Leiopotherapon unicolor – Spangled perch
Hephaestus fuliginosus – Sooty grunter
Hephaestus tulliensis – Khaki bream, Tully grunter
Scortum parviceps – Small-headed grunter
361
369
378
390
395
Kuhliidae
Kuhlia rupestris – Jungle perch
401
Apogonidae
Glossamia aprion – Mouth almighty
409
Toxotidae
Toxotes chatareus – Seven-spot archerfish
419
Mugilidae
Mugil cephalus – Sea mullet
426
Gobiidae
Glossogobius sp. 1 – False Celebes goby
Glossogobius aureus, Glossogobius giuris – Golden goby, Flathead goby
Glossogobius sp. 4 – Mulgrave River goby
Redigobius bikolanus – Speckled goby
Awaous acritosus – Roman-nosed goby
Mugilogobius notospilus – Pacific mangrove goby
Schismatogobius sp. – Scaleless goby
434
440
445
449
456
461
465
x
Eleotridae
Eleotris fusca, Eleotris melanosoma – Brown gudgeon, Ebony gudgeon
Bunaka gyrinoides – Greenback gauvina
Oxyeleotris lineolatus, Oxyeleotris selheimi – Sleepy cod, Striped sleepy cod
Oxyeleotris aruensis – Aru gudgeon
Giurus margaritacea – Snakehead gudgeon
Hypseleotris compressa – Empire gudgeon
Hypseleotris galii, Hypseleotris sp. 1 – Firetailed gudgeon, Midgley’s carp gudgeon
Hypseleotris klunzingeri – Western carp gudgeon
Gobiomorphus australis – Striped gudgeon
Gobiomorphus coxii – Cox’s gudgeon
Mogurnda adspersa, Mogurnda mogurnda – Purple-spotted gudgeon,
Northern trout gudgeon
Philypnodon grandiceps – Flathead gudgeon
Philypnodon sp. – Dwarf flathead gudgeon
468
473
477
487
491
498
510
521
530
538
544
558
568
Conclusion: prospects, threats and information gaps
575
Glossary of terms used in the text
585
Bibliography
601
Appendix 1: Fish species composition in rivers of north-eastern Australia
655
Appendix 2: Studies undertaken in rivers of north-eastern Australia
674
Index
681
xi
Acknowledgements
Department of Primary Industries, Fisheries), South East
Queensland Water Board, South East Queensland Water
Corporation, and the Wet Tropics Management Authority.
This book is a product of our research on the ecology and
flow requirements of fishes in Queensland rivers, amply
funded by the former Land and Water Resources Research
and Development Corporation (LWRRDC, now Land and
Water Australia), and generously supported by the former
Queensland Water Resources Commission, and former
Queensland Department of Primary Industries, Land Use
and Fisheries Branch (now Queensland Departments of
Natural Resources, Mines and Energy, and Queensland
Department of Primary Industries, Fisheries, respectively),
and Griffith University. Funding from the Co-operative
Research Centre for Tropical Rainforest Ecology and
Management (Rainforest CRC) supported our research,
and the Rainforest CRC and the Centre for Riverine
Landscapes, Griffith University, have subsidised this book
to make it more affordable. Professor Nigel Stork, Chief
Executive Officer of the Rainforest CRC and Jann O’Keefe
sought publication outlets for the book and negotiated our
contract with CSIRO Publishing. We sincerely thank Nigel
and the Rainforest CRC for supporting our research and
writing.
We also wish to thank all government agencies and agency
staff (e.g. rangers) and the numerous landholders and
aboriginal communities who allowed us access to field
sites, supported our work and shared their knowledge and
insights.
The following colleagues, friends and family members
have assisted in the field and in the laboratory - we are
deeply indebted to one and all: Steven Balcombe, Mark
Bensink, Jason Bird, David Blühdorn, Stacey Braun, Stuart
Bunn, Peter Buosi, Damien Burrows, Harry Burton, Brian
Bycroft, Hiram Caton, Nick Cilento, Paul Close, Dan
Clowes, Diane Conrick, Anthony Cutten, Felicity Cutten,
Huntly Cutten, Ellie Dore, Ashley Druve, Susan Dunlop,
John Endler, John Esdaile, Simon Hamlet, Debbie
Harrison, Karen Hedstrom, Alf Hogan, Peter James,
Daniel Kennard, Paul Kennard, Alex Langley, Matthew
Langworthy, Greg Lee, Bill Macfarlane, Stephen Mackay,
Nick Marsh, Chris Marshall, Jonathan Marshall, Peter
Mather, Greg Miller, John Mullen, Carl Murray, Peter
Negus, Richard Pearson, John Peeters, Tony Pusey, Martin
Read, Darren Renouf, Andrew Sheldon, Michael Smith,
Errol Stock, Brian Stockwell, Celia Thompson, Chris
Thompson, Rob Wager, Richard Ward, Selina Ward, Tony
Watson, Gary Werren, Rob Williams and Tim Wrigley.
Preparation of this book has entailed a major review of
existing literature and collation of the results of unpublished field research undertaken by the authors in freshwater systems throughout Queensland over the last 20 years.
Many people and institutions have assisted with this
research or provided funding support, in-kind resources,
data and advice. We particularly wish to thank many institutions and individuals for their commitment to the study
of freshwater fishes in Australia.
Sincere thanks are due to the following for stimulating
discussions on the ecology of freshwater fish and for provision of literature, reports and data, access to specimens of
fish species and identification of specimens, including fish
parasites: Gerry Allen, John Amprimo, Steven Balcombe,
Chris Barlow, Andrew Berghuis, Eldridge Birmingham,
Steve Brooks, Culum Brown, Damien Burrows, Niall
Connolly, Brendan Ebner, Craig Franklyn, Gary
Grossman, Jeff Gunston and Bruce Hansen and many
others from the Australia New Guinea Fishes Association,
Michael Hammer, Gene Helfman, Brett Herbert, Alf
Hogan, Jane Hughes, Paul Humphries, David Hurwood,
Michael Hutchison, Inter-Library Loans staff at Griffith
University, Peter Jackson, Jeff Johnson, Peter Johnston,
Peter Kind, John Koehn, Helen Larson, Keith Lewis, Mark
Lintermans, Chris Lupton, Roland Mackay, Chris
Marshall, Jonathan Marshall, Mark McGrouther, Craig
Moritz, Richard Pearson, Colton Perna, Claire Peterkin,
Phil Price, Tyson Roberts, John Ruffini, John Russell,
First, we gratefully acknowledge research grants and inkind support from the following agencies: Australian
Nature Conservation Agency, Australian National Parks
and Wildlife Service, Australian Water Research Advisory
Council, Co-operative Research Centre for Rainforest
Ecology and Management, Co-operative Research Centre
for Freshwater Ecology, Co-operative Research Centre for
Sustainable Tourism, Land and Water Resources Research
and Development Corporation, Moreton Bay Waterways
and Catchments Partnership, Queensland Department of
Environment and Heritage, Queensland Department
of Natural Resources, Mines and Energy, Queensland
Department of Primary Industries (Fisheries), Queensland
Environmental Protection Agency, Queensland National
Parks and Wildlife Service, Queensland Water Resources
Commission, Walkamin Research Station (Queensland
xiii
Nick Schofield, Clayton Sharpe, Bob Simpson, Jim Tait,
Rob Wager, John Ward, Alan Webb, Peter Unmack and
Tom Vanderbyll.
acknowledge Mariola Hoffmann for preparing the maps
presented in this book. We thank Elly Scheermeyer, Fiona
McKenzie-Smith and Darren Renouf for assistance with
references. We are also grateful to Maria Barrett, Petney
Dickson, Jason Elsmore, Daina Garklavs, Keith Officer,
Lacey Shaw, Deslie Smith, Stuart Taylor and many other
staff at Griffith University for administrative support and
the various tasks that supported the production of this
book. We apologise to anyone we have neglected to thank.
We warmly thank the following colleagues for reading and
commenting on various chapters: Culum Brown, Damien
Burrows, John Endler, Alf Hogan, Helen Larson, Steven
Mackay, Chris Marshall, Jonathan Marshall, Dugald
McGlashan, Colton Perna, Tarmo Raadik, John Russell,
Alisha Steward and Jim Tait. This book would no doubt
have benefited from further expert feedback from other
colleagues; unfortunately, time constraints precluded this.
Finally, we are indebted to CSIRO Publishing for taking on
our book and are particularly grateful to Nick Alexander
for his support throughout its production and to Briana
Elwood for assistance with formatting and editing considerations.
We appreciate the assistance of Aubrey Chandica and
Paul Martin with the provision of maps and gratefully
xiv
Introduction
flowing coastal rivers of Queensland and northern New
South Wales, although the range of many extends westward across much of northern Australia and southward
through coastal Victoria, South Australia and Tasmania.
North-eastern Australia contains the most diverse freshwater fish fauna in all of Australia, over 130 native species
in about 30 families, approximately half of the fauna of the
entire continent. This fauna includes some of the most
ancient species in Australia – the Queensland lungfish,
Neoceratodus forsteri, and the saratoga, Scleropages
leichardti – as well as one of the most recently discovered
Australian freshwater fish species, the Bloomfield River
cod, Guyu wujalwujalensis, found far to the north of its
nearest relatives, the cods and basses of south-eastern and
south-western Australia. In addition to these freshwater
fishes, the freshwater reaches of north-eastern Australian
rivers support many species from otherwise marine or
estuarine families, such as the Lutjanidae, Carangidae,
Gerreidae, Scatophagidae, and even sharks and stingrays (Carcharhinidae and Dasyatidae, respectively).
Unfortunately, five families (Belontiidae, Cichlidae,
Cobitidae, Cyprinidae and Poeciliidae) and at least 23
species of alien fishes have been introduced into freshwater systems of north-eastern Australia, many of which have
established self-sustaining populations, or may soon do so.
Attempts to establish other families alien to the continent
(e.g. Salmonidae) have so far failed in Queensland freshwaters. This book does not treat these two groups of
species in any detail as there is very little information on
the ecology of marine or estuarine vagrants in freshwaters,
and in the case of alien species, major reviews of their
distribution and ecology are currently being written by
others. We are here primarily concerned with the native
freshwater fishes occurring in easterly flowing drainages of
the Australian drainage division known as the North-east
Coast Division (Drainage I) as defined by the Queensland
Department of Natural Resources, Mines and Energy (see
Figure 1 in the section describing the study area). Species
found only in rivers draining into the Gulf of Carpentaria
and those occurring in Queensland sections of inland
systems draining central and southern Australian (Lake
Eyre, Bulloo-Bancannia and Murray-Darling drainage
divisions) are not fully covered here. Our reasons for
restricting the number of species covered are threefold: 1)
the fauna of this drainage division is currently most at risk
from human activities, 2) it is the fauna we know best and
that which we have examined in detail or for which a
substantial literature base exists, and 3) species omitted
from this treatment are covered to lesser or greater extents
in existing texts on Australian freshwater fishes. The 79
species covered in this book generally occur in easterly
The aim of this book is to provide information on the
freshwater fish fauna of north-eastern Australia in a format
that is rich in detail yet readily accessible to ecologists,
ichthyologists, environmental managers and consultants,
fishermen, hobbyists and the general public. Our treatment takes the reader on a journey – from a description of
each species, and an account of its taxonomy, systematics
and evolutionary history, biogeography, distribution
patterns and abundance – to its macro-, meso- and microhabitat requirements, environmental tolerances, reproductive biology and development, movement biology and
feeding ecology. We provide a pen and ink drawing of each
species to illustrate characters for identification, an illustrated key to native and alien species and many figures and
tables summarising detailed quantitative ecological information. Each chapter concludes with an account of the
conservation status of the species, current threats, knowledge gaps and management issues.
The increasing pace of development in north-eastern
Australia, particularly agricultural and water resource
development, currently places severe pressure on the
region’s aquatic environment and biota, including fish.
Although initiatives such as the Water Resource Planning
process in Queensland, and the move towards regional
Natural Resource Management Plans and conservation
strategies, are intended to minimise the impacts of increasing development, these efforts are placing increasing
demands on scientists and practitioners to provide high
quality ecological assessments and technical advice.
Managers, scientists and the public urgently need reliable
quantitative information upon which to base conservation
priorities, management strategies and monitoring protocols. Our coverage of the freshwater fish fauna of northeastern Australia is intended to support and strengthen
these planning initiatives, to foster the application of scientific principles and sound ecological data in the management of Queensland aquatic ecosystems, and in
consequence, to afford a high degree of protection to the
region’s unique fish fauna.
Several excellent books published in the last 25 years deal
with the freshwater fish fauna of Australia (Merrick and
Schmida (1984), Australian Freshwater Fish: Biology and
1
Freshwater Fishes of North-Eastern Australia
information they contain. All deal most comprehensively
with the fauna of southern Australia, an emphasis reflecting the amount of information available at the time of
production. Allen et al. (2002) [52] is a welcome and excellent addition particularly with regard to nomenclature, but
its field guide format necessarily limits the amount of
scientific detail on many topics needed for effective
management of the fish of north-eastern Australia. The
present treatment aims to complement these texts by
providing reference material in a standard format that is
both up-to-date and comprehensive, including published
material (some dating back over 100 years but still relevant) and unpublished documents (government and
consultancy reports, University theses) as well as the
authors’ extensive published information and unpublished
data sets.
Management [936]; Allen (1989), Freshwater Fishes of
Australia [34]; and Allen et al. (2002), Field Guide to the
Freshwater Fishes of Australia [52]). Other texts cover in
varying detail the fauna of individual regions (Allen
(1982), A Field Guide to the Inland Fishes of Western
Australia [33]; Larson and Martin (1989), Freshwater
Fishes of the Northern Territory [774]; Bishop et al. (2001),
Ecological Studies on the Freshwater Fishes of the Alligator
Rivers Region, Northern Territory: Autecology [193];
Herbert and Peeters (1995), Freshwater Fishes of Far North
Queensland [569]; McDowall (1996), Freshwater Fishes of
South-eastern Australia (2nd Ed.) [884]; Cadwallader and
Backhouse (1983), A Guide to the Freshwater Fish of
Victoria [270]; Koehn and O’Connor (1990), Biological
Information for Management of Native Fish in Victoria
[732]; Wager and Unmack (2000), Fishes of the Lake Eyre
Catchment of Central Australia [1354]; Moffat and Voller
(2002), Fish and Fish Habitat of the Queensland MurrayDarling Basin [959]), or selected components (Allen
(1995), Rainbowfishes in Nature and in the Aquarium
[38]).
We hope that this book will encourage greater research
effort on the region’s fish fauna and provide a comprehensive information resource allowing other researchers to
adopt a more quantitative and strategic framework for
their research. We have endeavoured to identify knowledge
gaps where they exist and suggest promising new avenues
for research. We also hope that this book will have wide
general interest and that readers will find this component
of Australia’s unique fauna as interesting as we do.
Several books [34, 884, 936] have become the ‘standard’
reference texts for Australian freshwater fishes and essential research tools for many aquatic biologists, yet are
now somewhat out of date, and limited in the amount of
2
Origins, structure and classification of fishes
The origin of fishes
The bony fishes (Class Osteichthys) are the most successful
and diverse group of vertebrates on Earth. Three major
groups or subclasses make up the Osteichthys: the rayfinned fishes (Actinopterygii), the lungfishes (Dipnoi) and
the predatory lobe-finned fishes (Crossopterygii). The
Actinopterygii are the most speciose group of living fishes,
containing more than 23 000 species, whereas the Dipnoi
is restricted to four species in three genera: Lepidosiren
from South America (1 species), Protopterus from Africa (2
species) and Neoceratodus from Australia (1 species). The
subclass Crossopterygii is restricted to a single species
Latimeria chalumnae, the coelocanth. (Some classification
schemes group the Dipnoi and the Crossopterygii within a
single subclass, the Sarcopterygii.)
and diversification during the Devonian period, similar to
that observed in the Dipnoi and Crossopterygii. These
early fishes, the palaeoniscoids, were characterised by a
long slender body, a large mouth gape with many small
teeth, small scales and a poorly ossified axial skeleton. By
the end of the Devonian however, the mouth gape had
shortened, the opercula bones had enlarged and the
micromeric scales characteristic of early palaeoniscoids
had been replaced by larger, rhombic scales. Over 40 separate families of palaeoniscoid fishes had evolved by the
Permian period (250–290 m.y.b.p.).
Actinopterygian evolution had given rise to the neopterygian fishes (to which belong the teleost fishes) by the end
of the Permian. These fishes are characterised by a vertical
suspensorium (where the lower jaws articulate with the
upper jaws by a vertically oriented quadrate bone), free
cheek bones, the condition where the dorsal and anal fin
rays are supported by an equal number of small bones,
fusion of the upper jaw bones along the midline and the
development of pharyngeal tooth plates. The first
teleostean fish evolved in the Triassic period (205–250
m.y.b.p.). These fishes are characterised by the presence of
uroneurals (small bones that stiffen the dorsal lobe of the
tail and support a series of dorsal fin rays), free movement
of the premaxilla independent of the maxilla and development of unpaired toothplates on the basibranchials. These
changes in jaw structure resulted in the evolution of a
protrusible mouth, which when coupled with the previous
change in the suspensorium, allowed huge diversification
in feeding mode. Changes in fin structure (possession of
rays and of uroneurals) greatly enhanced mobility and
manoeuvrability. Thus, the stage was set for the explosive
radiation evident in the extant teleost fishes. Many of the
modern groups of teleost fishes, at the family level, had
appeared by the Eocene period (45–57 m.y.b.p.) [820].
The evolutionary history of the bony fishes is described by
John Long [820] and is very briefly summarised here. The
origins of the Osteichthys date back to the Late Silurian
(approximately 410 million years before present), a time
when the seas were dominated by the Chondrichthyes
(sharks and rays), Acanthodii (spiny-finned fishes) and
especially Placodermi (armour-plated fishes). The Dipnoi
originally arose in marine environments during the
Devonian (355–410 m.y.b.p.), but have been confined to
freshwaters since the early Carboniferous (~340 m.y.b.p.).
The Dipnoi experienced a very rapid rate of evolutionary
change during the Devonian and early Carboniferous periods, resulting in the evolution of many different species.
During this period, there was a transition from gill-respiration to lung-assisted respiration and a transition from a
shredding to a crushing feeding mode. In addition, there
also occurred a change from the possession of two equallysized dorsal fins, separate anal fin and heterocercal caudal
fin to the possession of a shortened first dorsal fin and
merged second dorsal, caudal and anal fins (the condition
observed today). Fossils of Neoceratodus forsteri, the
Queensland lungfish, indicate that it has persisted in its
present form for over 100 million years.
The origin of Australia’s freshwater fishes
Australia’s freshwater fishes include both primary freshwater species (entire evolutionary history restricted to freshwater) and secondary freshwater species (freshwater forms
secondarily derived from marine stocks). However, unlike
other parts of the world, Australia has few primary freshwater fishes. These include N. forsteri, Scleropages jardinii,
S. leichardti and Lepidogalaxias salamandroides, and possibly members of the Galaxiidae and Retropinnidae [888,
936]. These fish may have ancient Gondwanan origins. For
example, fossils of Neoceratodus species have been found
The Crossopterygii also arose during the Devonian. This
group of predatory fishes experienced rapid diversification
during this period, especially during the Carboniferous,
and persisted throughout the Mesozoic era (250–135
m.y.b.p.). Some crossopterygiian species reached an estimated size of 6–7m.
The Actinopterygii (ray-finned fishes) first appear in the
Late Silurian fossil record followed by significant radiation
3
Freshwater Fishes of North-Eastern Australia
in Cretaceous deposits in Australia and South America
[52]. Similarly, the presence of bony-tongued fishes
(Osteoglossidae, the saratogas) in South America, Africa,
South-east Asia and Australia–New Guinea suggests that
the origins of this family also predate the fragmentation of
Gondwanaland [820]. Other families with a possible
Gondwanan origin include the Retropinidae,
Prototroctidae, Galaxiidae, Aplochitonidae and
Percichthyidae [888, 936]. These families are predominantly restricted to the southern half of the Australian
continent and are mostly inhabitants of cooler waters. The
presence of the percichthyid Guyu wujalwujalensis, a
possible Cretaceous relic [1091], in the Wet Tropics region,
and of Macquaria species in the Fitzroy River basin and
drainages of central Australia [52], suggests that these
southern Gondwanan elements may have once been more
widespread on the Australian continent.
with increasing latitude is less apparent, and spatial variation in species richness (at the basin level) is best explained
by variation in the magnitude of mean annual discharge
and seasonality/perenniality of the flow regime. More
species occur in rivers with large mean annual discharge
(which is not simply a function of catchment size) and less
species occur in rivers with a highly seasonal flow regime
[1093]. Second, Unmack [1340] observed that the extent
of endemism (the unique occurrence of a species in a
single region) varies across Australia, being greatest in
western (east and west Kimberley, Pilbara and south-western Western Australia), southern (south-western Victoria
and southern Tasmania) and central (Lake Eyre Basin and
Murray-Darling Basin) regions. The only region east of
these regions for which endemism is high is north-eastern
Queensland, which includes the Wet Tropics region.
Unmack’s analysis revealed a surprisingly high level of
endemism in the fauna; 47% of the Australian fauna
occurred in one region only. Third, classification analysis
of regional variation in faunal composition divided the
fauna into two major groups, basically equating to northern and southern Australia. The Fitzroy River south to the
Queensland border was included in the southern group.
The northern Australian group, excluding the arid central
regions (Bulloo, Lake Eyre and Barkley Tablelands),
divided into a cluster containing regions (Burdekin,
north-eastern Queensland and southern Cape York
Peninsula) located to the east of the Great Dividing Range
and a larger cluster located to the west.
The majority of Australia’s freshwater fishes are secondary
freshwater species derived from marine ancestors with
tropical Indo-Pacific affinities [1409]. Some authors
suggest that this component of the fauna is evolutionarily
young and that colonisation of the Australian continent by
marine ancestors probably occurred in the last 10 million
years or so (a late Miocene origin at maximum) [52, 936,
1409]. However, others have suggested a more extended
occupation of the Australian continent by some families.
For example, Vari [1346] postulated that ancestral
terapontid grunters may have populated the northern
shores of the Gondwanan supercontinent. Crowley [343]
suggested that freshwater invasion of Australian freshwaters by craterocephalid hardyheads occurred during the
Cretaceous or Palaeocene (>60 million y.b.p.). Families
typical of northern Australia and New Guinea such the
Ariidae, Plotosidae, Terapontidae and Eleotridae have
undergone substantial speciation in freshwater environments, yet elsewhere are almost entirely marine or estuarine. Freshwater habitats on the Australian continent have
undergone enormous change during the period over
which the teleost fishes arose, including several marine
transgressions as well as changes in climate and periodic
aridity. Undoubtedly such events have led to extinctions of
freshwater fish species and opened the way for colonisation of freshwater habitats by estuarine fishes.
Unmack’s [1340] analysis of the biogeography of
Australia’s freshwater fishes was restricted to freshwater
fishes that complete their entire life history in freshwater
(a definition more restricted than that used in this book).
As a consequence, many diadromous species with an estuarine or marine interval in the life history, such as eels and
many gudgeons or gobies, were not included. Their inclusion does not alter the broad outcomes of Unmack’s study
however, except to perhaps emphasize the distinctiveness
of those rivers draining east of the Great Dividing Range
[1093]. Rivers of northern Australia tend to have more
such species than do rivers of southern Australia.
Moreover, a catadromous reproductive strategy (i.e.
migration out of freshwaters to breed) is common in
northern Australian fishes. Cappo et al. [278] suggested
that the higher water temperatures of northern Australian
rivers may confer a metabolic advantage to euryhaline
species enabling more efficient osmoregulation. Gross et
al. [481] examined global trends in diadromy and found
catadromy to dominate in tropical regions and anadromy
to dominate in temperate regions. They proposed such a
pattern to be driven by latitudinal differences in the relative productivity of freshwater and marine habitats. In
Unmack [1340] recently examined the biogeography of
Australia’s freshwater fishes and the major features of that
analysis are summarised below. First, species richness
decreases significantly with latitude, echoing a general
global trend for greater freshwater fish diversity in tropical
regions [1007, 1057]. In addition to this gradient, arid
regions are less speciose. A more recent analysis of biogeographical patterns in north-eastern Australia by Pusey et
al. [1093], revealed that the trend of decreasing diversity
4
Origins, structure and classification of fishes
SUPERORDER Acanthopterygii
ORDER Perciformes
SUBORDER Percoidei
FAMILY Terapontidae
GENUS Hephaestus
SPECIES Hephaestus fuliginosus (Macleay, 1883)
tropical areas, the productivity of freshwater systems
exceeds that of marine systems.
The classification of fishes
All living organisms are related to one another in some
way, either closely as in the case of species within genera,
or distantly as in the case of species within different phyla.
Classification systems seek to organise a naming system
that reflects this degree of relatedness. Ideally, such a
system should reflect evolutionary history.
Some of these groups may be further subdivided. For
example, the Cairns rainbowfish Cairnsichthys rhombosomoides is placed with the tribe or clade Bedotiini, within
the subfamily Melanotaeniinae, within the family
Melanotaeniidae. Subgenera may also be designated (e.g.
the subgenus Chonophorus in the genus Awaous). Species
may often be divided into subspecies (e.g. the various
subspecies of Melanotaenia splendida such as
Melanotaenia splendida splendida and Melanotaenia splendida inornata).
Classification systems have been in existence for millennia. The famous 19th century anatomist Georges Cuvier
provides a fascinating account of the early development of
fish classification from the time of the ancient Egyptians,
to early Greek natural philosophers such as Aristotle, to
the European naturalists of the 16th and 17th century such
as Guillaume Rondelet and Hippolyte Salviani [354].
Indeed, natural classification schemes have probably
existed since the development of human language and
possibly reflected similarities in edibility, gross form and
risk of injury to the hunter or gatherer. However, early
classification schemes often poorly reflected the relationships between organisms. For example, the cetaceans
(whales, dolphins etc.) were included with fishes in most
classification systems well into the middle of the 17th
century [354].
Note that in the sooty grunter example listed above, the
species name is followed by the name of the authority that
first described this species, and the date in which this
occurred. In the case of H. fuliginosus, the name and date
are enclosed within parentheses. This is a nomenclatural
convention to denote that this species was first described
under another name (Therapon fuliginosus) and that the
present name was allocated following a revision of the
species. The authority and date are not enclosed in parentheses when the original name stands unaltered.
Peter Artedi, a Swedish natural philospher of the early 18th
century, attempted a consistent ichthyological classification scheme, building on the work of the English natural
philosophers John Ray and Francis Willughby. Artedi’s
scheme, based on the consistency of the skeleton, the opercula and the fin rays, was published in his 1738 treatise
Ichthyologia, sive Opera omnia de piscibus (edited and
published posthumously by his friend Carolus Linnaeus
following Artedi’s death by drowning in an Amsterdam
canal after a night of socialising at the age of 30).
Linnaeus’s most significant achievement was to formalise
a system of natural classification within a system of binomial nomenclature. In this system, closely related species
were arranged within genera and closely related genera
were arranged within families, and so on. It is a hierarchical system reflecting different degrees of relatedness and is
the system we use today (with some modification and
addition). Below is an example of a full classification for a
common north-eastern Australian fish, the sooty grunter.
The freshwater fishes (including alien species) of northeastern Australia can be arranged in the following classification scheme (to family level only). This classification is
based largely on that provided by Paxton and Eschmeyer
[1041], and Long [820].
PHYLUM CHORDATA
SUPERCLASS AGNATHA (JAWLESS FISHES)
CLASS CEPHALASPIDOMORPHA
Order Petromyzontiformes
Mordaciidae (Shorthead lampreys)
SUPERCLASS GNATHOSTOMATA (JAWED FISHES)
CLASS OSTEICHTHYES (BONY FISHES)
SUBCLASS DIPNOI
Order Ceratodontiformes
Ceratodontidae (lungfish)
SUBCLASS ACTINOPTERYGII (RAY-FINNED FISHES)
INFRACLASS NEOPTERYGII
DIVISION TELEOSTEI
Subdivision Osteoglossomorpha
Order Osteoglossiformes
Suborder Osteoglossoidei
Osteoglossidae (saratoga)
Subdivision Elopomorpha
Order Elopiformes
Megalopidae (tarpon)
PHYLUM Chordata
SUBPHYLUM Gnathostomata
CLASS Osteichthys
SUBCLASS Actinopterygii
INFRACLASS Neopterygii
DIVISION Euteleostei
5
Freshwater Fishes of North-Eastern Australia
Eleotridae (gudgeons)
Suborder Anabantoidei
Belontiidae (gouramis – alien)
Order Pleuronectiformes
Suborder Soleoidei
Soleidae (soles)
Order Angulliformes
Suborder Saccopharyngidae
Anguillidae (eels)
Subdivision Clupeomorpha
Order Clupeiformes
Suborder Clupeoidei
Clupeidae (herrings)
Engraulididae (anchovies)
Subdivision Euteleostei
Order Cypriniformes
Cyprinidae (carp – alien)
Cobitidae (loaches – alien)
Order Siluriformes
Ariidae (fork-tailed catfishes)
Plotosidae (eel-tailed catfishes)
Order Salmoniformes
Suborder Osmeroidei
Retropinnidae (smelts)
Galaxiidae (galaxiids)
Order Cyprinodontiformes
Suborder Cyprinodontoidei
Poeciliidae (topminnows – alien)
Order Beloniformes
Suborder Exoceotoidei
Hemiramphidae (halfbeaks)
Belonidae (longtoms, needlefish)
Order Atheriniformes
Suborder Atherinoidei
Atherinidae (hardyheads)
Melanotaeniidae (rainbowfishes)
Pseudomugilidae (blue-eyes)
Order Synbranchiformes
Synbranchidae (swamp eels)
Order Scorpaeniformes
Suborder Scorpaenoidei
Scorpaenidae (stonefishes)
Order Perciformes
Suborder Percoidei
Chandidae (glassfishes)
Centropomidae (barramundi)
Percichthyidae (bass, pygmy perch)
Terapontidae (grunters)
Kuhliidae (flagtails)
Apogonidae (cardinal fishes)
Toxotidae (archerfish)
Kurtidae (nurseryfish)
Cichlidae (tilapia – alien)
Suborder Mugiloidei
Mugilidae (mullet)
Suborder Labroidei
Cichlidae (tilapia – alien)
Suborder Gobioidei
Gobiidae (gobies)
Modern classification schemes strive to reflect the evolutionary history of a group rather than the overall gross
similarity of taxa within a group. That is, they try to represent the phylogeny of that group. Therefore, species within
a genus should be derived from a common ancestor and
be more closely related to one another than to species in
another genus. When species share a character that is
derived (an apomorphic character) from a common
ancestor, that character is said to be synapomorphic.
Plesiomorphy, in contrast, refers to primitive characters.
For example, in the terapontid grunters, the plesiomorphic condition of the gut is one of simple structure with
no looping or coiling. The more derived condition is one
in which the intestine is composed of more than one loop.
Genera such as Hephaestus, Scortum, Pingalla and
Syncomistes all share the synapomorphy of a gut possessed
of at least six loops. Pingalla and Syncomistes both possess
a gut composed of 11 loops. Thus, the derived or synapomorphic condition in these two genera is 11 loops whereas
the plesiomorphic condition is six loops. Note that there
are different levels of apomorphy. Every level of apomorphy defines the temporal order of modification occurring
between the pre-existing (plesiomorphic) and emerging
(apomorphic) characters of the transformation [868].
Although modern classification schemes strive to reflect
the evolutionary history of a group, this is not always
achieved. Occasionally a species, or number of species, is
allocated to one genus by one researcher to be later found
more closely allied to another genus. For example, many of
the gudgeons of north-eastern Australia were first placed
in the ‘catch-all’ genus Eleotris but were later found to be
more properly placed within a larger number of genera.
Such a generic grouping is therefore unnatural and does
not accurately reflect the group’s evolutionary history. The
genus is therefore termed paraphyletic. Modern classification schemes strive to arrange species or genera (or any
level of classification) in monophyletic groups.
Classification schemes are constantly being reviewed and
changed as new evidence becomes available or when new
evidence is inconsistent with current views. The introduction of modern genetic techniques such as DNA sequencing has been of special significance in this regard.
6
Origins, structure and classification of fishes
soft-rayed dorsal fin
spinous dorsal fin
(second dorsal)
(first dorsal) dorsal spines
dorsal scale sheath
operculum
soft ray
dorsal filament
posterior nostril
adipose fin
anterior nostril
lateral line scales
premaxilla
caudal
or tail fin
pectoral fin
horizontal scale rows
barbel
papilla
maxilla
Figure 1.
pelvic fin
ventral scutes genital
papilla anal spines
caudal peduncle
anal fin
anal scale sheath
Basic external anatomy of a generalised bony fish.
Fish anatomy
The classification of fishes is largely based on their
anatomy. It is therefore necessary to have some understanding of the general anatomy and osteology of fishes in
order to identify and classify them in the field or laboratory and to understand, in many cases, their ecology.
Extreme diversity of form is a feature of the bony fishes
more than any other vertebrate group and no description
of a single species is adequate to convey all the morphological variation present within the group. Figure 1 illustrates
the basic external morphology of a generalised bony fish.
gill rakers
on upper limb
gill rakers
on lower limb
gill filaments
The head region is clearly distinct from the body and
distinguished by a bony gill covering termed the operculum. This structure covers the gill arches and gill filaments
that function predominantly in gas exchange between the
fish and its environment (Fig. 2). The gill arches are distinguished by a series of protrusions termed rakers on the
anterior face of the arch. In some species, these rakers are
long and flexible, in others they may be shortened and
reduced to transverse plates or ridges, whereas in others
they may be reduced to a series of papillae only. The gill
rakers may function as sieving apparati in filter feeding
species. Gill rakers may be confined to the first and second
arches only and the shape and number are useful characters for distinguishing between different species.
Figure 2.
The structure of a gill arch of a bony fish.
located on the snout and are distinguished by reference to
their relative anterior or posterior position. Sensory pores
connected by canals may be present on the head of many
fishes. Similarly, many fishes possess rows of sensory papillae or pit canal organs on the head, and these structures are
usually located above and below the eyes, and on the cheek
or preoperculum. Some fish possess barbels that aid in the
detection of food. The number, length and position of the
barbels are important characters used to distinguish
between species. Barbel placement and nomenclature are
shown in Figure 3.
The upper jaw is divided into two sections, the premaxilla
and the maxilla (Figs. 1 and 7). Two pairs of nostrils are
7
Freshwater Fishes of North-Eastern Australia
V–VII; I, 11–15, indicating that this species possesses five
to seven spines in the first dorsal fin and one spine and 11
to 15 soft rays in the second dorsal fin.
nasal barbel
maxillary barbel
The anal fin is located on the ventral midline posterior of
the anus. This fin may contain both spines and segmented
rays. The final medial fin is the caudal or tailfin. Spines are
absent from this fin and support is provided by a series of
bones associated with the terminal vertebrae and by the
fin rays (Fig. 4). The caudal fin may be of a variety of
different shapes. The most frequent caudal fin shapes are
illustrated in Figure 5.
inner mental barbel
outer mental barbel
epurals (3)
Figure 3.
catfish.
procurrent rays
uroneurals (2)
Barbel placement and nomenclature in a plotosid
fin rays
antepenultimate
vertebra
The shape, position and orientation of the mouth are all
useful characters for distinguishing between species.
Position is most frequently described as terminal (end of
the snout), supraterminal (upper surface of the end of the
snout) or subterminal (lower surface of the end of the
snout), often accompanied by descriptions of the angle of
the gape (i.e. straight or oblique). In addition, the relative
prominence of the upper and lower jaws is frequently used
as a distinguishing character.
penultimate
vertebra
urostyle
(ultimate vertebra)
hypurals (6)
Figure 4. Generalised diagram of the teleost caudal
skeleton. (Redrawn after Cailliett et al. [276].)
Two sets of paired fins, the pelvic and pectoral fins, are
present in most species. The pectoral fins are located in the
anterior third of the body whereas the location of the
pelvic fins may vary in position among species (and may
often be an important diagnostic character) but invariably
they are located in the anterior two-thirds of the body.
These paired fins possess bony segmented fin rays. In
many taxa, the first ray of the pelvic fin forms a thickened
spine. Three to four medial rayed fins are also present. The
first and second dorsal fins are located, as the name
suggests, on the midline of the dorsal surface. A second
dorsal fin is not present in some groups of fishes and, in
some groups, the first dorsal fin is deeply notched to give
the impression of two dorsal fins. A third fleshy adipose fin
may be present in some species. The first dorsal fin is
usually supported by a series of spines whereas the second
dorsal fin may contain both spines and segmented rays. In
the second dorsal, pectoral, pelvic and anal fins of some
species (e.g. Craterocephalus spp.), a single unsegmented
ray sometimes separates the fin spine and the segmented
rays. The unsegmented ray is counted together with the
segmented rays in this book. In taxonomic descriptions,
counts of the number of spines present are usually distinguished from fin ray counts by the use of Roman numerals
to denote spines. For example, the dorsal fin formula for
the Cairns rainbowfish Cairnsichthys rhombosomoides is
a
b
c
d
Figure 5. Common shapes of the caudal fin: a) rounded; b)
truncated; c) emarginate; d) forked.
8
Origins, structure and classification of fishes
actually exposed. In some species, the scales may extend
out as a sheath onto the dorsal and anal fins (Fig. 1). There
are two main types of scale: cycloid and ctenoid (Fig. 6).
Another common type of scale is termed the lateral line
scale. These scales have a small tube or canal on the surface
that allows water to flow through to the lateral line sensory
system. The number, position and type of lateral line scales
are important characters for distinguishing between
species. A fourth type of scale, the ganoid scale, which is
rhombic in shape, is present in some primitive teleosts
such as gars and sturgeons. As fish grow, the scales also
grow by increments of bony tissue. Daily increments
(circuli) are wide during periods of rapid growth and
narrow during periods of slow growth. Successive periods
of slow growth result in the narrow circuli being located in
close proximity to form a growth ring or annulus. These
periods of slow growth usually occur with a return
frequency of one year, hence the term annuli, and can thus
be used to age fish.
The external surface of many fishes is covered by a layer of
scales, each deeply embedded in the epidermis and overlapping one another so that only about 30% of the scale is
a
circuli
annulus
focus
ctenii
b
focus
Fish osteology
The principal components of the teleost skeleton are the
axial vertebral column and caudal fin, the head (consisting
of the cranium, upper and lower jaws and the gill coverings, which are comprised of the opercular bone series,
preopercular and branchiostegal rays), the paired pectoral
and pelvic fins, and the medial dorsal and anal fins
(Fig. 7).
Radii
Figure 6.
Teleost fish scales: a) cylocid; b) ctenoid.
lepidotrichia
pterygiophore
vertebra
neural spine
hypurals
pectoral fin
opercula bones
preoperculum
cranium
premaxila
dentary
maxilla
branchiostegal
rays
pectoral girdle
Figure 7.
haemal spine
pleural rib
pelvic
girdle pelvic fin
Skeleton of a generalised perciform teleost fish. (Redrawn after Norman [996].)
9
Freshwater Fishes of North-Eastern Australia
small part, to successive changes in the structure of the
suspensorium and separation of the previously fused
maxilla and premaxilla, coupled with changes in the
attachment points of the respective muscles [276].
The head is composed of many individual bones, either
fused to one another, or free (although connected by cartilage) and articulating against one another (Fig. 8). The
head can be divided into two separate components based
roughly on this distinction [276]. The skull is comprised
of the neurocranium (10–11 bones), the orbital region (19
bones, including the lachrymal), and the otic region (20
bones). These bones unite to form a solid housing to
contain the brain and associated sensory systems (i.e.
optic, olfactory and auditory systems), and the roof of the
upper jaw, as well as a point of attachment and articulation
for many of the bones within the branchiocranial series.
Finally, the last bony component of the branchiocranial
region is the opercular series. This series is comprised of
the operculum (large flat bones comprising most of the
gill cover), the interoperculum, and the suboperculum and
preoperculum (a large pair of bones anterior of the opercular bones that partially cover the hyomandubular and
carry elements of the lateral line canal).
The second major region of the branchiocranium is the
hyoid region, comprised of the unpaired glossohyal and
urohyal bones, the paired interhyals. epihyals and ceratohyal bones and the branchiostegal rays. These bones collectively comprise the back of the buccal cavity and the points
of attachment of the gill arches. Each gill arch is comprised
of five bones, the pharyngobranchial, epibranchial, ceratobranchial, hypobranchial and basibranchial, and collectively these arches form the third and final region, the
branchial series.
The branchiocranial series is composed of over 60 separate
bones organised into three distinct regions: the
oromandibular region, the hyoid region and the branchial
series. The oromandibular region is comprised of the
upper jaw, the lower jaw, the suspensorium and the opercular series. The 36 bones that comprise this region are all
paired (i.e. 18 pairs). The lower jaw is composed of two
large pairs of fused bones, the dentary and the angular (or
articular), a third pair of much smaller bones termed the
retroangulars, and a fourth pair of bones termed the
sesamoid angulars which are involved in the attachment of
the mandibular adductor muscles responsible for mouth
closure. The shape, size and orientation of these bones are
often useful in the identification of different species or
reveal the phylogenetic relationships between taxa.
hyomandibular
parietal
parasphenoid
sphenoid
endopterygoid
frontal
nasal
There are several bones in the teleost skull that may bear
teeth (Fig. 9). The structure, size, type, position and
arrangement of teeth are all important characters used to
distinguish between different species.
a
supraoccipital
exoccipital
premaxillary
maxillary
vomerine
post temporal
palatine
lachrymal
premaxilla
pharyngeal
mesopterygoidal
operculum
dentary
maxilla
first gill arch
suboperculum
articular
quadrate
circumorbital
interoperculum
preoperculum
metapterygoid
b
dentary
Figure 8. Superficial facial bones and suspensorium of a
generalised teleost fish. Note that many of the bones
mentioned in the text are covered or obscured by the
superficial bones depicted here. (Redrawn after Calliette
et al. [276] and Hildebrand [575].)
tongue
pharyngeal
basibranchial
(hyoid)
The lower jaw articulates against the suspensorium, a
series of pairs of bones comprised of the palatines,
endopterygoids,
metapterygoids,
ectopterygoids,
quadrates, symplectics and hyomandibulars. The phenomenal diversity and success of the teleost fishes is due, in no
Figure 9. Bones within the mouth or buccal cavity that may
bear teeth in bony fishes: a) upper jaw, b) lower jaw.
(Redrawn after Calliette [276].)
10
Origins, structure and classification of fishes
groups of fishes (e.g. synbranchid eels and percichthyid
perches, respectively). Pterygiophores form the base of the
two medial fins. They are imbedded in the epaxial (dorsolateral) and hypaxial (ventrolateral) musculature. At the
proximal end of each pterygiophore is a small bone termed
the basal against which the fin ray articulates. Each fin ray
is controlled by three similar sets of muscles, the erector,
depressor and inclinators, which control forward, backward and lateral movement, respectively. The caudal fin is
composed of modified terminal and preterminal vertebrae, which support and strengthen the caudal fin (Fig. 4).
In many teleosts, the urostyle (the terminal segment of the
vertebral column) is comprised of the last two vertebrae
fused into a single element. Modified neural spines and
neural arches form plates termed the epurals and uroneurals, respectively, which when coupled with the modified
haemal arches known as the hypurals, form a strong yet
flexible base for the caudal fin rays.
The paired medial fins are part of two separate series of
bones known as the pectoral and pelvic girdles. These
structures form the point of attachment and articulation of
the fins and the associated fin rays. The term girdle is most
appropriate for the pectoral girdle as it almost encircles the
entire body just behind the opercula. This series of bones is
connected to the neurocranium by the posttemporal bone
at attachment points on the epiotic and oposthotic bones
[276] (Figs. 8 and 10). The nature of the posttemporal bone
is important in the identification of different genera of
terapontid grunter and the structure of the entire girdle is
important in the systematics of the percichthyids (cods,
bass and pygmy perches). The simpler pelvic girdle is
inserted under the pectoral girdle and consists of a pair of
plates called basipterygia to which the fin rays and pelvic
spines (when present) attach and articulate.
Meristic and morphometric characters
In addition to characters associated with skeletal anatomy,
many systematic studies use a combination of meristic and
morphometric characters to distinguish between species.
Meristic characters include such characters as the number
of fin spines and rays, number of gill rakers, number of
lateral line scales, vertical scale rows, number of cheek
scales. Note that these characters are all expressed as
counts.
post temporal
supracleithrum
cleithrum
Morphometric characters, in contrast, describe the condition or size of certain characters. For example, the size of
the head or of the eye, or the distance between the snout
and the start of the first dorsal fin (predorsal length) are all
morphometric characters. Figure 11 depicts many useful
and frequently used morphometric characters. Most
morphometric characters vary in size with increasing fish
size, therefore they need to be standardised in some
manner so that comparisons may be made between specimens of differing size. The most frequent mechanism for
standardising morphometric characters is to describe
them as a proportion of fish length, usually standard
length (the distance from the tip of the snout to the
hypural crease). Another frequently used denominator is
head length: thus it is not uncommon to see characters
such as mouth gape or maxilla length expressed as a
proportion of head length. In this way, the size of any
particular character may be reasonably compared across
fish of different size. Calliette et al. [276] provide a useful
discussion of the issues associated with standardisation of
morphometric characters.
scapula
actinosts
coracoid
Figure 10. The pectoral girdle of the percichthyid Guyu
wujalwujalensis. (Redrawn after Pusey et al. [1091].)
The axial skeleton (which technically includes the skull)
contains two types of vertebra. The precaudal vertebrae of
the abdominal region bear ribs, intermuscular bones and
neural spines but not haemal spines (Fig. 7). The caudal
vertebrae bear few ribs and have prominent neural as well
as haemal spines. The absolute number of caudal and
precaudal vertebrae and the relative number of these bones
are both important characters in the systematics of some
Standardisation by dividing by standard length or head
length assumes that the relative size of a character remains
constant with varying size of the fish. This is not always the
11
Freshwater Fishes of North-Eastern Australia
series of steps, to a final identification of an unknown fish.
The key is based to a large extent on characters that do not
require the use of a microscope or dissection to discern
(i.e. number of gill rakers or vertebrae), however such
characters are sometimes the most useful for separating
species and their use is therefore unavoidable.
Furthermore, small-bodied species cannot be examined
with great accuracy unless a microscope or magnifying
glass is used. We recommend that this key be used as a
guide only, and that tentative identifications derived from
it, be checked against the comprehensive description
provided for the relevant species or sent to a relevant taxonomic expert at a museum.
case. For example, in a study examining the distribution of
the rainbowfish Melanotaenia eachamensis in the Wet
Tropics region of northern Queensland, Pusey et al. [1105]
compared the meristics and morphometrics of many
populations of rainbowfishes with those of known populations of M. eachamensis and M. splendida splendida. Very
few morphometric characters were found to remain
invariate with increasing size: predorsal length, body
depth, snout length, and peduncle depth were the only
characters to satisfy this criterion. Other characters: head
length, head depth, eye diameter, mouth length and
peduncle length, all varied with length in an exponential
fashion, with an exponent less than one. Thus these characters were all relatively greater in smaller individuals than
in larger individuals. In such cases, better standardisation
may be achieved by dividing by standard length raised to
the power best describing the relationship between that
character and standard length.
The species covered in this key include both native and
alien species (non-native, introduced from other countries) found in north-eastern Australia. The key contains
some species not covered in depth in this book but which
may be encountered in rivers of north-eastern Australia.
Some species found occasionally in easterly flowing
streams of Cape York Peninsula are more properly considered fauna of drainages discharging into the Gulf of
Carpentaria, west of the Great Dividing Range; these
species are not covered in this book other than inclusion
in this key. When in doubt about a species’ identification,
consult widely and use the services of museum specialists.
The systematics of many groups of fishes is often in flux
Identification of the freshwater fishes of north-eastern
Australia
The identification of fishes can be a difficult task for the
non-specialist and specialist alike. We have included a
dichotomous key to aid in the identification of different
fishes in the field and laboratory. A dichotomous key is
basically a set of either/or questions that should lead, by a
total length
caudal fork length
standard length
snout length
body
depth
caudal
peduncle
length
predorsal length
head
length
caudal
peduncle
depth
head
depth
eye
diameter
maxilla length
Figure 11.
Commonly used morphometric characters. (Redrawn after Pusey et al. [1105].)
12
Origins, structure and classification of fishes
have used generic or family level reviews. Figures 21, 22,
23, 24 were redrawn after Allen [34] and Figures 38, 39, 41,
42 were redrawn after Allen and Cross [43]. In those cases
where undescribed species have been assigned species
numbers, we have retained the numbering system
presented in Allen et al. [52].
and the use of varied information sources is prudent. The
use of limited or out-of-date systematic resources too
often leads to circumstances where identification and
distributional information become less than useful.
Ideally, fish ecologists, aquatic biologists and consultants
should try to keep abreast of changes in the systematics of
freshwater fishes.
The key included below is based on a number of different
sources [34, 37, 43, 47, 773, 1346] but where possible we
13
Freshwater Fishes of North-Eastern Australia
Key to the native and alien fishes of north-eastern Australia
(alien species are denoted by *)
1a
1b
2a
2b
3a
3b
4a
4b
5a
5b
6a
6b
7a
Body elongated and eel-like........................................................................2
Body not elongated and eel-like .................................................................4
Barbels present (alien)..................................................................Cobitidae
Misgurnus anguillicaudatus*
Barbels absent..............................................................................................3
Pectoral fins absent ..............................................................Synbranchidae
Aa Gill opening a slit-like fold across ventral surface of head, not
attached to isthmus...........................................................................B
Ab Gill opening pore-like, triangular shaped, and internally attached
to the isthmus .........................................................Monopterus albus
Ba Colour blackish-green to reddish-brown; mottled; eye positioned
forward of the middle of the distance between end of mouth and
snout tip (note that there may be a number of undescribed species
of Ophisternon present in freshwaters of Queensland and the
species referred to as O. bengalense may not occur in Australia)
.......................................................................Ophisternon bengalense
Bb Colour brown to green; ventral surface lighter in colour; eye positioned posteriorly of the middle of the distance between end of the
mouth and snout tip........................................Ophisternon gutturale
Pectoral fins present...................................................................Anguillidae
Aa Colouration mottled, dorsal fin originating well in front of vertical
line through line anus (Fig. 1) ............................Anguilla reinhardtii
Ab Colouration uniform, dorsal fin originating only slightly in front of
anus (Fig. 2).......................................................................................B
Ba Jaws reaching back to eye or slightly beyond, vomerine tooth patch
broad, distribution does not extend north of the Burnett River
............................................................................................A. australis
Bb Jaws reaching well beyond eye, vomerine tooth patch long and
narrow, distribution does not extend far south of the Pioneer River
.............................................................................................A. obscura
Eyes not on the same side of head; body not greatly flattened ................5
Eyes on same side of head, body flattened .....................................Soleidae
Aa Dorsal rays 66–78; caudal rays 16; anal rays 53–59; caudal fin
narrow and pointed; lateral line scales 84–97 ...Brachirus salinarum
Ab Dorsal rays 70–75; caudal rays 18–20; anal rays 55–60; caudal fin
rounded; lateral line scales 77–81 .....................................B. selheimi
Pectoral and pelvic fins thick and flipperlike (Fig. 3) .......Ceratodontidae
Neoceratodus forsteri
Pectoral fins not thick, fleshy and flipperlike, fin rays easily visible
(Fig. 4)..........................................................................................................6
Barbels present on lower jaw, may or may not be present on upper jaw
(Figs. 5 and 6) ..............................................................................................7
Barbels absent from lower jaw, but single pair of barbels may be present
on upper jaw ............................................................................................... 9
Barbels short and paired (Fig. 5).........................................Osteoglossidae
Aa Dorsal rays 20–24; anal rays 28–32......................Scleropages jardinii
Ab Dorsal rays 15–19; anal rays 25–27 (Fitzroy River system only
unless translocated)..........................................................S. leichardti
14
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Key to native and alien fishes of north-eastern Australia
7b
8a
8b
Barbels long, 3 or 4 pairs (Fig. 6)................................................................8
Barbels in 4 pairs; dorsal, anal and caudal fins fused to form one continuous pointed fin...........................................................................Plotosidae
Aa Second dorsal fin originating either just anterior to or posterior to
vertical line through anus (Fig. 7)....................................................B
Ab Second dorsal fin originating well posterior to vertical line through
anus (Fig. 8) ......................................................................................C
Ba Jaws without teeth.............................................Anodontoglanis dahli
Bb Jaws with teeth.....................................................Tandanus tandanus
Ca Dorsal profile of head frequently concave; eyes relatively low set on
side of head; tail more or less pointed; few dorsal rays in fused
fin ......................................................................................................D
Cb Dorsal profile of head straight or slightly convex; eyes set in higher
position approaching dorsal profile; tail more rounded and extending relatively further onto dorsal profile ..........................................F
Da Lateral line discontinuous .......................................Porochilus obbesi
Db Lateral line continuous .....................................................................E
Ea Dorsal fin with sharp spine and 4 soft rays; pectoral fin with sharp
spine and 7 soft rays .........................................................P. argenteus
Eb Dorsal fine with spine and 5–7 soft rays; pectoral fin with sharp
spine and 9–11 soft rays.....................................................P. rendahli
Fa Dorsal fin tall; dorsal spine reduced to flexible cartilaginous ray
(Fig. 9) ........................................................Neosilurus mollespiculum
Fb Dorsal fin short or moderately elongated; dorsal spine rigid
(Fig. 10).............................................................................................G
Ga Dorsal fin short; nasal barbels extending back beyond eye
.....................................................................................N. brevidorsalis
Gb Dorsal fin moderately elongated; nasal barbels not extending back
beyond eye ........................................................................................H
Ha Confluent dorsal, anal and caudal fin comprised of 120–160 rays;
dorsal fin with 5–7 soft rays; pectoral fin with 11–13 rays; snout
elongated...................................................................................N. ater
Hb Confluent fins comprised of 115–135 rays; dorsal fin with 5–6 soft
rays; pectoral fins with 10–11 rays; snout not elongated ...N. hyrtlii
Barbels arranged in 3 pairs...............................................................Ariidae
Aa Raker-like processes present on back of all gill arches ....................B
Ab No raker-like process on back of first 2 gill arches .........................C
Ba Barbels long (30–47% of SL); palatal tooth patches arrayed as in
Fig. 11, vomerine and palatine patches in inner row separate in
smaller specimens ..........................................................Arius berneyi
Bb Barbels short (17–40% of SL); palatal tooth patches arrayed as in
Fig. 12...................................................................................A. graeffei
Ca Head broad; snout well rounded to squarish; maxillary barbels long
(22.7–50% of SL); inner row of palatal tooth patch consisting of
united palatine and vomerine patches as in Fig. 14.........A. leptaspis
Cb Head rectangular; snout squarish or truncate; maxillary barbels
short (16.6–24% of SL); inner row of palatal tooth patches
composed of four separate patches as in Fig. 13.............................D
Da Gill rakers on first arch 15–17, 16–19 on last arch, eye relatively
large, 12.9–21.8% of HL ...................................................A. midgleyi
Db Gill rakers on first arch 10–11, 11–14 on last arch, eye relatively
small, 8.9–15.3% of HL .......................................................A. paucus
15
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Freshwater Fishes of North-Eastern Australia
9a
9b
10a
10b
11a
11b
12a
12b
13a
13b
14a
14b
15a
15b
16a
16b
17a
17b
18a
18b
19a
Single dorsal fin (Fig. 15), but may be notched to give the appearance of
two separate fins (Fig. 16).........................................................................10
Two separate dorsal fins (Fig. 17).............................................................25
Mouth very small, oblique ........................................................................11
Mouth not very small and oblique or if small, head with short beak ....12
Lateral line present and curved, male anal fin not modified, oviparous
(alien) .........................................................................................Belontiidae
Trichogaster trichopterus*
Lateral line absent, male anal fin modified to form intromittent organ
(gonopodium), viviparous (live-bearing) (alien) .....................Poeciliidae
Aa Body deep, 50% of SL, prominent dark blotch at base of caudal fin,
body colour blue..........................................Xiphophorus maculatus*
Ab Body not noticeably deep, <50% of SL (except perhaps in pregnant
females), prominent caudal spot absent ..........................................B
Ba Dorsal spine present, anal spine present, dorsal fin originating
behind anal fin ..................................................Gambusia holbrooki*
Bb Dorsal spine absent, anal spine absent, dorsal fin originating in
front of anal fin.................................................................................C
Ca Dorsal fin rays 7–8, caudal fin not elongated to form sword............
Poecilia reticulata*
Cb Dorsal fin rays 11–14, ventral rays of caudal fin elongated to form
sword ..................................................................Xiphophorus helleri*
Ventral midline of breast or abdomen with series of serrations (skutes)
.......................................................................................................Clupeidae
Nematalosa erebi
Ventral midline of breast or abdomen without series of serrations .......13
Either or both upper or lower jaw elongated to form beak-like
structure.....................................................................................................14
Jaws not elongated to form beak-like structure.......................................15
Upper and lower jaws elongate (Fig. 18); well toothed; some teeth
enlarged and needle-like ..............................................................Belonidae
Strongylura krefftii
Lower jaw elongate (Fig. 19); teeth small, granular or cardiform
............................................................................................Hemiramphidae
Arramphus sclerolepis
Dorsal fin without spines..........................................................................16
Dorsal fin with spines ...............................................................................17
Adipose fin present (may be very small) .............................Retropinnidae
Retropinna semoni
Adipose fin absent ...................................................................Megalopidae
Megalops cyprinoides
Single dorsal fin without notch ................................................................18
Single dorsal fin notched to give impression of two fins ........................20
Dorsal fin with more than 10 spines (alien) ................................Cichlidae
Aa Dorsal rays 12–15, anal rays 10–12, lateral line scales 28–30, snout
blunt ...........................................................................Tilapia mariae*
Ab Dorsal rays 10–12, anal rays 9–10, lateral line scales 29–33, snout
elongated and pointed ............................Oreochromis mossambicus*
Dorsal fin with less than 10 spines ...........................................................19
Body rhombiform, dorsal fin roughly equal in size to anal fin, insertion
point of dorsal fin level with anal fin...........................................Toxotidae
Aa 5 or 6 (usually 5) dorsal spines ...............................Toxotes chatereus
16
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Key to native and alien fishes of north-eastern Australia
Ab
19b
20a
20b
21a
21b
4 dorsal spines; predominantly marine or estuarine ........................
.................................................................................Toxotes jaculatrix
Body not rhombiform, dorsal fin longer than anal fin and inserted well
forward of anal fin (alien)..........................................................Cyprinidae
Aa Barbels present on upper jaw ..................................Cyprinus carpio*
Ab Barbels absent on upper jaw.................................Carassius auratus*
Head with conspicuous spines .................................................................21
Head without conspicuous spines............................................................22
Moderate size (10–20 cm), never transparent, mottled brown/black
colour, more than 10 spines in dorsal fin .............................Scorpaenidae
Notesthes robusta
Small size (<10 cm); generally transparent or silver in colour; less than 10
spines in dorsal fin ......................................................................Chandidae
Aa Gill rakers reduced to rudimentary stumps, about 7–9 on lower
limb of first gill arch; enlarged and conspicuous pores on preorbital
...............................................................................Denariusa bandata
Ab Gill rakers well developed, 15 or more on lower limb of first gill
arch (including raker at angle); pores on preorbital, supraorbital
and preopercular bones not conspicuous........................................B
Ba Supraorbital spines usually 3–5 (rarely 2); nasal spine well
developed ..........................................................................................C
Bb Usually a single supraorbital spine (Fig. 20); nasal spine either well
developed or absent ..........................................................................E
Ca Hind margin of preoperculum with about 6–13 small serrae
(mostly estuarine) ...................................................Ambassis vachelli
Cb Hind margin of preoperculum usually smooth or weakly crenulate
without distinct serrae .....................................................................D
Da Soft anal rays usually 10, rarely 11; predorsal scales 16–18; eye relatively small, 10.7–12.7% of SL; caudal peduncle relatively short
(16.1–20.8% of SL) and deep (14.4–16.3% of SL) ........A. marianus
Db Soft anal rays usually 9; predorsal scales 11–14; eye larger,
13.0–13.9%; caudal peduncle more longer (20.6–22.2% of SL)
and more slender (13.0–14.8% of SL) (mostly estuarine)
.................................................................................A. gymnocephalus
Ea Lateral line continuous from upper edge of gill opening to caudal
fin base; predorsal scales 12–15; horizontal scale rows from anal fin
origin to base of dorsal fin 9 or 10; second dorsal spine slightly less
than or equal to third dorsal spine .......................................A. miops
Eb Lateral line either terminating on anterior portion of body or interrupted in middle section...................................................................F
Fa Nasal spine present; lateral line always well developed consisting of
8–13 tubed scales in anterior section and 9–14 in posterior section
(mostly estuarine).........................................................A. interruptus
Fb Nasal spine usually absent; lateral line often poorly developed
consisting of 9–14 tubed scales in anterior section and 0–15 tubed
or pitted scales in posterior section .................................................G
Ga Rakers on lower limb of first gill arch 24–29; dorsal and anal soft
rays usually 10 (occasionally 9 or 11); pectoral rays 14–15; base of
pectoral fin frequently blackish…..….…………...……A. macleayi
Gb Rakers on lower limb of first gill arch 15–20; dorsal and anal
soft rays usually 8 –9 (rarely 7 or 10); pectoral rays 11–14; base of
pectoral fin pale................................................................................H
17
Figure 20
Freshwater Fishes of North-Eastern Australia
Ha
22a
22b
23a
23b
24a
24b
Scales in longitudinal series from upper edge of gill opening to
caudal fin base 28–34; spinous dorsal fin relatively tall, 29.1–41.8%
of SL, usually >33%.…………………………………A. agrammus
Hb Scales in longitudinal series from upper edge of gill opening to
caudal fin base 24–26 (rarely 27); spinous dorsal fin usually shorter,
18.4–36.8% of SL, usually <33%….………..……………………I
Ia
Circumpeduncular scales usually 16, occasionally 15; height of
spinous dorsal fin 24.0–36.8% of SL, mean 28.5% .......Ambassis sp.
(formerly A. muelleri)
Ib
Circumpeduncular scales usually 14 or less; height of spinous
dorsal fin 18.4–27.6% of SL, mean 23.8 ...........................A. agassizii
Pelvic fin base in front, directly below, or immediately behind pectoral fin
base (Fig. 21).........................................................................Percichthyidae
Aa Small bodied (<7 cm); pelvic fins without extended filaments ........
Nannoperca oxleyana
Ab Moderate to large bodied, pelvic fins with extended filaments ......B
Ba Head broad and jaw depressed; no conspicuous open pores on
lower jaw; naturally confined to the Mary River but widely translocated ...................................................Maccullochella peelii mariensis
Bb Head deep and laterally compressed; lower jaw with or without
conspicuous pores ...........................................................................C
Ca Conspicuous pores on lower jaw absent......Macquaria novemaculeata
Cb Conspicuous pores on lower jaw present........................................D
Da Suboperculum and cleithrum without serrations; opercula spines
without serrations; natural Queensland distribution restricted to
the Fitzroy River and drainages of central Australia (extensive
translocation into other drainages has occurred and central
Australian population probably distinct species) ............................
.............................................................................Macquaria ambigua
Db Suboperculum and cleithrum with serrations; opercula spines
serrate; restricted to the Bloomfield River......Guyu wujalwujalensis
Pelvic fin origin well behind pectoral fin base (Fig. 22)..........................23
Lateral line extends onto caudal fin...................................Centropomidae
Lates calcarifer
Lateral line does not extend onto caudal fin............................................24
Dorsal spines 10; mouth large extending to below eye ...............Kuhliidae
Aa Maxilla reaching back to middle of eye; 9–10 soft anal rays; caudal
only slightly emarginate; caudal pigmentation generally restricted
to two dark blotches ..................................................Kuhlia rupestris
Ab Maxilla not reaching back to middle of eye; 11–12 soft anal rays;
caudal deeply emarginate, almost forked; caudal often entirely
darkly pigmented ...........................................................K. marginata
Dorsal spines 11 or more; mouth small to moderate in size, not reaching
back to eye; caudal fin without blotches except in estuarine forms
.................................................................................................Terapontidae
Aa Post temporal bone covered with skin and scales, not expanded
posteriorly and without serrated edge (Fig. 23) ..............................B
Ab Post temporal bone exposed posteriorly, expanded and serrate
posteriorly (Fig. 24) ..........................................................................E
Ba Lateral line scales 55–62; limited to the Mitchell River
.............................................................................Variichthys lacustris
Bb Lateral line scales usually <55; widespread .....................................C
Ca Body with 5–6 vertical black bars .....................Amniataba percoides
18
Figure 21
Figure 22
Figure 23
Figure 24
Key to native and alien fishes of north-eastern Australia
Cb
Da
Body without vertical black bars .....................................................D
Caudal fin with broad oblique black stripe across each lobe
(estuarine) ...................................................Amniataba caudivittatus
Db Caudal fin without black stripe...................Leiopotherapon unicolor
Ea Lower opercula spine greatly developed, extending beyond edge of
operculum (Fig. 25); caudal fin lobes with oblique dark stripes
(estuarine) ................................................................Therapon jarbua
Eb Lower opercula spine smaller, not extending beyond edge of operculum, caudal fin lobes without oblique stripes..............................F
Fa Teeth flattened, strongly depressible................................................G
Fb Teeth conical, nondepressible or only slightly depressible..............L
Ga Body not noticeably elongate, head not noticeably small; predorsal
scales <20..........................................................................................H
Gb Elongate body; elongate caudal peduncle; head small; predorsal
scales 20–25.......................................................................................K
Ha Limited to easterly flowing drainages ...............................................I
Hb Not occurring naturally in easterly flowing drainages.....................J
Ia
Lateral line scales 49–53; horizontal scale rows above lateral line
8–10; predorsal scales 16–20; check scales in 4–6 rows; confined to
the Burdekin River.................................................Scortum parviceps
Ib
Lateral line scales 52–61; horizontal scale rows above lateral line
11–13; predorsal scales 14–18; check scales in 5–6 rows; confined to
the Fitzroy River and possibly the Burdekin River also ........S. hillii
Ja
Body relatively deep, 43.5–47.6% of SL; limited to central
Australian drainages .............................................................S. barcoo
Jb
Body relatively slender, 35.7–42.7% of SL; limited to Gulf of
Carpentaria drainages ..........................................................S. ogilbyi
Ka Lateral line scales 49–56; confined to Lake Eyre and Bulloo
drainages....................................................................Bidyanus welchi
Kb Lateral line scales 55–62; naturally limited to Murray-Darling Basin
but widely translocated in Queensland ...............Bidyanus bidyanus
La Medium sized grunter with vivid gold and black barring; generally
limited to western drainages but also present in small number of
eastern drainages of Cape York Peninsula; lateral line scales 52–60
..................................................................................Hephaestus carbo
Lb Large grunter with generally uniform colour; lateral line scales
43–52 ................................................................................................M
Ma Pectoral fin base without dark band; pelvic fins reach back to anus
when depressed; lateral line scales 46–52; confined to the Wet
Tropics region...................................................................H. tulliensis
Mb Pectoral fin base with dark band; pelvic fins do not reach back to
anus when depressed; lateral line scales 43–51; widespread
........................................................................................H. fuliginosus
25a Pelvic fins inserted well behind level of pectoral fin base .......................26
25b Pelvic fins inserted approximately level or forward of pectoral fin base29
26a Three anal fin spines ....................................................................Mugilidae
(Note – most mullet are estuarine species and this key allows identification to species level for those species commonly encountered in freshwater only, otherwise identification is to genus only)
Aa Rear tip of maxilla not curved down below tip of premaxilla (Fig.
26) ................................................................................Mugil cephalus
Ab Rear tip of maxilla curved down below tip of premaxilla (Fig. 27) ..B
Ba Teeth present on vomer and palatines ........................Myxus petardi
19
Figure 25
Figure 26
Figure 27
Freshwater Fishes of North-Eastern Australia
Bb
Ca
26b
27a
27b
28a
28b
Teeth not present on vomer and palatines ......................................C
Scales cycloid, hind margin with digitations; rear tip of maxilla
hidden when mouth closed................................................Valamugil
Cb Scales cycloid or ctenoid, but without digitations on hind margin;
rear tip of maxilla apparent when mouth closed........................Liza
Anal fin with 1 spine .................................................................................27
Innermost pelvic fin ray not attached to belly by membrane; scales
present on belly between pelvic fin attachment and anus (Fig. 28)
....................................................................................................Atherinidae
Aa Vertical scale rows 27–30..........................Craterocephalus marjoriae
Ab Vertical scale rows 32–35 ....................................C. stercusmuscarum
(Note – this species is suggested to be composed of two subspecies
defined primarily by distribution and that an undescribed species, growing to larger size than the nominal form, exists in the upper reaches of the
North Johnstone and Barron rivers)
Innermost pelvic fin ray attached to belly by membrane (Fig. 29; scales
absent on belly between pelvic fin base and anus....................................28
Total anal fin rays usually 9–13; rigid fin spines absent; anal fin origin in
posterior half of body (by SL) .........................................Pseudomugilidae
Aa Body and median fins covered with small black dots; dorsal fin
origin about ? eye diameter anterior to level of anal fin origin
.........................................................................Pseudomugil gertrudae
Ab Body and fins without small black dots; dorsal fin origin nearly full
eye diamater anterior to anal fin origin ...........................................B
Ba Rays in second dorsal fin usually 6 or 7; rays in anal fin 7–10 usually
9; origin of second dorsal fin about level with third or fourth anal
ray.........................................................................................P. tenellus
Bb Rays in second dorsal fin 7–11, usually 7 or 9; rays in anal fin 10–13,
usually 10–12; origin of second dorsal fin about level with middle
anal rays.............................................................................................C
Ca Rays in second dorsal fin 7–11, usually 8 or 9; head pores relatively
large and conspicuous; mandibular pores present; maxillary teeth
usually exposed when mouth closed...................................P. signifer
Cb Rays in second dorsal fin 6–9, usually 7, occasionally 8; head pores
minute, inconspicuous; mandibular pores absent; maxillary teeth
hidden when mouth closed ...................................................P. mellis
Total anal fin rays usually 14–23 (except 10–12 in Iriatherina, which has a
rigid fin spine on anal fin); rigid fin spines present (except in
Rhadinocentrus and Cairnsichthys, both of which have more than 17 anal
fin rays); anal fin origin in anterior half of body or about middle of body
............................................................................................Melanotaeniidae
Aa No rigid fin spines present, all rays slender and flexible ................B
Ab Rigid fin spines present, usually at the beginning of the first dorsal
(except in Iriatherina), second dorsal, anal and pelvic fins ............C
Ba Lower jaw prominent (Fig. 30); exposed lateral part of maxillae
with single row of 15 or less widely separated teeth; horizontal scale
rows at level of anal fin origin 8–9...............Rhadinocentrus ornatus
Bb Jaws about equal; exposed lateral part of maxillae with numerous
teeth arranged in several rows; horizontal scale rows at level of anal
fin origin 10–11 .................................Cairnsichthys rhombosomoides
Ca All spines of first dorsal fin relatively soft and flexible; soft anal fin
rays 11–12; first few rays of second dorsal and anal fins extended as
elongate filaments in adult males; exposed premaxillary teeth
20
Figure 28
Figure 29
Figure 30
Key to native and alien fishes of north-eastern Australia
restricted to a single row of 7–8 canines .............Iriatherina werneri
Not as for Ca.....................................................................................D
Colour pattern consisting of 8–9 horizontal rows of narrow dark
stripes (sometimes broken and replaced by spots); the midlateral
stripe not expanded to form broad black stripe; acidic waters on
dune fields and lowland floodplains..…..Melanotaenia maccullochi
Db Colour pattern not as in Da..............................................................E
Ea Teeth of lower jaw in dense band without toothless groove separating row of teeth at front of jaw (Fig. 31); distinct black band (may
be interrupted) running along middle of side.................................F
Eb A toothless groove usually separating an enlarged row of teeth at
front of jaws and dense band of smaller teeth behind (Fig. 32);
distinct black band absent, usually replaced by a series of narrower
stripes although the midlateral one may be expanded to form a
diffuse dark band..............................................................................G
Fa Soft rays in second dorsal fin usually 8–11; anal fin rays usually
15–19; black midlateral stripe always continuous; body slender,
maximum depth not exceeding 34% of SL in males and 28% in
females; Cape York Peninsula............................................M. nigrans
Fb Soft rays in second dorsal fin usually 12–16; anal fin rays usually
18–23; black midlateral stripe frequently interrupted or at least faint
just behind the pectoral fins; body deep, maximum depth of 45% of
SL or greater in males, and 35% of SL in females .........M. trifasciata
Ga Vomer with a few feeble teeth on lateral section; body slender,
<31% in males and 28% in females; origin of first dorsal fin less
than 46% of SL; snout length less than 7% of SL; restricted to Wet
Tropics region...................................................................................H
Gb Vomer with a solid band of teeth of well developed teeth; body
deeper, >35% in males and 26–40% in females; origin of first dorsal
fin greater than 47% of SL; snout length greater than 8% of SL .....I
Ha Restricted to lakes and streams of the Atherton Tablelands at altitudes of 600 m.a.s.l. or greater ..................................M. eachamensis
Hb Restricted to forested tributary streams of the Johnstone River at
elevations of between 100 and 600 m.a.s.l ...................M. utcheensis
Ia
Deep bodied rainbowfish of streams and rivers, body depth of
males (>50 mm) 29–48.8% of SL, of females 26.4–40.8% of SL;
meristics and morphometrics extremely variable; range extends
from Cape York Peninsula to possibly Baffle Creek, several subspecies recognised...........................................................M. splendida
Ib
Less deep-bodied, body depth of males 28–35.7% of SL, of
females 26.3–31% of SL; not found north of about Baffle Creek
........................................................................................M. duboulayi
29a Spines of first dorsal sharp and rigid; 2 rigid spines at beginning of
anal fin; lateral line scales usually present (sometimes reduced or absent)
...................................................................................................Apogonidae
Glossamia aprion
29b Spines of first dorsal fin soft and flexible; a single flexible spine at the
beginning of the anal fin, lateral line scales absent..................................30
30a Pelvic fins fused to form disc-like structure ................................Gobiidae
Aa Head and body without scales............................Schismatogobius sp.
Ab Head and body with scales ...............................................................B
Ba Midlateral scales 49–100 or more ....................................................C
Bb Midlateral scales 25–38 except in Chlamydogobius ranunculus
Cb
Da
21
Figure 31
Figure 32
Freshwater Fishes of North-Eastern Australia
which may have as many as 52 but usually 45 or less midlateral
scales ..................................................................................................E
Ca Lower jaw with one row of teeth, at least 2 canines present near
middle of jaw; lower lip with a row of widely spaced conical teeth;
upper lip with papillae or one or more clefts along margin (Fig. 33)
......................................................................Sicyopterus lagocephalus
Cb Lower jaw with several rows of teeth, no canines; lower lip without
teeth; upper lip without papillae or clefts along margin ...............D
Da Gill arches and gill filaments papillose; broad dark bar or triangular
marking below eye absent .......................................Awaous acritosus
Db Gill arches and gill filaments not papillose; broad dark bar or triangular marking below eye present ...............Stenogobius psilosinionus
Ea Midlateral scales 32–52, usually >38 ...Chlamydogobius ranunculus
Eb Midlateral scales 25–38 .....................................................................F
Fa Lower jaw with one row of teeth; operculum scaleless
...................................................................................Stiphodon alleni
Fb Lower jaw with several rows of teeth; operculum scaled or scaleless
...........................................................................................................G
Ga Opercle scaleless or with small inconspicuous scales restricted to
uppermost part.................................................................................H
Gb Opercle fully covered by scales ........................................................Q
Ha First dorsal fin mostly black; caudal fin with 4–5 short blackish bars
along lower edge (mostly estuarine).........Psammogobius biocellatus
Hb First dorsal fin either clear or with black spot confined to rear half
of first dorsal fin.................................................................................I
Ia
Short barbels present on chin.......................Glossogobius bicirrhosis
Ib
Short barbels absent on chin ............................................................J
Ja
Lines of sensory papilla below eye arranged in vertical lines
(Fig. 34).....................................................................G. circumspectus
Jb
Lines of sensory papilla below eye arranged in horizontal lines
(Fig. 35) .............................................................................................K
Ka Breast scaled ......................................................................................L
Kb Breast naked or nearly so..................................................................P
La Predorsal scales large, 13–16 rows; infraorbital pore behind eye; 4
lateral line canal pores above preoperculum and operculum; lateral
canal tube above operculum present ....................Glossogobius sp. 1
Lb Predorsal scales small, usually 17–30 rows; infraorbital pore behind
eye; 2 lateral line canal pores above preoperculum and operculum
(some populations of G. aureus may have 3–4 lateral canal pores);
lateral canal tube above operculum present...................................M
Ma Papillae lines from middle of upper jaw to infraorbital pore behind
eye with distinct posterior branch under eye; longitudinal papillae
lines under eye composed of multiple rows of papillae ....G. giurus
Mb Papillae lines from middle of upper jaw to infraorbital pore behind
eye without distinct posterior branch under eye; longitudinal papillae lines under eye composed of a single row of papillae...............N
Na Scales absent from upper part of operculum .....................G. aureus
Nb Scales present on upper part of the operculum..............................O
Oa Predorasl scales 13–16 ................................................G. concavifrons
Ob Preporsal scales 18–24 ............................................Glossogobius sp. 2
Pa Predorsal area naked or with rudimentary scales only; confined to
Cape York Peninula and south New Guinea .........Glossogobius sp. 3
Pb Predorsal scales 10–12; confined to rivers of the Wet Tropics region
22
Figure 33
Figure 34
Figure 35
Key to native and alien fishes of north-eastern Australia
.................................................................................Glossogobius sp. 4
Midlateral scales 32–38; opercle covered with numerous small
scales; head pores absent (predominantly estuarine but commonly
found in freshwaters close to ocean)................................................R
Qb Midlateral scales 25–28; opercle covered with a few large scales;
head pores present...........................................................................W
Ra Predorsal scales reaching close behind eye and almost entering
interorbital space; anterior most scales on nape enlarged...............S
Rb Predorsal scales reaching to preoperculum or less, never entering
interorbital space; usually all scales small or equal in size, or absent
from predorsal midline.....................................................................T
Sa Second or third dorsal spine usually longest; predorsal scales 10-16;
anterior most few enlarged; side of head with two longitudinal
streaks; body with chequered pattern .............Mugilogobius mertoni
Sb First dorsal spine usually longest; predorsal scales 13–22; anteriormost often not much larger than others; side of head with distinct
reticulated pattern; body with oblique bars and blotches...M. filifer
Ta Circumpeduncular scales modally 12; caudal fin with two dark
spots at base ...................................................................M. notospilus
Tb Circumpeduncular scales modally 13–20; two or more dusky diagonal bands may be present on caudal fin ........................................U
Ua Predorsal scales 0–21 (most often 0–12); ctenoid scales on side of
body restricted to caudal peduncle and patch under pectoral
fin...................................................................................M. platynotus
Ub Predorsal scales 14–30, never absent; ctenoid scales on side of body
extending forward to below fifth ray of second dorsal or further..V
Va Ctenoid scales on side of body extending continuously up to
behind pectoral fin base, not broken into two areas..M. stigmaticus
Vb Ctenoid scales on side of body usually separated by a distinct gap
.....................................................................................M. platystomus
Wa First dorsal fin without prominent black spot (although fin may be
mottled darkly); no prominent oblique or vertical dark bar extending from eye, 3–5 short dark bars present on ventral most portion
of sides between anus and caudal fin base (predominantly
estuarine) ..........................................................................................X
Wb First dorsal fin with prominent black spot either ringed in yellow
or with anterior most part of fin yellow; prominent oblique or
vertical dark bar extending from eye, short dark bars between anus
and caudal fin base absent................................................................Y
Xa Cylindrical in transverse section; body with blotches, rarely forming vertical bars; transverse bars across head; maxillary not reaching past middle of eye........................................Redigobius bikolanus
Xb Laterally compressed, body with vertical bars; oblique bars radiating from eye; mouth large with maxillary extending well past eye;
not found north of the Noosa River ........................R. macrostomus
Ya Body with conspicuous oblique bar extending from below first
dorsal fin ...........................................................................R. balteatus
Yb Body without conspicuous oblique bar .........................R. chrysoma
30b Pelvic fins separate .......................................................................Eleotridae
Aa Midlateral scales <50 (usually <45) .................................................B
Ab Midlateral scales >45 (usually >60, except in Oxyeleotris nullipora
which has 30–38) ..............................................................................K
Ba Predorsal scales absent...............Hypseleotris sp. 2 (Lake’s gudgeon)
Qa
23
Freshwater Fishes of North-Eastern Australia
Bb
Ca
Cb
Da
Db
Ea
Eb
Fa
Fb
Ga
Gb
Ha
Predorsal scales present ....................................................................C
Midlateral scales 33–47, usually greater than 33.............................D
Midlateral scales 27–32, rarely 33.....................................................F
Total rays in first dorsal fin 6.........................Ophiocara porocephala
Total rays in first dorsal fin 7–9 .......................................................E
Midlateral scales 30–36 .......................................Mogurnda adspersa
Midlateral scales 37–48 .................................................M. mogurnda
Head laterally compressed (Fig. 36) ................................................G
Head moderately to greatly depressed (Fig. 37) ...............................J
Head pores present.........................................Hypseleotris compressa
Head pores absent ............................................................................H
Transverse scales rows 11–13; midlateral scales 31–43 ......................
................................................Hypsleotris sp. 1 (Midgley’s gudgeon)
Hb Transverse scale rows 9–11; midlateral scales 27–32 ........................I
Ia
Series of transverse papillary rows above and below the eye (Fig.
38) .................................................................................H. klunzingeri
Ib
Series of transverse papillary rows above and below the eyes absent
or only a single row present above the eye (Fig. 39)..............H. galii
Ja
Head more or less pointed; snout very elongate and greatly flattened; bony crests in interorbital space .............................Butis butis
Jb
Head more rounded; snout short and not greatly flattened; no bony
crests in interorbital space .................................Giurus margaritacea
Ka Lower rear corner of preopercle with an enlarged downward
curved, strong spine (may be obscured by flesh) (Fig. 40) .............L
Kb Lower rear corner of preopercle without enlarged spine ...............N
La Gill rakers on first arch 8–10; <40 predorsal scales; 5–6 transverse
lines of pit organ canals along lower edge of cheek...........................
...........................................................................Eleotris acanthopoma
Lb Gill rakers on first arch 10–13; >40 predorsal scales; 7–12 transverse
lines of pit organ canals along lower edge of cheek .......................M
Ma Gill rakers on first arch 12–13; midlateral scales 46–56; >40 predorsal scales; 7–9 transverse lines of pit organ canals.....E. melanosoma
Mb Gill rakers on first arch 10–12; midlateral scales 57–65; >42 predorsal scales; 8–12 transverse lines of pit organ canals...............E. fusca
Na Scales small, usually >50 in midlateral series (except for O. nullipora) ..................................................................................................O
Nb Scales larger, usually <45 in midlateral series..................................T
Oa Second dorsal fin rays I, 8–9; colour uniform, mottled or distinct
difference between dorsal and ventral sides.....................................P
Ob Second dorsal fin rays I, 11–14; distinct chevron-like markings on
sides ...................................................................................................R
Pa Teeth of jaws more or less uniform, or some only slightly enlarged
................................................................................Bunaka gyrinoides
Pb Teeth of jaws with outer row enlarged ............................................Q
Qa Anal, pelvic and pectoral fins spotted or barred, narrow white stripe
(or irregular white blotches) along midline; caudal fin slightly
pointed; papillae below eye arranged in six distinct vertical lines
Oxyeleotris selheimi
Qb Anal, pelvic and pectoral fins without spots or bars (dorsal and
caudal fins may be spotted); midlateral without white stripe; caudal
fin rounded; papillae below eye arranged in 9 indistinct vertical
lines plus 2 anterior oblique lines ..................................O. lineolatus
Ra Midlateral scales 30-38 ....................................................O. nullipora
24
Figure 36
Figure 37
Figure 38
Figure 39
Figure 40
Key to native and alien fishes of north-eastern Australia
Rb
Sa
Sb
Ta
Tb
Ua
Ub
Va
Vb
Midlateral scales >55.........................................................................S
Second dorsal I, 12–14; anal I, 10–12; predorsal scales 35–40; 3 head
pores forward of eye, 4 pores on preopercle margin and 2 on operculum .................................................................................O. aruensis
Second dorsal I, 11–12; anal I, 11–12; predorsal scales 37–45; 2 head
pores forward of eye, 5 pores on preopercle margin and 5 on operculum ...............................................................................O. fimbriata
Head strongly depressed, width about 1.5 times depth; mouth large
in adults, reaching to, or beyond, middle of eye; side of head scaleless .....................................................................................................U
Head rounded or truncate in side view, width about 0.8–1.2 times
depth; mouth smaller, ending below or before anterior part of
pupil; side of head scaled .................................................................V
Pectoral rays 16–20, usually 18–19; total gill rakers on first arch
14–20; gill openings reaching forward to below eye ................................
.......................................................................Philypnodon grandiceps
Pectoral rays usually 15–16; total gill rakers on first arch 11–12; gill
openings restricted, reaching to below rear margin of preopercle
....................................................................................Philypnodon sp.
Pectoral rays 18–19; midlateral scales 36–40 .....Gobiomorphus coxii
Pectoral rays 14–16; midlateral scales 30–34 ...................G. australis
25
Freshwater Fishes of North-Eastern Australia
Study area, data collection, analysis and presentation
with the fishes of the North-east Coast Drainage Division
(Fig. 1), a relatively narrow strip bounded by the Great
Dividing Range and the Coral Sea. Although this drainage
division represents only 5.8% of the continental area, its
rivers discharge almost 25% of the total annual discharge
of 34.6 x 107 ML [1409].
Study area
Australia can be divided into 12 major drainage divisions
based on climate, landform and the distribution of aquatic
habitat types (Fig. 1) [52, 936, 1409]. The biogeography of
Australia’s freshwater fishes is highly congruent with these
drainage divisions [1340]. This text is primarily concerned
AUSTRALIAN DRAINAGE DIVISIONS
Philippin es
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
Pacific
Ocean
Malaysia
New
Gu inea
Solomo n
Islands
Ind onesia
Vanu atu
Coral
Sea
Australia
Ind ian
Ocean
Fiji
New
Caledon ia
New
Zealand
Tasman
Sea
North-east Coast Division
South-east Coast Division
Tasmania Division
Murray-Darling Division
South Australia Gulf Division
South-west Coast Division
Indian Ocean Division
Timor Sea Division
Gulf of Carpentaria Division
Lake Eyre Division
Bulloo-Bancannia Division
Western Plateau Division
152°31'00"
-42°00'00"
Arnhem Land
Alligator Rivers
Region
Darwin
Kimberley
VIII
IX
Pilbara
XII
I
VII
X
Brisbane
XI
Perth
V
IV
II
VI
Sydney
Adelaide
Canberra
Melbourne
N
116°00'00"
-40°01'00"
0
500
1,000
III
Hobart
Kilometres
Figure 1. Map of Australia showing the major drainage divisions and some localities mentioned in the text. Base data
reproduced with the permission of the Queensland Department of Natural Resources, Mines and Energy.
26
Study area, data collection, analysis and presentation
QUEENSLAND DRAINAGE BASINS
Gulf of Carpentaria &
Wester n Cape York
Peninsula
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
928
927
137°13'00"
-11°20'40"
101
926
102
924
925
Easter n Cape York
Peninsula
Settlement
Mornington Island
Nicholson
Leichhardt
Morning
Flinders
Norman
Gilbert
Staaten
Mitchell
Coleman
Holroyd
Archer
Watson
Embley
Wenlock
Ducie
Jardine
Torres Strait Islands
101
102
103
104
105
106
107
Jacky Jacky
Olive-Pascoe
Lockhart
Stewart
Normanby
Jeannie
Endeavour
Wet Tropics
108
109
110
111
112
113
114
115
116
Daintree
Mossman
Barron
Mulgrave-Russell
Johnstone
Tully
Murray
Hinchinbrook Island
Herbert
South-eastern
Queensland
Central Queensland
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
Black
Ros s
Haughton
Burdekin
Don
Proserpine
Whitsunday Island
O'Connell
Pioneer
Plane
Styx
Shoalwater
Water Park
Fitzroy
Curtis Island
Calliope
Boyne
Baffle
Kolan
136
137
138
139
140
141
142
143
144
145
146
Burnett
Burrum
Mary
Fraser Island
Noosa
Maroochy
Pine
Brisbane
Stradbroke Islands
Logan-Albert
South Coast
103
923
Coen
922
104
Gulf of Carpentaria
and Western Cape York
Peninsula
Eastern Cape York Peninsula
106
921
920
105
107
919
108
109
911
110
Cairns
918
914
Wet Tropics
111
910
112
113
114
115
117
116
912
917
916
Townsville
118
119
913
121
120
122
123
124
IX
915
Mackay
125
I
Mount Isa
Central Queensland
126
129
Rockhampton
127
128
X
131
132
133
134
135
130
137
South-eastern
Queensland
139
Maryborough
136
138
140
141
IV
XI
Brisbane
142
144
143
146
N
145
154°00'45"
0
250
500
-29°45'00"
Kilometres
Figure 2. Map of the coastal drainage basins of Queensland and some locations mentioned in the text. Drainage basins
designations and numbering follow the Queensland Department of Natural Resources, Mines and Energy. Base data reproduced
with the permission of the Queensland Department of Natural Resources, Mines and Energy.
27
Freshwater Fishes of North-Eastern Australia
The North-east Coast Division contains almost one half of
all species of freshwater fishes found in Australia. Moreover,
many of the fishes of the North-east Coast Division are
widespread, occurring across northern Australia to the
Kimberley region or southward into the South-east Coast
drainage Division, which extends down through New South
Wales, Victoria and into South Australia. In addition, some
fauna are shared with the Murray-Darling Drainage
Division. The material presented in this book concerning
the ecology of fishes of the North-east Coast Division has
broad relevance for eastern Australia.
specifically for Australian climatic conditions, they do
serve to illustrate the diversity of climate present across
the continent. North-eastern Australia (as defined here)
traverses the tropical zone (from Cape York Peninsula
south to about Mackay) and the area further south which
is transitional between the tropical type and the warm
temperate type [1361].
Figure 3 illustrates some aspects of the climatic diversity
present in north-eastern Australia. The climate of eastern
Cape York Peninsula is typified by rainfall and temperature
data recorded at the township of Coen. Mean monthly
maximum temperatures rarely fall below 28°C and mean
monthly minima drop below 20°C only during the period
June to September. Very little rainfall occurs over the period
April to November. The period of greatest rainfall is related
to the development of the southern monsoonal trough and
most occurs in association with the passage of tropical
cyclonic weather systems. The climate of the Wet Tropics
region is also monsoonal. Only minor seasonal variation in
climate is experienced in Cairns, located at sea level. Mean
monthly maxima exceed 33°C in December only and fall
below 27°C in June and July only. Minimum monthly
temperatures average about 20°C and fall below 17°C in
July and August only. Maximum temperatures at Atherton,
located at an elevation of 753 m.a.s.l. on the Atherton
Tablelands to the immediate west of Cairns, are slightly
lower and vary more throughout the year. The range in
monthly mean temperatures at Atherton exceeds that for
Cairns. Mean monthly temperatures may approach 10°C
during the drier months and short periods of frost may
occur then also. Both Cairns and Atherton experience the
majority of rainfall during the summer monsoonal period
but also experience consistent rainfall during the period
May to November. Moisture laden south-easterly winds
deposit substantial rain during this period as they cross the
coast and are forced over the mountainous terrain typifying this area. This region contains Queensland’s two highest mountains (Mts. Bartle Frere and Bellenden Kerr, both
exceeding 1500 m in height) and is notable for being the
wettest region in Australia [27]. Although rainfall is basically seasonal in occurrence, there is little seasonal signal in
the number of rain days per month [27].
The North-east Coast Division (Figs. 1 and 2) extends
through more than 18° of latitude. Accordingly, there is an
enormous diversity of climate, flow regime, landform and
river type across this gradient. On the basis of these physical features, the North-east Coast Division can be further
subdivided into four secondary drainage divisions (Fig.
2), which also correspond with variations in fish species
composition (Appendix 1) [1340]. These four subdivisions are: Eastern Cape York Peninsula, the Wet Tropics
region, Central Queensland, and south-eastern
Queensland; each is composed of a number of separate
drainage basins. The majority of drainage basins are relatively small, with few exceeding 10 000 km2. Note that
some of these drainage basins are composed of more than
one, albeit small, separate river systems. Throughout this
book, the four secondary drainage divisions of the Northeast Coast Division, and the separate drainage basins
within them, are used as the basic spatial template for
discussions of fish species distribution and ecology. We
follow the drainage basin designations and numbering
system used by the Queensland Department of Natural
Resources and Mines.
Climate
Bridgewater [226] provides an overview of the Australian
climate in which he notes that of the seven major global
climate types identified by Walter and Leith [1361], four
occur in Australia. These are:
• Tropical type, characterised by some seasonality in
temperature and a concentration of rainfall in the
warmer months;
• Subtropical dry type, characterised by very low rainfall, high summer maximum temperatures and low
winter minima;
• Transitional zone with winter rainfall, characterised
by very little summer rainfall, typically no winter cold
season but permanent summer drought; and
• Warm temperate type, characterised by no noticeable
winter and year-round rainfall.
Climate records for Ayr located near the mouth of the
Burdekin River are typical for central Queensland and
reveal a climate dominated by maximum temperatures
and rainfall during the period December to April (Fig. 3).
Diel variation in temperature, particularly during the drier
months, is a feature of the region and although frosts are
not common at sea level, they may occur in the headwater
areas of the Burdekin River. Rainfall is erratic in incidence,
strongly influenced by cyclonic weather systems and varies
greatly from year to year [1089].
Whilst these are very broad categories intended for
characterisation of global climate regimes rather than
28
Study area, data collection, analysis and presentation
Discharge regimes
A river’s discharge regime is defined by the temporal variation in the amount of water being carried within its channel as a result of temporal variation in climate (rainfall,
temperature and evaporation). In addition, evapotranspiration and groundwater inputs also markedly affect
discharge regime. Flow regimes vary markedly throughout
north-eastern Australia. The Normanby River in Cape
York Peninsula has a distinctly seasonal flow regime with
most (86%) discharge occurring in January, February or
March (Fig. 4). Wet season flows break out of the stream
channel and inundate floodplain waterbodies. Very little
flow occurs from June to November and the river contracts
to a series of large isolated within-channel pools. Notably
however, while reduced flows during the dry season are
predictable in occurrence, wet seasons flows are less
predictable in timing and magnitude. The coefficient of
variation (CV) of mean annual discharge (standard deviation of the mean/mean x 100) is high (up to 105% [697])
indicating that many years lack a summer flood (‘failed
wet seasons’).
The climate of south-eastern Queensland, typified by that
recorded at Gympie in the Mary River drainage, and
Beaudesert in the Albert/Logan River drainage, is more
seasonal. Mean monthly thermal maxima and mean
monthly minima vary by about 10°C and 15°C, respectively,
throughout the year. The pattern of rainfall is less strongly
dominated by the summer monsoon and frequently influenced by the northward extension of temperate weather
systems [1095]. As detailed above, this region is transitional
between the tropical and warm temperate climate types
identified by Walter and Leith [1361].
In summary, the climate of north-eastern Australia
changes with latitude. Although maximum summer
temperatures vary little across the latitudinal gradient
encompassing north-eastern Australia (cf. Coen and
Beaudesert), the extent of diel variation increases significantly from about 10°C in the north to about 15°C in the
south. Moreover, the difference between mean summer
and winter temperatures increases as one moves south,
mainly as a result of a decrease in mean monthly thermal
minima. Seasonality is defined more by temporal variation in rainfall at low latitudes in the north whereas
temporal variation in temperature defines seasonal shifts
in climate in the south.
35
Coen
30
500
400
25
35
The flow regime of rivers of the Wet Tropics region is in
stark contrast to those of Cape York Peninsula. Rivers of
this region vary little in discharge from year to year (i.e.
500
Cairns
30
400
25
5
35
200
15
100
0
Ayr
30
500
400
25
100
10
5
35
500
Gympie
30
400
100
10
35
0
Beaudesert
30
500
400
300
20
200
2
0
200
0
15
15
100
200
15
300
20
10
300
25
25
15
400
5
0
300
20
500
20
200
10
30
300
20
15
Atherton
25
300
20
35
100
10
™
100
10
™
™
5
0
Month
5
0
Month
5
0
Month
Figure 3. Plots of mean daily minimum temperature (closed squares), mean daily maximum temperature (open squares) and
mean monthly rainfall (open circles) for each month at selected locations in eastern Queensland. The period of data record from
which means and ranges were calculated was >80 years for each location except Cairns (~50 years). Data source: Queensland
Bureau of Meteorology.
29
Freshwater Fishes of North-Eastern Australia
they exhibit low annual CV values). For example the
Mulgrave and Johnstone rivers have CV values of 28% and
34%, respectively [1096, 1100]. Rivers of this region are
perennial. The Johnstone River may cease to flow in as few
as 1 in every 50 years. Wet season flows dominate the
monthly hydrograph as they do in the Normanby River
(Fig. 4) but discharge during the dry season remains high,
contributing about 25% of mean annual flow. Two
features of the region contribute to this pattern. First, rainfall remains high during the dry season (Fig. 3). Second,
much of the catchments of some rivers of the Wet Tropics
region are composed of porous basalt, which acts as a large
aquifer contributing significant amounts of the groundwater throughout the year. Thus even small tributary
systems such as the upper North Johnstone River at
Malanda are perennial. Dry season flows tend to remain
very stable and there is a low likelihood of spates occurring during the period June to October [1093, 1096]. It
should be noted that the Mulgrave and Johnstone rivers
are located in the centre of the Wet Tropics region. Rivers
to the north and south grade into more seasonal flow
regimes characterised by a reduced contribution of dry
season flows to the annual total.
300
250
200
Normanby Riv er
Gauge105101A
2
150
(2,302 km )
The flow regimes of rivers of central Queensland, such as
the Burdekin River, are similar to those of eastern Cape
York Peninsula (Fig. 4). Most of the discharge occurs
during a well-defined summer wet season, with very little
discharge occurring outside of the months April to
November. The flow regimes of the Burdekin and Fitzroy
rivers have been identified as amongst the most variable in
the world [1076]. Wet season flow are dominated by one
or rarely two large flood events associated with cyclonic
weather systems which may occur at any time from
December to April [1089]. Wet seasons fail regularly in this
region leading to substantial year-to-year variation. The
CV of annual flow in the Burdekin River itself exceeds
100% whereas in some tributary systems, particularly in
the south-west, annual flows may be even more variable
[1089]. In contrast to the perennial flow regimes typical of
the Wet Tropics region, the flow regimes of rivers of central
Queensland are typified by long periods of very little flow
occasionally punctuated by extreme flood events.
The flow regimes of rivers in south-eastern Queensland
are different to that described for rivers further north. The
majority of stream flow occurs in the summer months of
Lower Mulgrav e Riv er
Gauge111007A
2
40
30
(520 km )
Upper Nth Johnstone
Riv er, Gauge112003A
2
(165 km )
200
150
100
20
50
10
0
0
100
50
0
1500
1250
300
Burdekin Riv er
Gauge120002C
Mary Riv er
Gauge138001A
250
2
2
(36,260 km )
(4,755 km )
1000
200
750
150
500
100
250
50
0
0
40
30
Albert Riv er
Gauge 145196A
2
(722 km )
20
10
Month
0
Month
Month
Figure 4. Variation in mean total monthly discharge for selected eastern Queensland Rivers. The catchment area (km2)
upstream of each gauging station is given in parentheses. The period of data record from which means were calculated was
>20 years for each gauge. Data source: Queensland Department of Natural Resources, Mines and Energy.
30
Study area, data collection, analysis and presentation
Figures 5 and 6 and Table 1 for details of drainage basins
and rivers examined within these regions), the details of
which are in the process of being published (see also [706,
707, 708, 1100, 1107, 1108, 1109]). This study was undertaken over the period 1994–1997 in the Wet Tropics region
and 1994–2003 in south-eastern Queensland. It involved
quantitative sampling of fish assemblages at 416 locations,
959 separate samples (location and sampling occasions)
and the collection of over 199 000 individual fish from 68
species (almost all of which were returned alive to the
water at the site of collection).
January to March, followed by a second minor peak in
discharge between April and July as a result of northern
penetration of low-pressure temperate weather systems
[1095]. The incidence and magnitude of these secondary
peaks in flows is quite unpredictable, as are summer wet
season flows, and thus rivers of this region tend to show
high annual CV values (100% or greater) [1100]. Tributary
streams tend to be considerably more variable than
lowland river systems and variability in discharge
decreases markedly with distance downstream [1095].
Despite the high variability in summer wet season flows
and therefore of total mean annual discharge, flows during
the dry season period of July to October are relatively
stable and vary little [949, 950, 951, 1095].
To simplify discussion of species frequency of occurrence,
abundance and biomass, data has been summarised for
rivers and streams in the Wet Tropics region grouped
according to drainage basin designation (Fig. 5), and for
south-eastern Queensland, also according to geographic
proximity and geomorphological similarity (Fig. 6 and
Appendix 1). Rivers and streams sampled in the Sunshine
Coast region (Noosa Basin 140 and Maroochy Basin 141)
generally drain sandy acid-wallum landscapes and have
been grouped together. Short coastal streams of the
Logan-Albert Basin draining into Redland Bay (Basin 145a
– Appendix 1) are small catchments quite dissimilar to the
Logan-Albert River proper and so have also been grouped
with other morphologically similar coastal streams of the
greater Moreton Bay region (i.e. those in the Pine Basin –
142) (Figure 6). All other rivers and streams have been
grouped according to their drainage basin designation
(Mary River – Basin 138; Brisbane River Basin – 143;
Logan-Albert River – 145a,b; South Coast rivers and
streams – Basin 146) (Fig. 6).
Study basins and site locations
The species summaries in this book are based on many
different sources of information gathered by many individuals and groups. Our own studies have occurred in a
variety of areas including basins in Cape York Peninsula
[697, 1099, 1101], the Wet Tropics region [49, 1085, 1087,
1091, 1096, 1097, 1100, 1104, 1107, 1108, 1109], central
Queensland [1079, 1081, 1082, 1089, 1098] and southeastern Queensland [84, 99, 104, 205, 699, 700, 701, 702,
704, 709, 1095, 1100, 1107]. The reader is referred to these
studies for more detail concerning site location and
sampling methods. Much of the information contained in
this book, especially that concerning habitat use, variation
in abundance and biomass, and aspects of life history, is
drawn from a recent comparative study undertaken in the
Wet Tropics region and south-eastern Queensland (see
Table 1. Sampling intensity in rivers and streams of the Wet Tropics region and south-eastern Queensland. See Figures 5 and 6
and Appendix 1 for river basin and sub-basin locations and designations.
Region/River
Number of
locations
Number of
samples
Number of
fish species
collected
51
56
11
83
190
11
32
37
19
7959
27 267
717
118
284
39
35 943
50
29
20
111
68
20
225
42
37
165
174
32
27
24
21
28
28
21
83 198
2557
4310
26 536
43 162
3558
Wet Tropics region
Mulgrave Russell River (Basin 111)
North and South Johnstone rivers (Basin 112)
Tully River (Basin 113)
Sub-total
South-eastern Queensland
Mary River (Basin 138)
Sunshine Coast rivers and streams (Basins 140b; 141)
Moreton Bay rivers and streams (Basins 142; 145a)
Brisbane River (Basin 143)
Logan-Albert River (Basin 145b,c)
South Coast rivers and streams (Basin 146)
Number of
individuals
collected
Sub-total
298
675
38
163 321
Total
416
959
68
199 264
31
Freshwater Fishes of North-Eastern Australia
146°06'00"
-16°55'00"
Cairns
111 Mulgrave-Russell
Basin
Mulgrave-Russell Rivers
Johnstone River
Tully River
Innisfail
112 Johnstone Basin
N
145°30'00"
-18°01'00"
113 Tully Basin
0
10
20
kilometres
Figure 5. Location of study sites in the Wet Tropics region of northern Queensland. Base data reproduced with the permission
of the Queensland Department of Natural Resources, Mines and Energy.
32
Study area, data collection, analysis and presentation
152°28'00"
-24°52'00"
Fraser Island
Mary River
Sunshine Coast rivers and streams
Moreton Bay rivers and streams
Brisbane River
Logan-Albert Rivers
South Coast rivers and streams
138 Mary Basin
140 Noosa Basin
!!
!
! !
!
!
!
!
!
!
141 Maroochy Basin
'
''
'
!!
'
'
'
'
'
''
''
'
'
''
'' '
'
'
' ' '
'
'
'
!!
'
'
=
'
''
'
'
'
143 Brisbane Basin
'
'
'
'
'
'
'
'
N
Bribie Island
'
' '
' '
'
'
'''
!
'
Moreton Island
=
= =
=
=
=
=
=
=
=
== =
=
=
'=
' ' '' '
' ' '
'
' '
'
'
' '
'
'
'
'
'
''
'
'
'
'
'
'
'
''
''
'
' '''
'
142 Pine Basin
Moreton
Bay
Brisbane
=
' = =
=
North
Stradbroke Island
South
Stradbroke Island
146 South Coast Basin
153°58'00"
0
35
70
-28°14'00"
kilometres
145 Logan-Albert Basin
Figure 6. Location of study sites in south-eastern Queensland. Base data reproduced with the permission of the Queensland
Department of Natural Resources, Mines and Energy.
33
Freshwater Fishes of North-Eastern Australia
lowland reaches of rivers in the Wet Tropics region further
constrained our ability to sample these habitats by these
methods. The ecology of fishes in lowland river reaches of
north-eastern Australia remains one of the least studied
aspects of this field in Australia and offers exciting potential for further research. The majority of study locations in
both the Wet Tropics region and south-eastern
Queensland were relatively undisturbed. However, some
of the sampling in south-eastern Queensland was undertaken as part of a project to examine the effects of human
activities on freshwater fish assemblages [709, 1255], and
some sites in this region were therefore impacted to varying degrees by land use activities (e.g. land clearing, grazing, cropping and urbanisation), water resource
development and local riparian and in-stream habitat
degradation.
Site selection and spatial distribution
The location of the individual sampling sites in the Wet
Tropics region are shown in Figure 5 and that of sampling
locations in south-eastern Queensland in Figure 6. Fish
and habitat sampling was conducted with the intention of
characterising as much of the environmental and biological variation possible in each selected stream reach within
the hierarchical organisation of habitats characteristic of
river networks. In south-eastern Queensland streams, at
least two contiguous hydraulic habitat units (i.e. riffles,
runs and pools) were usually sampled in each reach in
order to encompass this variation (Fig. 7), except during
dry periods when surface waters occasionally contracted
to shorter isolated pools. In rivers of northern
Queensland, a single hydraulic habitat unit was usually
sampled at each location. Study sites in the Wet Tropics
region were, on average, 34.1 ± 0.9 m in length and 347.1 ±
17.6 m2 in wetted area, and those in rivers of south-eastern
Queensland were of similar size: 38.6 ± 0.5 m stream
length and 313.3 ± 10.6 m2 wetted area. Note that all error
terms are listed as Standard Error throughout this book
unless otherwise stated.
Study sites were sampled over a range of seasonal and
hydrological conditions effectively encompassing the
range of flow conditions expected in these rivers and
regions (Fig. 8). Although fish assemblages were not
sampled during large floods, samples were frequently
collected as soon after flooding as practicable. The reader
should note that we sometimes present summaries of
information in which sampling occasions are grouped
(e.g. length-frequency data). We have used traditional
seasonal groups (i.e. summer, autumn, winter and spring)
for data collected in south-eastern Queensland but not the
Wet Tropics regions, as application of such seasonal categories is not appropriate in the latter region due to its tropical climate (see above).
Study sites were arrayed widely throughout each catchment from headwaters to downstream reaches, however
study site location was constrained by our choice of
sampling methodology (back-pack electrofishing and
seine-netting – see below). This limited our ability to
sample fish assemblages effectively and quantitatively in
large lowland river reaches with a depth of greater than 1.5
m. In addition, the presence of estuarine crocodiles in
River
Reach
Hydraulic unit
In-stream habitat
sampling point
Distance upstream (m)
40
Pool
Riffle
Sampling
location
Run
35
Bank habitat
sampling segment
30
25
Flow
20
15
10
5
Hydraulic
unit
0
E
D
C
B
A
1/6w 2/6w 3/6w 4/6w 5/6w
Right bank
Transect
Left bank
Figure 7. Spatial scale at which individual hydraulic units within each river reach were defined for sampling fish and habitat.
Also shown are the sampling points within each hydraulic unit where measurements of in-stream habitat and bank habitat
structure were undertaken.
34
Study area, data collection, analysis and presentation
25
These data were collected as part of the process for determining distribution and abundance at larger spatial scales.
The following data were estimated for each individual
collected during electrofishing and recorded on data
sheets:
• Mean water column velocity (portable flow meter)
• Focal point velocity (portable flow meter)
• Total water column depth (graduated stick)
• Focal point depth (graduated stick)
• Proportional substrate composition in one square
metre immediately below the fish (i.e. mud, sand, fine
gravel, coarse gravel, cobbles, rocks and bedrock)
• Distance to nearest potential refuge (i.e. microhabitat
structure)
• Distance to bank
Wet Tropics (n=284)
South-eastern Queensland (n=675)
20
15
10
5
0
Summer
Autumn
Winter
Spring
Summer
Month/Season
For fish less than 0.2 m from the nearest refuge, the type of
potential cover with which it was associated was recorded
(note that 0.2 m is an arbitrary distance only). The cover
elements identified were: the substratum itself, submerged
aquatic macrophytes, filamentous algae, leaf litter, emergent vegetation, submerged bank-side vegetation,
submerged overhanging vegetation, large woody debris,
small woody debris, undercut banks and root masses. Fish
>0.2 m from the nearest potential cover were recorded as
being in open water.
Figure 8. Distribution of sampling occasions in months and
seasons throughout the study period.
Collection and quantification of fish abundance levels
Fish assemblages at each site were intensively sampled
using the procedures detailed in Pusey et al. [1107]. Each
hydraulic unit was blocked upstream and downstream
with weighted seine nets (11 mm stretched-mesh) to
prevent fish movement into or out of the study area. The
site was sampled using a combination of repeated pass
electrofishing (Smith-Root model 12B Backpack
Electroshocker) and supplementary seine netting until few
or no further fish were collected. Usually four electrofishing passes and two seine hauls were required to collect all
fish present within a site. The intensive sampling regime
described here has been demonstrated to provide accurate
estimates of species composition and abundances in wadeable stream sites [1107].
Two problems with this method can be identified immediately. First, it relies on the investigator being able to see the
fish in question and to see its position within the habitat
milieu prior to it being stunned. Second, it must be
assumed that the observed microhabitat use does not
differ from a hypothetical condition that might exist without the presence of the observer and his or her electrofishing gear. These are potentially important biases and we
sought to minimise their influence in three ways. First,
microhabitat data was only collected when water clarity
was sufficiently high to allow observation. Second, microhabitat data was not recorded or used if the position of the
fish was unknown prior to it being stunned. Third, microhabitat data was only recorded for fish collected during
the first electrofishing pass, the assumption being that the
behaviour of fish changed significantly after they had
experienced the observer and the electrofisher for the first
time. In addition, we have, on occasions, conducted
snorkelling surveys and recorded habitat use data prior to
electrofishing in an attempt to assess the accuracy of habitat use data recorded during electrofishing. Habitat use
data generally matched quite closely for the two methods.
One possible exception is the estimation of focal point
depth and velocity for fish located in the bottom-third of
the water column but not in actual contact with the
substrate, especially when depth exceeds 1 m.
All fish collected were identified to species, counted, measured (standard length to the nearest mm) and all native
fish were returned alive to the point of capture. Alien fish
were euthanased (using benzocaine – MS222), and were
not returned to the water (in accordance with the
Queensland Fisheries Act 1994). The weight of each fish
(both native and alien species) was estimated by reference
to previously unpublished and existing relationships
between body length and mass for each species. Fish abundance and biomass data were transformed to numerical
densities (number of individuals.10m–2) and biomass
densities (g.10m–2) at each site.
Quantification of fish microhabitat use
Microhabitat use data for many of the fish species covered
in this text were colleted during sampling in the Mulgrave
and Russell rivers in the Wet Tropics region and in the
Mary and Albert rivers in south-eastern Queensland.
35
Freshwater Fishes of North-Eastern Australia
1:100 000 topographic maps using a digital planimeter and
also using Geographical Information System (GIS) data.
Riparian cover was estimated from multiple measures
(usually three) at each site on each occasion, using a handheld densiometer. Estimates of variables describing habitat structure at the meso- and microhabitat scale within
each site and on each occasion were based on multiple
samples within a combined bank transect and random
points scheme. An imaginary grid (40 rows and five
Quantification of habitat structure at macro-, mesoand microscales
A range of catchment and local scale environmental variables describing habitat structure (Table 2) was measured
at each site and on most sampling occasions according to a
standard protocol briefly described in Pusey et al. [1100]
and more fully here. Catchment descriptors for each site
(upstream catchment area, elevation, distance from stream
source and distance to river mouth) were estimated from
Table 2. Environmental variables estimated at each sampling location.
Variable/Measurement Unit
Catchment variables
Upstream catchment area (km2)
Distance from stream source (km)
Distance to river mouth (km)
Elevation (m.a.s.l.)
Site physical characteristics
Wetted stream width (m)
Riparian cover (%)
Water depth (cm)
Mean water velocity (ms–1)
Site gradient (%)
Substrate composition (% surface area)
Mud
Sand
Fine gravel
Coarse gravel
Cobble
Rock
Bedrock
Microhabitat structure (% surface area)
Aquatic macrophytes
Filamentous algae
Overhanging vegetation
Submerged vegetation
Emergent vegetation
Leaf litter
Large woody debris
Small woody debris
Undercut banks (% bank)
Root masses (% bank)
Water chemistry
Water temperature
Dissolved oxygen
pH
Conductivity
Turbidity
Description
Estimated using 1:100 000 topographic maps and digital planimeter or GIS
Estimated using 1:100 000 topographic maps and digital planimeter or GIS
Estimated using 1:100 000 topographic maps and digital planimeter or GIS
Estimated using 1:100 000 topographic maps and digital planimeter or GIS
Horizontal distance measured perpendicular to stream flow from bank to bank at existing
water surface using tape measure.
Hand-held densiometer.
Vertical distance from existing water surface to channel bottom measured using graduated
stick.
Speed at which water moves downstream. Measured with a Swoffer current velocity meter
at 0.6 of water column depth.
Measured for each hydraulic habitat unit using staff, dumpy and tripod.
(Visually estimated)
<0.06 mm (particle size)
0.06 mm–2.0 mm
2.0 mm–16.0 mm
16.0 mm–64.0 mm
64.0 mm–128.0 mm
>128.0 mm
(Visually estimated)
Submerged aquatic macrophytes and charaphytes.
Overhanging terrestrial vegetation in contact with water surface.
Submerged terrestrial vegetation along river margins (e.g. grasses and annual weeds).
Semi-aquatic vegetation (e.g. sedges and rushes).
Accumulations of leaf litter and fine woody material (<1 cm stem diameter)
Woody debris >15 cm minimum stem diameter.
Woody debris of <15 cm maximum stem diameter.
Bank overhanging water by at least 30 cm, and no more than 10 cm above water surface,
expressed as a proportion of wetted stream perimeter.
Submerged bankside root masses, expressed as a proportion of wetted stream perimeter.
Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems
DT50 data logger).
Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems
DT50 data logger).
Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems
DT50 data logger).
Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems
DT50 data logger).
Measured using water chemistry multimeter (Greenspan sensors and Pacific Data Systems
DT50 data logger).
36
Study area, data collection, analysis and presentation
random points (i.e. a sample size of 20 or more) with those
taken at a much reduced number of points (3) revealed
little difference [1093].
columns) was imposed on each site (Fig. 7) and the mesoand microscale variables listed in Table 2 were measured at
a series of previously selected random points across the
grid. The distance between the cross-sectional lines on the
imaginary grid was dependent on the length of the study
site, according to the formula: grid length interval = study
site length/40. Thus, grid lines were spaced at approximately 1 m intervals on average. The interval between
longitudinal grid lines was determined by the formula:
grid width interval = wetted stream width/6. Thus vertical
grid lines A and E in Figure 7 were one-sixth of the stream
width away from the left and right banks, respectively,
whereas grid line C was always in the centre of the wetted
stream width. In general, this scheme resulted in 20 measures for each parameter at each site. Habitat variables were
measured or estimated at each of these randomly selected
points. Substrate composition was estimated by eye for a
1 m2 quadrat centred on each survey point according to a
modified Wentworth scheme described in Pusey et al.
[1095] and detailed in Table 2. Average values (depth and
current velocity), or average proportion of mean wetted
site area (substrate composition and microhabitat
elements) were then estimated. With practice, the location
of each point is quickly committed to memory and the
process is rapid and efficient. A pilot study prior to the
main sampling program revealed that the in-stream habitat sampling scheme described above often failed to
include microscale habitat elements located close to the
bank (such as woody debris, macrophyte beds, banks of
leaf litter). In order to fully capture such elements, a series
of graduated bank transects was also established on both
banks. Transect width was set at: width = stream wetted
width/10 and the length of segments within each transect
set as length = site length/4. Microhabitat cover for each
element and substrate composition were estimated by eye
and expressed as a proportion of the area enclosed within
each segment of the bank transect. The extent of bank
associated root masses and undercuts was expressed as a
proportion of bank length in each segment. Thus eight
measures of these parameters were estimated at each site
Inter-regional comparison of habitat structure and
water quality
Figure 9 summarises the distribution of study sites within
each region across various macro- and mesoscale habitat
variables. These data represent the frequency distributions
of mean estimates of habitat parameters for each site across
the range of sites examined. Over 70% of sites in both
regions were located in streams with a catchment area of
less than 200 km2. A greater number of larger streams were
examined in south-eastern Queensland than in the Wet
Tropics region, reflecting differences in catchment area of
the rivers examined (see Fig. 2). Catchment size also influenced the distribution of sites with respect to distance
downstream from the stream source and upstream from
the river mouth. More sites distant from the river mouth
were examined in south-eastern Queensland than in the
Wet Tropics region. Sites in south-eastern Queensland were
distributed more evenly across the elevation gradient than
were sites in the Wet Tropics region. Rivers of the Wet
Tropics tend to have a short lowland section and then rise
very steeply to their headwaters (see [1096]). Some of these
rivers have an upper low gradient section located at high
elevation (>500 m) on the Atherton Tablelands.
Despite these differences at the landscape or macrohabitat
scale, study sites were arrayed similarly across the gradients of stream width, gradient and riparian cover.
Approximately 20% of sites in south-eastern Queensland
had localised patches greater than 1.25 m deep whereas
such depths were uncommon in streams sampled in the
Wet Tropics region. Mean site depth varied little between
regions however. Although sites within both regions
covered similar ranges in maximum current velocity
recorded in each site, comparatively fewer sites in the Wet
Tropics region had average current velocities less than 0.01
m.sec–1 (i.e. still water). This reflects the differences in
regional hydrology. Rivers and streams of the Wet Tropics
region rarely cease to flow.
Estimates of proportional cover and substrate composition derived from both schemes were then combined to
give an overall representation of the habitat structure of
each site by weighting the area characterised by each
method (i.e. estimates derived from bank transects characterised 20% of the wetted area whereas the random
points scheme characterised habit structure in the middle
80% of wetted area).
Substrate composition differed slightly between the two
regions (Fig. 10). Coarse gravel was the dominant particle
size in streams of south-eastern Queensland, whereas
rocks were the dominant particle size in streams of the Wet
Tropics. Bedrock was present in streams of this region also,
but was almost absent from streams of south-eastern
Queensland. The average contributions of mud, sand and
fine gravel were very similar in both regions.
Ambient water quality conditions (Table 2) at each site on
most sampling occasions were characterised by the mean
of three measurements for each parameter taken at each
site. A pilot study comparing measures taken at each of the
The two regions differ substantially with respect to the
types and abundance of different cover available to fishes.
Aquatic macrophytes and filamentous algae both
37
Freshwater Fishes of North-Eastern Australia
Figure 11 shows the frequency distribution of the random
points measures of current velocity, depth, substrate
composition and microhabitat cover elements. This figure
differs from data presented in Figures 9 and 10 wherein
the distribution of overall site means is presented. For
example, although aquatic macrophytes comprised, on
average, less than 1% of the area of sites in the Wet Tropics
region (Fig. 10), 6% of the random point measures were
positioned over a 1 m2 quadrat containing aquatic macrophytes. Comparing the same data for sites in south-eastern
Queensland indicates that aquatic macrophytes were more
commonly encountered and more extensive in areal coverage in this region. Data in Figure 11 is intended to allow
comprised about 10% of the area of sites located in
streams of south-eastern Queensland but were essentially
absent from study sites in the Wet Tropics region (Fig. 10).
Whether this is due to regional differences in hydrology,
canopy cover or nutrient status is unclear. Submerged
vegetation (para grass in the Wet Tropics region) was, on
average, more common in streams of the Wet Tropics
region but note that median values differ little between
regions. It is worth noting that para grass (Urochloa
(=Brachiaria) mutica) is able to establish in well-shaded
streams and is a potentially significant threat to the maintenance of habitat structure in rainforest streams [108,
250, 1092] and to freshwater fishes [94].
80
80
60
60
40
40
20
20
0
0
30
30
20
20
10
10
0
30
30
40
Distance from source (km)
Catchment area (km 2 )
40
50
0
Distance to mouth (km)
50
30
40
20
20
30
20
20
10
10
10
10
0
0
0
Mean wetted width (m)
Elevation (m)
0
Riparian cover (%)
Gradient (%)
30
30
20
20
10
10
0
0
Maximum depth (m)
30
20
Mean depth (m)
10
0
Maximum mean velocity (m/sec)
Mean velocity (m/sec)
Figure 9. Macro and mesoscale habitat characteristics of study sites located in rivers of the Wet Tropics region (solid bars, n =
118 locations and 284 mesohabitat unit samples) and south-eastern Queensland (open bars, n = 278 locations and 790
mesohabitat unit samples).
38
Study area, data collection, analysis and presentation
microhabitat preference would require that microhabitat
availability at only those sites in which a species occurred,
rather than across all sites examined (as is presented in
Figure 11), was used to base the comparison. To present
this information for individual species and study river was
beyond the scope of this text (see also section on Macro,
meso and microhabitat use below).
60
50
40
30
25
40
20
20
30
10
0
15
20
10
10
5
0
0
Mean water velocity (m/sec)
Total depth (m)
20
30
Substrate composition
40
15
20
10
10
5
30
0
0
20
10
Substrate composition
Microhabitat structure
Figure 11. Microhabitat availability in the Mulgrave and
Russell rivers, Wet Tropics region (closed bars, n = 5589
habitat sampling points), and the Mary and Albert rivers,
south-eastern Queensland (open bars, n = 9456 habitat
sampling points). Note that these data represent the
frequency distribution of random points measurements of
different microhabitat parameters.
0
Microhabitat structure
The ranges of water quality parameters encountered
during the study period are shown in Figure 12. Streams of
the Wet Tropics region tended to be warmer than those in
south-eastern Queensland, reflecting the latitudinal gradient shown in Figure 3. Very few sites were examined in
which temperature might be thought to be approaching
extreme levels. Similarly, most sites examined where welloxygenated. Streams of the Wet Tropics region tended to
be slightly more acidic than those of south-eastern
Queensland, although most were circum-neutral in acidity. Water clarity was high in both regions except in the
tannin-stained aquatic habitats of the coastal wallum
(Banksia dominated) ecosystems of south-eastern
Queensland. The two regions differ most with respect to
Figure 10. Box plots of variation in the substrate composition
and microhabitat structure of mesohabitats in rivers of the
Wet Tropics region of northern Queensland (closed circles, n =
284 mesohabitat unit samples) and south-eastern Queensland
(open circles, n = 790 mesohabitat unit samples). The lines at
the top, middle and bottom of each box represent the 75th
percentile, median and 25th percentile, respectively. Upper
and lower bars represent 90th and 10th percentiles and
means are represented by symbols.
the reader to assess the match between micohabitat use by
individual species and the availability of different microhabitats. Note however, that a quantitative assessment of
39
Freshwater Fishes of North-Eastern Australia
[1420]; an updated version of which is available online at
www.marine.csiro.au/caab.
electrical conductivity. Streams of the Wet Tropics region
rarely exceeded 100 µS.cm–1 whereas the majority of
streams examined in south-eastern Queensland exceeded
250 µS.cm–1.
40
50
30
40
30
20
20
10
10
0
0
Dissolved Oxygen (mg.L -1 )
Water temperature (o C)
100
50
80
40
60
30
20
40
10
20
0
0
pH
Conductivity (uS.cm -1 )
80
60
Description
This section is intended to provide the reader with a
detailed mechanism for confirming the identification of a
specimen determined through use of the dichotomous key
provided. We present standardised diagnoses and descriptions (meristics, morphometrics and colour patterns) of
species in life and in preservative. Where possible, we
provide length/weight relationships based on our
own data or sourced from the published literature.
Geographical or subspecific variation in appearance is
discussed and features allowing differentiation between
closely related species are highlighted. Wherever possible,
we have used the original description or subsequent taxonomic reviews as our main source of information.
However, when such sources contain limited or erroneous
data, we have used alternative sources or our own data sets.
A drawing is provided for each species that should enable
the reader to check meristic and morphometric characters
listed in the text. In most cases, these drawing were of
preserved specimens and the size, sex, locality and date of
collection are given. Occasionally, figures were based on
photographs of specimens. The year in which the figure
was drawn is also given.
40
Systematics
The nomenclatural history and details of synonomy are
given. Wherever possible, the results of morphological or
genetic studies examining phylogenetic and phylogeographic relationship are presented and discussed. The
chapters are arranged in approximate phylogenetic order
(after Paxton and Eschmeyer [1041]) and the systematics
of a particular family or genus is described in the summary
for the first species listed in each family or genus.
20
0
Turbidity (NTUs)
Figure 12. Water quality in streams of the Wet Tropics region
(closed bars, n = 233 mesohabitat unit samples) and southeastern Queensland (open bars, n = 778 mesohabitat unit
samples).
Distribution and abundance
A detailed account of the distribution of each species is
presented based on literature accounts and our own survey
results. The distribution of all fish species in coastal
drainage basins of Queensland is given in Appendix 1 and
the combined reference sources for these data are given in
Appendix 2. We present information on distribution at a
variety of scales from global, national, regional and individual river basins. We have not included maps detailing
the distribution for each species. Information regarding
the distribution of a particular species is often drawn from
a variety of sources, yet some basins may not have been
sampled adequately and it may be unknown whether a
species does occur there. Maps tend to give an overall
impression of distribution and do not highlight those
basins in which a species may be naturally absent or those
Data presentation and format of species summaries
Nomenclature
We have primarily followed the nomenclatural conventions used in Allen et al. [52] except where we have
received advice to the contrary from other taxonomists.
Common or vernacular names are given where available
and follow those given in Allen et al. [52]. Common names
often vary markedly across a species’ range, with the attendant risk of confusion between different researchers. If
common names are to be used and the potential for confusion removed or minimised, we recommend the adoption
of standardised common names. We have also listed a
unique code number of each species. This code is derived
from CSIRO’s Codes for Australian Aquatic Biota (CAAB)
40
Study area, data collection, analysis and presentation
25% of sites examined, some fish with limited distribution
may be dominant (high rank) in those sites in which they
occur, perhaps because they have highly restricted habitat
requirements, but contribute little to abundance over all
sites examined. Similar summaries are given for biomass
data. For each species the average and maximum numerical density and biomass density, respectively, for those sites
in each basin in which each species occurred are also
presented and discussed (note that biomass data was not
collected for a small proportion of samples in south-eastern Queensland).
for which inadequate data exists. We feel it important that
these factors be identified and that readers have the necessary information to make their own judgements about
patterns of distribution.
We have presented data concerning the abundance of
species in a variety of ways. First, data collected by us over
the period 1994–2003 is presented in a consistent tabular
format to facilitate comparison within and across drainage
basins and between regions. For example, Table 3 lists data
for the Fly-specked hardyhead Craterocephalus stercusmuscarum fulvus in drainages of south-eastern Queensland.
Data are listed for each basin and for all basins combined.
The proportion of the total number of locations in which
this species was collected is given as an indication of how
widespread each species is. For example, C. s. fulvus is a
relatively widespread species in south-eastern Queensland,
occurring in about one quarter of all locations examined.
Note that although this species is moderately common in
many river basins, especially the Mary River, it is absent
from the Logan-Albert River and rare in some other
streams and rivers. The proportional contribution of this
species to the total number of fish collected is given as %
abundance, as an indication of how abundant this species
is relative to other species found in the region or within
individual basins. Similarly, an indication of its ranked
abundance is also given. For example, C. s. fulvus was the
10th most abundant species collected in rivers of southeastern Queensland but contributed only 2.8% of the total
number of fish collected, and much less of the total
biomass. Also listed in parentheses are the equivalent
summaries at only those sites in which this species
occurred, to give an indication of the local abundance and
biomass of each species. For example, C. s. fulvus is relatively more common and contributes more to the total
number of fish collected in this reduced number of sites.
Although this is to be expected for a fish occurring in only
Second, we have attempted to summarise the findings of
studies in which quantitative electrofishing estimates of
abundance and biomass are not available but in which
abundance data are presented as catch per unit effort or as
relative abundance. We identify potential problems associated with comparison across studies employing different
methodologies.
Information drawn from the literature concerning distributional limits and abundance must be interpreted with
care, taking into account differences in concentration of
sampling effort and study site location, as well as differences in survey methodology (i.e. electrofishing, seine-,
gill- and hand-netting, bait trapping, visual census, ichthyocides). Different methods are often selective with respect
to the particular species or size of fish they collect.
However, abundance information derived from our
sampling of wadeable streams is directly comparable, as it
has been collected using standardised quantitative
sampling methods.
The distributional information summarised in Appendix
1 has been drawn from many studies undertaken over a
relatively long period. Some literature sources used were
published in the 1880s, for example. The abundance and
distribution of many species, particularly migratory
Table 3. Distribution, abundance and biomass data for Craterocephalus stercusmuscarum fulvus. Data summaries for a total of
4608 individuals collected from rivers in south-eastern Queensland over the period 1994–2003 [1093]. Data in parentheses
represent summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this
species occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Rank biomass
Mary River Sunshine Coast Moreton
rivers and
Bay rivers
streams
and streams
Brisbane
River
Logan-Albert
River
South Coast
rivers and
streams
25.8
62.0
3.4
15.0
36.0
—
10.0
2.82 (7.96)
3.82 (6.90)
0.04 (2.27)
1.55 (14.47)
5.05 (11.90)
—
0.59 (40.39)
10 (6)
9 (7)
22 (5)
9 (2)
6 (2)
—
14 (1)
0.21 (0.69)
0.27 (0.63)
0.01 (0.03)
0.24 (0.41)
0.63 (1.24)
—
0.11 (0.43)
19 (10)
14 (10)
14 (6)
10 (7)
10 (7)
—
13 (3)
Mean numerical density
(fish.10m–2)
0.99 ± 0.13
1.06 ± 0.17
0.03 ± 0.03
0.51 ± 0.16
0.88 ± 0.18
—
0.39 ± 0.37
Mean biomass density
(g.10m–2)
0.68 ± 0.32
0.71 ± 0.14
0.03 ± 0.03
0.25 ± 0.03
0.58 ± 0.15
—
0.34 ± 0.34
41
Freshwater Fishes of North-Eastern Australia
Table 4. Macro/mesohabitat use by Craterocephalus s. fulvus in
rivers of south-eastern Queensland. Data summaries for 4608
individuals collected from samples of 232 mesohabitat units at
76 locations between 1994 and 2003 [1093]. W.M. refers to
the mean weighted by abundance to reflect preference for
particular conditions.
species, is known or suspected to have contracted in recent
years due to deteriorating catchment condition, increasing
human pressures and an increase in the number of artificial barriers to fish movement caused by dams, weirs and
other infrastructure. The impacts of anthropogenic disturbances on fish species’ distributions and abundances are
treated in detail in the section on Conservation status,
threats and management requirements.
Min.
2
Catchment area (km )
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
Macro, meso and microhabitat use
We have presented data concerning macro- and mesoscale
habitat use in a consistent tabular form in order to facilitate comparison between species within regions or within
species across regions. Ontogenetic variation in habitat use
is examined for some large-bodied species and additional
information available in the literature is also discussed.
For example, Table 4 lists the habitat use of C. s. fulvus in
rivers of south-eastern Queensland. The minimum and
maximum values for each parameter are given to provide
an indication of the range of conditions over which a
species may be found. These data can be used in conjunction with information concerning a species’ distribution
within a catchment or region (e.g. Table 3) to gain a better
understanding of distribution and habitat use at large and
local spatial scales. For example, C. s. fulvus occurs in
catchments ranging from only 19.3 to 1540 km2 in area
(Table 4), yet data presented in Table 3 indicates that it is
not necessarily evenly distributed across that range. The
average of each habitat parameter calculated across all sites
in which each species occurred is also presented. In addition, we have included an estimate of mean habitat conditions weighted by the density of fish at each site. In effect,
each fish is the sample unit rather than the site. Weighting
the mean by density gives an approximation of particular
habitat conditions in which this species is most abundant
and which may be especially favoured or selected by a
species. For example, the difference between the average
and weighted average values for site gradient, mean water
velocity and the proportional contribution of sand to the
substrate composition (Table 4) indicate that, although C.
s. fulvus occurs on average, in streams with a gradient of
0.3%, an average current velocity of 0.14 m.sec–1 and
18.4% sand substrate, this species is more abundant in
sites in which the gradient and current velocity are
comparatively reduced and sand is more abundant.
Max.
Mean
W.M.
19.3 10211.7
9.0
270.0
4.0
311.0
0
240
0.7
46.8
0
80.0
1540.1
73.5
193.1
83
12.3
28.9
996.0
56.1
220.8
89
11.5
24.1
2.86
1.08
0.85
0.30
0.43
0.14
0.17
0.43
0.09
Gradient (%)
0
Mean depth (m)
0.05
Mean water velocity (m.sec–1)
0
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
99.6
100.0
56.7
70.9
65.8
41.1
76.0
8.4
18.4
21.9
30.1
16.8
3.0
1.4
7.5
31.8
22.6
24.7
12.1
0.9
0.4
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
64.5
65.9
26.7
65.7
43.3
43.3
31.0
15.5
50.0
58.8
19.8
11.8
1.5
8.6
2.3
9.1
3.8
3.0
8.5
12.1
23.2
15.5
0.9
15.0
3.5
6.9
2.9
2.4
3.9
6.9
0.20 m.sec–1). An example of microhabitat use histograms
for C. stercusmuscarum collected from the Wet Tropics
region and south-eastern Queensland is given in Figure
13. The microhabitat use data presented does not necessarily give an indication of habitat preference thus must be
interpreted with caution. Preference for a particular depth
class or sediment particle size for example, requires that
fish use such microhabitats more frequently than
predicted by chance due to the relative availability of that
habitat element in the environment. Although it is possible to represent a species preference for certain habitat
configurations by standardising habitat use data in relation to data on habitat availability, we have not done this
in a systematic quantifiable manner here as such a method
of standardisation still does not ensure that habitat preference information is transferable across sites with varying
habitat structure. The microhabitat use summaries
presented here were usually generated from a large
Mesoscale data describe the type of habitat (e.g. riffle, run
or pool) in which an individual species is found whereas
the microhabitat data reveal the type of conditions which
species occupy within that habitat. Microhabitat use data
is presented as a series of frequency histograms showing
the proportion of the total number of fish collected within
different categories (e.g. current velocity between 0.11 and
42
Study area, data collection, analysis and presentation
consistent tabular format detailing minimum, maximum
and mean values. Mindful of the potential for geographic
variation in water quality tolerance, we have presented
data for different populations wherever possible. The
number of samples upon which the summaries are based
is also given in most cases. We have relied extensively on
the information provided by Bishop et al. [193] concerning ambient water quality conditions experienced by fishes
in the Alligator Rivers region. In such cases, the number of
samples from which summaries are based, varies between
parameters. We have not listed sample size when these data
are presented. Note however, that the research by Bishop et
al. [193] occurred over a two year period, study locations
were sampled many times over a range of seasonal and
hydrological conditions and sample size for some parameters was often very large (>100 replicate measures). These
data are therefore very comprehensive and represent the
most detailed examination of the habitat requirement of
fishes in north-western Australia. We also present
summaries derived from the published work of other
researchers, particularly that of Hamar Midgley ([944,
946]). In such cases where minimum, maximum and
mean values are not explicitly stated we have reanalysed
the data presented in the original reports.
number of fish collected from a large number of sites and
sampling occasions and hence environmental conditions.
They do therefore represent a general guide to the microhabitat conditions commonly used by each species.
60
(a)
60
40
40
20
20
0
0
Focal point velocity (m/sec)
Mean water velocity (m/sec)
40
(c)
(b)
40
30
30
20
20
10
10
0
0
(d)
Relative depth
Total depth (cm)
40
(e)
(f)
Figure 13. Microhabitat use by Craterocephalus s.
stercusmuscarum in the Wet Tropics region (solid bars) and C.
s. fulvus in south-eastern Queensland (open bars). Summaries
derived from capture records for 78 individuals from the
Johnstone and Mulgrave rivers in the Wet Tropics region and
for 558 individuals from the Mary River, south-eastern
Queensland, over the period 1994–1997 [1093].
We must place several caveats on the extent to which data
describing ambient water quality conditions represents
tolerance per se. First, the data represents the conditions in
which fish occur. However, the fact that a species occurs in
particular conditions does not indicate that it prefers such
conditions nor does it indicate that its biology is unaffected by those conditions. Sublethal stresses may impact
on the fitness of an individual, yet it may, for whatever
reason, be forced to endure such conditions (e.g. during
circumstances when fish may be restricted to isolated pools
during extended periods of zero flows). Second, if the
lethal tolerance levels of a particular species are exceeded
at a site, then it will no longer occur there, and as a consequence this site will not be included in the sample. Third,
the majority of study sites were selected on the basis that
they were largely undisturbed, thus we intentionally
avoided sites with poor water quality. The main exception
to this was for a subset of moderately to highly degraded
sites in south-eastern Queensland.
Environmental tolerances
The tolerance of north-eastern Australian freshwater fishes
to extremes in water chemistry or toxicants is unknown
for most species. We review experimental data for each
species where available. In the absence of such data we
have presented summaries of ambient levels of five major
water quality parameters (temperature, dissolved oxygen,
pH, conductivity and turbidity) drawn from our own field
studies and the research of others. Data are presented in a
It is important to note that environmental tolerances are
likely to vary between life history stages (i.e. eggs and
larvae might be especially vulnerable) and may vary
considerably between different geographic populations
and between populations occurring in different habitat
types. For example, populations occurring in wetlands
may be more tolerant of hypoxia than are populations
occurring in streams, and populations occurring in high
elevation, well-shaded streams may be less tolerant of
40
30
30
20
20
10
10
0
0
Substrate composition
Microhabitat structure
43
Freshwater Fishes of North-Eastern Australia
appropriately applied to all species. These different maturity classifications are compared in Table 5. Another
method used to quantify reproductive development in
individuals and populations is the Gonadosomatic Index
(sometimes referred to as Gonosomatic Index) and abbreviated as GSI. It is a measure of the relative contribution of
the weight of the developing gonads to the total weight of
the individual and is estimated according to the formula:
GSI = gonad weight/total body weight x 100. Ideally, body
weight should refer to the body weight minus the weight
of any material within the gut. It is an effective way of
comparing temporal changes in reproductive development. For example, in some species the spawning period is
highly concentrated within a short period. Temporal
changes in GSI will reflect this, being low for most of the
year, then rapidly increasing as the spawning period
approaches, and peaking during the spawning period.
Other species with a more protracted spawning period
show a more gradual increase in GSI values. GSI values are
effective for comparing the reproductive investment of
individuals or populations. High GSI values are indicative
of high investment into reproduction. Short-lived species
often have high GSI values as they have a limited time in
which to reproduce. Longer-lived species may be able to
spawn over several years and therefore do not need to
invest so much effort in reproduction in any one year.
Female fish typically have higher GSI values than males.
elevated temperatures than are populations occurring in
lowland open streams. Notwithstanding these caveats, the
information presented here is the first comprehensive and
consistent examination of the water quality requirements
of the fish of north-eastern Australia. Experimental examination of sublethal and lethal effects of varying water
quality is urgently required.
Reproduction
In this section we review all known published studies for
each species. In addition, we present previously unpublished data concerning the life history of a small number
of species; the reader is referred to Pusey et al. [1108] for
details of methods used. In addition to the review of reproductive biology, summary data are listed in standardised
tabular format allowing the reader to quickly access information and identify knowledge gaps. Data listed covers
various aspects of reproductive biology such as fecundity,
spawning phenology, critical environmental thresholds,
and cues and age at maturity. Information concerning
embryology and larval development is also presented
where available.
The methods and terminology used in studies of fish
reproductive biology often vary greatly. We have attempted
to standardise terminology as much as possible, particularly that relating to fecundity. In many species, especially
those characterised by small size at maturity, the intraovarian eggs are not all at equivalent stages of development.
Rather, groups of eggs develop in concert, are simultaneously ovulated, and then oviposited in a batch. Another
batch then begins to develop. We have used the term batch
fecundity to refer to the number of large ovulated or near
ovulated eggs within an ovary in such species. Total fecundity refers to the number of ovulated and follicular eggs
other than primary oocytes (i.e. all yolked eggs) present
within the ovaries of an individual female. It is an instantaneous estimate of fecundity. Total fecundity can sometimes be taken to mean the total number of eggs produced
in a spawning season which may be much higher for batch,
repeat or protracted spawners. There is no real way to estimate this latter version of fecundity unless individual
females are followed throughout their reproductive life.
Movement
Fish move over a variety of spatial scales and for a range of
biological and ecological incentives. Some fish may only
move within their own home range, which may be as small
as a single pool or riffle, juveniles of some species may
undertake mass upstream dispersal movements, whereas
others may have a spawning migration into freshwater
habitats other than those occupied in periods outside of
the spawning season. Others may migrate out of freshwater
to estuarine or marine ecosystems. Migratory movements
may occur in the larval, juvenile or adult phase. Movement
is a critical aspect of the ecology of many riverine fishes
and one that is very easily disrupted (e.g. by artificial barriers), often with deleterious effects. Mallen-Cooper [852]
provides a very useful summary of migration in freshwater
fishes and McDowall [890] discusses in depth the various
types and functions of diadromous migration undertaken
by fishes. We provide a review of the movement/migration
biology of each species (i.e. migration pattern, time of year,
age at which migrations occur, critical habitats, anthropogenic factors impeding movement) where such information is available. A better understanding of the movement
biology of the fishes of north-eastern Australia is urgently
required and represents one of the greatest impediments to
better management of the fauna.
A number of schemes have been developed to characterise
the developmental stages of reproductively mature fishes
based on the visible appearance and size of the gonads.
Variation in the proportional contribution of different
reproductive stages to the total adult population can then
be used to estimate the timing and length of the spawning
period, and whether maturation occurs in one habitat or
another for example. However, the various schemes available and used in studies of species occurring in northern
Australia are not always consistent with one another or
44
Table 5. Generalised classifications of maturity stages in fishes, with approximate correspondence between them (modified from Bagenal and Braum [120]). Note that
allocation of a given individual to a particular maturity stage is partly subjective, species dependent (different fish species have varying reproductive morphology) and
dependent on whether specimens are fresh or preserved (it is difficult to extrude eggs and milt in preserved specimens).
Pollard [1061],
Bishop et al. [193]
Davis [360]
Beumer [173]
Milton and Arthington
[949, 951]
Pusey et al.
[1093, 1108]
I Virgin. Very small sexual
organs close to vertebral
column. Testes and
ovaries transparent,
colourless to grey. Eggs
invisible to naked eye.
I Immature. Young
individuals which have
not yet engaged in
reproduction; gonads
of very small size.
I Immature virgin. Testes
and ovaries thin and
threadlike, translucent and
colourless; sexes usually
indistinguishable.
I Immature virgin. Testes are strap-like with
little folding and twisting, translucent and
almost colourless. Ovaries are narrow and
small, colourless and generally translucent.
Some opaque white oocytes are visible to the
naked eye in larger ovaries.
I Juveniles.
Immature
individuals where
sexes are
indistinguishable.
Gonads are very
small.
I Juveniles. Gonads small,
testes almost indistinguishable, extremely thin and
almost colourless. Ovary
thin, translucent, without
visible oocytes (X40
magnification).
I Immature. Gonads
not visible or small,
thin and strap-like.
II Maturing virgin. Testes
and ovaries translucent,
grey-red. Length half, or
slightly more than half,
the length of ventral
cavity. Single eggs can be
seen with magnifying
glass.
II Resting stage.
Sexual products have
not yet begun to
develop; gonads of
very small size; eggs
not distinguishable to
the naked eye.
II Developing virgin and
recovering spent. Testes
thin and strap-like,
translucent and greyish,
sometimes with
melanophores. Ovaries
more rounded, translucent
and colourless, eggs not
evident to the naked eye.
II Developing virgin and recovering spent.
Testes of developing virgins are thicker,
translucent and white, and they begin to
twist and fold. Testes of recovering spent fish
are thicker, the main body of the testes
showing numerous translucent regions and
the lobes tending to be opaque off-white and
rough in texture. Ovaries are more rounded,
the ovary wall is thick and opaque, and
oocytes are creamy white and opaque.
II Inactive.
Immature (sexes
distinct) and
recovering
individuals. Gonads
small. Oocytes
distinguishable
under X40 (L.
unicolor) and X10
(M. splendida)
magnification.
II Inactive. Immature virgins
and recovering spent fish.
Testes thin, strap-like and
creamy-white. Ovaries small,
regularly shaped and
elongated. Oocytes
distinguishable (X10
magnification).
II Early developing.
Testes elongate,
whitish sac; ovary
pale orange, with few
oocytes, visible at
X20 magnification.
III Developing. Testes
and ovaries opaque,
reddish with blood
capillaries. Occupy about
half of ventral cavity. Eggs
visible to the eye as
whitish granular.
III Maturation. Testes
change from
transparent to a pale
rose colour; eggs are
distinguishable to the
naked eye; a very rapid
increase in weight of
the gonad is in
progress.
III Developing. Testes
thickening, opaque and
greyish-white, smooth
texture. Ovaries thickening,
opaque and pale yellowish,
eggs small but visible to the
naked eye.
III Developing. Testes are increasing in size,
the main body becoming opaque and white,
and the tips of lobes and lateral margins
becoming creamy-white. Ovaries increase in
size, the ovary wall becoming thinner and
translucent, and oocytes of various sizes are
present, larger oocytes being creamy white
and opaque.
III Maturing. Gonads
increased in size. Testes
swollen, pale, twisted and
folded and occupying at
least half of the body cavity.
Ovary swollen to fill width of
abdominal cavity, oocytes
visible to naked eye.
III Developing virgin
and resting adult.
Testes grey-white;
Ovaries orange, often
with red flecks, eggs
opaque, just visible to
the naked eye, small
oil droplets present in
larger oocytes.
IV Maturing. Testes
enlarged, opaque and
whitish, smooth texture.
Ovaries enlarged, opaque
and yellowish, eggs large.
IV Maturing. Testes are large, occupying half
of the body cavity, and the lobes and lateral
margins are creamy-white and rough in
texture. Ovaries occupy over half of the body
cavity, and the current season’s oocytes are
distinct in size from reserve oocytes and are
opaque and yellow.
III Maturing.
Gonads increasing
in size. Ovary of M.
splendida visible to
the naked eye and
of L. unicolor
distinguishable
under X10
magnification. Tips
of filaments on
oocytes of M.
splendida first begin
to appear.
IV Developing. Testes
reddish-white. No miltdrops appear under
pressure. Ovaries orange
reddish. Eggs clearly
discernible; opaque.
Testes and ovaries occupy
about two-thirds of
ventral cavity.
IV Late developing.
Testes opaque, white
to grey-white, no milt
present; ovaries
orange, eggs clearly
visible, opaque, larger
oil droplets present
throughout oocyte.
Study area, data collection, analysis and presentation
Nikolsky [993]
45
Kesteven [713]
Nikolsky [993]
Pollard [1061],
Bishop et al. [193]
Davis [360]
Beumer [173]
Milton and Arthington Pusey et al.
[949, 951]
[1093, 1108]
V Gravid. Sexual organs
filling ventral cavity.
Testes white, drops of
milt fall with pressure.
Eggs completely round,
some already translucent
and ripe.
IV Maturity. Sexual
products ripe; gonads
have achieved their
maximum weight, but
the sexual products are
still not extruded when
light pressure is
applied.
V Mature. Testes fill most of
the body cavity, opaque
and creamy-white, smooth
texture. Ovaries fill most of
body cavity, opaque and
yellow, eggs large.
V Mature. Testes are generally opaque
and creamy-white, but regions of the
main body are still slightly translucent,
and the testes occupy up to two-thirds of
the body cavity. Ovaries occupy most of
the body cavity, the ovary wall is very
thin and translucent, and oocytes are
large and yellow, tending to become
translucent.
VI Spawning. Milt and
roe run with slight
pressure. Most eggs
translucent with few
opaque eggs left in ovary.
V Reproduction.
Sexual products are
extruded in response
to very light pressure
on the belly; weight of
the gonads decreases
rapidly from the start
of spawning to its
completion.
VI Ripe. Testes fill body
cavity, opaque and pure
white, smooth and crumbly
texture, milt extruded by
pressure on abdominal wall.
Ovaries distend body cavity,
translucent pale golden,
eggs large and extruded by
pressure on abdominal wall
VI Ripe. Testes are opaque and white,
and milt can be extruded by applying
pressure to the abdominal wall. Ovaries
distended the body cavity. Oocytes are
large, translucent and lemon coloured,
and can be extruded by slight pressure
on the abdominal wall.
IV Ripe. Gonads have
achieved maximum size
and weight with oocytes
plainly visible in ovaries.
This stage culminates in
running ripe fish when milt
or oocytes may be readily
extruded from L. unicolor in
response to light pressure
on the abdominal region.
L. unicolor oocytes have a
single distinct oil-vacuole,
while M. splendida oocytes
are completely enveloped
by the filaments and have
between 14 and 30 oilvacuoles.
IV Ripe. Gonads have
reached maximum size.
Testes opaque and
white; milt can be easily
extruded with slight
abdominal pressure.
Ovary distends body
cavity. Oocytes large,
translucent yellow, easily
extruded with slight
pressure on abdomen.
VIII Spent. Testes and
ovaries empty, red. A few
eggs in the state of
reabsorption.
VI Spent condition.
The sexual products
have been discharged;
genital aperture
inflamed; gonads have
the appearance of
deflated sacs. The testes
usually containing some
residual sperm, and the
ovaries a few left-over
eggs.
VII Spent. Testes thin and
flaccid, greyish, sometimes
white areas (residual
sperm). Ovaries thin and
flaccid, translucent and
colourless to pale yellowish,
sometimes contain large
opaque-yellow residual
eggs.
VII Spent. Testes are thin and flaccid,
irregular in texture, and become translucent
while regions remain opaque and white
(residual sperm). Ovary wall is opaque, and
ovaries are flattened and irregular in shape.
Some large residual eggs may be present.
These tend to become opaque and creamywhite, and reduce in size as they are
reabsorbed.
II Recovering spent.
Testes translucent, greyred. Length half, or
slightly more than half,
the length of ventral
cavity. Single eggs can be
seen with magnifying
glass.
II Resting stage.
Sexual products have
been discharged;
inflammation around
the genital aperture
has subsided; gonads
of very small size. Eggs
not distinguishable to
the naked eye.
VII Spawning/spent. Not
yet fully empty. No
opaque eggs left in ovary.
46
V Spent. Gonads
virtually empty.
Testes normally with
some residual sperm
and ovaries with
some remaining
oocytes.
V Spent. Gonads reduced in
size, irregularly shaped.
Testes thin, flaccid and
virtually translucent. Ovary
reduced, small and flaccid,
some enlarged oocytes
remain but are irregularly
distributed within ovary.
V Gravid. Testes
white, and extrude
milt with pressure;
ovaries yellow-orange
with some
translucent, round
eggs, oil globules
forming single
polarized mass.
VI Running ripe.
Testes extrude milt
without pressure.
Ovaries with large
numbers of ovulated
eggs.
Freshwater Fishes of North-Eastern Australia
Kesteven [713]
Study area, data collection, analysis and presentation
Trophic ecology
Dietary information for each species was obtained from a
variety of sources including published literature, unpublished governmental and consultancy reports and unpublished data sets held by colleagues and collated elsewhere
[705]. In instances where the dietary data from each study
was presented separately for different sites, seasons and/or
size classes for an individual species, we summarised the
diet composition for each species within each study as a
weighted average (weighting based on abundance). Means
were weighted by abundances so as to represent the average condition for a given species and study. A full list of
sources for the diet data used in the present study is given
in the bibliography.
except when no volumetric, gravimetric or abundance
data was available for a particular species. Frequency data
was transformed so as to approach proportional representation by first ranking different items on the basis of their
frequency (i.e. the most frequent was ranked 1, the second
ranked 2, etc.), then inversed and divided by the sum of all
inverse ranks. For example, the proportional contribution
of the most frequently encountered item equals 0.66 when
the diet is composed of only two items and 0.54 when
there are three items.
Dietary data was summarised to the maximum taxonomic
resolution possible but we were constrained by the minimum level to which diet categories were distinguished in
the literature and the manner in which diet items were
pooled in many studies. Nevertheless, we distinguished
between food sources of autochthonous and those of
allochthonous origin, and between animal and vegetable
material, and we grouped items according to general similarities in prey habitat occupation and size. We were able
to distinguish 15 functional diet categories (Table 6).
Dietary information can be summarised in a variety of
forms, each method being subject to varying degrees of
bias and accuracy in estimating the relative importance of
individual dietary items to the total diet. The volumetric
contribution of individual items to a total diet, per cent
abundance (the numerical proportion of each diet item),
per cent dry weight and per cent wet weight were the most
commonly used method for data presentation across the
range of studies examined. We assumed that these methods estimated diet similarly. In studies where dietary data
was expressed using more than one of these methods for a
single species, the method approximating the volumetric
and then gravimetric contribution was preferred over
abundance data, although in the overwhelming majority
of such studies both methods indicated similar dietary
habits. We avoided using frequency of incidence data
We also discuss major spatial and temporal patterns in the
diet of each species where such information was available
in the literature. Ontogenetic variation in fish diets was
examined for large-bodied species for which sufficient
data was available. In these cases, age classes were recognised (termed juveniles and adults) and the body size
delimiting each age class was presented. Very little information on the trophic ecology of larval fishes is available
in the literature but was discussed where possible.
Table 6. Dietary categories used throughout the text.
Diet category
Description
Unidentified
Includes the unidentified fraction, together with unidentified items often referred to as ‘other’ or
‘miscellaneous’
Terrestrial insects (primarily Hymenoptera, especially Formicidae), arachnids and other terrestrial
invertebrates (e.g. annelids, isopods, gastropods)
Aerial forms of adult aquatic insects (primarily Diptera and occasionally Trichoptera, Ephemeroptera
and Odonata) and water surface invertebrates (e.g. Araneae, Gerridae and Collembola)
Mammals, birds, reptiles and amphibians
Terrestrial wood, bark, leaves, buds, fruits, seeds and pollen
Includes organic detritus and occasionally mud or sand
Includes aquatic macrophytes and charophytes
Includes filamentous and non-filamentous epiphytic algae and phytoplankton
Includes larval and adult stages of all aquatic insects occurring in the benthos and water column
Bivalves and aquatic gastropods
Decapod crustaceans
Copepoda, Cladocera, Ostracoda and Chonchostraca
Includes amphipods, isopods, oligocheate and polycheate worms, nematodes, Nematomorpha and
Hirudinea
Hydracarina, Rotifera, Hydra
Includes bones, scales and eggs
Terrestrial invertebrates
Aerial and surface aquatic
invertebrates
Terrestrial vertebrates
Terrestrial vegetation
Detritus
Aquatic vegetation
Algae
Aquatic insects
Molluscs
Macrocrustaceans
Microcrustaceans
Other macroinvertebrates
Other microinvertebrates
Fish
47
Freshwater Fishes of North-Eastern Australia
existing and potential threats for each species or for different populations based on published data, recovery plans,
consultancy reports, and our own information and interpretations. Each chapter concludes with a forecast of the
future conservation status of the species and/or our
perception of the major management issues needing
attention by means of restoration, recovery or conservation actions.
Conservation status, threats and management
The current conservation status of each species is given as
listed in the Action Plan for Australian Freshwater Fishes by
Wager and Jackson [1353], and the Australian Society for
Fish Biology Conservation Status of Australian Fishes –
2003 [117]. We also report the conservation status of
species listed under the Environment Protection and
Biodiversity Conservation Act 1999 (EPBC Act) and State
legislation, where applicable. Following this we summarise
48
Neoceratodus forsteri (Krefft, 1870)
Queensland lungfish
37 046001
Family: Ceratodontidae
Description
Neoceratodus forsteri is a large species growing to 1500
mm, commonly to about 1000 mm [52]. Larger fish
weighing 20 kg are not unusual [672, 690]. The largest
lungfish caught by Illidge [626] from the Burnett River,
south-eastern Queensland, in the 1890s weighed ~12.3 kg.
O’Connor [1008] recorded a range of 825–1125 mm for
109 fish from the Mary River, south-eastern Queensland.
Brooks and Kind [238] reported that lungfish from the
Burnett River spanned 345–1420 mm TL and weighed
485–25 000 g, with a mean length of 906 ± 199.63 mm and
mean weight of 7523 ± 4563 grams; most (80%) lungfish
exceeding 1200 mm TL were females. The equation best
describing the relationship between length (TL in mm)
and weight (W in g) for 2361 individuals from the Burnett
River (range 450–1305) is W = 9.96 x 10–6 L2.98, r2 = 0.956,
p<0.0001; both sexes follow similar growth patterns except
that females grow to larger size [238]. Figure: composite,
drawn from photographs; drawn 2003.
tail is long and pointed. Pectoral fins large, fleshy and
flipper-like; pelvic fins are situated well back on the body
and are also fleshy and flipper-like. Each paired fin has an
archipterygium (‘ancient wing’) with segmented axis and
preaxial and postaxial branches [763]. Thin cartilaginous
fin rays are formed in the dermis of the skin, separate from
the cartilaginous archipterygium; these rays support the
fin web [763]. The skeleton is partly ossified, partly cartilaginous, the vertebrae are pure cartilage, the ribs are
hollow tubes filled with cartilaginous substance [742].
Large cycloid scales cover the body, ten rows on each side,
grading to small scales on fins, each scale embedded in an
epithelial pocket; scales overlap extensively such that
vulnerable areas of the body are covered by a thickness of
at least four scales. The third row of scales from the dorsal
surface of the body is marked by a relatively indistinct
lateral line that perforates the thick overlying scales at
intervals [742]. Two unusually large and thick interlocking
scales cover the back of the head where the bony skull is
thin. Mouth small and subterminal in position; the anterior naris partly outside the upper lip and partly within;
posterior part of the naris inside the mouth cavity.
Dentition (see also Trophic ecology, below) is unusual; two
incisors, restricted to upper jaw, are flat, slightly bent and
The following description of N. forsteri is taken largely
from Allen et al. [52], Kemp [688, 690] and Krefft [742].
Adult fish have a wide flat head, and stout elongated body.
Dorsal fin commences on the middle of the back and is
confluent with the caudal and anal fins; the diphycercal
49
Freshwater Fishes of North-Eastern Australia
after the mottling has disappeared. The belly of a small
lungfish is a muddy pink colour. Juveniles are capable of
rapid colour changes in response to light but this ability is
gradually lost as the pigment becomes denser [688].
denticulated on hind margin; these are followed by dental
plates on upper and lower jaws [742]. Eyes small; snout
and lips naked; well-endowed with sense organs (pores).
Sense lines over the head show a series of pits connected
by a subdermal canal. The distinguishing feature of N.
forsteri is the possession of lungs used to breathe air, and
gills used for respiration in water [1380]. Gills are developed on all branchial bars; the lung is a single long sac situated above and extending the length of the coelomic
cavity, formed by a ventral outgrowth of the gut [478, 488,
1318]. Internally, the lung is divided into compartments
by septa formed by infolding of the walls; each compartment is further divided to form a spongy alveolar region;
blood capillaries run through this region of increased
surface area, close enough to the air space in the lung to
effect gaseous exchange [478]. The lung is connected with
the pharynx by the pneumatic duct; a buccal force-pump
like that of Amphibia fills the lung with air; exhalation is
effected by contraction of smooth muscles in the walls of
the lung [478].
Systematics
When Krefft [742] first described the Queensland lungfish
in 1870 he believed it to be a giant amphibian “allied to the
genus Lepidosiren”. He also recognised the similarity of its
dentition to fossil tooth plates of a creature known as
Ceratodus thought to have been like a shark, hence the
generic name (meaning ‘horned tooth’). The newly discovered fish became known as Ceratodus forsteri, after William
Forster (Minister for Lands in the New South Wales
Government) who provided two specimens to Krefft for
scientific description [1381]. In 1871, Günther [488]
published the first anatomical description of the lungfish
in the journal ‘Nature’ and was adamant that the teeth of
the living fish were indistinguishable from those of fossil
forms. This view persisted until 1891 when Teller [1306]
described a fossil calvarium (skull), associated with typical
ceratodont tooth plates. This skull differed significantly
from the skull of the extant fish [688] and Teller [1306]
accordingly reserved Ceratodus for the fossil forms and
gave the recent genus a new name, Epiceratodus. By then,
however, de Castelnau [374] had described a living lungfish from Australia that he believed differed from
Ceratodus forsteri in both body proportions and teeth. He
named it Neoceratodus blanchardi, but within a year
retracted this designation, recognising that he had
described a juvenile lungfish (610 mm long) with teeth no
different, on fuller examination, to those of C. forsteri
[375]. By the laws of priority, the living species became
known thereafter as Neoceratodus forsteri [688].
Neoceratodus forsteri has an unusually large karyotype
(2n = 54), very large chromosomes and cells, and the cells
have high nuclear DNA relative to other vertebrates but
less than reported for lungfishes of the family
Lepidosirenidae [1153]. Joss [672] has discussed the
phylogenetic and physiological significance of these findings, for example, large cell sizes result in lowered capacity
for gaseous exchange and consequently very reduced
metabolic rate, which in turn is correlated with a slow
growth rate and long life cycle.
Adult fish are usually dark brown or olive-brown over
most of the body with an underbelly that varies in colour
from whitish to muddy salmon-pink [690]. The pink
colour is much brighter during the breeding season, especially in males, otherwise there are no obvious distinguishing sexual characteristics [688]. The pink colour of the
flesh has given rise to the common name of ‘salmon’ in
some writings. Longman [824] noted that N. forsteri from
the Burnett River had a narrow white margin to the paired
fins and that this feature was also observed by Bashford
Dean. Longman also noted a narrow whitish margin on
the scales surrounding the eye [824].
Neoceratodus forsteri is one of five extant representatives of
the ancient and once speciose air-breathing Dipnoi (lungfishes) that flourished in the Devonian (c. 413–365 m.y.b.p.)
and is the most primitive surviving member of this lineage
[420, 1153]. It is the only extant member of the family
Ceratodontidae, confined to Australia [52]. Fossil tooth
plates discovered at Lightning Ridge, New South Wales, are
indistinguishable from those of living N. forsteri indicating
that this species was already present in the Early Cretaceous
(c. 140–165 m.y.b.p.) [689, 693]; an opalised tooth discovered at Walgett, New South Wales, places this species in the
Upper Cretaceous [294]. Neoceratodus forsteri is therefore
the oldest living dipnoan species [693], the South American
and African lungfishes of the family Lepidosirenidae being
more recently derived [169]. Fossil records indicate that in
the Miocene (15 million years ago) there were nine species
of lungfishes in Australia, living in lakes and rivers in
central, eastern and northern Australia [688]. Neoceratodus
Juvenile fish have different body proportions to those of
mature fish. The head is rounder, the fins relatively smaller
and the trunk more slender. The mouth is initially terminal but shifts back as the fish grows. The dorsal fin reaches
to the back of the head in young juveniles and gradually
moves caudally, until it extends only to the middorsal
region in the adult fish. Juveniles are distinctly mottled
with a ground colour of gold or olive-brown. There are
also patches of intense dark pigment which persist long
50
Neoceratodus forsteri
Other translocations of N. forsteri were made into the
North Pine River (eight individuals), a lagoon near the
Albert River (five individuals), the upper Coomera River
(16 individuals) and the Condamine River near Warwick
(21 individuals) [1317]. All translocations were undertaken because O’Connor [1008] and others (e.g. Illidge
[626] and Bancroft [123]) believed that the species was
becoming extinct within its natural distribution [164,
841]. The fate of these translocations is poorly documented. There have not been any recent surveys to ascertain whether the introductions into the Coomera River
were successful. No lungfish have been recorded during
surveys of the Condamine River [664], nor has recent
extensive sampling at numerous locations in the Albert
River yielded N. forsteri [1093]. Thomas Bancroft wanted
to establish a hatchery at Blue Lake on North Stradbroke
Island for production of N. forsteri but failed to raise the
necessary interest and funds [841]. However, a few lungfish were released into Blue Lake and 18-Mile Swamp on
the island, evidently unsuccessfully [690, 1316, 1317]; no
past or recent surveys of these freshwater systems have
recorded this species [84, 105, 154, 1316]. On the mainland, introductions of N. forsteri, both official and independent of any authority, have resulted in viable
populations in several sizeable waterbodies including Lake
Manchester and Gold Creek Reservoir near Brisbane [690]
and the impoundments of Somerset and Wivenhoe dams
situated in the middle Brisbane River [688]. According to
Thomson [1317] stocks in Enoggera Reservoir and the
Brisbane River have thrived and provided a source of specimens for scientific research all over the world. However,
Kemp [164] has stated that the population in Enoggera
Reservoir declined after spraying of water hyacinth
(Eichhornia crassipes) in 1974 eliminated the main spawning substrate for N. forsteri. Every specimen caught in
Enoggera Reservoir recently has been very old [1422]. This
species has also been stocked in impoundments in the
Logan and Caboolture rivers.
forsteri was one of them. It once extended to the centre of
the Australian continent (Lake Eyre drainage) prior to the
Pleistocene (c. 1.6 m.y.b.p.) [1257].
Neoceratodus forsteri displays low allelic diversity at
allozyme and mtDNA loci and minimal genetic differentiation between populations from the Mary, Burnett and
Brisbane (possibly a translocated population) catchments;
average heterozygosity across all loci was found to be 0.03
[420]. Frentiu et al. [420] suggested that this low level of
genetic variation at allozyme and mtDNA loci could be
attributed to population ‘bottlenecks’ associated with periods of range contraction, probably during the Pleistocene,
and/or in recent times during the periods of episodic or
prolonged drought that are known to reduce some reaches
of these river systems to a series of isolated pools [1093,
1095]. Long generation times [238] and the vulnerability
of juvenile lungfish to predators [127, 1380] are thought to
contribute to slow recovery of lungfish populations after
periods of population contraction [420]. The minimal level
of genetic differentiation between the geographically separate Mary and Burnett river populations was attributed to
historical connection of these systems, probably at the
height of the Pleistocene when sea levels were lower than at
present [420]. Hughes et al. [606] attributed similar
patterns of genetic variation in the Oxleyan pygmy perch,
Nannoperca oxleyana, to historical confluence and admixture of drainages in this area of south-eastern Queensland.
Distribution and abundance
Neoceratodus forsteri is restricted to river systems of southeastern Queensland [52], where it occurs naturally in the
Burnett and Mary rivers and possibly also the Brisbane
River [690]. There is disagreement as to whether the
Brisbane River population formed part of the species’
natural range at the time of European settlement, or is the
product of translocations made in 1895 and 1896 for acclimatisation purposes [1008, 1317]. O’Connor [1008]
reported several transfers of N. forsteri into the Brisbane
River basin. Five fish went into a dam near Cressbrook
connecting with the Brisbane River during floods, two
individuals into a pond in the city Botanic Gardens (adjacent to the Brisbane River) and eight individuals into
Enoggera Reservoir on Enoggera Creek, draining into the
estuary of the Brisbane River [1008]. Kemp [690] believes
it unlikely that the five lungfish introduced into
Cressbrook Dam could be responsible for the whole of the
lungfish population in the Brisbane River, for several
compelling reasons. However, genetic analysis of allozyme
and mtDNA loci has shown that the Mary and Brisbane
river populations share a rare haplotype (haplotype G), a
finding that Frentiu et al. [420] believe is ‘most consistent
with a translocation scenario’.
The most recent surveys of N. forsteri in its natural range
are those of Brooks and Kind [238]. They captured N.
forsteri in the Burnett River from the Ben Anderson
Barrage (AMTD 23.9 km) to approximately AMTD 335
km, and also within the Boyne River to the wall of
Boondooma Dam and upstream to the gorge sections of
both the Auburn River and Barambah Creek. They could
find little evidence that N. forsteri occurs upstream from
Barambah Gorge, despite extensive sampling in Barambah
Creek and in Bjelke-Petersen Dam, Silverleaf Weir and
Joe Sippel Weir [238]. Neoceratodus forsteri was one of
the most regularly encountered fish species during
surveys conducted between January 1997 and February
2000, when the total catch of lungfish (by targeted boat
51
Freshwater Fishes of North-Eastern Australia
Environmental tolerances
There is very little quantitative information on the environmental tolerances of N. forsteri. Kemp [692] stated that
this species prefers deep pools at temperature of 15–25°C.
Laboratory experiments have shown that 25°C is close to
the preferred temperature for juveniles (27–51 g in weight)
of this species, and that it is relatively cold hardy, living in
areas of the Brisbane River with an annual thermal range of
11–31°C [479]. Tolerance of a similar thermal range
(10–30°C) is indicated by field data recorded by Brooks and
Kind [238] at sites sampled for evidence of spawning. Data
in Table 1 summarise records from sites where evidence of
spawning activity was obtained (14/15 sites) and hence,
mature N. forsteri had been present. Neoceratodus forsteri
occurs in neutral to mildly basic waters of low to moderate
conductivity and relatively high dissolved oxygen concentration. Brooks and Kind [238] found that water transparency was significantly higher at sites where spawning
had occurred, however this could be a consequence of the
preference for spawning in dense macrophyte beds that are
more likely to be found in relatively clear water.
electrofishing and monofilament panel nets) was 2888
individuals [238]. Catches varied over time (annually and
seasonally) and among river sections but the overall
pattern was an increase in mean catch per unit effort
(CPUE) with distance downstream from AMTD 321 km
at the township of Ceratodus [238]. Higher catches at
some sites during winter or spring surveys were attributed
to spawning aggregations, whereas high catches in autumn
were thought to reflect aggregations in deeper waterholes
at the onset of the dry season [238].
Macro/meso/microhabitat use
Neoceratodus forsteri lives in slow-flowing rivers and still
water including reservoirs with some aquatic vegetation
along the banks, and is most common in deep pools [52].
Their preferred depth is 3–10 m [692]. According to Kemp
[692], lungfish live in groups, under submerged logs, in
dense banks of aquatic macrophytes or in underwater
caves formed by removal of substrate under tree roots in
the river bank. This species is found over mud, sand and
gravel bottoms. In the Mary River, N. forsteri is closely
associated with overhanging vegetation, submerged
woody debris, and dense macrophyte beds, whereas areas
of open water were largely avoided [238]. In the Burnett
River, very young fish <100 mm TL were captured in habitats similar to those used for spawning (see below), as were
juveniles <300 mm TL, usually within dense beds of
aquatic macrophytes over sand and gravel substrates
[238]. However, the largest juveniles were captured
amongst Hydrilla verticillata, a species rarely used as a site
for spawning. Most juveniles were captured at depths less
than 300 mm with the largest fish captured at the greatest
depths [238]. Immature N. forsteri (300–700 mm) were
most often captured in areas of dense submerged wood,
undercut banks and dense aquatic macrophytes [238]. We
have electrofished several individuals of similar size in
large slow-flowing pools in the main channel of the Mary
River in relatively shallow water (~1.3 m), close to the
bank, among large log piles interspersed with aquatic
macrophytes over sand and fine gravel substrates [1093].
We collected a further two fish (single individuals on two
separate occasions) among submerged terrestrial grasses
in fast-flowing runs in Wide Bay Creek (<0.45 m mean
depth, >0.27 m.sec–1 mean velocity), a large tributary of
the Mary River. It is presumed that these fish were in the
process of moving through these likely sub-optimal habitats after dispersing from dry-season refuges as both
sampling occasions coincided with periods of elevated
discharge immediately following prolonged dry periods
(> nine months) during which time Wide Bay Creek had
dried out to a series of isolated pools.
Günther [488, 489] suggested that the possession of a lung
enabled N. forsteri to live in aquatic habitats subject to
seasonal stagnancy. He wrote ‘when the fish is compelled
to sojourn in thick muddy water charged with gases which
are the product of decomposing organic matter (and this
must be the case very frequently during droughts which
annually exhaust the creeks of tropical Australia), it
commences to breathe air with its lung’ [488]. This view
persisted for almost 100 years until finally dispelled by
Grigg [480] in 1964. His field measurements at 22 sites in
the Mary and Burnett rivers revealed dissolved oxygen
concentrations ranging from 7–13.2 ppm under ‘the very
situations considered by Günther and others to provide
challenging respiratory problems’ [480]. Oxygen supersaturation at many sites was attributed to convection due to
diurnal temperature fluctuations, circulation by wind,
influxes of well-oxygenated water from riffles/runs and the
presence of abundant aquatic vegetation [480]. Grigg
[480] showed that juvenile and mature N. forsteri are more
active at night, and surface to breathe more often at night
or during flooding ‘when the fish would be forced into
activity as it fights the current’. Respirometry studies on
juvenile fish confirmed that individuals forced into activity supplemented aquatic respiration via the gills by
surfacing to take air [480]. Neoceratodus forsteri is incapable of surviving complete desiccation [480], and does
not survive dry seasons by secreting a mucous cocoon and
burying itself in bottom muds, as does Protopterus [1256].
However, N. forsteri can survive out of water for several
days if the surface of the skin is constantly moist, using the
lungs to respire [672].
52
Neoceratodus forsteri
Neoceratodus forsteri has complex courtship behaviour
observed during studies in the wild [235, 477, 687] and in
captivity [688, 760, 762, 764]. Grigg [477] described three
distinct phases, firstly a searching phase when the fish
ranged over a large area, possibly searching for potential
spawning sites. Kemp [687] also described pairs of fish
performing circling movements at the surface of the water
close to beds of aquatic plants. During this phase, N. forsteri
breathes air more frequently and usually more noisily than
normal, possibly reflecting a greater physiological requirement for oxygen [125]. Individual fish have been observed
to breathe air at regular intervals of about 20 minutes, with
air breathing accompanied by a distinct loud burp made in
the air with the lips clear of the water [687]. Kesteven [714]
suggested that noisy breathing is a form of mating call, and
Kemp [687] observed that lungfish seem to do their noisy
breathing in concert, even responding to each other, close
to but not within the areas where eggs are laid [688]. The
next phase involves behaviour described by Grigg [477] as
‘follow the leader’ during which one fish, presumably the
male, shows interest in the cloaca of the female, nudging
her with his snout. The same fish occasionally took a piece
of aquatic plant into its mouth and waved it about. Brooks
[235] observed that up to eight individuals may be involved
in follow-the-leader behaviour. Grigg [477] suggested that
nudging the female probably stimulates her to spawn. In
the third phase, the fish dive together through aquatic vegetation, the male following the female and presumably shedding milt over the eggs. When spawning actually occurs a
pair of fish lie on their sides or become entwined [688].
Grigg [477] observed that spawning fish shake their tails
from side to side possibly to facilitate the flow of reproductive products. Brooks [235] observed this behaviour immediately prior to the completion of spawning and proposed
that it could serve to disperse the eggs. Lambkin [762]
described slightly different spawning behaviour of N.
forsteri held in large outdoor ponds.
Table 1. Physicochemical data for Neoceratodus forsteri at
14 sites in the Burnett River surveyed between 1995 and
2000 [238].
Parameter
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (Secchi depth in cm)
Min.
Max.
Mean
10.0
6.9
7.0
421.0
50.0
30.0
15.6
9.1
1165.0
150.0
19.9
10.5
7.9
716.0
77.4
Reproductive biology
Neoceratodus forsteri spawns and completes its entire life
cycle in freshwater systems and has been bred in captivity
[477, 673, 685, 686, 687, 688, 691, 1038]. It is a slow-growing species, with age at first breeding of populations in the
Burnett River estimated to be 17 years for males and 22
years for females [238], however, Johnson [664] remarked
that these estimates may be exaggerated and recommended more work on this aspect of reproductive biology.
Length at maturity varies widely in both sexes (Table 2). In
the Burnett River, males became mature at 738–790 mm
TL (mean 767 mm) and females at 814–854 mm TL (mean
834 mm) [238]. Neoceratodus forsteri may commence to
spawn from mid-July, August or September and spawning
may continue to November/December but eggs are most
abundant during September and October [688]. Spawning
can occur at temperatures between 16 and 26°C and
usually commences within three months of the winter
solstice [687]. Kemp [687] noted that spawning precedes
spring rains and is completed before heavy rains [125],
that is, before the increased stream flows characteristic of
December and January in south-eastern Queensland
[1095]. Aside from stream flow and the availability of
submerged aquatic vegetation, the stimulus for spawning
is believed to be day length [687]. Brooks and Kind [238]
remarked that very little attention has been given to the
influence of flow rates on spawning site selection. Brooks
[235] demonstrated that flowing water is not essential for
spawning of this species, but suggested that eggs laid at
depths >0.3 m in still water typically settle deep in aquatic
macrophytes and die as a result of low dissolved oxygen
levels. Viable eggs were collected in both still and flowing
water in the Burnett River [238]. Highest densities of early
stage eggs were associated with intermediate flow velocities (0.2 m.sec–1), low turbidity, a broad range of temperatures (maximum 36°C), high dissolved oxygen levels,
depths of 400–600 mm and moderate to high densities of
aquatic macrophytes 160–350 mm in height [235, 238].
Kemp [685] noted that temperatures of 10 and 30°C. were
lethal to cleaving eggs.
Eggs of N. forsteri are usually deposited singly, occasionally
in pairs, very rarely in clusters [687]. The male fish
fertilises each egg as it emerges and the eggs are deposited
in dense aquatic vegetation [687, 688]. The newly laid egg
is enclosed in a jelly envelope and is sticky for a short while
until silt and small aquatic organisms have covered it, and
it remains sticky for long enough to become attached to
submerged vegetation [688]. Eggs are also negatively
buoyant and may fall to the substrate if not attached to
vegetation or some other type of substrate; such eggs are
considered unlikely to survive to hatching. Neoceratodus
forsteri is selective in the choice of spawning site [688,
691]. Kemp [687, 688] recorded eggs on aquatic plants
rooted in sand or in gravel in slow or fast flowing water
(but not in still water), in areas where the vegetation was
53
Freshwater Fishes of North-Eastern Australia
[124]. The epithelial cells of embryonic N. forsteri are
sensitive to mechanical stimuli and excitable, similar to the
skin impulse system of embryonic and larval Amphibia
[208]. Bone et al. [208] suggested that this sensory system
may permit embryos to escape precociously from the jelly
envelope when attacked by predators. Newly hatched
larvae of N. forsteri develop a ciliary current over the skin
surface which continues for more than six weeks of larval
life, and the gill surfaces under the opercula also become
ciliated [1379]. Whiting and Bone [1379] suggested that
the ciliary current could provide respiratory exchange
across the skin and gills without necessitating any movements of the jaw or branchial apparatus, which are welldeveloped at this stage. A secondary role of the current
may be to keep the skin of unprotected larvae free of
debris, parasites, and predatory protozoans that may
attack and erode the fins of larval lungfish [1379]. Both
roles of the ciliary current may be adaptive for larvae that
are totally unprotected by a nest or burrow, nor guarded
by the male parent, as occurs in other dipnoans.
shaded or in full sun, and on plants with and without
epiphytic algae, but not on aquatic plants ‘infested with
slimy algae’ or in stagnant water or in areas where there
was loose debris on the water surface. She considered that
plant growth form (e.g. dense masses of vegetation), location (e.g. plants situated against a bank) and morphology
(e.g. the roots of bottlebrush, Callistemon sp. and water
hyacinth, Eichhornia crassipes) were important features of
spawning sites [687]. In Enoggera Reservoir, eggs
deposited into the root mass of water hyacinth clumps
were laid over an area of 1–5 m2, on the roots and occasionally in partly submerged floats of the plant, in positions varying from near the surface to a depth of 1 m
[687]. Some eggs were laid so high on the root mass of
water hyacinth that a drop in water level would leave them
exposed [687]. Brooks and Kind [238] found that structurally complex plant species contained higher densities of
eggs than those with less complex growth forms, concluding, as have Kemp [687, 688] and other observers [691],
that the suitability of a spawning site does not depend
upon the particular plant species but on the provision of
suitable microhabitat for both eggs and larval lungfish,
and food supplies for the newly hatched fish. Illidge [626]
reported finding the eggs of N. forsteri deposited on the
sides and bottom of submerged logs.
The larvae of N. forsteri are reported not to feed for 2–3
weeks, while yolk is still present [686]. By the time the yolk
is fully utilised, a spiral valve has developed in the intestine
and the fish starts to feed. They have been described as
essentially bottom feeders and approach their food in jerky
movements [1165]. Small N. forsteri show a gradual
change in body form as they develop but there is no externally detectable metamorphosis and no obvious point at
which they can be termed adult as opposed to larvae [686].
Johnston and Bancroft [667] described a very young specimen of N. forsteri as measuring 17 mm at six weeks posthatching. Bancroft [128] recorded wide variation in the
(preserved) length at age of N. forsteri held in captivity: 12
fish aged three months were 23–40 mm long (presumably
total length), 18 fish aged five months were 26–44 mm, at
eight months 25 fish were 26–55 mm, at 10 months 17 fish
40–62 mm, and at 12 months 19 fish were 33–72 mm long.
Young lungfish come to the surface to breathe air when
they are about 25 mm long [480, 690]. They are reported
to do so only when stream water is laden with silt, as in
times of flood, when it is stagnant, drying out and low in
oxygen or when the fish is unusually active [480, 690].
Neoceratodus forsteri spawns during the day and at night
[688]. It does not make a nest and there is no guarding or
parental care once the eggs are laid [687]. Female N. forsteri
have a large ovary and the potential to lay many eggs, but
produces hundreds of eggs at most in the wild [687],
whereas in captivity Hegedus [564] recorded 200 eggs laid
at one time and Moreno [964] (cited in Kemp [687])
reported 500–600 eggs at a single event. This species does
not necessarily spawn every year, however, a good spawning season occurs every five years, irrespective of environmental conditions (Kemp, pers. comm. to Brooks [235]).
The following account of egg development is based largely
on Kemp [686, 687, 688]. The newly laid egg is hemispherical in shape, delicate, heavily yolked and enclosed in a
single vitelline and triple jelly envelope. The egg itself is
about 3 mm in diameter, and with the jelly envelope has a
total diameter of 1 cm. Cleavage is rapid, with the largecelled blastula stage reached in 36 hours and the smallcelled blastula stage reached after a further 18 hours. Head
structures and pigmentation start to appear by day 17 and
hatching occurs from 23–30 days [688]. Upon hatching
the young fish is close to 10 mm, ‘inconspicuous and beautiful’ [1379]. During its first week of life it lies on its side,
hiding in the weeds and moving only when stimulated by
touch, but from time to time swimming spontaneously
[123, 626, 687, 688, 1379]. Recently emerged larvae often
retreat back into the gelatinous envelope when disturbed
The collection of juvenile N. forsteri has proved difficult
ever since the species was first discovered in 1870, despite
numerous attempts to collect small lungfish using a wide
array of gear (including liming and use of dynamite).
Bancroft [123, 125] feared that no juveniles survived their
many predators in a normal year and, like Welsby [1373],
erroneously thought that juveniles buried themselves in
the mud for up to three years. Concern about the perceived
lack of juvenile recruitment led to the many translocations
of N. forsteri described above. However, from 1876
54
Neoceratodus forsteri
The reproductive biology of N. forsteri has many unusual
features. Joss [672] is investigating the idea that surviving
lungfish may be neotenic, i.e. they are larvae that have
grown and become reproductively mature without metamorphosing.
onward, a spate of records of juvenile N. forsteri (61 cm in
length or less with weights of 2 kg or less) appeared in the
literature; full details are recorded by Kemp [688].
According to Kemp, numerous juvenile N. forsteri were
caught in the Mary and Brisbane rivers in the early 1980s,
in sand and gravel substrates near banks of aquatic vegetation. They were captured using electrofishing methods, a
previously unavailable technique. However, in recent
surveys in the Burnett River, Brooks and Kind [238]
caught only 23 juveniles <300 mm TL, 19 by push-net and
four by electrofishing. They concluded that juvenile
recruitment of N. forsteri had been poor since 1996, coinciding with poor conditions for spawning (e.g. few aquatic
macrophytes in shallow water) in 1997, 1998 and 1999.
The eggs, larvae and juveniles of N. forsteri are vulnerable
to aquatic predators (shrimps, insects such as beetles and
odonates, and small fish) [1380].
Movement
Neoceratodus forsteri is reputed to be a sluggish and inactive fish but is capable of rapid escape movements using its
strong tail [688, 690]. This species is usually quiet and
unresponsive by day (except in the breeding season) but
becomes more active in the late afternoon and evening
when it moves around feeding [480, 688]. Movements are
usually slow and sinuous, using the tail with or without
the use of the fins [688]. The fins are used to brace the
body of the fish against the substrate when the fish is feeding, a behaviour displayed by N. forsteri when only a few
Table 2. Life history data for Neoceratodus forsteri.
Age at sexual maturity (years)
Spawning of Burnett River populations commences at 15–17 years in males, 20–22 years
in females [18, 238, 664]
Minimum length of ripe females (mm)
In the Burnett River, females mature at 814–854 mm TL (mean 834 mm) [238]
Minimum length of ripe males (mm)
In the Burnett River, males mature at 738–790 mm TL (mean 767 mm) [238]
Longevity (years)
Adults long-lived, at least 20–25 years [1380], with a claim that they possibly live to
60–100 years of age [18]
Sex ratio
1:1 [238]
Spawning activity
Spawn from mid-July, August or September to November/December; occasionally
January to March [235]; eggs are most abundant during September and October [688]
Critical temperature for spawning
16–26°C [687]
Inducement to spawning
Day length; spawning usually commences within three months of the winter solstice;
usually occurs before heavy rains, but may occur during or after rain [687]
Minimum GSI of ripe females (%)
?
Minimum GSI of ripe males (%)
?
Fecundity (number of ova)
Females produce hundreds of eggs at most in the wild; 200 and 500–600 eggs laid at
one time in captivity [687]
Fecundity/length relationship
?
Egg size (diameter in mm)
3 mm; total diameter of 10 mm inclusive of jelly envelope [687]
Frequency of spawning
Females may release eggs in batches when spawning conditions and habitats are
suitable; if unsuitable, female may not spawn [688]
Oviposition and spawning site
Both still and flowing water; highest densities associated with intermediate flow
velocities (0.2 m.sec–1), low turbidity, a broad range of temperatures, high dissolved
oxygen levels, depths of 0.4–0.6 m and moderate to high densities of aquatic
macrophytes 0.16–0.35 m in height [238]
Spawning migration
None in natural river conditions; adults migrate out of impoundments into suitable
riverine spawning sites [238]
Parental care
None [687, 688]
Time to hatching
4–5 weeks after oviposition [127]; 23–30 days [688]
Length at hatching (mm)
10 mm [1379]
Length at feeding
?
Age at first feeding
2–3 weeks [686]
Age at loss of yolk
Around 2–3 weeks [686]
Duration of larval development
No externally detectable metamorphosis [686]
Length at metamorphosis
–
55
Freshwater Fishes of North-Eastern Australia
centimetres long [688]. This species is able to slither
through wet grass with the assistance of a downhill slope
but cannot support its body weight on the fins without the
additional support of water [626]. Lungfish do not crawl
up onto land or projecting logs to bask, as sometimes
reported in early literature [690, 1380].
Another individual was located in the same position
during 23/34 tracking events over the period August 1998
and January 2001. It moved upstream between October
and December 1999 and between September and
December 2000, that is, at times corresponding to the
spawning season. This fish entered shallow, heavily vegetation glides during each movement event and remained
within the glide for several weeks before returning to the
same rock outcrop it had left [238]. Increased flow rates
resulted in a tendency towards increased downstream
movement of individual fish. There was also evidence of
upstream movements during the spawning seasons of
1999 and 2000, especially during August–October 1999,
when several fish were returning from long distance movements downstream following increased flows earlier in the
year [238].
Grigg [480] demonstrated experimentally that more
frequent air breathing was correlated with periods of
greater activity at night, when N. forsteri uses the lung as a
supplementary organ of respiration. To breathe air, the fish
may rise to the surface and exhale air through the mouth,
then inhale and dive forwards, or rise to the surface,
breathe, and reverse back into the water [688]. In juveniles,
facultative air breathing develops when the fish are 25 mm
long [686].
Neoceratodus forsteri is essentially a sedentary species
exhibiting strong site fidelity within a restricted area, such
that home ranges rarely extend beyond a single pool or
occasionally, two adjacent pools [238]. Brooks and Kind
[238] recorded the following details during radio-tagging
studies in the Burnett and Mary rivers. Of 12 individuals
(685–1070 mm TL, weight 2750–10 100 grams) tracked
every 3–4 weeks between 1998 and 2001, only four were
located more than 1000 m from the site of release.
Movements of all tracked fish were independent of water
temperature and stream discharge. The pattern of movement involved strong fidelity to particular sites within
pools (usually against the banks or adjacent to large rock
formations) during daylight, and free movement of fish
throughout the pools at night, resulting in extensive overlap of individual home ranges. Two fish moved through
the downstream riffle and continued downstream but all
other movements were in the upstream direction, and at
times, four individuals moved upstream into a series of
pools containing dense beds of aquatic macrophytes,
negotiating a large riffle zone to do so [238].
Tag and recapture studies confirmed the patterns of movement of N. forsteri described above [238]. Movement data
were collected for 124 recaptured fish (25 females, 30
males and 69 unsexed fish, 470–1240 mm TL) at liberty
for periods from 7–928 days (mean 352 ± 239 days). Fish
tagged in impounded areas moved distances ranging from
16 900 m downstream to 35 400 m upstream, compared to
the longest distance moved in a natural riverine area (2900
km). Approximately 20% of all recaptures of tagged fish
occurred within 100 m of the tagging location, 50% were
caught within 1000 m and only 17 fish (13%) moved more
than 5000 m. Mean movement between release and recapture was 206 (± 5500 m) and there was no significant
difference in the number of individuals making movements upstream or downstream, nor any differences in
movement direction or distance between male and female
fish. One tagged fish was captured in the Walla Weir fish
lock, however none of the radio-tagged fish entered this
device. Some fish captured in Jones Weir moved out of the
main channel upstream into the Boyne River during the
1999 spawning season, and also into the Auburn River
[238].
Movements of radio-tagged N. forsteri within impounded
sections of the Burnett River were strikingly different
[238]. The mean total range of five lungfish released
downstream from Walla Weir (i.e. within the river reach
impounded by Ben Anderson Barrage) was 28 740 m
compared to 6450 m within Walla Weir, and 1667 m in the
riverine section at Goodnight Scrub. Larger fish ranged
over wider areas but total ranges were similar for both
sexes. Mean monthly movements in this group of fish
ranged from zero in the month immediately following
release to more than 9 km in January 2001, with fish regularly traversing the area from below Walla Weir (AMTD
74.5 km) to Ben Anderson Barrage (AMTD 23.9 km). One
individual traversed the 48 km distance from Walla Weir
to Ben Anderson Barrage on at least four occasions.
These movement studies suggest that N. forsteri does not
follow a set migratory path but may actively seek out suitable spawning habitat between July and December [238].
Mature fish in impounded areas appear to move out of
artificially ponded habitat and upstream into shallow,
free-flowing reaches to spawn. Movements within Walla
Weir (lower Burnett River) shortly after it was closed and
the natural river became impounded were little different
to those of lungfish in unimpounded reaches [238]. The
limited movements of lungfish in this pondage were interpreted as the normal localised movements of mature, resident individuals habituated to spawning close to, or
within, their home range [238].
56
Neoceratodus forsteri
that had passed into the gut without being crushed by the
tooth plates. Recent accounts indicate that in captivity
adult N. forsteri consume a wide range of animal foods,
fish, insect larvae, crustaceans, molluscs, worms, tadpoles,
dead toads, meat, offal, egg yolk, dried dog or poultry food,
Vallisneria spiralis, Hydrilla verticillata, filamentous algae
and water hyacinth rootlets [694]. Jaw movements generally crush the food but vary with the type of food being
eaten [688]. Soft foods such as worms and plants are
partially crushed with a few quick bites and then swallowed, such that the plant fragments found in faeces can
still be identified [688]. Molluscs are often pushed out and
pulled back in several times, and particles of food may
escape from the operculum, even in mature fish [688].
Movement of the prey in and out of the mouth accompanied by strong adduction of the jaws to crush prey between
the massive tooth plates is typical of lungfishes and is
described in detail for Lepidosiren [152]. These crushing
movements are accompanied by hydraulic transport of the
food, achieved by movements of the hyoid apparatus, to
position the prey within the oral cavity (analogous to the
functions of the tongue in tetrapods [152]). Neoceratodus
forsteri displays the most primitive version of these biomechanical feeding adaptations and behaviours [152].
The distribution of N. forsteri is restricted in the Burnett
River catchment by natural barriers to movement, for
example within the gorge areas of the Auburn River and
Barambah Creek [238]. Man-made barriers also restrict
the movements of this species, for example, Boondooma
Dam presently constrains its distribution within the Boyne
River [238]. The presence of tidal barriers (e.g. in the
Burnett River, Mary River and Tinana Creek) may further
impact on lungfish by preventing or hindering recolonisation of freshwaters if displaced by floods to brackish estuarine areas downstream of tidal barrages. Fish strandings
leading to death also occasionally occur within and downstream of dams and weirs in the Burnett River spillway due
to rapid reductions in discharge and flaws in the design of
the spillways [700].
Trophic ecology
Although no quantitative dietary data is available in the
published literature, anecdotal observations clearly indicate that the diet of N. forsteri changes with development
and is correlated with a change in dentition [684]. When
feedings begins, dentition is of the ‘hold and catch’ type
consisting of simple groups of isolated cusps, three in each
tooth plate. The larvae are essentially bottom feeders
[1165] taking microcrustaceans (Daphnia, brine shrimp)
and small Tubifex worms, occasionally supplemented with
filamentous algae [684, 685]. Large items as big as the fish
itself may be captured, only to escape via the gill slits, and
digestion is often ineffective, such that live worms have
been reported to leave the gut via the anus, or by breaking
through the gut and body walls [688]. During larval
growth, the sharp tooth cusps fuse in ridges radiating from
a point situated posterolingually; cusps are added to the
labial ends of the ridges and more ridges are added posteriorly, producing a total of seven ridges in each tooth plate
[684]. Each tooth grows in thickness, the tooth plate grows
outwards and is resorbed from the inner angle at the same
time, and more cusps grow between the ridges, thus forming the crushing surface. Vomerine teeth grow in the same
way by fusion of isolated cusps and the addition of new
cusps at the labial end of the tooth plate, and they too
thicken over time [684]. Initially vomerine tooth plates are
low-based with long cusps but they develop into highbased low cusped incisiform tooth plates in adult fish.
Conservation status, threats and management
Early accounts suggest that N. forsteri is a valuable food
fish, however Spencer [1257] described the flesh as very
oily, coarse and disagreeable, and seldom eaten except by
those who could afford ‘nothing better’. Spencer felt that
consumption by humans would be unlikely to cause rapid
extermination of this species [1257]. That was in 1892.
Today, over 100 years later, other human activities threaten
the Queensland lungfish, particularly water resource
development [18, 253, 323, 472, 1418, 1422].
The taking of N. forsteri has been prohibited since the
lungfish was declared a protected species under the
Queensland Fish and Oyster Act 1914, and it was placed on
the CITES list in 1977 [692]. Neoceratodus forsteri is
currently protected from fishing, and collection for educational or research purposes requires a permit in
Queensland under the Fisheries Act 1994, and from the
Commonwealth Government [692]. Unfortunately, N.
forsteri was listed as Non-Threatened in the 1993 Action
Plan for Freshwater Fishes [1353]. By 1995, numerous
individuals and organisations were deeply concerned
about the possible impact of the construction of a new
weir (Walla Weir) on the lower Burnett River within the
core distribution and prime habitat of N. forsteri [18, 323,
472, 1418, 1422]. A nomination put forward in 1997 to
have the species listed as Endangered under the
Endangered Species Protection Act 1992 was unsuccessful.
Illidge [626] reported that adults of N. forsteri use the
vomerine teeth to gnaw the bark of trees growing in the
water and also consume moss and grass fallen into the
water and the seed-pods of Eucalyptus. Whitley [1380]
noted that the blossoms of Eucalyptus falling on the surface
are eagerly consumed, and Spencer [936] reported that the
alimentary canals of lungfish examined in late September
(1891) were filled with the fruit of Eucalyptus tereticornis
57
Freshwater Fishes of North-Eastern Australia
This nomination was assessed by the Commonwealth
Endangered Species Scientific Subcommittee as not meeting the relevant criteria as ‘its numbers have not been
reduced to such a critical level, and its habitats so drastically reduced, that it is in immediate danger of extinction’
[18]. In Queensland, N. forsteri was not even listed as
threatened under the Queensland Nature Conservation Act
1992. An independent review of the impacts of the Walla
Weir proposal on N. forsteri and the Elseya turtle recommended the establishment of a long-term program of
research to ascertain its status [207]. The Boardman review
[207] recommended collection of baseline data on distribution, genetic diversity, population size and age structure,
migration, spawning sites, hatching rates and juvenile
recruitment. Studies on the habitat requirements of juveniles and the effect of fluctuating water levels were also
recommended [207]. The research program, led by Brooks
and Kind [238], yielded many essential facts relating to the
ecology of N. forsteri and paved the way for a new nomination for its protection as Vulnerable under the Environment
Protection and Biodiversity Conservation Act 1999 (EPBC
Act). After considerable delay, Neoceratodus forsteri was
included in the category of Vulnerable under section 78 of
the EPBC Act in late 2003 [18]. However, this species is not
listed under the World Conservation Union (IUCN) ‘Red’
List or the Australian Society for Fish Biology (ASFB)
‘Conservation Status of Australian Fishes’ listing.
Brooks and Kind [238] established that there has been a
marked decline in the quality and extent of breeding habitat of N. forsteri in the Burnett River due to impoundment
of 26% of the core distribution. While impoundments
provide habitat and feeding grounds for this species, the
particular conditions suitable for successful spawning
rarely occur within impounded areas. Generally, spawning
habitat is characterised by relatively shallow water and
dense macrophyte cover [238], whereas impoundments
tend to be steep-sided with deep water and fluctuating
water-levels, conditions that are not suitable for the
growth of macrophytes. Brooks [235] observed that a
rapid reduction in water level (250 mm) in Bingera Weir
on the lower Burnett River (AMTD 54.5 km) exposed
many shallow spawning areas (predominantly beds of
Vallisneria) and caused the death of a large number of
eggs. Furthermore, impoundments probably do not
provide suitable nursery habitat for juveniles of N. forsteri
(<300 mm) as the young fish remain for some time after
hatching in habitats similar to those used for spawning,
primarily dense aquatic macrophytes [238]. Juveniles are
believed to be susceptible to stranding or loss of sheltered
habitat and food supplies caused by rapid decreases in
water level, until such time as they move into deeper water
[18]. Increases in water level may have little effect on juvenile N. forsteri until macrophytes die three to four weeks
after inundation [238].
This species is potentially threatened in much of its core
distribution in the Burnett and Mary rivers: 26% of this
core distribution is presently impounded by weirs and
dams, with a further 13% likely to be impounded if
proposed water infrastructure developments for the
Burnett River catchment go ahead [238]. Water infrastructure developments are also planned for the Mary River.
The effects of new dams and weirs are likely to be significant. Barriers to movement and altered flow regimes
downstream of dams for irrigation purposes could lead to
the disruption of existing population structure and cause
loss of genetic variation, leading to inbreeding depression,
possibly culminating in extinction [420]. There has been
debate as to whether the Queensland lungfish in the
Brisbane and North Pine rivers are natural or translocated
populations and the status of most of these populations is
unknown. The conservation value of self-maintaining
translocated populations of N. forsteri is also unclear. In
areas where it occurs naturally, this species has inherently
low genetic variation [420], and, as only limited numbers
of individuals from one natural site were used to establish
the translocated populations, these new populations are
likely to have particularly low genetic diversity. It is possible that only the natural populations possess the full
evolutionary potential of the species [18, 420].
Queensland lungfish are slow-growing, with age of first
breeding estimated to be 15–17 years for males and 20–22
years for females. Adults have a high survival rate and are
long-lived (at least 20–25 years [1380]), with a claim that
they possibly live to 60–100 years of age [18]. Large adults
have recently been found to be relatively common in various localities, and there is no evidence of decline in adult
numbers, however, it is suspected that recruitment into
the adult population is inherently low. Juveniles are more
difficult to observe and locate than adults and little is
known of their distribution, abundance and ecology. From
recent surveys in the Burnett River, Brooks and Kind [238]
concluded that juvenile recruitment of N. forsteri had been
poor since 1996, coinciding with poor conditions for
spawning (e.g. few aquatic macrophytes in shallow water)
in 1997, 1998 and 1999. Johnson [664] remarked that for a
long-lived species with naturally low mortality rates,
successful spawning and juvenile recruitment is not essential every year, and may only occur irregularly, possibly in
medium to long-term cycles, even in natural systems. The
length of these cycles could easily mask potentially deleterious impacts on recruitment for many years, whereas
large adults could remain common for decades and give
no indication of incipient population decline in the longer
term.
58
Neoceratodus forsteri
The vulnerable status now afforded to N. forsteri by the
Commonwealth EPBC Act has not inhibited further water
resource development in the Burnett River. The proposed
Burnett River Dam situated at AMTD 131.2 km (a place
called Paradise) has been approved by the Commonwealth
and Queensland Governments. The maximum height of
the dam wall will be 37.1 m and at full supply level it will
have a capacity of 300 000 ML, a length of 45 km and
extend over an area of 2950 ha [253]. The Environmental
Impact Statement for the Burnett River Dam places
little emphasis on the requirements of N. forsteri.
Environmental flow releases from the dam are expected to
maintain spawning sites and juvenile habitat downstream
[253], however the impounded area may not provide
either [238]. Monitoring of N. forsteri abundance, health
and recruitment in the impoundment and downstream
has been recommended as part of the development plan
for the new dam [253]. Consideration will be given to the
translocation of N. forsteri into areas of the catchment
where natural and man-made barriers prevent access to
potentially useable habitat [253]. The development of
Water Resource Plans for the Burnett and Mary River
catchments represents an opportunity to address the
possible implications of altered flow regimes for lungfish
habitat, movement, spawning and recruitment processes
[701]. The ultimate fate of the Queensland lungfish,
Neoceratodus forsteri, probably the world’s oldest living
vertebrate species, remains to be seen.
There are concerns that the Queensland lungfish is threatened by alien and translocated native fishes that have been
introduced into the Burnett and Mary river systems, and
are capable of predating on eggs and young and competing with adults for breeding habitat [700, 701]. Introduced
fishes may also contribute to future declines in the number
of breeding adults [18]. One of the alien species, the
Mozambique mouthbrooder or tilapia (Oreochromis
mossambicus) has been declared a noxious and threatening
alien species in Queensland [79, 95, 103]. It is present in
Boondooma Dam on the Burnett River [593] and could
become established within the natural range of N. forsteri
in this catchment. Details of its ecology and impacts in
Australia can be found in Arthington and Blühdorn [86]
and related publications [79, 95, 103].
In summary, there have been losses or reductions in quality of the breeding and nursery habitat of N. forsteri
amounting to 26% of the core habitat in the main channels of the Burnett and Mary Rivers [18, 238]. In addition,
the breeding and nursery habitat of this species will
continue to be threatened by further water infrastructure
development and associated agricultural land use in these
highly populated areas. The impact of alien and translocated fishes in these river systems is not known, but could
well result in a further population reduction. On the basis
of these losses and threats, there is sufficient evidence to
indicate that the adult breeding population of N. forsteri
will undergo a substantial decline over the next three
generations. Therefore, the species has been categorised as
‘Vulnerable’ under the EPBC Act [18].
59
Scleropages leichardti Günther, 1864
Saratoga
37 088002
Family: Osteoglossidae
Description
Dorsal fin: 15–19; Anal fin: 25–27; Dorsal profile straight,
non-sloping; jaw steeply inclined, mouth pointing
dorsally. Figure: composite, drawn from photographs;
drawn 2003.
eggs in the buccal cavity. Colour: brown to dark green
dorsally with silver sheen, grading to pale green ventrally.
Dorsal and lateral scales with one or two pink spots near
margin. Medial fins dark with faint pink spots. Whitley
[1386] cites a personal communication in which a cardinal red specimen is described. Scleropages leichardti is
unlikely to be confused with any other species except S.
jardinii, but given the restricted distribution of the former
(see below), confusion is unlikely.
Scleropages leichardti grows to large size, reaching a maximum length of approximately 1000 mm but more
commonly to about 500 mm [52]. The body is long and
compressed with the dorsal and anal fins positioned posteriorly. The body is moderately deep (24% of SL) [42],
slightly more so in females [938]. Length-weight relationships, where weight is in g and total length is in mm, for
female and male fish, respectively are: W = 5.649 x
10–7L3.432 and W = 5.272 x 10–7L3.432; pooled n = 125 [938].
Head length less than one-quarter of standard length
(greater than one-quarter in S. jardinii). The mouth is
dorsally oriented, steeply sloping and extends back to rear
margin of eye (in contrast to S. jardinii in which it projects
back well beyond reach of the eye) [42]. We have noted
from inspection of photographs that the jaw extends past
the rear margin of the eye in some specimens and this
character may not be very useful. External sexual dimorphism is lacking in this species [938], however mouth size
may be greater in females given that this sex incubates the
Systematics
Osteoglossidae is an ancient group of primary freshwater
fishes with a distribution (Africa, South America, Southeast Asia and Australia) suggestive of an origin well prior
to the fragmentation of the Gondwanan supercontinent
[573]. Fossil osteoglossids are known from Eocene
deposits [52, 1413] and Saville-Kent [1197] provides a
figure of an extinct osteoglossid Phareodus queenslandicus
from tertiary clay shale in south-eastern Queensland. The
family contains four extant genera: Arapaima Müller,
Heterotis Rüppell (ex Ehrenberg), Osteoglossum Vandelli
and Scleropages Günther. Scleropages contains two
Australian species S. leichardti Günther, S. jardinii (SavilleKent) and a third species S. formosus (Schlegel and Müller)
60
Scleropages leichardti
scattered locations east of the Great Dividing Range on
Cape York Peninsula including the Olive, Pascoe and
Lockhart rivers [571, 1349], Harmer Creek and an
unnamed lake in the Shelburne Bay area [571].
from Indonesia, Malaysia, Thailand, Cambodia and
Vietnam.
Scleropages leichardti was first collected in 1845 by the
German explorer Friedrich Leichhardt while encamped on
the McKenzie River. It was subsequently described by
Günther in 1864 but the type locality was listed as the
Burdekin River [490]. Günther consistently misspelt
Leichhardt’s name throughout the description and in the
trivial name but according to the rules of International
Code for Zoological Nomenclature the trivial name stands
as leichardti without the extra ‘h’ [165]. Nonetheless, the
trivial name frequently appears as leichhardti [165, 1042].
The only synonym is Osteoglossum guentheri Castelnau,
1876 and the type locality for this species is also listed as
the Burdekin River [286, 1042].
Macro/meso/microhabitat use
Quantitative information on habitat use by S. leichardti is
lacking. Qualitatively, it has been stated that S. leichardti
prefers long deep turbid waterholes, with a reduced flow
rate and abundant snags, undercut banks and overhanging
vegetation [753, 936, 942, 1386]. It may do well in
impounded waters [160]. This species spends considerable
time at the water’s surface patrolling the river banks,
retreating to deeper water or snags and undercuts when
threatened [470, 1386]. Access to deep water may be important at times of high water temperature (>31°C) [934].
The vernacular name for S. leichardti is often listed as spotted barramundi [470, 1181, 1386]. Whitley [1386] believed
the name was a corruption of the aboriginal word burrumundi, while Grant [470] believed the original aboriginal
name was burrumunda, later corrupted to barramunda,
then barramundi. However, Saville-Kent used the term
barrimundi in his 1892 description of S. jardinii [1197].
The name barramundi has been used for both Australian
species of Scleropages, Lates calcarifer and Neoceratodus
forsteri [470]. We recommend, in order to avoid the confusion so common with vernacular names, that barramundi
be used as the common name for Lates calcarifer only and
that the names saratoga and northern saratoga be used for
S. leichardti and S. jardinii, respectively.
Environmental tolerances
Few data are available concerning the environmental tolerances or ambient water quality conditions experienced by
S. leichardti. The range of water quality conditions in
which this species was recorded by Midgley [942] was:
22.5–31°C, 3.6–8.3 mg O2.L–1, pH 7.2–8.3 and 12–90 cm
Secchi disc depth. Lake and Midgley [756] believed S.
leichardti tolerant of high turbidity levels and gave a Secchi
disc depth of 3.8 cm as the most turbid conditions in
which they had recorded this species. These authors report
that S. leichardti can live in water temperatures of 7–40°C
but that prolonged exposure (three to four weeks) to
temperatures less than 10°C results in death.
Distribution and abundance
Scleropages leichardti is endemic to the Fitzroy River
system [52]. Within this river, S. leichardti occurs in the
Dawson, McKenzie, Don, Isaacs and Connor rivers [160,
942]. Midgley [942] recorded S. leichardti from only three
of 19 study sites and qualitatively recorded it as rare at each
site. Berghuis and Long [160] found it to be more widespread, occurring in six of 19 sites, but this species was not
abundant, comprising 0.6% of the total catch only, at an
average catch rate of 0.0125 fish.m–1.hr–1. This species is
thought to be highly territorial [52, 934] and rarely reaches
high abundance [938].
Reproduction
Scleropages leichardti exhibits a significant degree of
parental care; the female incubates the eggs in the buccal
cavity and guards the young until they are old enough to
leave. Spawning is by direct pairing, after a prolonged
courtship period [934], occurring from September to
November (but mostly in October) when water temperatures exceed 22–23°C (Table 1). The eggs are large (10 mm
diameter), few in number, and maturation is delayed until
the fourth or fifth year of life when large size is attained
(Table 1).
Errors in specifying the type locality (i.e. Burdekin River
instead of Fitzroy River) have been promulgated sufficiently
to result in the distribution being extended to this river in
some texts [470]. This species has been translocated into
some catchments of the Burdekin basin and many other
water storages in south-eastern Queensland (e.g. Mary,
Brisbane, Logan-Albert and Burnett rivers) [593, 1349].
Longevity is unknown but probably exceeds six to seven
years. Whitley [1386] cites a personal communication in
which efforts to catch a particularly distinctive red specimen had occurred for at least seven years. Whitley even
speculates at a life span measured in decades [1386]. Long
life, delayed maturation, low fecundity and large egg size
are features common to most fishes exhibiting parental
care.
Scleropages jardinii is patchily distributed across northern
Australia west of the Great Dividing Range [52] and a few
Spawning has not been observed (the mechanics of fertilisation and transfer of the eggs to the buccal cavity are
61
Freshwater Fishes of North-Eastern Australia
three days [934]. The young quickly establish small territories but will shoal together if abundances are in excess of
habitat suitable for the establishment of territories. It is
noteworthy that territorial behaviour is assumed so early
in life and it is tempting to speculate that the female’s first
patrols, in which the young are released, involve some
assessment of the quality of juvenile habitat. Furthermore,
occasional displays of aggression to other incubating
females may be intended to reduce juvenile competition
for territories.
unknown), but probably occurs at dusk [934]. Larval
development is rapid; hatching occurs after 10–14 days at
22–30°C.
During the incubation period, the female does not eat nor
show signs of aggression to non-incubating females,
although aggression towards other incubating females,
which may be distinguished from non-incubating fish by a
conspicuous white chin, may occur [934]. The larvae hatch
at an advanced state of development, closely resembling
the adult form with the exception of the possession of a
large yolk sac. Growth is rapid and a length of 35–40 mm
is attained after four weeks. It is at this size that the young
make their first forays away from the female. The female
moves close to the river-bank where the young are
released. They remain close to the mother’s head as she
slowly patrols the riverbank, returning rapidly to the safety
of the buccal cavity when required. The interval between
the first release of the young and the final release is about
Juvenile growth is rapid also. Under culture conditions, a
length of 110–110 mm may be reached six weeks after
incubation ceases [934] and length of 150–200 mm may
be reached after six months [1194]. A length and weight of
560 mm and 1700 g, respectively, may be reached after
three years under culture conditions [756] but these
growth rates probably exceed that experienced in the wild
[938].
Table 1. Life history data for Scleropages leichardti. Information on reproductive biology drawn from a number of studies
undertaken principally under culture conditions.
Age at sexual maturity (months)
Maturation commences at three years but spawning occurs at four years of age [756],
five years [938]
Minimum length of ripe females (mm)
360 mm TL [797]; >560 mm, growth rates of cultured fish greater than that of wild
fish [934, 938]
Minimum length of ripe males (mm)
355 mm TL [797]; >560 mm , growth rates of males may be greater than females [756]
Longevity (years)
? at least 7 years [1386], probably in excess of 8 years
Sex ratio
?
Peak spawning activity
Mid-October [756], September/October [934], October/November [1194]
Critical temperature for spawning
>23°C [756], 22–23°C [934]
Inducement to spawning
? Temperature
Mean GSI of ripe females (%)
?
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
Low: 30–130 [14]; 78–173 [756]
Fecundity/length relationship
78 eggs at 476 mm TL, 110 eggs at 550 mm TL, 173 eggs at 660 mm TL [756]
Egg size
10 mm [756]
Frequency of spawning
Once per season for females, twice or more for males with long recovery period (several
weeks) between spawnings
Oviposition and spawning site
Unknown, spawning probably takes place at night [934]
Spawning migration
?
Parental care
Buccal incubation by female, incubation and brooding may last 5–6 weeks
[126, 756, 934]
Time to hatching
10–14 days at 23-30°C [756]; 5–6 weeks [14]
Length at hatching (mm)
15 mm [934], newly hatched larvae 36 mm TL [756]
Length at feeding
At maximum 35–0 mm TL [934]
Age at first feeding
At maximum, 30 days post-hatch
Age at loss of yolk sac
?
Duration of larval development
Hatch at advanced state of development, larvae with adult appearance with the
exception of presence of large yolk sac [756]
Length at metamorphosis
? 15–25 mm
62
Scleropages leichardti
Movement
Other than that described above, little is known of the
movement biology of this species. Scleropages leichardti
has not been recorded moving through fishways.
expressed. However, given the large number (15 and
rising) of impoundments in the Fitzroy River basin, it
seems critical to determine whether such habitats are
indeed beneficial to this species.
Any fish exhibiting the life history traits of delayed maturation and reduced fecundity as shown by S. leichardti will
be more vulnerable than early maturing highly fecund
species. Scleropages leichardti is exploited by both recreational fishers and the aquarium fish industry (collection
of brood stock only), the extent of which is controlled by
bag limits and collecting restrictions [1194]. This species
is widely translocated in Queensland and the collection of
broodstock may also place pressure on this species.
Trophic ecology
No quantitative information on the trophic ecology of S.
leichardti is available. This species has been described as a
surface feeder on insects, crustaceans, frogs and fish [52].
Scleropages jardinii in the Northern Territory has a diet
dominated by aquatic insects (54%), terrestrial insects
(12%), terrestrial plant material (10%) and fish (9%)
[191]. Sambell [1194] believed that S. leichardti were less
adept at catching small fish than S. jardinii because of the
dorsal orientation of the eyes.
Water regulation has greatly altered the natural flow
regimes of the various rivers in the Fitzroy River basin
[380]. The extent to which these changes interfere with the
reproductive phenology of adults and the development
and recruitment success of juveniles remains unknown.
Similarly, many aquatic habitats of the river are seriously
degraded [380]. Loss of riparian integrity and of bank
associated structures (i.e. woody debris, root masses and
undercuts) is likely to impact on this species by reducing
food supply (i.e. terrestrial insects) and habitat quality.
The fact that this species is territorial suggests that
localised reductions in abundance are unlikely to be naturally remediated by colonisation in anything but the
medium to longer term.
Conservation status, threats and management
Scleropages leichardti was listed as Rare in 1993 [1353] and
more recently as Lower Risk–Near Threatened [117].
Midgley [942] expressed concern about declining
numbers of this species in 1979, but in more recent
research in the Fitzroy River, Berghuis and Long [160]
believed that the population was secure because the
creation of impoundments in the Fitzroy River basin had
increased the area suitable for this species. However,
Berghuis and Long failed to collect S. leichardti at sites
close to those established by Midgley and failed to collect
any specimens in the upper Dawson River, although
unpublished data apparently suggests that this species still
commonly occurs there. Moreover, Midgley’s study
included impounded waters and S. leichardti was absent
from these habitat types despite being present in earlier
years. The two studies are difficult to use to determine the
current status of S. leichardti given differences in sampling
regime and the manner in which abundances were
Given the endemic status of this species, its phylogenetic
significance, and unique biology, we find it very surprising
and alarming that so little is known about S. leichardti.
This in itself is one of the most serious threats to the
continued survival of this species, especially given that it is
restricted to one of the most developed river basins in
Queensland.
63
Megalops cyprinoides (Broussonet, 1782)
Tarpon, Oxeye Herring
37 054001
Family: Megalopidae
anterior margin of the eye. The lower jaw is prominent, its
two branches separated by a bony gular plate. Eyes large
and covered by an adipose eyelid. Scales large; lateral line
well-developed with tubes branching. Pectoral fins set low
on profile and with long axillary process. Axillary process
also present on pelvic fins. Well-vascularised swim bladder
present and lying below and in contact with skull. Tail
deeply forked. The extended filament of the dorsal fin is
absent in specimens below about 56 mm in length. Colour
in life: bluish-green to olive dorsally grading through silver
on flanks and white on belly. Fins frequently a pale yellow.
Colour in preservative: essentially the same as in life except
silver colour of flanks and yellow colour of fins less vibrant.
Description
First dorsal fin: 16–21, last ray forming prominent filament; Anal fin: 24–31; Pectoral fin: 15 or 16; Pelvic fin: 10
or 11; Gill rakers on first arch: 15–17 + 30–35; Lateral line
scales: 36–40; spines on fins absent [37, 422]. Figure:
composite, drawn from photographs of adult and juvenile
specimens, Burdekin River; drawn 2002.
Megalops cyprinoides is a large fish with a fusiform,
compressed body, unlikely to be confused with any other
species except in the juvenile stage, when it may be
confused with juvenile clupeids. Maximum sizes reported
for this species vary from 1000 mm [936, 977] to 1300 mm
[37] and as large as 1500 mm [470]. Fish of this size are
rarely collected (especially from freshwaters) and maximum sizes of less than 500 mm are more the norm [193,
313]. Coates [313] reports a length/weight relationship for
tarpon from the Sepik River of W = 9.96 x 10–6 L3.1; n = 156,
r2 = 0.95 where W = weight in g and L = SL in mm. Bishop
et al. [193] report a length weight relationship for tarpon in
the Alligator River region of W = 2.4 x 10–2 L2.83; n = 155, r2
= 0.833 where W = weight in g and L = CFL in cm.
Megalops cyprinoides produce a leptocephalus-like larva
that is flat, band-like, transparent and with a forked tail.
Larvae develop teeth early in life at about 11 mm [594,
1347].
Although M. cyprinoides provides excellent sport on light
line, opinions vary as to its culinary quality. Early accounts
suggest it is good eating but Grant [470] dismisses it as
poor quality even after extensive preparation. This species
is an important component of the subsistence fisheries of
Papua New Guinea [313].
The mouth of M. cyprinoides is terminal, toothless in the
adult stage, oblique and large, extending back beyond the
64
Megalops cyprinoides
Megalops cyprinoides has been recorded from most
drainages of the eastern side of Cape York Peninsula
including the Olive, Claudie, Lockhart, Pascoe, Stewart,
Starke, Howick, McIvor, Endeavor, Harmer, Normanby
and Annan rivers [571, 697, 1349] as well as some smaller
streams (Massey Creek and Three Quarter Mile Creek)
[571] and dune lakes of the Cape Flattery region [1101].
Tarpon are found in most rivers of the Wet Tropics region,
being been recorded from the Daintree, Saltwater,
Mossman, Barron, Russell/Mulgrave, Johnstone, Moresby,
Tully/Murray and Herbert River drainages [583, 584, 643,
1177, 1183, 1184, 1185, 1187, 1349]. This species was not
collected from the smaller systems of the Hull River, or
Maria and Liverpool creeks [1179].
Systematics
Megalops cyprinoides has been variously placed within the
Elopidae (the giant herrings) or Megalopidae, with the
latter being currently accepted [406]. Both families are
ancient: Merrick and Schmida [936] suggest that megalopid fossils have been found in Upper Jurassic deposits,
Wilson and Williams [1413] list fossil Elopidae in Late
Cretaceous deposits, and Long (1733] provides a drawing
of a fossilised otolith of the extinct Megalops lissa from the
Miocene. The extant Megalopidae contains a single genus
comprised of two species: Megalops atlanticus and M. cyprinoides. Phylogenetic relationships among the superorder
Elopomorpha, a grouping which includes all teleost fishes
that possess a specialised leptocephalus larva (including the
Megalopidae and Anguillidae), are discussed in Obermiller
and Pfeiler [1437] and Inoue et al. [1434].
Further south, M. cyprinoides has been recorded in the
Black Alice River [275], St. Margarets Creek [1053], the
Houghton River [255], the Baratta wetlands [1046] and
the Burdekin River [587, 591, 847, 940, 1098]. Its distribution in the Burdekin River extends upstream to include the
Bowen River although it is no longer common in this
system due to the barrier imposed by the Clare Weir. It is
still common in wetlands of the Burdekin delta (C. Perna,
pers. comm.).
Megalops was first erected by Lacepède in 1803 with the
type species for the genus being M. filamentosus (=cyprinoides). Megalops cyprinoides was first described and
placed in the genus Clupea by Broussonet in 1782, based
on material collected during Captain Cook’s voyages in the
Pacific. Not unexpectedly, given the large range of this
species, there are numerous other synonyms for M. cyprinoides. These include: M. cundinga Hamilton 1822, M.
curtifilis Richardson 1846, M. indicus Valenciennes 1847,
M. macropthalmus Bleeker 1851, M. macropterus Bleeker
1866, M. oligolepis Bleeker 1866, M. setipinnis Richardson
1843, and M. stagier Castelnau 1878.
Megalops cyprinoides has been recorded from the Pioneer
River [1081] and the Shoalwater Bay region [1328].
Tarpon were formerly widespread in the Fitzroy River but
the numerous impoundments on this system have reduced
its present distribution [659, 942, 1274]. Impoundments
have similarly affected this species in the Burnett River [11,
700, 1173, 1276]. Tarpon have been recorded from the
Burrum, Mary, Noosa, Brisbane and Logan-Albert rivers
[168, 643, 701, 702, 881, 1349] and from Moreton Bay
[881, 969] and North Stradbroke Island [988]. This species
has been recorded from artificial habitats (e.g. golf course
lakes) in the Gold Coast region of southern Queensland
(J. Tait, pers. comm.).
Distribution and abundance
Megalops cyprinoides is a very widespread species, its range
extending from east Africa to South-east Asia including
Japan, Australasia and some islands of the west Pacific. The
Australasian distribution is similarly large. This species
occurs in rivers of both northern and southern Papua New
Guinea and Irian Jaya [37, 42, 46, 51, 316, 495]. The
Australian range includes rivers of the Kimberley region
[45], being recorded from the Fitzroy [620, 779], Carson
and Ord rivers [620]. This species is widespread across the
Northern Territory and has been recorded from the
Victoria [946] and Daly [945] river systems, drainages of
the Alligator Rivers region [193, 772, 1064, 1416], and
drainages of Arnhem Land [944]. Tarpon have been
recorded from the Leichhardt River in the Gulf region of
Queensland [1093] and is probably present in most rivers
of this region. Rivers draining the western side of Cape
York Peninsula in which M. cyprinoides has been collected
include the Embley, Mitchell, Coleman, Ducie, Watson,
Archer, Edward, Holroyd, Wenlock and Jardine rivers [41,
571, 643, 1349]. Its distribution in the Mitchell River
extends as far upstream as the Walsh River [1186]. Tarpon
have also been recorded from swamps and lagoons of the
Weipa area [571].
Lake [748] lists M. cyprinoides as a member of the freshwater fish fauna of New South Wales and later suggested that
it was restricted to the northern rivers of the state [755].
Krefft reported catching M. cyprinoides on fly in the
Hawkesbury River in the early 1860s [741]. It appears to
be uncommon or no longer present in New South Wales as
it was not collected in the recent comprehensive NSW
Fisheries survey [554].
Macro/meso/microhabitat use
The life history of Megalops cyprinoides is complex, involving a variety of different habitats at different life stages.
The habitat requirements of the larval and juvenile forms
are more fully described in the sections on reproductive
and movement below. Subadult and early-maturing adult
65
Freshwater Fishes of North-Eastern Australia
Table 1. Physicochemical data for the tarpon Megalops
cyprinoides. Summaries are drawn from two separate studies
undertaken in northern Australia [193, 697]. Note the
difference in units used to described turbity.
forms are found in a variety of freshwater habitats and
may penetrate many hundreds of kilometres upstream.
Roberts [1147] reported M. cyprinoides 905 km upstream
in the Fly River of Papua New Guinea and Coates [313]
reports it present 530 km upstream in the Sepik River
(although it may have been present further upstream
where little sampling was undertaken). Similarly extensive
upstream distributions have also been reported for
Australian rivers (see above). In the Sepik River, tarpon
have been recorded from the main river channel, major
lowland tributaries, oxbow floodplain lakes and on the
floodplain itself [313]. However, it was reported that the
floodplain was not the preferred habitat, that tarpon were
absent from low order streams and deep water habitats
were preferred. In contrast, tarpon in the Alligator Rivers
region have been recorded from escarpment habitats near
the headwaters. The majority of fish collected by Bishop et
al. [193] were from lentic habitats such as floodplain,
lowland muddy and corridor lagoons as well as the main
channel. These authors noted that M. cyprinoides was most
abundant in lagoons with plentiful submerged and floating-attached macrophytes, but that at times would move
out of such habitats to feed extensively on migrating rainbowfishes. Bishop et al. [193] noted a preference for
deeper waters also.
Parameter
Min.
Max.
Mean
Alligator Rivers region (n = 20)
Water temperature (°C)
23
34
Dissolved oxygen (mg.L-1)
1.9
9.7
pH
5.3
9.1
Conductivity (µS.cm-1)
2
200
Turbidity (cm)
4
270
86
Normanby River floodplain (n = 12)
Water temperature (°C)
22.9
29.4
Dissolved oxygen (mg.L-1)
1.1
7.1
pH
6.1
8.2
Conductivity (µS.cm-1)
9.8
391
Turbidity (NTU)
2.1
8.1
23.9
3.6
7.1
220.6
5.3
29.8
6.2
6.5
with dissolved oxygen levels of 0.2 mg O2.L–1 [583]. This
species is obviously very tolerant of low levels of dissolved
oxygen primarily because of its ability to extract oxygen
directly from the atmosphere. Megalops cyprinoides was
not recorded in a large fish kill in Magela Creek for which
hypoxia was implicated as the primary cause [187] and
Bishop et al. [193] attributed its survival to its ability to
breath air.
Coates [313] observed that tarpon fed extensively underneath floating mats of Salvinia. This same behaviour has
been observed in floodplain habitats of the Burdekin River
delta (C. Perna, unpubl. obs.). Floodplain water bodies
experience precipitous declines in water quality, especially
dissolved oxygen levels, when floating weeds such as
Salvinia and water hyacinth (Eichhornia crassipes) proliferate. In such cases, tarpon (which is a facultative airbreather), and other species capable of accessing the
relatively well-oxygenated layer of surface water (e.g. the
alien Gambusia holbrooki), are the dominant species.
Air breathing in M. cyprinoides has not been studied but
has been for M. atlanticus [444], a summary of which is
included below. This species is a bimodal breather with gas
exchange occurring across the walls of the swim bladder.
Species of Megalops are the only marine nektonic species
to use bimodal breathing and the only marine fishes to use
respiratory gas bladders. The wall of the gas bladder in M.
atlanticus has four rows of highly vascularised tissue. The
extent of vascularisation of the bladder in M. cyprinoides is
greater in fish collected from hypoxic waters than in welloxygenated waters (C. Perna, pers. comm.). In M. atlanticus, air is expelled from beneath the opercula as the fish
rises to the surface. If denied access to air after exhalation,
M. atlanticus cannot maintain neutral buoyancy. Air is
inhaled by expansion of the buccal and opercular cavities,
accompanied by abduction of the gular plate. The inhaled
air is forced into the gas bladder, after the mouth closes, by
compression of the buccal and opercular cavities. This
behaviour of rising to the surface and gulping air has been
termed ‘rolling’ and has been observed to occur in leptocephalus-like larvae also [594]. Bishop et al. suggested that
rolling was more frequently observed when oxygen levels
were low [193]. Air breathing, or at least the ‘rolling’
behaviour associated with air breathing, has been observed
in larval M. cyprinoides also [302].
Environmental tolerances
Megalops cyprinoides is a tropical species and the water
temperatures given in Table 1 reflect this distribution.
However, given that its distribution extends down the east
coast to at least Brisbane, this species may be able to tolerate lower water temperatures than indicated here. The
closely related M. atlanticus has been recorded from
temperatures as low as 12°C [444].
Megalops cyprinoides has been recorded across a wide
range of dissolved oxygen concentrations and is tolerant
of hypoxic conditions (Table 1). Oxygen levels in floodplain habitats of the Burdekin River delta, in which this
species is common, frequently descend as low as 0.2–1%
saturation (C. Perna, pers. comm.). Hogan and Graham
recorded this species in wetlands of the Tully Murray River
66
Megalops cyprinoides
The related species M. atlanticus is not an obligate air
breather, surviving for at least two weeks when denied
access to air. This species will however, breath air in
normoxic waters, presumably to maintain buoyancy
[444]. Air breathing frequency in M. atlanticus increases
with increasing temperature and decreasing oxygen saturation. At temperatures above 29°C, the frequency of air
breathing is independent of oxygen levels [444]. The
frequency of air breathing in M. atlanticus increases with
increasing sulphide concentrations also. High levels of
sulphide inhibit respiration by disrupting the function of
both haemoglobin and cytochrome c. Megalops atlanticus
is tolerant of very high levels of sulphide (240 µmoles.L–1)
when air breathing frequency is higher than that recorded
for anoxic conditions.
probably achieves sexual maturity in the second year of life
when lengths in excess of 300 mm are attained.
Juvenile individuals smaller than that observed by Bishop
et al. [193] have been recorded from freshwaters elsewhere.
Taylor [1304] reports the presence of a 66 mm juvenile in
a freshwater lagoon with connection to an estuarine
mangrove habitat in Arnhem Land. Small fish of this size
have been collected from lagoons of the Burdekin River
delta also (C. Perna, pers. comm.). In an early dry season
survey of the fishes of Gunpowder Creek, approximately
200 km from the river mouth of the Leichhardt River, we
collected numerous M. cyprionoides between 25–50 mm
SL [1093]. Obviously such small fish must be capable of
rapid extensive movement.
The spawning habitat of M. cyprinoides is unknown other
than it occurs in the near-shore marine or estuarine environment. This species produces a leptocephalus-like larva
that undergoes most of its development in saline supralittoral tidal swamp environments. Opinions differ as to
whether the leptocephali actively migrate into such habitats [29] or are simply passively carried in on rising tides
[302], however Wade [1347] demonstrated that postlarvae were capable of independent movement and migration. Davis [370] studied the temporal dynamics of
supralittoral swamp fishes near Darwin and found M.
cyprinoides to be very common, accounting for 13% of all
fish collected during the early wet season. Leptocephali
were present in the tidal swamp from October to March,
although peak numbers occurred in December and
January. Initially, numbers appeared greatest during the
full moon phase until numbers increased sufficiently to
swamp any apparent temporal variation in recruitment.
Juvenile fishes (i.e. those having undergone metamorphosis) were, in contrast, present only from December
onwards and abundances levels were correlated with tidal
phases. Megalops cyprinoides was the most numerically
dominant species during neap tides and was amongst the
top three species with respect to length of residency.
Russell and Garrett [1174] also found M. cyprinoides
larvae during December in supralittoral swamps of the
Norman River estuary, northern Queensland; they were
uncommon however.
Megalops cyprinoides has been recorded across a reasonably wide range of pH (5.3 to 9.1) (Table 1). We have
collected adult M. cyprinoides from dystrophic dune lakes
of the Cape Flattery region, where pH levels may
frequently be in the range of 4–5 [1101]. The conductivity
levels depicted in Table 1 indicate fresh waters but given
that both larvae and adult tarpon occur in marine and
estuarine environments, salinity tolerance must extend
across a wide range. Larval tarpon are able to withstand
abrupt transfer from brackish to freshwater but acclimation is generally a gradual process [29]. The range of water
clarity across which it has been collected suggests that
tarpon are tolerant of elevated turbidity. However, the
extent to which high turbidity interferes with the ability of
tarpon to locate prey remains unknown.
The conditions in which M. cyprinoides has been recorded
and the tolerances inferred from these conditions plus
insights gained from comparison with M. atlanticus,
suggest that tarpon are hardy and well-adapted to inhabit
seasonal wetlands that experience substantial fluctuations
in dissolved oxygen, turbidity, pH and sulphide levels.
Reproductive biology
Detailed information on many aspects of the reproductive
biology of Megalops cyprinoides is lacking, principally
because this species moves out of freshwater environments
to spawn. Bishop et al. [193] records some information on
reproductive biology of this species, however sample sizes
were not large. Most fish collected were immature, with the
length frequency distribution being essentially unimodal
with a mean of 246 mm CFL. The smallest fish collected by
these authors was 137 mm CFL occurred in the mid-wet and
mid-dry seasons, suggestive of a recruitment pulse occurring during the mid-wet when estuarine connections occur.
Male maturation commenced at the end of the dry season.
Based on growth estimates provided by Alikunhi and
Nagaraja Rao [29] and Bishop et al. [193], M. cyprinoides
Fecundity estimates are unavailable for M. cyprinoides.
Hollister [594] cites data for a 56 kg M. atlanticus producing 12 million small (0.67–0.75 mm), non-buoyant, nonadhesive eggs. Given that M. cyprinoides does not reach
such large size, it is unlikely to be a fecund as its congener.
Nonetheless, this species probably produces hundreds of
thousands of small eggs similar to M. atlanticus. Estimates
of reproductive effort in M. cyprinoides indicate a maximum female GSI of about 7% [313]. Bishop et al. [193]
67
Freshwater Fishes of North-Eastern Australia
Table 2. Life history data for the tarpon Megalops cyprinoides.
Age at sexual maturity (months)
12–24 months
Minimum length of ripe females (mm)
Alligator Rivers region – 300 mm CFL (estimate only) [193]
Sepik River – 410 mm female recorded with developed gonads [313]
Minimum length of ripe males (mm)
Alligator River region – 300 mm [193]
Longevity (years)
?
Sex ratio (female to male)
?
Occurrence of ripe fish
?
Peak spawning activity
Summer wet season [193]
India – suggestions of a year-round breeding phenology with a peak during the
monsoonal months [1347]
Critical temperature for spawning
?
Inducement to spawning
?
Mean GSI of ripe females (%)
7% [313]
Mean GSI of ripe males (%)
<1%, although maturity stage low [193]
Fecundity (number of ova)
?
Fecundity/length relationship
?
Egg size
?
Frequency of spawning
Possibly several times over life span
Oviposition and spawning site
Near-shore marine
Spawning migration
Parental care
None
Time to hatching
?
Length at hatching (mm)
?
Length at free swimming stage (mm)
11
Length at metamorphosis (mm)
17
Duration of larval development
Up to several weeks
Age at loss of yolk sack
?
Age at first feeding
Probably very soon after hatching
list much smaller values (<1%) for fish from the Alligator
Rivers region. However, it must be borne in mind that the
entire sample was collected from freshwaters and that
complete gonad maturation probably occurs in marine or
estuarine habitats.
anus, and a change in the shape, appearance and size of the
head. Further details on metamorphosis and early development can be found in Tsukamoto and Okiyama [1444].
Movement
From the above discussion, it is evident that movement is
a feature of many phases during the life history. After
metamorphosis, juvenile tarpon migrate out of supralittoral habitats and move upstream. It is unknown whether
this movement is made en masse or involves single individuals. However, the 32 juveniles we recorded in
Gunpowder Creek were all between 32 and 50 mm SL,
suggesting that migration may have been coordinated
within this age class. Moreover, it indicates that substantial
upstream movements are made at very small size.
The smallest size recorded for the larvae of M. cyprinoides
is about 11 mm [1347], such fish already have well-developed teeth, a long and well-developed alimentary canal
and the air bladder is a club-like evagination of the
alimentary canal. Growth is gradual until the leptocephalus achieves a length of 25–26 mm whereupon the
body commences to shrink back to a length of about 16
mm [1347]. This latter process is protracted, taking up to
seven weeks. However, Alikunhi and Nagaraja Rao [29]
suggest that shrinkage may occur over the space of as little
as seven days when larvae are acclimated to freshwater over
24 hours. Larvae can tolerate direct transfer from brackish
to freshwater although acclimation usually occurs over a
longer period [1347]. Outstanding features of metamorphosis other than shrinkage in body length include:
forward migration of the dorsal and anal fins and of the
Megalops cyprinoides have been recorded moving through,
or attempting to move through, various fishway structures
in Queensland rivers [11, 158, 159, 232, 587, 740, 1276].
However, in all cases numbers have been low. For example,
Russell [1173] recorded only eight individuals ascending
the fishway on the Burnett River barrage over a 32-month
68
Megalops cyprinoides
period. Ascending fish were between 33 and 180 mm in
length. A further two fish, both 30 mm in length, were
recorded moving downstream through this fishway.
Kowarsky and Ross [740] detected small numbers of fish
between 139–370 mm in length, ascending the fishway on
the Fitzroy River barrage during March and April only.
Similarly small numbers were recorded moving through
the fishway on the Burnett River barrage in these months,
and Broadfoot et al. [232] recorded 18 individuals moving
through the Kolan Weir fishway at times of little flow. In
most of these studies, the size range of fishes sampled
(when given) indicates that the majority of upstream
migrating fish are of relatively small size. For example,
sizes ranges for fish trapped in the Tinana, Kolan, Burnett
and Fitzroy barrage fishways were 106–206 mm (TL),
89–142 mm (CFL), 30–180 mm (TL) and 139–370 mm
(TL), respectively. Hogan et al. [587] recorded much larger
fish (300–450 mm TL) attempting to ascend the Clare
Weir fishway on the Burdekin River under a variety of flow
condition (65 466–127 467 ML.day–1). In the Sepik River,
M. cyprinoides enter the river at lengths of about 100 mm
between April and July, and individuals less than 250 mm
in length move upstream between May and August (i.e.
the early dry season) [313].
classified it as a marine species that was widely distributed
throughout the estuary in the wet and early dry seasons
only.
Trophic ecology
The dietary summary provided in Figure 1 was drawn
from three separate studies. The first was undertaken by
Bishop et al. [193] in the Alligator Rivers region and
included 79 individuals ranging in size from about 150
mm to 400 mm CFL; the second was by Kennard [697] in
floodplain lagoons of the Normanby River and included
25 individuals ranging in size from 180 to 400 mm SL
[697]; and the third included three individuals of 400, 420
and 640 mm SL collected in the lower Burdekin River
[1080].
The diet of M. cyprinoides, although reasonably diverse, is
dominated by aquatic insects and fish (chandids, rainbowfishes, plotosid catfishes, Pseudomugil tenellus and
Hypseleotris compressa). The extent of piscivory varied
between studies, with fish comprising 31% of the total for
tarpon from the Alligator Rivers region and 21.6% of the
diet of fish from the Normanby River floodplain. Fish were
absent from the guts of three fish collected in the Burdekin
River. Both Bishop et al. [193] and Kennard [697] showed
that piscivory varied in importance with season. Fish were
most important in the early, mid- and late wet season diets
in the Alligator Rivers region. Bishop et al. noted that
tarpon would establish feeding stations where they preyed
heavily on migrating rainbowfishes. Fish accounted for
22% of the early dry season diet of tarpon in the Normanby
River but were almost absent (1.8%) in the late dry when
terrestrially derived prey were more important (16.2%).
An extensive upstream migration is not necessarily an
obligate part of the life history. For example, tarpon less
than 350 mm TL are common in wetland habitats of the
Burdekin River delta: they may however be entrained in
pumping works and artificially delivered into these
systems (C. Perna, pers. comm.). Nonetheless, it appears
that many small individuals do migrate upstream where
they make use of main channel and off-channel habitats.
If upstream movements by juveniles occurs during periods of low flow late in the wet season or in the early dry
season, it is unlikely that access to many off-channel waterbodies exists at this time. Further lateral movement may
occur when water levels rise at the beginning of the following wet season.
Unidentified (15.4%)
Fish (29.0%)
Terrestrial invertebrates (4.6%)
Aerial aquatic invertebrates (1.6%)
Terrestrial vegetation (1.3%)
Detritus (3.3%)
Bishop et al. [193] found that M. cyprinoides less than 300
mm CFL were most common in floodplain, lowland and
corridor lagoons but that fish larger than this were often
recorded from lowland sandy creeks during the wet
season. Such a shift in habitat use may presage a downstream spawning migration. These authors believed that
adult tarpon migrate back upstream after spawning, citing
as evidence observations of spent females congregated
below, and trying to negotiate, a roadside culvert. Coates
[313], in contrast, suggested that no upstream migration
was made after spawning and that spent fish remained in
estuarine, near-shore marine environments. Cyrus and
Blaber [356] found that the distribution of M. cyprinoides
in the estuary of the Embley River varied seasonally and
Microcrustaceans (4.0%)
Macrocrustaceans (6.0%)
Aquatic insects (34.6%)
Figure 1. The average diet of the tarpon Megalops cyprinoides.
The summary is derived from three separate studies
undertaken in northern Australia (see text for details) and
mean contributions have been weighted by sample size.
Terrestrially-derived foods are important in the diet,
accounting for about 8% overall. We observed that two
adult tarpon from the dystrophic dune lakes of Cape
Flattery region consumed little other than terrestrial insects.
69
Freshwater Fishes of North-Eastern Australia
faces many of the same pressures. These are principally
associated with degradation of estuarine and supralittoral
habitats necessary for larvae and juveniles and the need to
move freely between different habitats throughout their
life history. Although tarpon are frequently found in offchannel habitats of less than optimal water quality and
condition, access to such habitats may not always be
assured. Water resource developments that interfere with
upstream or downstream movement are likely to impact
on this species in the long term. Similarly, infrastructure
sufficiently large enough to capture large flood events may
affect tarpon by reducing the extent of lateral flooding.
The presence of microcrustacea in the diet is noteworthy
given the size of M. cyprinoides. This food type comprised
8.4% of the overall diet of fish in the Normanby River
(11.4% and 0% in the early and late dry seasons, respectively). Microcrustaceans (Cladocera) were present and
important (14%) in the diet of Alligator River tarpon in
the mid-dry season only.
The diversity of diet evident in Figure 1 is of interest not
only for the range of prey consumed but also the range of
habitats from which prey are obtained (i.e. surface,
midwater and benthos). A diversity of feeding styles is also
evident, for this species is not only capable of preying
upon fast-moving fishes but also upon fishes with protective spines, as well as planktonic microcrustaceans, macrocrustacean (prawns) and a range of small benthic insect
larvae.
Given the piscivorous nature of M. cyprinoides, this species
is probably of significance in determining the assemblage
structure and abundance of smaller fishes in some habitats, particularly enclosed off-channel wetlands. In the
wetlands of the Burdekin River delta, this species may play
a significant role in controlling the abundance of pest
species such as Gambusia holbrooki (C. Perna, pers. comm.)
and its absence may allow Gambusia to achieve abundance
levels sufficiently high to impact on other native species.
Coates [313] described the diet of tarpon from the Sepik
River [313]. Fish were also important in this river (17%)
but included a less diverse range of species being dominated by Giurus margeratacea and Oxyeleotris spp. Prawns
comprised 20% of the diet and terrestrial insects a further
13%. The contribution made by terrestrially-derived prey
was probably higher as some insect orders were grouped
in a prey class termed ‘larger insect larvae’. Insect larvae
comprised about 40% of the diet. Such a diet is well within
the range depicted in Figure 1.
Given the scant information available about the ecology of
the adult form, it is difficult to say what pressures may be
faced by this life history stage. This species forms only a
minor component of the bycatch from commercial barramundi harvesting [501] and does not appear under threat
from this activity. Recreational fishing is similarly not
expected to pose any major threat given the poor culinary
value of this species: most individuals are released after
capture.
Noble [994], reporting on the laboratory rearing of M.
cyprionoides larvae, noted that post larvae preferred copepods over other prey, and also noted the preponderance of
copepods in the diet of larvae reported in other Indian
studies of this species. As larvae grow, foraging is focused
first on large microcrustaceans, then on such prey as
isopods with an eventual transition to prawns.
There remain many aspects of the ecology of this species
for which information enabling effective management is
lacking. Megalops cyprinoides is not unique in this regard.
Absence of data should be regarded as a threatening
process in itself. There is potential for fishway studies to
increase our knowledge of this species’ ecology, provided
that information other than simply length and number of
fish passing through the fishway is collected.
Conservation status, threats and management
Megalops cyprinoides is classified as Non-Threatened
[1353]. However, the ecology of this species parallels
that of the barramundi in many ways, and accordingly it
70
Anguilla australis Richardson, 1841
Shortfinned eel
37 056001
Anguilla obscura Günther, 1872
Pacific shortfinned eel
37 056004
Anguilla reinhardtii Steindachner, 1867
Longfinned eel
37 056002
Family: Anguillidae
to about half the distance of the jaw teeth; anterior nostrils
long, projecting forwards over upper lip; eyes small in
immature specimens, increasing in relative size at maturity; gill openings small and vertically orientated. Dorsal
fin confluent with caudal and anal fins, originating slightly
in front or level with the anal fin, without spines. Pelvic
fins absent; pectoral fins small and ovate, positioned just
behind gill openings. Scales inconspicuous, deeply embedded in thick, fleshy skin, skin covered in characteristic
slime. Lateral line distinct.
Description
Anguilla australis
Dorsal fin confluent with caudal fin and anal fin, originating slightly in front or level with anal fin; Pectoral fin:
14–16 rays; Pelvic fins absent; Scales indistinct; Vertebrae:
109–116 [52, 178, 401].
Anguilla australis is a medium to large sized eel. Beumer
[178] lists a maximum length of around 1100 mm TL and
weight of 3.2 kg. Merrick and Schmida [936] list a maximum weight of 6.8 kg but suggest it is usually much
smaller. Males attain smaller maximum size (up to 500
mm TL and 250 g) than do females [178, 891]. The largest
specimen we have collected in south-eastern Queensland
was 350 mm SL [1093]. The equation describing the relationship between length (TL in mm) and weight (W in g)
for a population in the Douglas River (eastern Tasmania)
[1244] is:
Log W = 3.4 Log L – 3.477, r2 = 0.984, p<0.001, n = 80,
range = ~ 80–520 mm TL.
Small juvenile eels (known collectively for all Anguilla
species as ‘glass eels’) recently metamorphosed from the
leptocephalus stage and in the process of moving into
estuaries and lowland rivers are transparent but can be
distinguished from other eel species in south-eastern
Australia by the position of the origin of the dorsal fin.
Fully pigmented juvenile eels (known as ‘brown elvers’)
rapidly assume adult colouration after entering freshwaters (often called ‘yellow eels’ by this stage). The uniform
colouration of elvers and adults of A. australis is characteristic of this species in south-eastern Australia and varies
from coppery or golden to olive-green on the dorsal and
lateral surfaces, becoming paler greyish to silvery-white on
the ventral surface. The dorsal surface of mature adults
Anguilla australis has an elongate, cylindrical body and a
small head; mouth large, extending to below the eye;
toothless groove between maxillary teeth absent; vomerine
teeth forming a broad club-shaped patch extending back
71
Freshwater Fishes of North-Eastern Australia
the mean and maximum length of this species were 242
and 1350 mm SL, respectively, with 85.6% of the sample
being less than 350 mm SL [1093]. Of 5121 specimens
collected from streams of south-eastern Queensland over
the period 1994–2000, the mean and maximum length of
this species were 239 and 1300 mm SL, respectively, with
the majority (80% of individuals) 350 mm SL or less
[1093].
becomes darker and contrasts markedly with the silver
belly (often referred to as ‘silver eels’) on commencement
of the downstream migration to oceanic spawning
grounds [52, 177, 178, 401, 936].
Anguilla obscura
Dorsal fin confluent with caudal fin and anal fin, originating slightly in front or level with anal fin; Pectoral fin:
14–20 rays; Pelvic fins absent; Scales indistinct; Vertebrae:
101–107 [37, 52, 178, 401].
Equations describing the relationship between length (SL
or TL in mm) and weight (W in g) are available for the
following populations:
Anguilla obscura is a medium to large sized eel reported to
reach 1200 mm TL but is more commonly around 600 mm
TL [33, 754]. The largest specimen collected in the
Normanby River, eastern Cape York Peninsula, was 600
mm SL [697]. The largest specimen collected in the Wet
Tropics region of northern Queensland was 800 mm SL,
but the average length of 21 individuals was 171 mm SL
[1093]. Beumer et al. [183] collected a 1050 mm TL female
from the South Johnstone River. No length–weight equation is available for this species but it is generally similar in
size and shape to A. australis.
Mulgrave and Johnstone Rivers (Wet Tropics) [1093]: W
= 4.91 x 10–8 SL3.686; r2 = 0.953, p<0.001, n = 100, range =
93–890 mm SL.
Douglas River (eastern Tasmania) [1244]: Log W = 3.548
Log TL – 3.567, r2 = 0.996, p<0.001, n = 71, range = ~
50–1200 mm TL.
Mouth large, extending well behind the eyes; maxillary
teeth separated by a toothless groove; vomerine teeth
forming a narrow patch extending backward around the
same distance as the jaw teeth; the dorsal fin originates well
forward of the anal fin. The glass eel stage of A. reinhardtii
can be recognised by the position of the origin of the
dorsal fin, which is characteristic of this species throughout eastern Australia (but see below). The distinct mottled
or marbled colouration is also characteristic of this
species: dorsal surface varying from olive-green to brownish, becoming paler laterally and ventrally. Median fin dark
brown; pectoral fins commonly yellowish. Adults usually
lose their mottled pattern and become bright silvery after
commencement of the downstream migration to oceanic
spawning grounds [37, 52, 178, 401, 936].
Mouth large, extending well behind the eyes; toothless
groove between maxillary teeth absent; vomerine teeth
forming a narrow patch extending backward around
three-quarters or less of the distance of the jaw teeth; eyes
dorsally positioned in large adult specimens. Dorsal fin
origin slightly in front or level with the anal fin. Colour
varying from silver or yellowish to dark brown on the
dorsal and lateral surfaces, becoming paler on the ventral
surface. The uniform colour and position of the origin of
the dorsal fin are diagnostic of this species in north-eastern Australia [37, 52, 401, 936].
Anguilla reinhardtii
Dorsal fin confluent with caudal fin and anal fin, originating well forward of anal fin; Pectoral fin: 16–20 rays; Pelvic
fins absent; Scales indistinct; Vertebrae: 104–110 [52, 178,
401]. Figure: drawn from photographs of mature specimen 815 mm SL, lowland creek, North Johnstone River,
September 1995; drawn 2002.
A fourth eel species, A. megastoma, may occur occasionally
in north-eastern Australia [1085, 1087]. This species is
most similar to A. reinhardtii in having a mottled colouration and a dorsal fin originating well forward of the anus.
It differs in having a larger mouth (33–45% of HL versus
20–31% in A. reinhardtii) and lacking a tooth groove
between the maxillary teeth [37].
Anguilla reinhardtii is a very large eel. Merrick and
Schmida [936] list a maximum documented length of
2000 mm TL and weight of 16.3 kg, but recount reliable
reports of this species attaining 3000 mm TL in deep
isolated lakes where downstream migrations may be
prevented for long periods of time. Beumer [178] listed a
maximum length of around 1650 mm TL and weight of 22
kg. This species is more common to 1000 mm TL and
males are thought to reach smaller maximum size (up to
650 mm TL and 600 g) than females [52, 178]. Of 1376
specimens collected from rivers of the Wet Tropics region,
Systematics
Anguillidae is presently considered to contain 15 species
within a single genus Anguilla [52]. It is a very widespread
family occurring in temperate and tropical waters of the
northern Atlantic, Indian and western Pacific oceans, and
coastal rivers of adjacent landmasses. Up to six species of
Anguilla have been recorded in Australia, five of which
occur in the north-eastern part of the continent. Anguilla
bicolor McClelland, 1844 [874] is widespread in the Indian
Ocean and western Pacific region including New Guinea;
72
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
the Burdekin River used in the description of A. marginipinnis by Macleay, 1883 [847] was recognised by Schmidt
[1205] as A. obscura, the remaining specimens being
synonymous with A. reinhardtii. Refer to Ege [401] for a
detailed examination of the synonymy of A. obscura and
A. reinhardtii.
in Australia it occurs only in the Kimberley region of
northern Western Australia and is not treated further here.
Anguilla megastoma Kaup, 1856 [679] is widespread in the
central and western Pacific region including New Guinea;
in Australia it is known only from a single specimen (~700
mm TL) collected by us in the Daintree River in the Wet
Tropics region of northern Queensland [1085, 1087].
Anguilla marmorata Quoy and Gaimard, 1824 is widespread in the Indo-West Pacific region including New
Guinea [37]. In Australia a single glass eel of this species
was recently recorded in the lower Daintree River by DPI
fisheries staff (M. Hutchison pers. comm.). It would appear
that the Australian records of A. megastoma and A.
marmorata are extra-limital and these species will not be
treated further here.
The lepocephalus larval stage characteristic of the
Anguillidae and other Anguilliformes such as conger,
moray and snake eels, occurs in only three other groups of
fishes, the Elopiformes (tarpon and ten pounders),
Sacchopharyngiformes (bobtail eels, swallowers and whiptail gulpers) and the Notacanthiformes (deep sea spiny
eels). All are marine and for this reason, Anguillidae is
considered to be derived from marine stocks and given
that two-thirds of all Anguilla species are tropical, probably from tropical marine stocks [1330]. Seven of the
world’s 15 species of Anguilla occur around the western
Pacific.
Anguilla australis was first described by Richardson in
1844 [1137]. In 1928, Schmidt [1205] revised the taxonomy of the Australian eels and, on the basis of small but
consistent differences in dorsal fin insertions and vertebral
counts, proposed two subspecies: A. australis occidentalis
in Australia and A. australis orientalis in New Zealand.
Griffin [475] reviewed the New Zealand anguillids in 1936
and renamed the Australian subspecies A. a. australis and
the New Zealand subspecies A. a. schmidtii. In his
comprehensive review of the genus in 1939, Ege [401]
agreed with these subspecific designations and this view
remained generally accepted for almost four decades until
questioned by Jellyman [645] and McDowall [891]. In
1999, Dijkstra and Jellyman [382] presented mitochondrial DNA data demonstrating a lack of genetic differentiation between Australian and New Zealand populations
and concluded that the subspecies should therefore be
considered a single species, A. australis.
Ege [401] presented an early phyologeny based on
morphometrics and meristics but subsequent molecular
analyses [63, 1330] have revealed that the external
morphological characters used by Ege (including dorsal
fin length) are adaptive and may not reflect phylogenetic
relationships [63].
Studies of mtDNA sequence divergence in some species of
Anguilla have indicated that A. celebesensis [1330] or A.
marmorata [137] is most similar to ancestral forms, but a
subsequent study which included all 15 species of Anguilla
revealed A. borneensis from Borneo Island as the most
likely basal species [63, 1333]. The following scenario has
been proposed to explain the phylogeny and biogeography
of Anguillidae [63, 1330, 1333]. An ancestral stock similar
to A. borneensis, which evolved around present day
Indonesia in the Cretaceous-Eocene period, gave rise to two
stocks. In one, the leptocephalus larvae dispersed widely via
the east to west flowing Paleocircumglobal Equatorial
current in the Tethys Sea, giving rise to the precursor of the
Indo-Pacific species A. rostrata (North America), A. anguilla
(Europe and northern Africa) and A. mossambica (eastern
Africa). The second stock included the ancestor of the
Oceania lineage that dispersed south-westwards by the
South Equatorial Current to form A. australis and A. dieffenbachii in Australia and New Zealand. A second divergence event within the ancestral stock was thought to have
occurred during the Oligocene (30 m.y.b.p.), giving rise to
A. japonica which dispersed northward via the North Pacific
Gyre, and the Indo-Pacific species including A. obscura and
A. reinhardtii. The position of A. reinhardtii is ambiguous
[63] but it appears that this species and A. australis are only
distantly related (relatively) and arrived on the Australian
continent at different times.
The absence of genetic variation in A. australis glass eels
from New Zealand led Smith et al. [1251] to conclude that
all individuals in this species are derived from a single
spawning population. However, these authors found
significant genetic variation among A. australis populations from different localities in New Zealand, which they
suggested was due to selection, perhaps mediated by water
temperature, in the juvenile to adult phase (i.e. after
recruitment into the freshwater environment).
Steindachner [1262] first described A. reinhardtii in 1867
and A. obscura was first described by Günther [489] in
1871. Perhaps as a result of their widespread distribution
in the south-western Pacific and eastern Australia, and
their sympatry with other anguillids, both species appear
in the literature under several different names, all due to
erroneous determinations rather than being specifically
connected with the descriptions of supposed new species
[401]. For example, one of the co-types (syntype) from
73
Freshwater Fishes of North-Eastern Australia
It was present in low numbers at sites in which it occurred
(13th most abundant species forming 1.29% of the total
abundance at these sites). In these sites, A. australis most
commonly occurred with the following species (listed in
decreasing order of relative abundance): G. holbrooki, R.
semoni, M. duboulayi, A. reinhardtii, and H. compressa.
Anguilla australis was the 27th most important species in
terms of biomass, forming only 0.02% of the total biomass
of fish collected by us and contributing less than 0.1% to
the total biomass collected within individual drainage
basins. Across all rivers, average and maximum numerical
densities recorded in 47 hydraulic habitat samples (i.e.
riffles, runs or pools) were 0.14 individuals.10m–2 and 2.00
individuals.10m–2, respectively. Average and maximum
biomass densities at 33 of these sites were 0.63 g.10m–2 and
7.41 g.10m–2, respectively. Other surveys in south-eastern
Queensland have recorded this species in similarly low
numbers [643, 768]. Fishway studies [1276, 1277] and
targeted surveys [912, 915] have revealed that although
glass eels are relatively common in south-eastern
Queensland, only a very small proportion appear to
recruit to the adult population [912, 1169]. Less than 1%
of eels collected by commercial harvesting in freshwaters
of south-eastern Queensland are A. australis [1169].
Russell [915] concluded that large barriers present in
many of the lowland streams in this area may prevent A.
australis from reaching freshwaters as the upstream migration period of juveniles occurs predominantly in the
winter months when river discharges are low. McKinnon
et al. [912] suggested that an increased recruitment success
of A. reinhardtii relative to A. australis in south-eastern
Queensland freshwaters, despite equivalent levels of abundance in the estuarine population, may arise because A.
reinhardtii is better adapted to higher temperatures in
tropical and subtropical areas than cooler areas further
south, which appear to suit A. australis.
Distribution and abundance
Anguilla australis
This species is widespread in the western Pacific including
New Caledonia, New Zealand, Chatham Islands, Norfolk
Island, Lord Howe Island and coastal drainages of eastern
Australia between the Burnett River in south-eastern
Queensland, south and west to Mt. Gambier in South
Australia [52, 178, 401]. The veracity of several isolated
records of this species in the Murray-Darling Basin [52,
178] is uncertain [1338]. It is also present in streams on
Flinders and Vansittart islands in Bass Strait and is widespread in coastal drainages of Tasmania [52, 178, 423].
Anguilla australis is also present on Bribie and Moreton
islands, off the south-eastern Queensland coast. A
Queensland Museum record of this species from the
Pioneer River in central Queensland is probably erroneous
as it was based on a very small glass eel that was most likely
A. obscura [1081]. Records of A. australis in Japan are
undoubtedly escapees from aquaculture facilities [1283].
Anguilla australis is relatively uncommon in Queensland
but has been recorded in most basins from the Burnett
River south to the border with New South Wales. Glass eels
and elvers have been collected in the Burnett River [1276,
1277] but it is not clear whether individuals recruit to the
adult population in freshwater reaches of this river. It has
not been recorded from the Elliott River but a few
Queensland Museum records exist for small streams of the
Burrum Basin [661]. We collected only 122 individuals
(80% of which were less than 120 mm SL) during surveys
of streams and rivers from the Mary River south to the
Queensland–New South Wales border [1093]. Although it
was present at 10.1% of all locations sampled (Table 1), it
was only the 24th most abundant species collected (0.07%
of the total number of fishes collected) and was not
common or widespread within individual drainage basins.
Table 1. Distribution, abundance and biomass data for Anguilla australis in rivers of south-eastern Queensland. Data summaries
for a total of 122 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per cent
and rank abundance and per cent and rank biomass, respectively, at those sites in which this species occurred.
Total
% locations
Mary River Sunshine Coast Moreton Bay
rivers and
rivers and
streams
streams
Brisbane
River
Logan-Albert
River
South Coast
rivers and
streams
10.1
4.0
20.7
10.0
1.8
23.5
10.0
0.07 (1.29)
0.01 (0.32)
0.31 (1.64)
0.16 (2.05)
0.01 (0.71)
0.21 (1.35)
0.25 (3.53)
24 (13)
22 (13)
13 (8)
19 (8)
24 (10)
17 (12)
16 (7)
0.02 (0.89)
0.01 (0.11)
0.08 (42.43)
–
0.02 (0.81)
0.06 (1.12)
0.03 (0.14)
27 (8)
24 (12)
9 (2)
–
24 (8)
19 (7)
14 (7)
Mean numerical density
(fish.10m–2)
0.14 ± 0.04
0.05 ± 0.02
0.08 ± 0.03
0.09 ± 0.03
0.21 ± 0.02
0.17 ± 0.07
0.03 ± 0.02
Mean biomass density
(g.10m–2)
0.63 ± 0.26
0.08 ± 0.04
1.39 ± 0.00
–
1.08 ± 0.65
0.68 ± 0.34
0.03 ± 0.00
% abundance
Rank abundance
% biomass
Rank biomass
74
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
[1099], it rarely exceeded 5% of the total number of fish
collected at each site. This species is widespread and relatively abundant in the Wet Tropics region, however. It was
recorded in all drainage basins examined in an extensive
survey of the region; present in 77% of all sites examined
and contributed 6.2% of the total number of fishes
collected [1085, 1087]. Subsequent surveys in the region
have collected this species from every drainage examined
[643, 979, 1179, 1183, 1184, 1185].
Anguilla australis is widespread but not overly common in
freshwaters of northern New South Wales and appears to
be more abundant in freshwaters toward the southern end
of its range in southern New South Wales, Victoria and
Tasmania [188, 437, 814, 1066, 1201]. Sloane [1245]
reported that this species was widespread and abundant in
Tasmanian streams and maximum numerical densities of
14 individuals.10m–2 and maximum biomass densities of
230.1 g.10m–2 have been recorded [759, 1245].
Its ubiquity in the region is matched by its distribution
within river systems. Anguilla reinhardtii occurred in over
90% of all locations sampled in the Johnstone and
Mulgrave/Russell rivers (Table 2). Overall, it was the
seventh most abundant species collected over the period
1994–1997 but was proportionally more abundant in the
Mulgrave than the Johnstone River, perhaps because the
latter is characterised by steep cascades and waterfalls in its
middle reaches. The sequential reduction in abundance
upstream in the Johnstone River reduces the mean density
of this species estimated over all sites. Note however, that
the proportional contribution of eels to total biomass
collected is higher in the Johnstone River, presumably
because these same barriers selectively filter out smaller
individuals. Density values estimated for these rivers
(Table 2) approximate those seen in rivers of south-eastern Queensland as do biomass densities (Table 3).
Although this species is the most dominant with respect to
biomass in these Wet Tropics rivers, the proportional
contribution of eels to the total biomass (43%) is lower
than that seen in south-eastern Queensland probably
because rivers of the Wet Tropics region contain more
large-bodied species than do rivers to the south [1093].
Anguilla obscura
This species is widespread in the south-western tropical
Pacific from New Guinea east to the Society Islands. It is
also present in coastal drainages of north-eastern Australia
between the Jardine River near the tip of Cape York
Peninsula, throughout eastern Queensland as far south as
the Burnett River in south-eastern Queensland [37, 183,
597, 1349]. A reliable record of A. obscura occurring on
Fraser Island also exists (M. Hutchison, pers. comm.).
Although widespread in most drainage basins of northeastern Queensland, A. obscura is usually uncommon
[569]. For example, over the period 1994–1997, we
collected 24 individuals only from rivers of the Wet
Tropics, making this species the 32nd most abundant
species collected in this region (from a total of 38 species).
Estimates of average density were low (0.17 ± 0.04 individuals.10m2, 1.15% of total abundance, n = 20 sites)
although the contribution of A. obscura to total biomass
was relatively high (27.2 ± 19.7 g.10m-2, 9.6% of total
biomass, n = 20 sites) by virtue of its large size.
Anguilla reinhardtii
This species occurs in New Caledonia, New Guinea and in
coastal drainages of eastern Australia between the Jardine
River near the tip of Cape York Peninsula, southwards
throughout eastern Queensland, New South Wales to the
vicinity of Melbourne in Victoria. A record of this species
in the Murray-Darling Basin has been reported from the
lower Goulburn River, a tributary of the Murray River,
Victoria [607]. It is also present on Fraser, Bribie, Moreton
and North Stradbroke islands, off the south-eastern
Queensland coast, on Lord Howe Island off the central
New South Wales coast and in northern and eastern
Tasmania [37, 178, 423, 597]. Anguilla reinhardtii has also
been reported from the north-western coast of New
Zealand, where it may have been present in low numbers
since the early 1970s and is thought to have increased in
abundance in recent years [649, 895].
Table 2. Distribution, abundance and biomass data for
Anguilla reinhardtii in the Wet Tropics region. Data summaries
for a total of 1768 individuals collected from rivers in the Wet
Tropics region over the period 1994–1997 [1093]. Data in
parentheses represent summaries for per cent and rank
abundance and per cent and rank biomass, respectively at
those sites in which this species occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Rank biomass
Anguilla reinhardtii has been collected from all river basins
in eastern Cape York Peninsula but appears to be relatively
uncommon except in the most southern drainages of this
region [1223]. Although present at all locations sampled
in the Normanby River by Kennard [697] and Pusey et al.
75
Mulgrave
River
Johnstone
River
92
95.4
92.9
5.0 (9.0)
8.9 (13.9)
3.3 (6.5)
6 (4)
10 (9)
7 (7)
43.1 (45.4)
1 (1)
40.9 (41.1) 46.3 (47.5)
1 (1)
1 (1)
Mean numerical density
(fish.10m–2)
0.32 ± 0.03
0.56 ± 0.06 0.19 ± 0.02
Mean biomass density
(g.10m–2)
90.8 ± 27.5 44.7 ± 7.8
60.1 ± 10.6
Freshwater Fishes of North-Eastern Australia
south to the Queensland–New South Wales border.
Surveys undertaken by us between 1994 and 2003 in
south-eastern Queensland [1093] collected a total of 7694
individuals and A. reinhardtii was present at 69.5% of all
locations sampled (Table 3). Overall, it was the eighth
most abundant species collected (4.7% of the total
number of fishes collected) and was the eighth most abundant species at sites in which it occurred (6.2%). In these
sites, A. reinhardtii most commonly occurred with the
following species (listed in decreasing order of relative
abundance): P. signifer, R. semoni, M. duboulayi, C. marjoriae and G. holbrooki. It was generally widespread in each
major river basin surveyed in south-eastern Queensland
occurring in over 60% of locations sampled. The Brisbane
River is an exception and the presence of Wivenhoe Dam
(a large dam in the central part of the catchment) probably restricts the upstream dispersal of A. reinhardtii [704].
This species is widespread and generally common
throughout coastal drainages of central Queensland and
has been recorded in almost all rivers of the region. It was
the eighth most abundant species collected by electrofishing in the Burdekin River and contributed 3.3% of the
total collected by this method [1098]. Notably, this study
showed that A. reinhardtii is generally restricted to the
lower reaches of the river downstream of the Burdekin
Falls Dam and to its lowland tributaries. Some large individuals still occur upstream of the dam and in Lake
Dalrymple [1082], although their numbers are declining
as such individuals emigrate at times of high flow and
because recruitment is denied by the presence of the dam.
Berghuis and Long [160] found A. reinhardtii to be
contrastingly rare in the Fitzroy River, collecting only four
specimens over a two-year period. These authors
cautioned however, that A. reinhardtii was widespread in
this river and that the sampling methods used (gill netting
and baited traps) were ineffective methods for sampling
eels. Addition of electrofishing to the suite of methods
used is essential if the distribution and abundance of A.
reinhardtii and the impact of the numerous weirs and
reservoirs in this river are to be quantified. The problem of
method bias was also identified in a review of the fish
fauna of the Pioneer River [1081]. Although electrofishing
revealed this species to be widespread and common, studies lacking this collecting method greatly underestimated
its distribution and abundance.
This species achieved the highest relative abundances in
the Logan-Albert and South Coast basins where it formed
7.8% and 13.9% of the total catch, respectively. By virtue
of the large size attained by this species and its relative
abundance, A. reinhardtii dominated the total biomass of
fishes collected in each basin (except for small streams of
the Moreton coastal region) and overall comprised 66.9%
of the total biomass. Across all rivers, average and maximum numerical densities recorded in 709 hydraulic
habitat samples (i.e. riffles, runs or pools) were 0.43 individuals.10m–2 and 12.37 individuals.10m–2, respectively.
Average and maximum biomass densities at 538 of these
sites were 46.98 g.10m–2 and 671.81 g.10m–2, respectively.
Small eels (≤150 mm SL, corresponding to three years or
younger [1244]) were present in equivalent numerical
densities to larger fish (>150 mm SL, 3+ years [1244]).
Mean densities of 0.35 and 0.32 individuals.10m–2 were
observed for these two size classes, respectively, in hydraulic
habitats where this species occurred in south-eastern
In south-eastern Queensland, this species is also widespread and generally common. In a review of existing fish
sampling studies in the Burnett River, Kennard [1103]
noted that it had been collected at 19 of 63 locations
surveyed (11th most widespread species in the catchment)
and formed 0.5% of the total number of fishes collected
(14th most abundant). South of the Burnett River it is
present and generally common in all other drainage basins
Table 3. Distribution, abundance and biomass data for Anguilla reinhardtii in rivers in south-eastern Queensland. Data summaries
for a total of 7694 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per
cent and rank abundance and per cent and rank biomass, respectively, at those sites in which this species occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Rank biomass
Mary River Sunshine Coast Moreton Bay
rivers and
rivers and
streams
streams
Brisbane
River
Logan-Albert South Coast
River
rivers and
streams
69.5
86.0
65.5
60.0
45.9
94.1
90.0
4.71 (6.20)
3.81 (4.69)
5.24 (9.59)
0.90 (2.52)
1.81 (4.24)
7.83 (9.60)
13.86 (16.44)
8 (8)
10 (7)
6 (5)
12 (6)
12 (7)
6 (5)
3 (2)
66.88 (68.84) 77.92 (80.82) 95.80 (97.13) 25.62 (27.86) 44.46 (58.04) 47.26 (47.96) 75.59 (76.36)
1 (1)
1 (1)
1 (1)
2 (2)
1 (1)
1 (1)
1 (1)
Mean numerical density
(fish.10m–2)
0.43 ± 0.03
0.26 ± 0.02
0.25 ± 0.07
0.12 ± 0.02
0.36 ± 0.07
0.72 ± 0.09
0.44 ± 0.10
Mean biomass density
(g.10m–2)
46.98 ± 3.59
46.08 ± 5.14 87.47 ± 39.58 27.74 ± 18.65 57.22 ± 13.40 45.52 ± 5.70 34.52 ± 11.36
76
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
Table 4. Macro/mesohabitat use by Anguilla australis in rivers
of south-eastern Queensland. Data summaries for 122
individuals collected from samples of 47 mesohabitat units at
28 locations between 1994 and 2003 [1093]. W.M. refers to
the mean weighted by abundance to reflect preference for
particular conditions.
Queensland (n = 306 and 517 samples for small and large
eels, respectively) [1093]. In contrast, the larger size class
formed much greater biomass densities (mean and maximum biomass of 49.38 and 690.98 g.10m–2, respectively)
than small eels (mean and maximum biomass of 0.94 and
13.14 g.10m–2, respectively) (n = 503 and 293 samples for
large and small eels, respectively) [1093].
Parameter
Anguilla reinhardtii appears to be relatively common and
widespread in coastal rivers of New South Wales and
Victoria [188, 437, 814, 1066, 1201]. Sloane [1245]
reported that A. reinhardtii was less widespread than A.
australis in Tasmanian streams but was common in northern and eastern coastal streams. Maximum numerical
densities of 4.0 individuals.10m-2 and maximum biomass
densities of 1146.6 g.10m–2 were recorded in these rivers
[1244, 1245]
2
Catchment area (km )
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
Min.
Max.
Mean
W.M.
6.0
3.0
4.0
0
1.2
11.1
1426.4
100.0
152.0
180
21.9
91.0
254.2
36.0
54.4
42
8.2
45.4
208.8
31.7
50.9
38
5.1
53.2
Gradient (%)
0
Mean depth (m)
0.10
Mean water velocity (m.sec–1) 0
Macro/mesohabitat use
Anguilla australis is reported to be essentially a still water
species but is found in a variety of lotic and lentic habitats
including coastal and insular streams, lakes, swamps and
lagoons, and in large lowland rivers. Glass eels and elvers
commonly occur in estuarine areas and the freshwaterestuarine interface of lowland rivers, and the final stage of
the life cycle is spent in oceanic waters [52, 178, 936, 1093].
Glass eels have also been collected in the surf zone of open
beaches in New South Wales and Victoria [171]. In rivers
and streams of south-eastern Queensland, A. australis
occurs at low to moderate elevations (0–180 m.a.s.l.) but
most commonly at less than 40 m.a.s.l. (Table 4). This
species most frequently occurs in the middle to lower
sections of rivers and short coastal streams (within 50 km
of the river mouth), but has been recorded up to 152 km
upstream from the mouth of the Logan River (Table 4). It
is present in small to moderate-sized streams and rivers
(range = 1.2–21.9 m width) but is more common in
streams around 5 m wide and with moderate riparian
cover. In streams of south-eastern Queensland, A. australis
most commonly occurs in runs characterised by moderate
gradient (<0.65% weighted mean gradient), moderate
depth (0.31 m weighted mean depth) and moderate mean
water velocity (weighted mean = 0.14 m.sec–1). We have
also collected this species in shallow fast-flowing riffles
and deeper slow-flowing pools (Table 4). This species is
most abundant in mesohabitats with fine substrates (sand
and gravel) and where submerged leaf-litter beds, woody
debris, undercut banks and particularly root masses are
common.
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobbles (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0.1
0
0
0
0
2.30
1.05
0.55
0.58
0.42
0.14
0.65
0.31
0.14
90.8
100.0
42.6
78.2
52.4
44.0
20.2
7.8
25.5
14.6
25.8
17.0
4.5
4.6
6.9
43.5
9.6
21.2
13.6
2.1
3.1
20.1
25.1
11.9
58.2
18.8
49.9
29.9
15.3
56.7
56.7
2.4
2.3
1.4
5.6
1.1
12.8
9.1
4.2
11.7
20.9
2.1
1.6
1.1
5.9
1.4
12.5
8.1
4.1
11.5
23.8
pools of the Normanby River, located up to 160 km
upstream of the river mouth [697]. We have also recorded
a single very large individual of this species in the upper
Burdekin River near Charters Towers [1093]. Glass eels
and elvers commonly occur in estuarine areas and the
freshwater-estuarine interface of lowland rivers, and the
final stage of the life cycle is spent in oceanic waters [52,
936, 1093]. In the Wet Tropics region, this species is
restricted to lowland reaches and small swampy tributaries at an elevation less than 20 m.a.s.l. It also occurs in
floodplain wetlands of this region [583, 584, 1085, 1087].
Anguilla reinhardtii is reported to prefer more flowing
waters in comparison to other Australian anguillids but it
is found in a wide range of lentic and lotic habitats including coastal and insular streams, lakes, swamps and
lagoons, and in large lowland river and floodplain habitats. Glass eels and elvers commonly occur in estuarine
areas and the freshwater-estuarine interface of lowland
Anguilla obscura is reported to occur in generally similar
habitats as A. australis including the lower reaches of rivers
and brackish coastal lagoons [52, 936]. We have collected
this species in floodplain lagoons and main river channel
77
Freshwater Fishes of North-Eastern Australia
rivers, and the final stage of the life cycle is spent in oceanic
waters [52, 178, 697, 936, 1093]. Glass eels have also been
collected in the surf zone of open beaches in New South
Wales and Victoria [171]. Unlike other eels, large adults of
this species also commonly occur near the surface in the
deep offshore waters of large impoundments [936].
Table 5. Macro/mesohabitat use by Anguilla reinhardtii in the
Wet Tropics region. Data summaries for 1376 individuals
collected from 92 locations in the Johnstone and Mulgrave
rivers between 1994 and 2003 [1093]. W.M. refers to the
mean weighted by abundance to reflect preference for
particular conditions.
Anguilla reinhardtii in the Wet Tropics region occurs over
a wide range of macrohabitat conditions ranging from
large, low gradient rivers and very small, adventitious
streams located at low elevation near the river mouth to
headwater streams and cascades located distant from the
river mouth and at elevations greater than 700 m.a.s.l.
(Table 5). The average macrohabitat is a stream about 11
m wide, at an elevation of less than 100 m.a.s.l., about 40
km from the river mouth, with a gradient of 0.95%, with
an intact riparian canopy. Comparison of average and
weighted average values suggest that this species of eel is
more abundant in similar streams with a slightly more
open canopy, higher gradient and located at about 70
m.a.s.l. (Table 5). Ontogenetic variation in macrohabitat
use occurs in the Wet Tropics region. Large adult eels
(>500 mm SL) occur more commonly more distant from
the river mouth than do smaller adult (300–500 mm SL)
or juvenile and subadult (>300 mm SL) eels (weighted
means = 43, 41 and 37 km, respectively), at higher elevation (155, 121, 52 m.a.s.l., respectively), in higher gradient
(1.13, 0.95, 0.93%, respectively), deeper (0.36, 0.32, 0.31
m) streams with a more extensive riparian canopy (43.3,
36.3, 29.6%). These data suggest that A. reinhardtii either
migrates upstream as it grows or that small eels are
excluded from habitats favoured by large eels, or both.
Parameter
Min.
2
Catchment area (km )
Distance from source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
0.13
0.5
8.1
5
2.0
0
Gradient (%)
0
Mean depth (m)
0.1
Mean water velocity (m.sec–1) 0
Anguilla reinhardtii occurs in streams of a diverse substrate
composition reflecting the wide distribution of this species
in rivers of the Wet Tropics. The largest size class tends to
be more abundant in reaches dominated by sand (15.6%)
fine gravel (21.5%) and rocks (21%) whereas juveniles
were most abundant in reaches with a substratum dominated by cobble (29%) and rocks (21%). Juvenile and subadult eels occupied reaches with an intermediate substrate
type. This species occurs in reaches with a wide variety and
availability of instream cover, even in streams choked by
introduced para grass. It does not achieve high abundance
in such streams however, and younger eels appear to be
less abundant than older age classes in streams with abundant para grass (weighted means = 6, 11.8, 13% for juvenile, subadult and adult eels, respectively) (Table 5). Few
other ontogenetic differences in the abundance of instream cover elements were evident [1093].
Max.
Mean
W.M.
515.5
67.0
104.5
790
53.7
90
67.5
14.0
40.8
95.1
11.3
39
70.3
15.3
38.6
68.1
12.4
31.5
7.33
0.87
0.56
0.76
0.36
0.18
0.95
0.32
0.25
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobbles (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
48.0
88.0
73.0
73.0
55.0
81.0
98.0
4.2
14.6
21.7
14.0
14.6
23.2
7.7
2.3
12.2
17.6
16.5
19.4
28.0
4.0
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
23.7
6.9
33.0
91.0
10.0
81.2
12.5
11.4
35.0
67.0
0.9
0.2
2.0
8.6
2.8
8.8
1.8
1.5
5.7
12.4
0.6
0.1
2.0
7.2
1.8
6.9
1.5
1.4
4.6
9.2
400 m.a.s.l. (Table 6). It most commonly occurs around
100 km upstream of the river mouth and at elevations
around 75 m.a.s.l. It is present in a wide range of stream
sizes (1.1–46.8 m width) but is more common in streams
of intermediate width (9.3 m weighted mean width) and
with low to moderate riparian cover (<40%). Juvenile A.
reinhardtii were more common at low elevations and
closer to the river mouth than adults (weighted mean
elevation 65 and 110 m.a.s.l. for juveniles and adults
respectively; weighted mean distance to river mouth 96 and
127 km for juveniles and adults, respectively), reflecting the
progressive upstream movement of this catadromous
species with growth [1093]. We observed generally little
ontogenetic variation in the mesohabitat use of A. reinhardtii in south-eastern Queensland. Except for the very
largest individuals which were most common in deep slowflowing pools, juveniles and adults were most common in
main channel rapids, riffles and runs characterised by high
gradients (weighted mean 1.3%), relatively shallow depths
Anguilla reinhardtii is widely distributed in rivers and
streams of south-eastern Queensland, ranging between 0.5
and 303 km from the river mouth and at elevations up to
78
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
(weighted mean 0.26 m), and high water velocities
(weighted mean 0.29 m.sec–1) (Table 6, [1093]). These data
tend to support the earlier generalisation that A. reinhardtii prefers faster-flowing waters than other Australian
eels. Juveniles and adults were collected in mesohabitats
with similarly coarse substrates, dominated by coarse
gravel, cobbles and rocks. There was apparently little selection for mesohabitats with particular submerged cover
attributes and little ontogenetic variation in this pattern
(Table 6, [1093]). This is unsurprising given the frequency
with which A. reinhardtii occurred in rapids and riffles
where submerged cover other than that provided by the
coarse substrate is generally uncommon [1093].
(usually less than 0.2 m.sec–1) but occasionally in higher
mean and focal velocities (Fig. 1a and b). It was usually
collected in shallow water depths, most often between 10
and 40 cm (Fig. 1c). A benthic species, it usually occupied
the lower third of the water column, most commonly in
direct contact with the substrate (Fig. 1d). It usually
occurred over sand, fine gravel and coarse gravel (Fig. 1e).
This species showed no preference for areas close to the
stream-bank as an equal number of fish were collected in
areas less than and greater than 1 m from the bank [1093].
It was most frequently collected in close association with
the substrate, and less commonly near aquatic macrophytes, woody debris, undercut banks and root masses
(Fig. 1f).
Table 6. Macro/mesohabitat use by Anguilla reinhardtii in
rivers of south-eastern Queensland. Data summaries for 7694
individuals collected from samples of 709 mesohabitat units
at 203 locations between 1994 and 2003 [1093]. W.M. refers
to the mean weighted by abundance to reflect preference for
particular conditions.
(a)
(b)
40
30
30
20
20
10
Parameter
Catchment area (km2)
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
Min.
Max.
5.0 10211.7
3.0
270.0
0.5
303.0
0
400
1.1
46.8
0
95.8
Mean
W.M.
10
0
818.7 1159.5
47.2
56.1
110.2 100.2
74
76
9.4
9.3
39.5
36.1
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
60
40
30
Gradient (%)
0
Mean depth (m)
0.06
Mean water velocity (m.sec–1) 0
3.02
1.05
0.87
0.54
0.39
0.16
1.34
0.26
0.29
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobbles (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
100.0
100.0
82.7
82.1
66.8
65.0
76.0
5.0
15.6
18.6
26.7
23.1
9.1
2.0
1.9
6.2
10.4
26.3
35.2
18.5
1.4
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
69.6
65.9
26.7
65.7
50.0
92.6
37.6
26.8
96.3
100.0
9.3
6.9
1.3
4.8
1.5
11.8
4.1
3.2
12.5
17.9
7.7
6.9
0.8
5.0
0.9
6.9
3.0
2.2
4.9
10.0
40
20
20
10
0
0
Total depth (cm)
30
(e)
30
20
20
10
10
0
0
Substrate composition
Microhabitat use
Microhabitat use of A. australis in rivers of south-eastern
Queensland generally reflected the pattern observed in
mesohabitat use. This species was most frequently
collected from areas of low to moderate water velocity
Relative depth
(f)
Microhabitat structure
Figure 1. Microhabitat use by Anguilla australis. Data derived
from capture records for 46 individuals collected in the Mary
and Albert rivers, south-eastern Queensland over the period
1994–1997 [1093].
79
Freshwater Fishes of North-Eastern Australia
results of conflict with a larger individual [1093]. In southeastern Queensland, the presence of bite marks on eels is
much less common, except during very dry periods when
densities of eels are higher and opportunities for interactions between eels are presumably more frequent [1093].
In streams of the Wet Tropics region, various aspects of
microhabitat use by A. reinhardtii change subtly as this
species ages. Most individuals collected were from current
velocities of between 0.1 and 0.3 m.sec-1, reflecting the
average current velocities present in those sites in which it
occurs. There is little ontogenetic difference in the pattern
of microhabitat use with respect to current velocity except
a greater number of large adult eels (>500 mm SL)
occurred in faster currents up to about 1 m.sec–1 (Fig. 2a).
About half of all eels collected were from areas experiencing no current at all and most (>80%) were from areas
with current velocities less than 0.2 m.sec–1 (Fig. 2b). This
species was collected over a wide range of depths but all
age classes were most commonly collected from depths less
than 0.6 m (Fig. 2c). Juvenile and subadults (<300 mm
SL) were most commonly collected from depths of
between 0.1 to 0.3 m, and adults (300–500 mm SL) and
large adults (>500 mm SL) from depths of 0.4 to 0.6 m,
although proportionally more large fish were collected
from depths greater than 0.6 m than any other size class
(Fig. 2d). Juvenile and subadults were more commonly
collected (80% of this size class) in the bottom 10% of the
water column (Fig. 2d), often in direct contact with the
substratum. About 60% of adult fish were collected from
the bottom 10% of the water column and only ~35% of
large adult eels were collected in this depth zone. Despite
these differences, this species was most frequently
collected from the bottom 50% of the water column. All
age classes were collected over a variety of substrate types,
reflecting the composition evident at larger spatial scales
(Table 5). There was a slight tendency for juveniles and
subadults to occur more frequently over a substratum
dominated by gravel and cobbles and for adult fish to be
more frequent over a substratum dominated by rocks and
sand. Few of any size class were collected over areas of mud
or bedrock (Fig. 2e). The three age classes differ most in
their use of cover. Juveniles and subadults were most
frequently collected from within the interstices of the
substratum or insinuated well within banks of leaf litter.
Large adult fish also used leaf litter as cover but were more
frequently recorded in association with woody debris,
undercut banks and root masses. Adults were intermediate
between these age classes with respect to cover although
both this age class and juvenile and subadult fish appear
to avoid undercut banks. In north-eastern Queensland it is
very rare to collect an eel, even a small individual, which
does not have a recent bite mark of another eel somewhere
on its body. Such marks suggest that eels of all sizes interact aggressively with one another, and are perhaps indicative of substantial territorial behaviour. In many cases,
these bite marks, although not deep, are very clear and
their length and width give a reasonable indication of the
size of the aggressor. Such marked eels usually display the
(a)
60
(b)
30
40
20
10
20
0
0
Mean water velocity (m/sec)
30
(c)
Focal point velocity (m/sec)
80
(d)
60
20
40
10
20
0
30
0
(e)
Relative depth
Total depth (cm)
(f)
20
40
10
20
0
0
Substrate composition
Microhabitat structure
Figure 2. Microhabitat use by Anguilla reinhardtii juveniles
and subadults (<300 mm SL: solid bars, n = 509), adults
(300–500 mm SL: hatched bars, n = 85) and large adults
(>500 mm SL: open bars, n = 176) in the Wet Tropics region.
Summaries derived from capture records from the Johnstone
and Mulgrave rivers, northern Queensland, over the period
1994–1997 [1093].
In streams of south-eastern Queensland, A. reinhardtii was
collected from a wide range of water velocities including
very fast-flowing water, although adults were more
common in slower flowing water than juveniles (Fig. 3a
and b). Focal-point velocities were slightly lower than
mean velocities, reflecting the benthic habit of this species
(Fig. 3d) and usual refuge within coarse substrates where
80
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
velocities are lower (Fig. 3f). This species was usually
collected in water depths less than 50 cm with adults
slightly more common in deeper water than juveniles (Fig.
3c). Anguilla reinhardtii was usually found among coarse
substrates (coarse gravel, cobbles and rocks, Figure 3e),
reflecting their availability in the rapids, riffles and runs
where this species most commonly occurred (see above).
Adults were more common close to the river-bank than
juveniles (44% of adults collected within 1 m of the bank
versus 27% of juveniles [1093]) but both age classes were
almost always found in close association with some form
of submerged cover; usually within the interstices of
coarse substrates (Fig. 3f). Juveniles were more common
in this microhabitat type whereas adults were slightly
more common among woody debris, undercut banks and
root masses.
40
(a)
40
30
30
20
20
10
10
0
0
40
Environmental tolerances
Anguillid eels are a notoriously hardy group of fish but
quantitative information on tolerances to water quality
extremes is lacking. Harris and Gehrke [553] classified A.
australis and A. reinhardtii as tolerant of water quality
degradation. Anguillids are very tolerant of hypoxic conditions [417] and able to survive out of water for long periods by absorbing oxygen from the atmosphere through the
skin, as long as it remains moist [891] or by gulping air
[417]. Maturing eels in freshwater possess a significant
hypo-osmoregulatory ability [394].
In south-eastern Queensland, A. australis has been
collected over a relatively wide range of physicochemical
conditions reflecting those expected for streams and rivers
of this region. (Table 7). It appears to tolerate low dissolved
oxygen concentrations (field minimum of 2.6 mg.L–1).
We have collected this species in slightly acidic to basic
water conditions (pH range 5.9–8.5) (Table 7) and at
temperatures ranging from 8.4 to 27.8°C. The maximum
turbidity at which this species has been recorded in southeastern Queensland is 112.3 NTU, but it more commonly
occurs in less turbid waters (mean 10.9 NTU). We have
collected this species in freshwaters up to 1231.7 µS.cm–1
conductivity.
(b)
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
Anguilla obscura has been recorded over a range of water
quality conditions (Table 7) reflecting its distribution in
northern rivers and floodplain habitats [697, 1093]. It is
tolerant of moderate hypoxia (e.g. in floodplain lagoons of
the Normanby River) and occurs most commonly in
slightly acidic waters. The conductivity values presented in
Table 7 indicate that it occurs in very freshwaters but it
obviously tolerates much higher salinity levels given its life
history.
80
30
60
20
40
10
20
0
0
Total depth (cm)
Relative depth
(e)
In the Wet Tropics region, A. reinhardtii occurs across a
range of water quality conditions typical of rainforest
streams and rivers of this region (Table 7). The minimum
temperature recorded (13.3°C) occurred during July in a
stream located on the Atherton Tablelands, whereas the
maximum (32.7°C) was recorded in November at a site
with little riparian cover and at a time of reduced flow.
Streams of this region tend to be well-oxygenated
throughout the year and to be of very low conductivity.
This species occurs across a wide pH range but the average
value is circumneutral. Occasional periods of high turbidity occur in streams of the Wet Tropics region in association with periods of intense rainfall and usually in streams
receiving drainage from agriculture. Such turbid periods
are usually transitory and on average this species occurs in
clear waters. Given the very wide distribution of this
species in rivers of the Wet Tropics region, the values given
in Table 7 approximate those expected for streams and
(f)
40
30
30
20
20
10
10
0
0
Substrate composition
Microhabitat structure
Figure 3. Microhabitat use by Anguilla reinhardtii in southeastern Queensland. Data derived from capture records for
810 juvenile (<150 mm SL: solid bars) and 911 adult (>150
mm SL: open bars) individuals collected in the Mary and
Albert rivers, south-eastern Queensland, over the period
1994–1997 [1093].
81
Freshwater Fishes of North-Eastern Australia
rivers of the region. In south-eastern Queensland, A. reinhardtii has been collected over a relatively wide range of
physicochemical conditions also reflecting those expected
for streams and rivers of this region. (Table 7).
Australian statutory health limits (0.5 µg.g–1 wet weight)
leading Beumer and Bacher [181] to conclude that
consumption of these species would be well within
‘acceptable daily intake’ recommended by the World
Health Organization.
Table 7. Physicochemical data for Anguilla australis, A.
obscura, and A. reinhardtii. Data summaries are from a
number of studies conducted in a range of rivers and habitats
across north-eastern Australia (the number of sites from each
study is given in parentheses).
Parameter
Min.
Max.
Anguilla australis
South-eastern Queensland [1093] (n = 39)
Temperature (°C)
8.4
27.8
Dissolved oxygen (mg.L–1)
2.6
10.4
pH
5.9
8.5
Conductivity (µS.cm–1)
110.0
1231.7
Turbidity (NTU)
0.5
112.3
Reproduction, development and movement biology
Anguillids are considered by many to be catadromous:
adults undertake distinct spawning migrations from freshwaters, downstream and seaward to distant oceanic
spawning grounds in the Coral Sea, and the young migrate
back to freshwaters to complete their life cycle. The emerging view however, is that catadromy is not obligatory for
some anguillids, including at least one Australian species
[1048, 1331, 1332, 1333]. Rather, catadromy in anguillids
is facultative, with freshwater, estuarine and marine residents more appropriately considered as contrasting
ecophenotypes [1331, 1332]. Evidence from strontiumcalcium ratios in otoliths of adult eels of several species
(A. anguilla, A. japonica, and A. reinhardtii) has revealed
that some individuals appear to have an exclusively marine
history and never enter freshwater, others may move
repeatedly between freshwater and the estuary during their
extended occupancy in coastal catchments, and others
enter freshwater and remain there until adulthood before
making the return spawning migration to the ocean [1048,
1331, 1332, 1333]. It has been postulated [1331, 1333] that
latitudinal variation in the productivity of riverine versus
marine habitats, or the presence of other potentially
competing marine anguilliformes, may explain apparent
regional variation in the frequency of individuals remaining in marine environments versus those entering estuaries or freshwaters. However, hypotheses about the
duration and frequency of marine residency and of
contrasting ecophenotypes are based mainly on examination of temperate zone populations. Further research is
required before these hypotheses can be extended to tropical eel populations. Nevertheless, it has been speculated
that individuals with a primarily ocean-based life history
may contribute substantially to future recruitment [1331,
1332]; a view with important implications for the management of anguillid species that are currently the focus of
intensive freshwater and estuarine fisheries for live export
and aquaculture operations (see Conservation status,
threats and management, pp. 90).
Mean
18.4
7.3
7.4
386.2
10.9
Anguilla obscura
Normanby River [697] (n=3)
Temperature (°C)
23.9
29.4
Dissolved oxygen (mg.L–1)
2.0
6.2
pH
6.1
8.1
Conductivity (µS.cm–1)
97.8
250.3
Turbidity (NTU)
3.3
8.6
25.8
3.5
6.9
188.9
6.2
Wet Tropics region [1093] (n = 15)
Temperature (°C)
19.9
27.4
Dissolved oxygen (mg.L-1)
5.6
8.8
pH
4.5
7.9
Conductivity (µS.cm-1)
6.0
63.8
Turbidity (NTU)
0.3
7.2
23.9
7.1
6.4
38.9
1.32
Anguilla reinhardtii
Wet Tropics region [1093] (n = 200)
Temperature (°C)
13.3
32.7
Dissolved oxygen (mg.L–1)
5.1
12.4
pH
4.5
8.5
Conductivity (µS.cm–1)
5.6
67.6
Turbidity (NTU)
29.7
0.1
22.7
7.2
7.1
34.4
3.6
South-eastern Queensland [1093] (n = 440)
Temperature (°C)
8.4
31.7
19.5
Dissolved oxygen (mg.L–1)
0.3
16.2
7.6
pH
5.6
9.1
7.6
Conductivity (µS.cm–1)
19.5
2247.0
456.4
Turbidity (NTU)
0.4
331.4
8.8
Beumer and Bacher [181] suggested that A. australis and
A. reinhardtii could be effective indicators of local mercury
concentrations in inland waters of Victoria as both species
are carnivorous, feeding at all levels of the food chain, and
because they probably have a relatively small home range
during their yellow eel phase in freshwaters. In their 1982
study, total mercury concentrations in the axial tissues of
most individuals examined were found to be below
What follows is an overview of the current understanding
of the life cycle of the three Australian species of Anguilla
considered in this text, with a focus on the freshwater
ecophenotype described above.
Sloane [1244] estimated ages of A. australis and A. reinhardtii from the Douglas River in eastern Tasmania using
the marginal growth increments of burnt otoliths. An
82
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
annual growth ring was formed in the otoliths of both
species at the end of winter, occurring slightly earlier in A.
australis. The main period of growth in both species coincided with increasing water temperatures (15–22°C)
during late spring and early summer. In Victoria, heightened activity of both species also occurred during spring
and summer coinciding with elevated discharges and
inundation of marginal areas due to rains occurring in late
winter and spring [175]. Estimates of growth rates and
ages based on otolith annuli indicated substantial interspecific, intraspecific and spatial variation in growth [252,
1244]. Nevertheless, available data from Australian
streams indicates that A. australis appears to have a slower
growth rate and live for a shorter period of time than does
A. reinhardtii. Sloan [1244] estimated that a 250 mm TL
individual of A. australis would have spent approximately
12 years in freshwater, whereas a similarly sized individual
of A. reinhardtii would require only seven years. The
largest A. australis specimen aged in his study was about
500 mm TL and was estimated to be approximately 32
years old; an equivalent sized A. reinhardtii would be about
21 years old. Age estimates of the largest specimens of A.
reinhardtii were variable but individuals between 1000 and
1200 mm TL were estimated to be between 35 and 45 years
of age [1244]. A validation of otolith age determination in
A. reinhardtii is provided by Pease et al. [1438]. Further
information on sexual and spatial variation in size and age
of A. reinhardtii is available in Walsh et al. [1445].
Quantitative estimates of fecundity in Australian anguillids are not available. A single large migrating female of A.
reinhardtii estimated to contain several million eggs has
been collected and A. australis is thought to be similarly
fecund [936, 1393]. Fecundity estimates of A. dieffenbachii
from New Zealand varied between 1 and 20 million eggs
for fish between 700–1500 mm TL, intraovarian eggs were
0.33 mm diameter or larger, and the gonads contributed
8–10% of body weight at the commencement of migration [891, 1324, 1325]. The fecundity of A. australis from
New Zealand ranged from about 1.5 to 3 million eggs in
migrating females between 500 and 800 mm, intraovarian
eggs were 0.22 mm diameter, and the gonads contributed
about 3.5% of body weight [891, 1324, 1325]. DeSilva et
al. [377] report that migrating A. australis from southeastern Australian estuaries had GSIs up to 3.2%.
Very little information is available concerning the sexual
development and fecundity of Australian anguillids. The
sex of eels is very difficult to determine by external examination, but in A. reinhardtii and other species, gender can
be established by internal macroscopic examination of the
gonads [891, 1360]. Histology is necessary to accurately
define stages of gonadal development, particularly in individuals less than around 600 mm in length [1360]. The
anatomy of anguillids is unusual in that female fishes are
without oviducts (the gymnovarian condition), the eggs
pass directly into the peritoneal cavity and then through
pores or funnels to the exterior [891, 1308]. The gonads of
some individuals of A. obscura [183] and A. dieffenbachii
[818], but not A. reinhardtii [1360], have been reported to
show signs of intersexuality. Walsh et al. [1360] provide
details on the macroscopic and microscopic structure and
development of the gonads in freshwater and estuarine
specimens of A. reinhardtii from New South Wales. This
species displayed asynchronous gamete development, the
most advanced cells present in the gonads of migrating
males were spermatocytes; those of females were pre-vitellogenic oocytes [1360]. Gonadal development was positively correlated with body size in females, this relationship
less apparent in males [1360]. Walsh et al. [1360] estimated that that sexual differentiation in A. reinhardtii
The size and age at which eels commence the spawning
migration varies widely, perhaps in response to the wide
range of habitat conditions occupied, and the distance to
the spawning grounds [1360]. Larsson et al. [776]
suggested that European eels are triggered to migrate when
the proportion of body lipid exceeds a threshold necessary
to accomplish the migration and final development of the
gonads. Sloane [1246] reported that migrating adult A.
australis (almost all female fish) in Tasmania varied in
length (range 840–1110 mm TL, mean 945 mm TL) and
age (range 18–30 years, mean 22.1 years). De Silva et al.
[377] reported the average length, mass and age of females
as 832 mm TL, 1051 g and 17.2 years, respectively. No
equivalent data for male A. australis are available. Beumer
et al. [183] collected mature females of A. obscura ranging
from 595–1050 mm TL. Walsh et al. [1360] observed that
sexual maturity in A. reinhardtii occurred over a wide size
range in both sexes, but estimated that the minimum size
at which this species commenced migration was 740 mm
TL in females and 440 mm TL in males, but noted that
such estimates may be inflated given the small number of
eels examined (71 males and 637 females) [1360].
Migrating male A. australis and A. dieffenbachii in New
Zealand are reported to also be generally smaller and
younger than females [891, 1323]. It has been suggested
occurred at approximately 590 mm TL. Female A. australis
and A. reinhardtii are often collected in freshwaters in
greater numbers than males [936, 1360, 1445] and sexspecific variation in habitat choice has been observed elsewhere [891, 1025]. Observed sex ratios are probably
strongly influenced by the sampling methods used and the
habitats in which the populations were sampled [1360]. It
has been suggested that environmental factors such as
salinity may influence sex determination in Australian eels
[1027] but sex determination may also be controlled in
part by genetics [891].
83
Freshwater Fishes of North-Eastern Australia
that the larger size and hence higher fecundity of female eels
would be selectively advantageous, given the high risks associated with the long migration to the spawning grounds;
males on the other hand are able to produce large quantities
of sperm at comparatively smaller size and so would be
favoured by an ability to grow rapidly to a size large enough
to make the spawning migration [566, 567, 891].
collections of leptocephali indicate that in the three
Australian species considered here, spawning occurs in the
Coral Sea off the north-eastern Australian coast, possibly
in the area encircled by New Caledonia, Fiji, Tahiti and the
Solomon Islands [64, 178, 645, 891, 912, 1308]. It is uncertain whether the spawning locations of the Australian
species are geographically separated in this area [64]. Little
is known of the route or duration of the long oceanic
migration to the spawning grounds, but for eels originating from south-eastern Australia, the distance to the
spawning grounds may be up to 5000 km [177, 912].
Walsh et al. [1360] suggested that the comparatively early
stages of gonadal development at migration observed in
both sexes of A. reinhardtii may indicate that this species
needs to travel further or may take longer to reach the
spawning grounds than some other anguillid species (but
see Shiao et al. [1439]. Silver eels of other species have been
recorded swimming at speeds up to 2–2.5 km.hr–1 and
50–60 km per day, suggesting that it may take over three
months for eels from some parts of Australia to reach the
spawning grounds [177, 645, 912]. Tsukamoto et al. [1333]
suggested that adult eels probably do not migrate in
schools to the spawning grounds on the basis of body form
and behaviour of adult eels and the fact that migrating
adults have occasionally been collected singly at sea. Adult
migrating eels appear to undertake vertical migrations at
sea [1259, 1307], possibly in response to variations in light
and water temperature, and are capable of swimming at
great depths. Tesch [1307] tracked A. anguilla at depths
ranging from less than 50 m to at least 400 m below the
water surface and the remains of anguillids have been
found in the stomachs of benthic fish caught at depths of
over 700 m [1126]. It is unknown how adult eels locate the
spawning ground but navigation may be facilitated by an
ability to orientate to the earth’s magnetic field [1155,
1307, 1308]. Volcanic seamounts, which may have unique
geomagnetic and geopotential anomalies, may function as
cues for orientation also [1333, 1443].
Immediately preceding and during the early stages of the
spawning migration, a range of morphological, biochemical and physiological transformations take place. A distinct
counter-shading colour pattern develops, the snout
becomes chisel-shaped, the head becomes dorsoventrally
flattened, the eyes increase in size, the pectoral fins enlarge
and the tail becomes paddle shaped. Such changes are
assumed to improve locomotory mechanics and survival
in the marine environment. Biochemical adjustments
include changes in the mobilisation and composition of
stored fatty acids in response to the energetic demands of
long-distance migration, maturation and gonad recrudescence. Physiological adjustments include osmoregulatory
and ionoregulatory changes associated with transition
from fresh water to saline water [377, 394, 891].
Downstream migrations of Australian eels may occur over
an extended period but appear to reach a peak during
summer and autumn. The cues for movement are not well
understood but eels are often, but not always, observed
moving during flood conditions, which may trigger or at
least facilitate downstream movements [55, 210, 232, 936,
1246, 1393]. Other factors such as temperature and day
length may also be important [1246]. Cyclical annual variation in the number of eels undertaking downstream
migrations has also been reported [936]. The downstream
and seaward migration of eels can result in a substantial
loss of organic matter (in the form of fish flesh) from the
freshwater environment, particularly in areas of low
productivity [1249].
Beumer [177] reported that silver eels congregate briefly
in estuaries and then migrate seaward to the spawning
grounds. These outward migrations may be influenced by
lunar phase and light intensity. Males are thought to leave
estuaries earlier than females but swim more slowly
(perhaps because they are smaller), thereby arriving at the
spawning grounds at approximately the same time as
females [177]. A similar pattern has been observed in New
Zealand eels [891] and Tsukamoto et al. [1333] suggested
that aggregation in space and time of reproductively
mature adults would facilitate physiological synchronisation of the sexes and improved reproductive success.
Eels are believed to cease feeding during the oceanic migration, and are thought to invest much of their energy
reserves into gonad production and final maturation so
that they are ready to spawn upon reaching the spawning
grounds [891]. Jellyman [645] estimated that spawning of
A. australis occurred between June and September on the
basis of the collection dates of leptocephali of known sizes,
together with data on growth rates of Northern
Hemisphere eels. Evidence from A. japonica suggests that
spawning does not occur continuously over the long
spawning season, but that eels are synchronised to spawn
periodically once a month during the new moon [1443].
Nothing is known of the spawning behaviour or the precise
conditions where spawning occurs but it is thought to take
The precise location of spawning of Australian eels is
unknown as very few adult eels have been collected at sea.
Projections based on knowledge of oceanic currents and
84
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
interactions between oceanic currents and movement of
leptocephali and glass eels. McKinnon et al. [912] proposed
a model whereby the East Australian Current bifurcates,
transporting leptocephali northwards along the
Queensland coast and southwards along the southern
Queensland and Northern New South Wales coasts.
place at considerable depths, possibly at about 350 m. The
adults are thought to perish soon after spawning; it is
extremely unlikely that they undertake a return migration
to freshwater [891, 1308].
The eggs are small and pelagic, floating upwards towards
the surface [891, 936, 1308]. The maximum diameter of
intraovarian eggs of A. rostrata (up to 950 mm TL) was
0.37 mm, but more commonly ranged between 0.2–0.3
mm [335]. Few details are available on many aspects of
embryological and larval development of anguillids as the
eggs of very few species have been successfully fertilised,
hatched or reared in captivity (but see [819, 1049, 1072,
1073]). Lokman and Young [819] managed to successfully
hatch the eggs of A. australis after about 45 hours of incubation at room temperature. Larvae were around 2.5 mm
at hatching and grew to about 5.3 mm after five days but
larvae did not survive beyond this point [819].
Once they reach the edge of the continental shelf in eastern Australia, active swimming may be required for leptocephali to detrain from the oceanic currents [645]. In New
Zealand waters, detrainment may occur several hundred
kilometres off the continental shelf but it is unknown how
larvae gain an awareness of the direction and proximity of
land and hence orientate towards it [645].
Very little information is available concerning the duration of the oceanic transport of leptocephali before metamorphosis, but it may be highly variable and depend at
least in part on the relative location along the eastern
Australian coast of detrainment and metamorphosis [645,
1225]. Based on data from microstructure and microchemistry of A. australis otoliths, the unvalidated age at
the commencement of metamorphosis was estimated at
138–198 days for glass eels collected in south-eastern
Queensland [66]. Shiao et al. [1225] estimated that glass
eels collected in estuaries from the Albert River north to
the Fitzroy River were significantly younger than those
collected further south, suggesting that leptocephali metamorphosed earlier and were faster growing in north-eastern Australia than in south-eastern Australia. McKinnon
et al. [912] estimated the mean ages at metamorphosis for
glass eels of A. australis and A. reinhardtii collected from
the Albert River estuary were 153.4 days ± 16.8 SD and 124
days ± 15.8 SD, respectively. For further comparative data
see also Shiao et al. [1439].
Leptocephali larvae are very rarely collected in the ocean,
but several Indo-Pacific eel species have been collected in
trawls at depths ranging from around 30 to 200 m [655].
These leptocephali are small (usually less than about
50–60 mm TL), have slender heads, peculiar large
forward-pointing teeth, and a flat, ribbon or leaf-shaped
body that is gelatinous and transparent [891].
Leptocephali may gain their nutrition by active feeding on
plankton or by absorption of nutrients in the seawater
through the skin, the latter being postulated to explain the
unusual flattened shape and high surface area of the body
of leptocephali [891, 1055].
Australian eel leptocephali are thought to be transported
from the spawning grounds to the Australian continental
shelf by oceanic currents [64, 171, 645, 912]. Leptocephali
are generally believed to be transported passively and to be
very weak swimmers, their flattened shape possibly facilitating transport on oceanic currents, but several
researchers [288, 891, 1032] have reported that leptocephali undertake vertical migrations and may be capable
of swimming across current flows.
During metamorphosis, a reduction in body length and
width and a loss of teeth occurs, and feeding is thought to
cease for a short period [1308]. Anguilla australis leptocephali range from 53–54 mm TL immediately preceding
metamorphosis [401]. As leptocephali transform into glass
eels they absorb the gelatinous body, and assume the characteristic elongate and slender eel shape, but remain transparent: they are now known as glass eels [891]. Early-stage
glass eels may vary between about 47–73 mm for A.
australis and 46–65 mm TL for A. reinhardtii [401].
The warm South Equatorial and East Australian currents
are thought to carry leptocephali from the tropical spawning grounds [64, 171, 645], but interactions with the cooler
currents of the Central Tasman Mass, North Bass Strait
Mass and the Sub-Antarctic Current at certain times of
year, and longer term changes in the El Niño Southern
Oscillation Cycle and hence oceanic currents, may influence
the species composition, timing, abundance and size of glass
eels delivered to the eastern Australian coast [171, 1047] and
elsewhere [303, 649, 895]. Mechanisms for the delivery of
leptocephali and glass eels of A. reinhardtii and A. obscura to
the north-eastern Australian coast are poorly understood,
as is the effect that the fringing Great Barrier Reef has on
Following metamorphosis, glass eels move shoreward; one
Northern Hemisphere species has been observed drifting
in a vertical position close to the water surface [1410]. The
time between metamorphosis in A. australis and A. reinhardtii, and the age at recruitment to the upper Albert
River estuary in south-eastern Queensland has been estimated at 40.8 ± 7.8 and 39.8 ± 5.6 days, respectively, giving
total approximate ages for glass eel recruitment to this part
85
Freshwater Fishes of North-Eastern Australia
assignation of developmental stages based on pigmentation). The degree of pigmentation is related to the time
since metamorphosis, with developmental rates probably
more related to ambient temperature than salinity or other
environmental factors [464]. Other morphological
changes occurring during this period include the development of a new set of teeth, the formation of the stomach
and the development of an extra loop in the intestine [891,
936].
of the estuary of 194.2 ± 22.8 and 164.1 ± 14.8 days for
each species, respectively. Arai et al. [66] estimated that
glass eel recruitment of A. australis to the upper Albert
River estuary occurred between 186–239 days [66].
The seasonal phenology of invasions to particular coastal
localities is associated with the southward and westward
movement of leptocephali on oceanic currents and
recruitment of glass eels along the Australian coastline and
hence may vary with latitudinal and longitudinal position
[171, 464, 1247]. Several studies have shown that A. reinhardtii recruitment to tropical and subtropical estuaries of
Queensland and northern New South Wales occurs over
extended periods throughout the year [171, 740, 1169].
Anguilla australis recruitment to temperate estuaries in
southern New South Wales, Victoria and Tasmania occurs
over similarly long periods [171, 464, 1247]. Each species
shows distinct, but often not exclusive, seasonal peaks in
glass eel abundance [171, 1047, 1169]. Seasonal and interannual variation in recruitment may serve to temporally
isolate the recruitment into freshwater habitats of
sympatric species such as A. reinhardtii and A. australis
[913, 1047].
Mass invasion of coastal and estuarine waters is followed
by a secondary upstream migration into freshwaters. This
two-stage process involves semi-passive tidal advection
and active swimming of glass eels into and within estuaries [912]. A period allowing the eels to acclimate to
reduced salinity is followed by an active upstream swimming phase undertaken by later developing glass eels and
early pigmented elvers. These secondary migrations are
thought to commence at or near the upper tidal limit of
brackish lowland rivers [464, 648, 1247, 1308]. These
mass-invasions of glass eels are known colloquially in
England, Australia and elsewhere as ‘eel-fares’ [180, 418,
500, 1382, 1393] and is the origin of the term elvers [180].
Glass eels and elvers may remain in estuaries prior to the
upstream migration for a period of about two weeks [647,
648, 1047]. They can however move considerable distances
during this period: mark-recapture data for A. australis in
the Albert River revealed that this species moved large
distances (up to 12 km) over a relatively short period of
time (2–3 days) [912]. Upstream migrations may take
place for extended periods throughout the year but their
phenology is highly variable [401, 936, 1205, 1243, 1247],
perhaps as a result of the variability inherent in the
numbers and timing of glass eel invasion. Fishway studies
in Queensland indicate that the upstream movement of
glass eels and elvers of A. reinhardtii is protracted but
concentrated during spring and summer [232, 740, 1173,
1275, 1276]. Various cues initiating upstream movement
such as interactions between prevailing light conditions
(time of day and day length), water temperature, salinity
and river discharge have been suggested, although the
process is poorly understood [1047, 1243, 1247, 1248,
1277, 1356].
Interspecific, seasonal and interannual variation in the
relative abundance, age and size of glass eels observed in
estuaries along the eastern Australian coast and elsewhere
has been attributed to such factors as: differences in adult
spawning locations and spawning times; variation in the
relative spawning success of adult eels and consequent
recruitment pulses; variation in primary and secondary
productivity and hence food availability for leptocephali;
the intensity and direction of offshore and inshore oceanic
currents; and the actual distance from the spawning location to the site of estuarine invasion [171, 381, 912, 1047].
In addition to these largely extrinsic factors, a range of
other localised environmental factors (and possibly
biological factors) may be important [464]. Eels are
known to have extremely sensitive olfactory organs [1308]
and some species are thought to be attracted to estuaries
by the presence of particular organic chemoattractants in
the water discharging from estuaries [337, 873, 1252, 1253,
1254, 1326, 1327]. Other factors such as lunar periodicity,
light intensity, variation in tidal magnitude (and hence
tidal flow), water temperature, turbidity, salinity and the
magnitude of freshwater discharge have also been identified as potentially important cues for glass eel invasion of
estuaries and longitudinal movement within rivers [171,
464, 912, 913, 1047, 1233] (see McKinnon et al. [912] and
Tesch et al. [1308] for recent discussions).
Elvers and developing eels colonise a range of freshwater
habitats and are capable of penetrating far upstream (see
Macro/mesohabitat use, pp. 77). Jellyman [646] estimated
that movement rates of elvers in New Zealand streams
were around 1.5–2 km per day. Eels are renowned for their
ability to overcome obstacles to movement such as dams,
weirs and waterfalls, which impede but do not prevent
upstream passage [178]. Elvers are able to climb such
obstacles by adhering, through friction and surface
tension, to damp surfaces. Eels have also been observed
During their residency in estuaries and brackish lowland
rivers, glass eels acclimate to the reduced salinities and
develop rapidly into fully pigmented elvers (see Strubberg
[1271] for details of a widely used scheme for the
86
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
1274, 1275, 1276]. The swimming abilities of glass eels of
A. australis and A. reinhardtii may be well below that
needed to negotiate the high water velocities frequently
observed in fishways in Queensland and elsewhere [182,
496, 543, 1274]. Hydraulic flume experiments [769] indicate that the maximum sustained and burst swimming
speeds of A. australis glass eels (mean 54.2 mm TL) were
0.29 and 0.79 m.sec–1, respectively, and those of A. reinhardtii
(mean 51.2 mm TL) were 0.32 and 0.75 m.sec–1, respectively [769]. On the basis of these results, Langdon and
slithering up wet banks and traversing short distances over
damp ground to bypass such obstacles [500, 711, 936,
1356]. Eels are sensitive to barriers to movement however,
and small individuals may have difficulty ascending fishways. Many fishways on weirs and tidal barrages in
Queensland are characterised by high water velocities,
high turbulence and, in the case of some vertical-slot
designs, have smooth-sided walls in each vertical slot
which may prevent or impede the ability of glass eels to
climb along the wetted margins within the fishway [769,
Table 8. Life history information for three Australian species of Anguilla. Information is listed for individual species where
available, otherwise it is listed under Anguilla spp. as many aspects of the life cycle may be generally similar.
Age at sexual maturity
A. australis – ? Migrating females 840–1110 mm TL (mean 945 mm TL) [1246]
A. reinhardtii –? Migrating females 832 mm TL (mean length) [377]
Minimum length of ripe females (mm)
A. australis – ? No fully mature females have been collected (but see age of migrating
females above)
A. obscura – ? Mature individuals ranged between 595–1050 mm TL [183]
A. reinhardtii – ? No fully mature individuals have been collected but the mean length of
maturing females (Stage 3 of Walsh et al. [1360]) was about 1025 mm TL
Minimum length of ripe males
A. australis – ? No fully mature fish have been collected
A. reinhardtii – ? No fully mature individuals have been collected but the mean length of
maturing males (Stage 3 of Walsh et al. [1360]) was about 550 mm TL
Longevity
A. australis – ? >32 years [1244]
A. reinhardtii – ? >45 years [1244]
Sex ratio
A. australis – ? Females often more abundant in freshwaters than males [936, 1360]
A. reinhardtii – ? Females often more abundant in freshwaters than males [936, 1360]
Peak spawning activity
A. australis – ? Outward migration to spawning grounds occurs over an extended period
during summer and autumn; spawning possibly occurs between June and September
[645]
A. reinhardtii – ? Outward migration to spawning grounds occurs over an extended
period during summer and autumn; timing of spawning is unknown
Critical temperature for spawning
?
Inducement to spawning
A. australis – ? Cues for migration to spawning grounds probably involve a combination
of biological (e.g. body size, lipid concentration, stage of gonadal development) and
environmental (temperature, day length, discharge) factors
Mean GSI of ripe females (%)
A. australis – ? Up to 3.5% in migrating eels [891, 1324, 1325]
Mean GSI of ripe males (%)
?
Fecundity (number of ova)
A. australis – ? 1.5–3 million eggs in migrating eels [1324]
A. reinhardtii – ? ‘several million’ eggs [936, 1393]
Fecundity/length relationship
?
Egg size
A. australis – Intravovarian eggs of migrating eels 0.22 mm diameter [891, 1324, 1325],
1.55 mm post-fertilisation [819]
Frequency of spawning
Anguilla spp. – Adults probably spawn once and then die [891, 1308]
Oviposition and spawning site
Anguilla spp. – ? Probably in the Coral Sea and at considerable depths [891, 1308]
Spawning migration
Anguilla spp. – Facultative catadromy (see text for details)
Parental care
Anguilla spp. – None known
Time to hatching
A. australis – ~45 hours [819]
Length at hatching (mm)
A. australis – ~2.5 mm TL [819]
Length at feeding
?
Age at first feeding
?
Duration of larval development
A. australis – Variable, mean 153.4 days ± 16.8 SD for specimens from Albert River [912]
A. reinhardtii – Variable, mean 124 days ± 15.8 SD for specimens from Albert River [912]
Length at metamorphosis
A. australis – 47–73 mm TL (early-stage glass eels) [401]
A. reinhardtii – 46–65 mm TL (early-stage glass eels) [401]
87
Freshwater Fishes of North-Eastern Australia
substrate [936]. Some anguillids also show marked diel
variation in activity; A. australis and A. dieffenbachii in
New Zealand were demonstrated to be nocturnally active
(associated with foraging) and to seek refuge within the
substrate during the day [453, 1191].
Collins [769] recommended that mean and maximum
velocities through fishways should not exceed 0.30 and
0.75 m.sec–1, respectively. To further facilitate passage,
several researchers [747, 769, 954, 1275, 1277] have advocated the inclusion of roughening substrates within the
cells of existing and future vertical slot fishways, and the
construction of eel passes that may specifically permit the
passage of glass eels and elvers.
Trophic ecology
Anguilla australis is a carnivorous species, relying on
generally small-sized food items as juveniles and switching
to larger diet items and a more diverse array of food types
with growth (Fig. 5). The diet of elvers and subadults
(≤200 mm TL) is dominated by aquatic insects (86.0%);
small amounts of molluscs (11.0%) and macrocrustaceans
(3.0%) are also consumed. Adult fish consume a wide
range of food types, probably reflecting the wide array of
habitats in which this large mobile predator can forage.
Aquatic insects (30.0%), fish (22.9%), and material
foraged from the water’s surface (terrestrial vegetation
(7.4%), terrestrial invertebrates (4.5%) and terrestrial
vertebrates (3.1%)) were the most important diet items
consumed by adults. Large crustaceans (6.5%), molluscs
(5.8%, aquatic algae (5.1%) and microcrustaceans (4.4%)
A number of studies in south-eastern Australia [175, 1208,
1244], have described a trend of decreasing abundance and
concomitant increasing size and age of A. australis and A.
reinhardtii with increasing distance from the sea, although
this is less evident in rivers and streams of south-eastern
Queensland [1093]. This pattern may be due to an avoidance of habitats characterised by low permanence, lower
winter temperatures and reduced food availability (in the
form of catadromous forage fish such as galaxiids) in high
elevation upland streams [1, 1208, 1244]. Predation by
larger eels may be important also. Migrating eels must pass
through a series of environmental ‘filters’ imposed by
physical barriers, sub-optimal habitats and biological
interactions on their progressive movement upstream.
Little information is available concerning the local movement patterns of Australian eels during the long period of
residence in freshwaters. Beumer [175] undertook a study
of the local movement of A. australis in a lentic freshwater
wetland of coastal Victoria. Of 1051 eels tagged and
released, 194 were recaptured over the two-year study
period. The maximum linear distance travelled was 3715
m for two individuals at liberty for 36 and 79 days, respectively. Three individuals recaptured after just 24 h had
moved between 145 and 200 m. There was no relationship
between eel size and number of days at liberty or distance
moved. Instead, movement activity was closely related to
variations in water temperature and feeding. The majority
of individuals exhibited limited movement (77% of fish
moved 400 m or less within 150 days of liberty) leading
Beumer [175] to estimate a home range of around 400 m
for this species. Pease et al. [1438] concluded that A. reinhardtii has a very restricted home range of 300 m or less.
Beumer [175] and others (see Tesch et al. [1308]) have
suggested that eel home range size is strongly related to the
size of the waterbody in which they occur. The presence of
large eels may influence the movement of smaller eels. In a
defaunation experiment in river reaches of the Wet Tropics
region, the removal of a large individual was usually
accompanied by the subsequent appearance of a number
of smaller eels. Interestingly, the combined biomass of
these interlopers was often very similar to the biomass of
the eel removed [1093]. Movement activity may be much
reduced at low temperatures (below 10°C) when eels are
thought to become dormant, burying themselves in the
A. australis juveniles (n = 24)
Macrocrustaceans (3.0%)
Molluscs (11.0%)
Aquatic insects (86.0%)
A. australis adults (n = 513)
Unidentified (1.9%)
Terrestrial invertebrates (4.0%)
Terrestrial vertebrates (3.1%)
Fish (22.9%)
Terrestrial vegetation (7.4%)
Detritus (0.1%)
Aquatic macrophytes (0.5%)
Algae (5.1%)
Other microinvertebrates (0.1%)
Microcrustaceans (4.4%)
Macrocrustaceans (6.5%)
Molluscs (5.8%)
Other macroinvertebrates (8.3%)
Aquatic insects (30.0%)
Figure 4. The mean diet of Anguilla australis juveniles (≤~200
mm SL) and adults (>~200 mm SL) (sample sizes for each age
class are given in parentheses). Data derived from stomach
contents analysis of fish from New South Wales [1133, 1134],
Victoria [175, 595] and Tasmania [758, 1244].
88
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
vegetation (7.7%) and terrestrial invertebrates (4.3%)
were also consumed. Bunn et al. [248] noted that the
isotopic signature of a small number of eels from Bamboo
Creek, a degraded lowland tributary of the Johnstone
River, indicated a diet dominated by terrestrial insects.
Anguilla reinhardtii is likely to be an important top predator in many aquatic environments of north-eastern
Australia, given its size, high local density and predatory
habit. Beumer [175] observed that A. reinhardtii in a
coastal Victorian wetland fed throughout the year and that
feeding activity was greatest in spring and summer.
Beumer [175] reported that A. reinhardtii was cannibalistic and Sloane [1244] observed the remains of A. australis
in the stomachs of A. reinhardtii and further suggested that
also formed minor components of the diet of this species.
Anguilla australis has been reported to go without food for
up to 10 months and may cease feeding at low water
temperatures [936]. Beumer [175] observed that A.
australis in a coastal Victorian wetland fed throughout the
year but that feeding activity was greatest in spring and
summer. Sagar and Glova [1191] reported diel feeding
activity in A. australis in New Zealand: individuals of all
sizes fed between dusk and dawn irrespective of size, but
smaller individuals were more crepuscular. Beumer [175]
reported the presence of unidentified eels in the diet of A.
australis in coastal Victoria, and suggested that cannibalism may be a feature characteristic of eel species.
Very little information is available concerning the diet of A.
obscura but it is likely to be very similar to that observed for
A. reinhardtii and A. australis. The diet of three individuals
from the Wet Tropics region of northern Queensland
(330–400 mm SL) comprised terrestrial invertebrates
(33.0%), molluscs (21.0%), aquatic insects (13.0%) and
unidentifiable material. These data most likely do not
adequately represent the true diet of A. obscura.
A. reinhardtii juveniles (n = 76)
Fish (0.8%)
Macrocrustaceans (3.4%)
Unidentified (3.0%)
Terrestrial invertebrates (2.7%)
Detritus (0.5%)
Aerial aq. Invertebrates (0.5%)
Unidentified (33.0%)
Molluscs (21.0%)
Aquatic insects (89.2%)
A. reinhardtii adults (n = 321)
Aquatic insects (13.0%)
Unidentified (0.9%)
Terrestrial invertebrates (4.3%)
Terrestrial vertebrates (0.7%)
Terrestrial vegetation (7.9%)
Fish (28.2%)
Detritus (0.5%)
Aquatic macrophytes (0.1%)
Algae (4.6%)
Terrestrial invertebrates (33.0%)
Figure 5. The mean diet of Anguilla obscura. Data derived
from stomach contents analysis of three individuals from the
Wet Tropics region of northern Queensland [1097].
Aquatic insects (30.3%)
The diet of A. reinhardtii is generally similar to that of A.
australis with carnivory and ontogentic variation features
of the diet (Fig. 6). The diet of elvers and subadults (≤200
mm TL) is dominated by aquatic insects (89.2%). Only
small amounts of microcrustaceans (3.4%), terrestrial
invertebrates (2.7%) and fish (0.8%) are consumed occasionally. Adults prey upon a wide range of food types,
including macroscopic items such as fish (28.2%), macrocrustaceans (21.4%) and terrestrial vertebrates (0.7%).
Aquatic insects (30.3%) were an important component of
the diet of this species and aquatic algae (4.6%), terrestrial
Macrocrustaceans (21.4%)
Molluscs (0.7%)
Other macroinvertebrates (0.4%)
Figure 6. The mean diet of Anguilla reinhardtii juveniles
(≤~200 mm SL) and adults (>~200 mm SL) (sample sizes for
each age class are given in parentheses). Data derived from
stomach contents analysis of fish from eastern Cape York
Peninsula [599, 697, 1099], the Wet Tropics region of
northern Queensland [1097], central Queensland [1080],
south-eastern Queensland [80, 205], New South Wales [1133,
1134], Victoria [175] and Tasmania [1244].
89
Freshwater Fishes of North-Eastern Australia
species for export and aquaculture operations is becoming
increasingly prevalent in eastern Australia. The world
aquaculture production of freshwater anguillids is
currently thought to exceed 216 000 t per annum, worth
over US$915 million and is based largely on the culture of
the European eel A. anguilla, and the Japanese eel, A.
japonica [462]. Despite a decline in eel stocks in many
areas over recent years due to a combination of overfishing
and environmental changes impacting on recruitment
[289, 290], commercial eel production has increased
substantially due in part to improved aquaculture techniques and sourcing of alternative seedstock [462, 464].
Interest in the potential for eel culture in Australia has
increased over recent years [462, 464]. Currently, eel
production is based on A. australis and A. reinhardtii and
total production is estimated as 5000–7000 t per annum,
worth AUD$4–6.5 million (as at 2002) [462]. The vast
majority of production in Australia comes from the
harvest of elvers and subadults from wild riverine fisheries. These life stages are then transferred to semicontrolled lentic waterbodies (e.g. lakes, swamps and
wetlands) where they are grown under natural conditions
until they reach a marketable size and are exported to
Europe and Asia [464, 1240].
interspecific competition for food and space between these
species may be intense at times in the Douglas River,
Tasmania. The frequent observation of eel bite marks on
eels in the Wet Tropics and the observation of replacement
by smaller eels following defaunation, also support suggestions that eels compete intensely for food and space.
Conservation status, threats and management
Anguilla australis, A. obscura and A. reinhardtii are listed as
Non-Threatened by Wager and Jackson [1353]. We suggest
that these listings remain valid on the basis of existing
data. The status of A. megastoma in north-eastern
Queensland is uncertain as a single individual has been
collected from the Daintree River only [1085, 1087]; the
presence of this species in north-eastern Australia requires
confirmation.
The widespread distribution of north-eastern Australian
eels and their complex life cycle: involving marine and
freshwater stages, distinct migration phases, remote
spawning grounds, extended larval stage and long period
to sexual maturity suggests that they may face and be
vulnerable to a range of threats throughout the long lifespan. The frequently high local abundance of these largebodied species in freshwaters, together with their usual
position at the top of the aquatic food chain, indicates that
eels may play an important role in the structuring of fish
and aquatic invertebrate communities and the transfer of
energy within trophic levels at local scales. Although it is
premature to label eels as ‘keystone’ species, it is difficult to
conclude that the presence of a 20 kg, highly mobile predator ranging over 400 m of stream, is without effect. Any
natural or anthropogenic impacts on the distribution and
abundance of eels may have far-reaching consequences for
other aquatic and semi-aquatic species.
Recent interest has focused on the potential for harvesting
of wild glass eels for subsequent grow-out in aquaculture
facilities [462, 464]. Recent major studies by Gooley et al.
[464] and Gooley and Ingram [462] have attempted to
evaluate the status of glass eel stocks in eastern Australia,
but the high spatial and temporal variability in glass eel
recruitment to eastern Australian estuaries has precluded
a reliable estimate of the total eel stocks in this region
[462]. Effective informed management of the glass eel
fishery in Australia is also hampered by an absence of
fundamental information on basic life-history attributes
of Australian anguillids, an absence of long-term data on
eel stocks in Australian waters and hence the ability to
accurately assess the determinants of variability in glass eel
recruitment, and ignorance about the role that eels play in
the ecology of rivers.
The movement of millions of glass eels and elvers across
marine/estuarine/freshwater ecosystem boundaries represents an enormous transfer of marine-derived carbon, the
significance of which is unknown but potentially high. The
migration of adult eels out of freshwaters and estuaries
represents a similarly large transfer of energy across
ecosystem boundaries. Despite the undoubted climbing
ability of eels, the imposition of barriers to movement by
structures such as dams, weirs and tidal barrages is an
important determinant of eel distribution and abundance.
Changes to the natural flow regime (e.g. timing, magnitude frequency and duration of flows), independent of the
imposition of barriers, may also impact on eels by affecting possible cues for downstream migration of adults, and
cues for the recruitment of glass eels into estuaries and the
upstream migration of glass eels and elvers to freshwaters.
It has been suggested that commercial harvesting of
particular eel species may be undertaken with minimal
environmental impact in areas where a disproportionate
ratio of migration of A. australis to A. reinhardtii into estuaries occurs, compared with recruitment into the catchment proper. Areas at the extremes of the natural range of
each species have been suggested as candidate locations
for intensive eel harvesting (e.g. south-eastern Queensland
in the case of A. australis). Although, numbers of A.
australis recruiting to the adult population in freshwaters
of south-eastern Queensland may represent only a very
small proportion of the number of glass eels attempting to
Overfishing is one of the most serious threats to eel populations in Australia as commercial harvesting of several
90
Anguilla australis, Anguilla obscura, Anguilla reinhardtii
biodiversity [184, 912]. Large quantities of small-bodied
and juvenile fish species (some of commercial importance), cructaceans and other aquatic invertebrates are
frequently caught during passive netting of glass eels and
mortalities are reported to often be very high [912]. Semiaquatic reptiles and mammals and birds are also occasionally captured during eel harvesting [184]. Options for
bycatch reduction are the subject of continuing research
and management planning [22, 462].
do so, it would seem that additional impact on glass eel
abundance in estuaries by harvesting would further
decrease the likelihood that A. australis will enter freshwaters. Clearly further evaluation and long-term monitoring
are required before it could be concluded that commercial
harvesting of glass eels could be undertaken in an ecologically sustainable manner in these areas or elsewhere.
Eels have traditionally been an important source of food
for the indigenous rainforest people of the Wet Tropics
region. Concern about a decline in eel numbers over the
last 50 years has been expressed to the senior author by
some elders. That such concern exists in the absence of
widespread harvesting of glass eels in this region suggests
that other factors may currently place pressure on these
species.
The wide distribution of Australian eels in the Asia-Pacific
region necessitates the coordinated management of eel
stocks across state and national boundaries, an imperative
facilitated by the establishment in 1997 of the Australia
and New Zealand Eel Reference Group (ANZERG),
comprised primarily of Government aquaculture and fisheries representatives [914]. It is hoped that ANZERG will
help to ensure conservation and management of South
Pacific eel stocks in an environmentally sustainable
manner.
Bycatch of aquatic and semi-aquatic biota during intensive glass eel harvesting in estuaries and lowland rivers is
another potential source of impact on aquatic ecosystem
91
Nematalosa erebi (Günther, 1868)
Bony bream, Bony herring, Australian river gizzard shad
37 085019
Family: Clupeidae
collected by seine-netting but also list a maximum Total
Length of 419 mm (in their Table 3). A maximum length
of 350 mm SL was recorded by us in a sample of 3123 fish
from the Burdekin River [1093]. Note that the type of
length measurement used varies between studies. By
applying conversion factors (1.14 for CFL, 1.23 for SL)
[422], estimates of maximum total length for the Northern
Territory and Burdekin River populations of 410 mm and
430 mm may be made. These data suggest little difference
in maximum size across this species’ range.
Description
Dorsal fin: 14–19; Anal: 17–27; Pectoral: 14–18; Pelvic: 8;
Vertical scale rows: 40–46. All fins spineless. Last ray of
dorsal fin elongated to form a long filament in larger fish.
Distinct line of scutes present on ventral margin, particularly between pelvic and anal fins. Head scaleless. Snout
blunt and rounded, mouth small, lower jaw with central
notch that fits a central groove in the upper jaw on closure.
Body deep and laterally compressed. Scales cycloid, easily
dislodged [52, 936]. Nematalosa erebi is easily recognised
and unlikely to be confused with any other species except
in northern lowland rivers that may be colonised briefly
by other clupeid species. The sexes are externally indistinguishable. Figure: composite, drawn from photographs of
adult specimens, 221–262 mm SL, Burdekin River,
November 1991; drawn 2002.
Bishop et al. [193] list the relationship between length
(CFL in cm) and weight (in g) as: W = 0.012 L3.12; n = 845,
r2 = 1.0, p<0.001. Harris and Gehrke [553] list the relationship between weight (g) and length (CFL in mm) as W
= 0.862 x 10–5 L3.1227. Arthington et al. [101] list the relationship between length (SL in cm) and weight (g) as W =
0.017 L3.113; n = 1223, r2 = 0.964, p<0.001 for bony bream
in Barambah Creek, a tributary of the Burnett River. These
data indicate that there is little indication of differences in
size and shape across this species’ range. However, these
relationships predict weights in excess of those listed by
Puckridge and Walker [1075] for a sample of 27 gravid
female fish from the River Murray, suggesting northern
populations may be heavier for a given length.
Nematalosa erebi is a moderate-sized fish with most specimens between 150–300 mm SL. Maximum size is
suggested to be 470 mm (TL) and 2.0 kg [936]. Bishop et
al. [193] recorded a maximum length of between 355 and
365 mm FL for a sample of 723 fish from the Alligator
Rivers region in the Northern Territory. Puckridge and
Walker [1075] recorded a maximum length of between
360 and 380 mm TL for a sample of approximately 600 fish
92
Nematalosa erebi
Nematalosa elongatus (Macleay), Fluvialosa bulleri
Whitley, 1948; Fluvialosa paracome Whitley, 1948;
Fluvialosa richardsoni (Castelnau), and Fluvialosa erebi
(Günther). The type specimen was collected from the
Mary River, Queensland. The large number of synonyms
reflects, in part, the extent to which different populations
were classified as distinct species [678].
The larvae of N. erebi are small and eel-like and easily
distinguished from the larvae of other species with the
possible exception of the larvae of Retropinna semoni.
Smelt have a higher myomere count, however (54 versus
45) [1075]. The yolk sac of bony bream is absorbed very
early in ontogeny (<3.5 mm TL). The larvae are largely
unpigmented except for a line of melanophores along the
dorsal border of the gut (visible throughout larval development), a single melanophore located anterior to the
cleithrum (after 6 mm TL) and a fine line of melanophores
along the hindmost two-thirds of the gut [1075].
Distribution and abundance
Nematalosa erebi is arguably the most widespread of
Australia’s freshwater fishes, rivalled only by the spangled
perch. This species has been recorded from the Pilbara and
Kimberley regions of Western Australia, throughout the
Northern Territory including its arid interior, the arid
interior of South Australia (i.e. rivers of the Lake Eyre
basin including Lake Eyre itself [455, 1341] and of the
Bullo-Bancannia basin [947]) and most major basins of
Queensland as far south as the Albert River. Its presence in
New South Wales and Victoria is limited to the MurrayDarling Basin [52]. Various texts [34, 52] indicate that the
distribution of N. erebi does not extend north of the
Burdekin River on the east coast but this is not entirely
true. The distribution includes the Wet Tropics region
[1087], northward to the Stewart River [571, 1099] and
including the Annan [599], Endeavour [571] and
Normanby [697, 1099] rivers. This species was not
recorded from the McIvor, Starke or Howick rivers within
this range, or from the Lockhart, Pascoe, Claudie or Olive
rivers further to the north, during the extensive CYPLUS
surveys of 1993 [571]. Whilst these data do suggest that its
distribution is not continuous in this part of Queensland,
focused surveys (using gill nets and boat electrofishing)
are needed to confirm the absence of bony bream.
Nonetheless, several other species are absent from these
rivers also (sooty grunter for example) whilst several
species not typical of rivers of the east coast are present in
some of these rivers (coal grunter for example), and this
area would appear to be one of biogeographic significance.
Various texts list the distribution of bony bream as extending into southern Papua New Guinea, but Allen [37]
believed its occurrence there doubtful and based on
misidentification of either N. papuensis (Munro) or N.
flyensis Wongratana, both of which are morphologically
very similar to bony bream.
Colour in life: bright silvery-white, sometimes greenishgrey on back. Fins either clear or opaque white. A reddish
tinge to the body, and particularly the head region (see
Figure 48 in Merrick and Schmida [936]), occurs and may
be associated with breeding. This colour variation has
been observed in the Burdekin River population also
[1093] and is thus not restricted to the Murray River
population [678]. Colour in preservative: white to light
tan, silvery appearance retained but greatly subdued.
Systematics
The family Clupeidae is composed of over 200 species of
small to medium sized, silvery fish commonly called
sardines, pilchards, herrings or sprats. The family is found
mainly in the shallow inshore habitats of the Indo-Pacific
although many species occur in freshwater and estuarine
habitats. About 32 species from 15 genera are known from
Australia [1042]. Clupeids are the single most important
family in the fisheries of the world, comprising nearly 20%
of the total catch [52]. A small bony bream fishery exists in
the lower Murray (predominantly in Lake Alexandrina),
landings of 1000 t were recorded in 1990. Catches are
destined for use as crayfish bait [678]. Human consumption is limited, although bony bream were canned as food
for the troops during WWII [884]: no doubt contributing
to the war effort and hastening the conflict’s end.
Diagnostic characters include: the presence of specialised
scales on the belly (scutes); the absence of fin spines;
silvery, easily shed cycloid scales, the absence of a lateral
line, and a small terminal mouth without teeth (or if present, teeth are very small) [1042]. Only two Australia
clupeids occur exclusively in freshwaters: Nematalosa erebi
(Günther) and Potamalosa richmondia; although others
such as Nematalosa come (Richardson) and Herklotsichthys
castelnaui (Ogilby) are occasionally found in freshwaters.
Nematalosa erebi is an abundant species. This species
comprised 7.5% of the 27 742 fishes collected in the NSW
Rivers Survey and was the second most abundant species
[553]. This figure underestimates its abundance however,
given it was absent from two of the four major regions
sampled. Bony bream comprised 17.8% of the catch from
the Murray-Darling Basin and was approximately five
times more abundant in the Darling River than it was in
The genus Nematalosa was described by Regan in 1917, the
type species being Clupea nasus Bloch, by subsequent
designation. The bony bream was originally described as
Chatoessus erebi by Günther in 1868. Additional synonyms
include Chatoessus richardsoni Castelnau, 1873; Chatoessus
elongatus Macleay, 1883; Chatoessus horni Zeitz, 1896;
93
Freshwater Fishes of North-Eastern Australia
In an extensive study of the fishes of the Fitzroy River, N.
erebi was encountered at all sites examined (21 sites) and
was the most abundant species collected [160]. It was present at all sites on all occasions except one and abundances
did not vary greatly between sampling occasion over a
three year period. This observation of stable population
size is in contrast to that observed by us in the Burdekin
River and in Barker/Barambah Creek in the Burnett River
drainage [101]. Extreme flooding in the Burdekin River,
associated with Cyclone Joy in 1991, resulted in greatly
depressed abundance levels. However, it was not known
whether this reduction was due to flood-associated
mortality and removal, or whether populations had simply
moved downstream following their detritus/periphyton
food source. Whatever the case, population sizes had
recovered substantially within 12 months. Seasonal reductions in abundance, from maximum catches of 200–300
fish per sample in summer to less than 20 fish per sample
in winter, were recorded in Barker/Barambah Creek [101].
A marked decline in seine-netting catches over the period
June to August, corresponding to the period of lowest
water temperatures, also occurred in the lower Murray
River [1075]. Winter reductions in abundance may be
related to increased susceptibility and frequency of infection by pathogens (see below). Body condition has been
shown to deteriorate over the winter months [101].
the Murray. This species was frequently the most abundant species at individual sites [1201]. Puckridge and
Walker [1075] believed that in contrast to many other
species, bony bream had not declined in abundance since
the advent of flow regulation in the Murray River.
However, this assertion was based on fisheries landings
that showed an increase over the period 1970–1990
(approximately). In contrast, Gehrke [435] showed that
the abundance of N. erebi was significantly lower in regulated reaches than in unregulated reaches of the MurrayDarling River. Recruitment may have been modified in
regulated reaches also, as a smaller proportion of the
population was composed of small fish.
Bishop et al. [193] recorded N. erebi from 21 of 26 regularly sampled sites within the Alligator Rivers region of the
Northern Territory. Overall, it contributed 2.6% to the
total number of fish collected and was in the top quartile
of species ranked by abundance. Abundance levels varied
between habitat types, being most abundant in lowland
backflow billabongs (5.48%) and least abundant in escarpment habitats (0–0.5%).
Bony bream comprised 48% of the total gill-netting catch
in a study undertaken in the Normanby River [1098].
Similarly high abundances were recorded by Kennard
[697] in floodplain lagoons of the Normanby River.
Nematalosa erebi comprised 42% of the 1301 fish from six
lagoons and 43% of 318 fish from two main river sites
collected by gill-netting. No N. erebi were collected by electrofishing in this study. Only six individuals were collected
by electrofishing in an extensive survey of the freshwater
fishes of the Wet Tropics region despite its occurrence at
relatively high abundance in the lower reaches of these
rainforest rivers [1087].
Macro/meso/microhabitat use
Nematalosa erebi has been recorded from a wide array of
habitats ranging from salt lakes, lowland rivers, floodplain
billabongs and lagoons, impoundments to rainforest
streams. Merrick and Schmida [936] suggest that the only
riverine habitats not used by N. erebi are ‘higher, cooler,
faster flowing, clear upper reaches’. They caution however
that this may reflect low abundance of their preferred food
resources; macrophytes and detritus. In fact, in the Wet
Tropics region, bony bream are naturally found in mesohabitats typified by high elevation (100 m.a.s.l.), cool clear
water of moderate flow. Translocated populations also do
well at much higher elevations (i.e. on the Atherton
Tablelands). It seems that the array of habitats occupied by
bony bream is limited only by access and possibly by minimum water temperatures.
The estimation of bony bream abundance is highly influenced by sampling methodology. For example, bony
bream comprised only 1% of the electrofishing catch (total
n = 3630) in a three-year study of the fishes of the
Burdekin River, whereas it comprised 36% of the seinenetting catch (total n = 121 987) and an enormous 64% of
the gill-net catch (total n = 1720). These data indicate the
care needed when comparing abundance levels between
studies. Moreover, in the case of gill-netting, net placement has a large influence on total bony bream catch. For
example, nets set perpendicular to the bank will catch
significantly more bony bream than nets set parallel
[1093]. It is noteworthy that despite its high abundance
elsewhere in the Burdekin River, N. erebi is either absent or
at very low abundance in off-channel lagoon habitats of
the lower Burdekin River (Perna and Cappo, unpubl.
data). Perna (pers. comm.) attributed this pattern to the
effects of degraded water quality and weed infestation in
these lagoons.
Nonetheless, abundance levels do vary spatially, corresponding to spatial variation in mesohabitat characteristics. In the Burdekin River, bony bream abundance was
negatively associated with moderate to fast water velocity
(>0.3 m.sec–1) and the proportional contribution of gravel
and cobble to substrate composition (the latter possibly
resulting only because of autocorrelation with the former)
[1098]. However, bony bream do occur in fast flowing
boulder strewn habitats such as occur in many rivers of
the Wet Tropics. It is likely that water velocity/abundance
94
Nematalosa erebi
maximum value of 38°C is probably approaching the
upper limit for this species. The minimum value listed
(15°C) was for a rainforest stream during winter. Only one
individual was collected at this time. Glover [455] lists
minimum and maximum water temperatures of 14 and
30°C, respectively, for central Australian populations of N.
erebi. Merrick and Schmida [936] list bony bream as being
able to tolerate temperatures as low as 9°C.
relationships vary from location to location, if they exist at
all.
Substantial ontogenetic variation in habitat use by bony
bream in a large floodplain river of the Northern
Territiory was described by Bishop et al. [193]. Small juvenile fishes were most commonly collected from corridor
and lowland channel lagoons and to a lesser extent, corridor anabranch lagoons and pools in sandy creekbeds.
Larger juveniles and small adults were more widely
dispersed across a range of lowland lagoon habitats. Larger
adults were more restricted to corridor and floodplain
lagoons and of these only the largest were recorded from
escarpment habitats. No bony bream were collected from
escarpment stream habitats. Reproductively active fish
(stage VI and VII) were collected from muddy lowland
lagoons.
Table 1. Physicochemical data for Nematalosa erebi. Data
derived from different studies across the northern distribution
of bony bream (see text). Dissolved oxygen values listed for the
Alligator Rivers region are surface values, bottom values are
given in parentheses. Turbidity values are given as NTU except
where designated by * where water clarity is given as Secchi
disc depths in centimetres. ** denotes that water conductivity is
given as the concentration in mg.L–1 of total dissolved solids.
Surprisingly, given this species’ wide distribution and
abundance, little information on its microhabitat usage or
preferences is available. It is not frequently collected by
back-pack electrofishing and consequently, we have very
meagre habitat records for this species. Nonetheless, this
species is infrequently associated with microhabitat cover
elements such as woody debris and macrophyte beds,
preferring to take refuge amongst the relative protection of
its fellows. Comparison of seine- and gill-netting catches
in the Burdekin River [1093] suggest that fish below 250
mm SL are most common in open shallow areas (30–150
cm) whereas fish larger than this are rarely found in such
shallow habitats. Bony bream form a large part of the diet
of many piscivorous water birds [1167] and avoidance of
shallow habitats may reduce predation. Extremely high
numbers of bony bream may be collected by seine-netting
over sand/fine gravel in moderate depths, particularly
when water clarity is sufficiently elevated to provide
refuge. For example, catches of 500–1000 individuals per
haul (50 m seine, 9 mm stretched mesh) were not uncommon during a study in the Burdekin River [1093].
Although bony bream may be observed throughout the
water column, they are most commonly found in the lower
one-third.
Parameter
Min.
Max.
Mean
Alligator Rivers region [193]
Water temperature (°C)
23.0
38.0
31.0
Dissolved oxygen (mg.L–1)
2.7 (0.2) 9.7 (9.5) 6.3 (3.9)
pH
5.1
8.6
6.2
Conductivity (µS.cm–1)
2.0
198.0
Turbidity (cm)*
1
360
65
Cape York Peninsula (n = 6) [1094]
Water temperature (°C)
21.0
27.0
24.0
Dissolved oxygen (mg.L–1)
7.3
11.0
8.8
pH
6.43
8.44
7.21
Conductivity (µS.cm-1)
80.0
420.0
180.1
Turbidity (NTU)
0.7
5.4
2.0
Normanby River floodplain lagoons (n = 12) [697]
Water temperature (°C)
22.9
33.4
25.9
Dissolved oxygen (mg.L–1)
1.1
7.7
3.46
pH
6.0
9.1
7.05
Conductivity (µS.cm–1)
80.0
412.0
184.1
Turbidity (NTU)
2.1
120.0
14.5
Wet Tropics region (n = 8) [1085]
Water temperature (°C)
23.6
32.7
Dissolved oxygen (mg.L–1)
5.76
8.14
pH
7.10
8.0
Conductivity (µS.cm–1)
8.3
67.6
Turbidity (NTU)
1.7
29.7
Environmental tolerances
Despite the near ubiquity and importance of bony bream
in northern Australian freshwaters, information on the
physicochemical tolerance of this species is lacking.
Inferences must therefore be based on water quality information from sites in which N. erebi have been collected.
The normal caveats about the extent to which such data
adequately describe tolerance therefore apply.
The range in average temperature values listed in Table 1
reflects the fact that the studies from which these data were
derived were all conducted in northern Australia. The
95
27.2
6.77
7.54
42.6
11.9
Burdekin River (n = 43) [1098]
Water temperature (°C)
15.0
31.0
Dissolved oxygen (mg.L–1)
4.0
12.0
pH
6.66
8.46
Conductivity (µS.cm–1)
50.0
780.0
Turbidity (NTU)
0.3
20.0
25.1
7.92
7.64
395.0
4.0
Fitzroy River (n = 11) [942]
Water temperature (°C)
24.0
29.0
Dissolved oxygen (mg.L–1)
4.8
11.0
pH
6.9
8.8
Conductivity (mg.L–1)**
70
770
Turbidity (cm)*
4
160
26.2
7.35
7.91
205
76.3
Freshwater Fishes of North-Eastern Australia
invasion) were believed responsible for the near-absence
of N. erebi from floodplain lagoons of the Burdekin River
delta (C. Perna, pers. comm.). Bishop et al. [193] observed
N. erebi in a fishkill at Leichardt Lagoon in the Alligator
Rivers region when surface DO levels dropped to 0.1
mg.L–1.
It is probable that substantial local adaptation to low water
temperatures occurs. For example, Puckridge et al. [1078]
list data showing that bony bream occur in waters as cold
as 12°C in the Murray-Darling River. However, rates of
infection by the fungus Saprolegnia parasitica and the
bacterium Aeromonas hydrophila, which leads to mycotic
dermatitis, increased dramatically when water temperatures descended to 12°C. These authors suggested that low
winter water temperatures depress the immune response
of bony bream allowing mycotic dermatitis to develop.
Increased rates of infection by the protozoan parasite
Chilodonella hexasticha in central Australian populations
of bony bream have also been associated with decreased
winter water temperatures [767]. Lake [754] believed that
hypolimnetic releases from the Hume (Murray River) and
Burrinjuck (Murrumbidgee River) dams that lowered
summer water temperatures to 16 to 18°C (a 6°C drop
below expected river temperatures) had resulted in a
decline in abundance of bony bream for several hundred
kilometres downstream.
Nematalosa erebi has been recorded from waters of a
moderately large range of acidity: 5.1 to 9.1 pH units. The
pH range within each study area listed in Table 1 is somewhat smaller however, ranging from 0.9 units (Wet
Tropics) to 3.5 units (Alligator Rivers region) and averaging only 2.2 pH units. In general, N. erebi occurs more
frequently in neutral to slightly basic waters although it is
evident that this varies between regions (i.e. the Alligator
Rivers’ population), suggesting localised adaptation,
within limits, to the existing array of habitats of varying
water quality. It is notable that N. erebi has not been
recorded from highly acidic habitats such as dune lakes
[1101]. Herbert and Peeters [569] implicate elevated pH
resulting from drainage works exposing potential acid
sulphate soils as the major cause of some massive kills of
bony bream in northern Queensland. Notably, the
disjunction in distribution along the east coast of Cape
York Peninsula discussed above, involves rivers draining
extensive peaty swamps and dune fields notable for their
low pH (i.e. <5) [1101].
The substantial range in maximum temperatures listed in
Table 1 (27 to 38°C) in large part reflects the climatic
differences between regions and the time of year in which
samples were collected. For example, the maximum
temperature recorded for rivers of the Cape York region
(27°C) is much lower than that for floodplain lagoons in
the same region, simply because the former sites were
sampled in the winter dry season only whereas the latter
were sampled over the full climatic year. Although N. erebi
is evidently able to tolerate water temperatures as high as
38°C (for at least short periods) and is routinely found at
temperatures between 27 and 35°C, we suggest that it preferentially avoids very warm waters, if possible. For example, water temperatures in excess of 31°C were routinely
recorded in sites located on the upper Burdekin River at
the end of the dry season (November) but such sites lacked
bony bream. This species is the most common (in terms of
abundance and biomass) of the river’s fishes and was present at such sites when temperatures were lower. The
simplest explanation is that N. erebi avoid habitats of high
water temperature if egress from such sites is possible.
Nematalosa erebi tolerates waters of a wide range of salinities, ranging from the highly dilute waters of rainforest
streams of the Wet Tropics regions to more conductive
waters of the Burdekin River (Table 1). However, the values
presented in Table 1 are all indicative of very fresh water.
Elsewhere this species has been recorded from salt lakes
with salinities approaching that of sea water. Ruello [1167]
reported that bony bream were present in Lake Eyre when
surface salinity was approximately 39‰ but also included
accounts of bony bream persistence at salinities approaching double this value. Whatever the case, the existing data
indicates an extremely wide salinity tolerance befitting the
most widely distributed Australian freshwater fish.
Not unsurprisingly, N. erebi has been recorded from a wide
variety of water clarities with a tendency to be most
common in waters of moderate turbidity, perhaps reflecting more their preferred habitat (slow-flowing lowland
rivers) rather than water clarity per se. Burrows et al. [256]
recorded bony bream in the Belyando River in turbidities
as high as 581 NTU. The extent of long-term persistence in
such turbid waters is unknown as are reproductive, energetic and trophic responses (i.e. fecundity, condition and
diet).
Bony bream have been recorded from waters with a large
range in dissolved oxygen concentrations although the
average values listed in Table 1 indicate that N. erebi are
most commonly collected from well-oxygenated waters.
Nonetheless, N. erebi have been recorded from hypoxic
waters such as floodplain lagoons of the Alligator Rivers
region and of the Normanby River. However, such conditions are far from optimal. Bony bream tend to reduce
activity greatly under hypoxia, the extent to which this
inhibits food intake or growth in hypoxic habits is
unknown. Low oxygen levels (in concert with prolific weed
Information on the tolerance of bony bream to toxicants
is, in general, lacking. We have observed highly significant
96
Nematalosa erebi
toxic effects of copper and indirect effects of copper on its
microalgal food source.
reductions in the abundance of N. erebi in stream reaches
receiving mine effluents containing elevated concentrations of copper [1093] possibly in response to the direct
Table 2. Life history data for Nematalosa erebi. Data drawn from the work of Puckridge and Walker [1075] in the lower Murray
River, Arthington et al. [101] in the Burnett River drainage and Bishop et al. [193] in the Alligator Rivers region.
Age at sexual maturity (months)
Murray River – 12–24 months (males) and 24 months(females); median lengths 159 and
199 mm TL, respectively
Burnett River – gender discernible at 115 mm SL and 127 mm SL for males and females,
respectively
Alligator Rivers – 12–15 months (males) and 12–15 months (females); length at first
maturity 130 and 140 mm CFL, respectively
Minimum length of ripe females (mm)
Murray River – approximately 150 mm TL
Burnett River – 202 mm SL although spent fish as small as 187 mm recorded
Alligator Rivers – 140 mm CFL
Minimum length of ripe males (mm)
Murray River – approximately 130 mm although a small number of precocious males
approximately 110 mm TL observed
Burnett River – 204 mm SL although spent fish as small as 117 mm SL recorded
Alligator Rivers - 130 mm CFL, no precocious males observed
Longevity (years)
Probably up to 5 years
Sex ratio (males to females)
Murray River – 0.86: 1; females more abundant in larger size classes
Burnett River – 0.70: 1; females more abundant in larger size classes
Alligator Rivers – 1:1
Peak spawning activity
Murray River – December to February
Burnett River – GSI values elevated from October to March, some ripe individuals
present in April
Alligator Rivers – spawning continuous but majority occurring from December to March
Critical temperature for spawning
Murray River –18–20°C
Burnett River – 22°C
Alligator Rivers – data not given but likely to be >24–28°C
Inducement to spawning
Murray River - unknown but apparently unrelated to flooding
Burnett River – unknown but postulated to involve interactive effects of temperature and
daylength
Mean GSI of ripe females (%)
Murray River – 8–9%
Burnett River – 5.8 ± 0.3% (SE)
Alligator River – 4–5%
Mean GSI of ripe males (%)
Murray River – data not given
Burnett River – 3.2 ± 0.1% (SE)
Alligator Rivers – 3–4%
Fecundity (number of ova)
Murray River – 33 000–880 000
Alligator Rivers – 80 000–230 000
Fecundity/length relationship
Murray River – log F = 3.923 + 3.725(log TL in mm); n = 27, r2 = 0.88, p<0.001
Egg size (mm)
Murray River – 0.83 ± 0.04 mm (water-hardened)
Alligator Rivers – 0.41–0.43 mm (in situ oocytes)
Frequency of spawning
Females homochronic, males may remain on spawning grounds longer and participate
in several spawnings. Heterochrony possible in northern populations
Oviposition and spawning site
Murray River – shallow sandy embayments
Alligator Rivers – muddy lagoons
Spawning migration
Inferred – see section on movement
Parental care
None
Time to hatching
Unknown but likely to be rapid
Length at hatching (mm)
Unknown but likely to be 2–3 mm
Length at feeding
Yolk sac absorption complete by 3.5 mm TL
Age at first feeding
?
Age at loss of yolk sac
?
Duration of larval development
?
Length at metamorphosis
Squamation commences at 26 mm TL, complete by 35–40 mm TL
97
Freshwater Fishes of North-Eastern Australia
(October–December). Elsewhere in northern Queensland,
temporal changes in population age structure suggest a
more protracted breeding season. New recruits were
present in both wet and dry season samples in the
Burdekin River [1080] and in both early and late dry
season samples in floodplain lagoons of the Normanby
River [697]. It would be most instructive to determine
whether spawning phenology becomes more pronounced,
or commences earlier in the year, with increasing latitude
over the length of the Murray-Darling system and to assess
whether other life history adjustments are necessary as a
result.
Overall, and as expected for such a widely distributed and
abundant species, N. erebi appears highly tolerant of a
wide range of environmental conditions. However, by the
same token, we find it disturbing that there a few experimental data on the tolerances of this species. Its potential
as a biomonitor, which given its huge distribution across a
range of regions, rivers and habitats, its abundance and
trophic position (see below) is considerable, cannot be
realised until such data are available.
Reproduction
Nematalosa erebi has a reproductive biology similar to
many of the clupeid fishes. It matures early in its life,
usually in its first or second year. Female fish mature more
slowly than do males and may attain greater size. The data
presented in Table 2 suggests that female fish may mature
more slowly in southern populations. There is no strong
evidence however to suggest that they mature at much
greater size than do northern populations. The data
presented in Table 2 suggests that individual female fish
may spawn up to four, but more commonly three, times
over their life span. However, given the intensity of predation on this species (by both birds and fishes, and in northern rivers by crocodiles also), it is unlikely that all but a
very few spawn more than once. Sex ratios tend towards
unity in the northern population whereas females were
found to be more abundant (mostly because of a dominance of females in the upper size classes) in the Murray
and Burnett rivers. However, Puckridge and Walker [1075]
found proportionally more males than females in the
vicinity of spawning grounds leading them to suggest that
males may stay on the grounds longer than females.
A short, pronounced breeding season in the southern
population appears to indeed be related to a number of
other life history adjustments. GSI values of female fish in
this region were approximately double those observed in
the northern population. The population in the Burnett
River appears to have an intermediate female GSI value,
consistent with the hypothesis that selection for a short
breeding season also results in selection for comparatively
elevated instantaneous reproductive effort. It would be
instructive to know whether northern populations spawn
more than once in a season.
Although the estimates of fecundity in the Northern
Territory population are based on only three specimens,
the data suggests that fecundity may be lower there than in
the Murray River, thus leading to the observed reduction
in GSI values. Although egg size appears greater in the
southern population, which may also lead to increased GSI
values, it must be emphasised that the estimates of egg size
in the Murray River population are based on ovulated,
water-hardened eggs whereas Bishop et al. [193] based
their estimate on the size of follicular oocytes.
Geographical variation in spawning phenology is apparent. Populations in the Murray River have a well-defined
summer breeding season, the timing of which is unrelated
to flooding. Recruitment may benefit from coincidence
with flooding however [1075]. In contrast, year-round
spawning, with a peak in the early wet season, was
observed in the tropical Alligator River. An intermediate
phenology was observed in the Burnett River, south-eastern Queensland, where maximum GSI values were
recorded over the period October to March/April;
although reproductively active fish were present in all
sampling occasions except from June to August (the coldest months). Minimum temperatures associated with
spawning ranged from 18–20°C in the Murray River, 22°C
in the Burnett River and 24–28°C in the Alligator River.
These studies suggest that water temperature exerts some
influence on spawning phenology, with spawning in
southern populations being limited to the warmer
summer months. Llewellyn [814] reported that bony
bream in New South Wales spawn early in the year
These data suggest that the life history of bony bream is
relatively flexible, as might be expected for a species with a
distribution encompassing wet tropical, wet/dry tropic,
subtropical, arid and temperate environments. Puckridge
and Walker [1075] noted that N. erebi was much more
fecund than other related gizzard shads, and further, that
the rate of increase in fecundity with increasing size was
also much greater. These authors suggested that these
features enabled very rapid recovery of population size
after unfavourable environmental conditions. Such a rapid
recovery was observed in the Burdekin River following
extreme flooding associated with the passage of Cyclone
Joy over the catchment in January 1991. Flooding reduced
bony bream abundances by almost 80%. Population levels
had increased to 77% of pre-flood levels within a year and
returned to pre-flood levels after 18 months. Recovery was
initially achieved through equal contributions by immigration and production but production was the greatest
98
Nematalosa erebi
use described by Bishop et al. [193] indicates substantial
movement by juvenile fish also. Long-term monitoring of
fishes in the Burdekin River [1082] revealed that recolonisation of reaches after a large flood was partly achieved by
the immigration of both small (<75 mm SL) and intermediate-sized fish (75–250 mm SL). These data suggest that
small and intermediate sized fish make substantial movements not associated with reproduction. Such fish may
track spatial and temporal variation in their detrital/
microalgal food base.
contributor in the second half of the recovery period
[1082].
Spawning takes place in shallow still-water habitats. In the
Murray River, spawning was suggested to take place in
sandy embayments whereas the population in the Alligator
River spawns in muddy lagoons. Spawning in lagoons of
the Normanby River was also recorded by Kennard [697].
In the upper Burdekin River, which lacks off-channel
lagoons, spawning probably takes place in backwaters. The
eggs are apparently demersal at the time of spawning but
later become buoyant [1075].
Puckridge and Walker [1075] implied the existence of
movement associated with reproduction in the Murray
River by designating certain areas as spawning grounds.
Similarly, the distinction between adult and juvenile habitats in the Alligator Rivers region [193] suggests that adults
make spawning-associated migrations into spawning
grounds. It seems to us that focused studies on the movement biology of N. erebi would be a fruitful area of
research and one that is needed to identify the precise
mechanisms by which river regulation impacts on this
species [435].
Larval development is, at least initially, rapid, particularly
with regard to absorption of the yolk sac. This suggests
that bony bream larvae may be highly reliant on the presence of an abundant phyto/microzooplankton bloom
early in its life.
Movement
Information on the movement biology of this species is
limited and derived primarily from studies on fishway efficacy or inferred from studies of reproductive biology.
Trophic ecology
The dietary information presented in Figure 1 is
summarised from a total of 11 different studies drawn
from the lower Murray River (number of individuals = 98)
[115]; the Pilbara region (n = 9) [358]; Cooper Creek in
central Queensland (n = 90) [246]; a tributary of the
Burnett River in south-eastern Queensland (n = 499) [99,
205]; the Burdekin River (n = 514) [1093]; the Wet Tropics
region (n = 14) [99, 1097]; Cape York Peninsula (n = 118)
[697, 1099] and the Alligator Rivers region (n = 471)
Stuart [1274] found that N. erebi was the second most
abundant fish moving (upstream movement recorded
only) through a fishway located 64 km from the mouth of
the Fitzroy River. Up to 400 fish were recorded moving
through the fishway, of a modified slot design, each day.
Movement through the fishway occurred throughout the
year but was least in late summer/early autumn. Nearly all
(~95%) of the fish collected were less than 100 mm in
length, with the remainder being greater than 250 mm
length. Fish as small as 25 mm were found to negotiate the
fishway although comparison of the size distributions of
samples from the top and bottom of the fishway and of
fish congregated below the fishway revealed that the
processes of entry and passage through the fishway both
selectively reduced the numbers of small individuals.
Movement was predominantly diurnal, an observation
that has also been made on populations in the Murray
River [854]. Upstream movement in fishways will apparently cease, followed by a return to the base of the fishway,
if the upstream passage cannot be negotiated before
sundown [854]. Clearly therefore, N. erebi must be able to
negotiate any fishway (or natural obstacle) within the
space of a single diurnal period.
Terrestrial invertebrates (1.0%)
Microcrustaceans (10.7%)
Unidentified (8.0%)
Molluscs (1.8%)
Aquatic insects (5.1%)
Algae (14.7%)
Aquatic Macrophytes (1.4%)
Juveniles comprised the bulk of N. erebi recorded moving
through a fishway on the Burnett River [1173]. Large
congregations of juvenile fish below small barriers such as
road crossings and culverts are commonly observed in the
Mary River in south-eastern Queensland with the inference being that such fish had been prevented from
upstream migrations. The ontogenetic variation in habitat
Detritus (57.3%)
Figure 1. Mean diet of Nematalosa erebi. Data derived from a
total of 1813 individuals drawn from 11 different studies (see
text).
99
Freshwater Fishes of North-Eastern Australia
[193]. Note that the total sample is numerically dominated
by fish from north-eastern and northern Australia (the
summary means upon which Figure 1 is based are
weighted by abundance) and substantial geographical and
habitat-based variation in diet occurs (see below). Also,
note that the samples contain both juvenile and adult fish
and ontogenetic variation in diet is a feature of the trophic
ecology of this species.
Microplankton, aquatic insects, and small molluscs collectively comprise about one-fifth of the average diet. In the
Murray River, microcrustacea contributed 55% of the diet
of juveniles and 27% of the diet of adults [115]. A similarly high contribution (35%) was reported for fish from
Cooper Creek [246]. This food source was completely
absent from, or contributed less than 1% to, the diet of
bony bream from the Burdekin River or rivers of the Wet
Tropics and Cape York Peninsula. Notably, however it was
present and relatively important in the diet of some neosilurid catfishes in the Burdekin River and its absence from
bony bream was not therefore due to an absence of this
food source from the system. It should be emphasised here
that although small amounts of Cladocera and copepods
were present in the food class collectively termed ‘microcrustacea’, this class was dominated by ostracods. The
consumption of microcrustacea therefore does not here
reflect a planktivorous feeding habitat but rather one
dominated by grazing on the benthos. This feeding strategy is in contrast to many other species of gizzard shad.
Nematalosa erebi is primarily a detritivore/algivore. The
algal contribution is dominated by microbenthic algae
such as desmids and diatoms. The contribution of detritus
to the diet, whilst certainly significant, may not be as great
as is depicted in Figure 1 due to methodological
constraints on the estimation of the relative contribution
of different food types. For example, in our analysis of the
diet of N. erebi from the Burdekin River, we did not quantitatively distinguish between detritus and microalgae.
Microalgae were present and important in these fish
however, and probably contributed about one-third of the
volume of the food class collectively termed ‘detritus’.
Kennard [697], in contrast, did distinguish between
microalgae and organic detritus in a study of fishes in
floodplain lagoons of the Normanby River and found no
contribution by microalgae to the diet. Thus some
accounts of a high contribution by organic detritus to the
diet of bony bream must be considered as indicating real
importance and may reflect the effect of habitat structure
(i.e. lagoons versus river habitats) on trophic style.
Ontogenetic variation in diet is pronounced. For example,
the greater consumption of microcrustacea by juvenile fish
compared to adults in the Murray River has already been
described above. In the Burdekin River, small N. erebi (<80
mm) fed almost exclusively on chironomid midge larvae,
and as such, were trophically similar to the juveniles of
most other species in this system. The same observation
has been recorded for bony bream in floodplain lagoons of
Cooper Creek [246].
The relative contribution of benthic microalgae to the diet
apparently varies geographically also. For example, no
algae were recorded from the diet of either adult or juvenile fish from the Murray River [115], whereas algae
contributed 10% of the diet of fish from Cooper Creek,
between 11 and 22% of the diet of fish from the Burnett
River drainage, 36% of the diet of fish from the Alligator
River, 50% of the diet of fish from the Annan River [99]
and 92% of the diet of fish from the Pilbara region [358].
A more pronounced consumption of aquatic vegetation is
an outstanding feature of the differences in trophic ecology of fishes in northern Australian compared to southern
Australia [705]. The full extent and relative importance of
detrivory and algivory in this species remains to be determined although such work, using isotopic tracing, is
underway in Cooper Creek (S. Bunn and P. Davies, pers.
comm.) and in the Border Rivers region of eastern
Queensland (Medeiros and Arthington, pers. comm.).
Until such results are known, it is probably safe to say that
at least half of the adult diet is composed of benthic
microalgae, but also that the relative importance of algae
to the diet varies between rivers and also within the riverine landscape and with ontogeny.
Nematalosa erebi is consumed by a wide variety of other
species and is probably the most frequently consumed
prey species in freshwater habitats. Herbert and Peeters
[569] suggest that N. erebi forms over 90% of the diet of
stocked barramundi in Lake Tinaroo on the upper Barron
River. Nematalosa erebi are also consumed in large
numbers by piscivorous birds such as cormorants and
pelicans [1167]. Bony bream are an important component
of aquatic food webs as their consumption by high trophic
level consumers results in very rapid transmission of
aquatic primary production (microalgae) and of terrestrial primary production (organic detritus) through the
aquatic food web. In addition, bony bream have been
suggested to be able to elevate nutrient levels in impoundments [569], presumably by increasing the resuspension
of organic sediment and attached nutrients during feeding
or by faecal liberation. This species may therefore potentially alter the trophic status of an impoundment if
biomass is high. In riverine systems, the movement of large
schools of bony bream may result in substantial export or
import of nutrients.
100
Nematalosa erebi
mortality. Further, the apparent intolerance of bony bream
to low pH, suggests that floodplain developments that
disturb potential acid sulphate soils are likely to negatively
impact on this species.
Conservation status, threats and management
Nematalosa erebi is listed as Non-Threatened by Wager
and Jackson [1353]. Given its wide distribution and generally high abundance, it is probably secure. However, river
regulation does impact on abundance levels and possibly
also on recruitment processes [435] and some aspects of
water resource management may therefore threaten this
species. Nematalosa erebi is a widespread, mobile, highly
abundant consumer, trophically located near the base of
the riverine food web. As such, it is ecologically very
important. By virtue of its detrivorous and algivorous
habits and the fact that it forms the principal prey species
for many piscivorous fishes, N. erebi is an important
component of the aquatic food web and in the transfer of
energy and carbon between trophic levels. As such,
impacts on abundance and population size structure may
have far reaching effects for entire aquatic systems.
Declines in the abundance of this species would, in all likelihood, foreshadow or even cause major changes in the
abundance of other aquatic organisms.
Movement is an integral part of the biology of this species.
The imposition of barriers in the riverine landscape may
prevent fish from tracking resources, accessing spawning
areas or replenishing populations perturbed by natural or
anthropogenic disturbance. Fish passage devices such as
fish ladders obviously allow the passage of bony bream but
must allow both upstream and downstream movement,
and for the passage of individuals of all size classes, and
must be negotiable within the space of a single diurnal
period.
Further research is required to elucidate the reproductive
responses of bony bream to different flow events, particularly the mortality response of larvae to elevated flow.
From a perspective of environmental flow management, a
critical consideration is the extent to which modified flow
regimes alter the distribution and availability of food
resources, such as microcrustacea during early growth,
and organic detritus and microalgae later in life. The latter
may be highly susceptible to disturbance resulting from
the mobilisation of fine particle substrates. In addition,
increased turbidity may negatively impact on periphyton
growth, reducing the abundance of this food source.
Increased sedimentation may also reduce the quality of the
detrital food base (i.e. by smothering or dilution of
organic particles by inorganic particles).
Several aspects of its biology need consideration in any
sphere of environmental management. First, although
abundant and widely distributed, N. erebi may be negatively impacted by low water temperatures (depressing
reproduction and immune responsiveness), low oxygen
concentrations and by low pH. Hypolimnetic releases
from storages are therefore likely to have severe consequences for this species. Seasonal or diurnal oxygen depletion, such as occurs in nutrient enriched or weed infested
off-channel habitats, is also likely to lead to increased
101
Arius graeffei Kner and Steindachner, 1866
Arius leptaspis (Bleeker, 1862)
Arius midgleyi Kailola and Pierce, 1988
Fork-tailed catfish
37 188005
37 188006
37 188010
Family: Ariidae
The equation describing the relationship between length
(SL in mm) and weight (in g) for both male and female
fish from the Clarence River is: W = 2.045 x 10–6 L3.39; r2 =
0.941, p<0.001 [1141]. Bishop et al. [193] report a length
(CFL in cm)/weight (g) relationship of W = 9.21 x 10–3
L3.189; r2 = 0.98, n = 41, p<0.001. The description below is
drawn from Kailola [676]. Body robust, elongate; anterior
profile straight, moderately steep, elevated slightly before
dorsal fin; mouth moderately broad and slightly curved;
snout rounded, moderately fleshy upper lip extending
beyond mouth gape, teeth usually concealed when mouth
closed; shallow groove may be present between nostrils,
posterior nostril ovate to elliptical, anterior nostril with
flap just concealing opening; eye ovate, dorsolateral, positioned slightly anterior of middle of head. Maxillary
barbel extending past head to base of pectoral fin or just
beyond. Jaw teeth in arched curved band, fine, sharp and
depressible, arranged in six to nine irregular series, edentulous space separating each side of mandibular tooth
band. Palatal teeth villiform, patches arranged as in Figure
1. Raker-like processes on the back of all arches. Head
shield finely and somewhat sharply granulated, arranged
in series along each side of dorsomedian groove, radiating
outward and over occipital process; shield beginning over
Description
Ariidae is a large family of mostly marine catfishes. Six
species (Arius graeffei, A. leptaspis, A. midgleyi, A. berneyi
(Whitley, 1941), Arius paucus Kailola, 2000 and Cinetodus
froggatti Ramsay and Ogilby, 1866) regularly occur in
freshwaters of northern Australia [52, 675]. Only the first
three species are treated here. Arius leptaspis does not
occur in easterly flowing rivers of northern Australia but is
included here because separation of these species has
proved difficult in the past. The descriptions below are
most comprehensive for A. graeffei and A. midgleyi as these
species are more likely to be encountered in the area
covered by this book and because descriptions of A.
leptaspis have in the past been contaminated by inclusion
of other species within the series examined [676, 1304].
Arius graeffei
Dorsal fin: I, 7; Pectoral: I, 10–11; Anal: 15–19; Caudal fin:
15 (7+8) primary rays; Gill rakers on first arch: 17–22, 6–8
on upper limb; Free vertebrae: 45–48. Figure: composite,
drawn from photographs of specimens 250–350 mm SL,
Burdekin River; drawn 2002.
Arius graeffei is a medium to large-sized catfish, commonly
reaching 350 mm SL, occasionally to 600 mm [52, 676].
102
Arius graeffei, Arius leptaspis, Arius midgleyi
before base of occipital process. Pelvic fin shape variable as
in A. graeffei. Colour in life: dorsal surface dark grey, blackish or coppery-brown, becoming paler ventrally, series of
vertical rows of golden dots often present on upper flanks.
Medial and pelvic fins often with a white margin. Colour
in preservative: similar but vertical rows of dots greatly
subdued [52, 676, 677, 936].
middle of eye. Dorsal and pectoral spines thick, with
pattern of longitudinal striae, posterior margin of dorsal
spine usually smooth, occasionally with low serrae near
tip; pelvic spines stoutly serrate on posterior margin.
Pelvic fin shape variable; in males base narrow, fin rays
rarely reaching anal fin origin; in females, base broad,
inner elements become thickened and develop a pad or
hook with sexual maturity, fin rays frequently reaching
fourth to sixth anal ray. Colour in life: dark brown, deepblue, fawn or dark ochre above, becoming yellowish-cream
or white on undersides, occasionally stippled on belly.
Maxillary barbels black or dark brown, mental barbels
dark or pale. Piebalding or blotching and albinism have
been reported [936]. Colour in preservative: similar but
blue and irridescence lost.
Arius midgleyi
Dorsal fin: I, 7; Pectoral: I, 9–11; Anal: 16–19; Gill rakers
on first arch: 15–17; Gill rakers on last arch: 16–19; Free
vertebrae: 47–50 [675, 677].
Arius midgleyi is a large catfish that may reach 1.3 or 1.4 m
in length and 28 kg in weight but is usually <500mm SL
[52, 677, 697]. The description below is drawn entirely
from Kailola and Pierce [677]. Body sleek and robust,
rather compressed, tapering posteriorly. Snout broad and
truncate, lateral head profile triangular and narrow,
predorsal flat, interorbital region flat. Mouth broad,
curved; lips thin at front of jaws and thick at corners; teeth
in upper jaw either not or partly visible when mouth
closed although often just visible at sides of mouth.
Nostrils ovate, placed well forward, anterior nostril
directly before or slightly lateral to posterior nostril, on
which skin flap just conceals opening. Eye rounded to
oblong, dorsolaterally placed, visible when viewed from
above. Barbels thin and tapered, maxillary barbel reaching
just beyond head to pectoral fin base (16–25% SL). Jaw
teeth small, sharp and depressible, embedded in tissue,
arranged in irregular series (16–24 in upper jaw, 10–15 in
lower jaw); lower jaw band separated by narrow edentulous space at symphysis. Palatal tooth patches arrayed as in
Figure 1. Gill rakers rigid and sharp tipped, as long as gill
filaments. Raker-like process absent from posterior face of
first arch and usually second arch; 11–17 on rear of third
arch; low thick pad of tissue usually present on posterior
face of second arch but absent from all others. Head shield
usually concealed by tissue in small fish and often in larger
fish also; when exposed, shield very granular, extending
forward to above eye, to origin of gill opening and over
occipital process. Dorsomedial head groove distinct, long
and lanceolate. Numerous fine papillae distributed on
snout, anterior two-thirds of head and occasionally on
breast. Dorsal and pectoral spines sharp, moderately to
very thick, anterior border roughened by granules and low
dentae; posterior border of dorsal spine with no or few
serrae, when present restricted to upper half. Pectoral
spine with up to 20 short, saw-like serrae on posterior
margin. Sexual difference in pelvic fins as described above.
Colour in life: highly variable, perhaps relative to habitat
and locality; dorsal surface ochre, brown, olive-brown, or
smokey to dark blue, grading abruptly to white or cream
Figure 1. Palatal tooth patch arrangement. Redrawn after
Allen [34].
Arius leptaspis Dorsal fin: I, 7; Pectoral: I, 9–11; Anal:
16–20; Gill rakers on first arch: 13–22 [52, 676].
Arius leptaspis is a medium to large-sized catfish,
commonly reaching 350 mm SL, occasionally to 600 mm
[52, 193]. The equation describing the relationship
between length (CFL in cm) and weight (W in g) is W =
1.46 x 10–2 L3.1; r2 = 0.966, n = 740, p<0.001 [193]. Body
robust, elongate; anterior profile straight, moderately
steep, elevated slightly before dorsal fin; snout rounded,
head not greatly flattened, mouth moderately broad and
curved; moderately fleshy upper lip extending just beyond
mouth gape. Maxillary barbel extending well past head,
often beyond base of pectoral fin, 22–51% of SL [677].
Palatal teeth villiform, patches arranged as in Figure 1.
Raker-like processes not present on the back of all arches.
Head shield extensive and finely granulated, occipital
process broad, dorsomedian groove terminating well
103
Freshwater Fishes of North-Eastern Australia
described as Hexanematichthys leptaspis by Bleeker in 1862
[200] from material collected in southern New Guinea but
was later placed within Arius by Paxton et al. [1042]. All
references to this species east of the Great Dividing Range
are apparently attributable to A. graeffei [1142].
ventrally. Pectoral and pelvic fins dark above, pale below;
anal fin brown or bluish-brown, sometimes with white
margins. Maxillary barbels dark, mental barbels pale.
Piebalding sometimes observed. Colour in preservative: as
above except pale ventral surface tends to a fawn colour.
Fins and barbels as in life except blue fades to dark brown.
Arius midgleyi was described by Kailola and Pierce in 1988
[677] from material collected across a range of rivers from
the Fitzroy River in Western Australia to the Flinders and
Mitchell Rivers of the Gulf of Carpentaria region. Hamar
Midgley first recognised the existence of this species and
referred to it as ‘shovel nosed catfish’ in his reports on the
freshwater fishes of northern Australia [944, 945, 946].
Arius midgleyi is similar to A. leptaspis and many of the
specimens included in the series used by Taylor [1304] to
describe A. leptaspis from the Arnhem Land region were
the former species [677]. In addition, specimens of A.
graeffei were also included in the series used by Taylor to
represent A. leptaspis [676]. Taylor [1304] believed that A.
graeffei and A. leptaspis represented a single species; a
suggestion refuted by Kailola [676]. Material from the
Flinders River within the type series of A. midgleyi was
recently found to contain yet another species, A. paucus
[675].
Arius midgleyi is most similar to A. leptaspis but is easily
distinguished by differences in size (A. midgleyi is larger),
relative size of barbels (shorter in A. midgleyi), head shape
(square in A. midgleyi), head width (narrower in A. midgleyi) and head shield (described above).
Systematics
Ariidae is a large, circum-globally distributed, tropical and
subtropical, family of fishes, commonly referred to as sea
catfishes, containing approximately 80 species within
about 14 genera [37, 52, 677]. The family has a long history
of occupation of freshwater environments: fossil ariids
appear in North American Eocene freshwater deposits
[1413]. Arius contains more than 40 species, of which
about 18 species occur in freshwater habitats of Australia
and New Guinea [52, 677].
Arius was first formally described by Valenciennes in 1840
[677] although Taylor [1304] suggests that the genus had
been described previously by Lacépède in 1803 as
Tachysurus (type species T. sinensis) based on a Chinese
painting of an unknown catfish. Wheeler and Baddockway
[1376] showed that Tachysurus is of uncertain status but
definitely not an ariid catfish. Kailola and Pierce [677]
suggested that division of Arius into distinct subgenera is
probably warranted.
Arius paucus is very similar to A. midgleyi, differing only in
the number of gill rakers on the first arch (10–11 versus
15–17 in A. midgleyi), the number of rakers on the last
arch (11–14 versus 16–19 in A. midgleyi) and the size of
the eye (8.9–15.3% of HL versus 12.9–21.8% of HL in A.
midgleyi).
Distribution and abundance
Arius graeffei
This species occurs in New Guinea and Australia and is
widely distributed across northern and south-eastern
Australia, extending from the Ashburton River in the
Pilbara region of Western Australia to the Hunter River in
New South Wales [52, 676]. The southern limit of this
species may have contracted recently as A. graeffei has not
been recorded from the Hunter River in recent years [553]
and is uncommon in the Richmond and Clarence rivers
(0.6% of total catch for the North Coast region) [553]
despite once being common [1140].
The nomenclatural history of the three species covered
here is complex. Arius graeffei was described in 1867 from
material collected in Samoa (location doubtful) in 1866
[725] but the name was rarely used and became replaced
by A. australis, described by Günther in the same year
[486] from material collected in the Hunter River of New
South Wales. Notably, it no longer seems to occur in this
river. Castelnau also described this species as A. curtisii in
1878 from material collected in the Moreton Bay region of
Queensland [284]. Kailola [676] resolved the nomeclatural problem, reinstating A. graeffei as the valid name and
demoting A. australis and A. curtisii to junior synonym
status. Reference to this species under the names
Tachysurus graeffei, Netuma australis, Neoarius curtisii,
Neoarius australis and Pararius graeffei may be found also
[1042]. An extra ‘i’ is frequently seen in misspellings of the
species epithet.
Records of A. graeffei in rivers draining to the southern
portion of the Gulf of Carpentaria region are remarkably
scant, being limited to the Flinders River [676]. Whether
this represents a real disjunction in distribution (this
species is present in Arnhem Land [676, 1304]), or reflects
the limited survey work undertaken in the area, is unclear.
This species was not recorded from the Gilbert River in
recent research [643]. Arius graeffei has been recorded
from the Mitchell (including its tributary systems the
The nomenclatural history of A. leptaspis is less torturous;
however the name has frequently been given in error to
eastern populations of A. graeffei. This species was first
104
Arius graeffei, Arius leptaspis, Arius midgleyi
The distribution of A. leptaspis in Queensland is patchy
and somewhat restricted. This species has been recorded
from the Flinders and Norman rivers of the Gulf region
[979] and the Mitchell, Coleman, Archer, Embley,
Wenlock, Ducie and Jardine rivers [41, 356, 571, 1349]. It
does not occur west of the Great Dividing Range and early
records of its presence here are attributable to A. graeffei.
Palmer and Walsh rivers), Coleman, Chapman, Archer,
Watson, Embley, Wenlock, Ducie and Jardine rivers of
western Cape York Peninsula [41, 356, 571, 643, 676, 1186,
1349].
Despite apparently occurring in rivers of the east coast of
Queensland [52], there are no reliable literature accounts
of its presence in any rivers from Cape York Peninsula to
the Burdekin River region with the exception of a single
record for the estuarine portion of the Barron River in the
Wet Tropics region [1187]. Halliday et al. [501] report the
presence of sea catfishes in the bycatch of several fisheries
operating in the Wet Tropics region but did not identify
which species were involved. This species has been
recorded from the Haughton River [255] and from several
locations in the lower Burdekin and Bowen rivers [586,
591, 847, 940, 1046, 1098]. Arius graeffei apparently once
occurred in floodplain lagoons of this catchment [847] but
no longer does so ([1046], C. Perna, pers. comm.). It may
no longer occur upstream of the Collinsville Weir in the
Bowen River [591, 956] despite having once occurred there
[940]. This species comprised <0.1% and 3.2% of the total
seine- and gill-netting catches in a study undertaken in the
Burdekin River over the period 1989–1992.
Arius midgleyi
This species is reported to occur in southern New Guinea
and northern Australia [52] but Kailola [675] states that it
is endemic to Australia. The Australian distribution
extends seemingly continuously from the Fitzroy River in
the Kimberley region of western Australia to the Calvert
River near the Northern Territory–Queensland border
[677]. This species is listed as rare in the Robertson and
Calvert rivers [677], both of which drain into the southwestern portion of the Gulf of Carpentaria. Kailola and
Pierce [677] intimate that A. midgleyi is present but rare in
drainages between Arnhem Land and the Flinders River,
but provide no locality information. It is important to
note that Kailola [675] believed that the distribution of A.
midgleyi and A. paucus were clearly disjunct, with the latter
occurring eastward of and including the Roper River and
including all rivers draining into the Gulf of Carpentaria.
However, the material forming the type series contained
very little material from Cape York Peninsula and the
references cited by Kailola [675] to support statements
about the distributional limits of A. paucus do not specifically include surveys undertaken in this region. Whilst
acknowledging the fact that A. paucus may extend eastward into rivers of Cape York Peninsula, we feel it prudent
to retain the name A. midgleyi for this taxon in this discussion until further evidence to the contrary becomes available.
Arius graeffei occurs in the Pioneer River [1081], and is
common and widely distributed in the Fitzroy River Basin,
Queensland. Berghuis and Long [160] recorded it from
eight of 11 primary study sites and two of eight secondary
sites, and it was the second most abundant species (after
N. erebi) in gill-netting catches. Midgley found this species
at nine of 15 sites in the river where its abundance varied
between common and abundant [942]. The distribution
of A. graeffei in the Fitzroy River Basin includes the Fitzroy,
McKenzie, Don, Dawson, Isaac and Connors rivers and
Princhester Creek [160, 659, 740, 942, 1274].
Arius midgleyi is widely distributed north of the Flinders
River in westerly flowing rivers of Cape York Peninsula
occurring in the Gilbert, Staaten, Mitchell (including its
tributaries the Lynd, Walsh and Palmer rivers), Edward,
Coleman, Holroyd and Archer rivers [571, 643, 677, 1186,
1349].
South of the Fitzroy River, A. graeffei has been recorded
from the Boyne [1349], Kolan [232, 1349], Burnett [11,
102, 1173, 1276], Isis [1305], Mary [159, 643, 847, 1349],
Noosa [1349], Brisbane [662, 1349] and Logan-Albert
rivers [1349]. This species also occurs on Fraser Island [77].
Arius leptaspis
This species occurs in northern Australia and southern
New Guinea [52]. In north-western Australia, the distribution of this species extends from the King River in
Western Australia through to the Northern
Territory–Queensland border [193, 944, 945, 1304]. Arius
leptaspis is widely distributed in the Alligator Rivers region
occurring at 20/26 sites regularly examined by Bishop et
al. [193]. Notably, A. graeffei was infrequently collected in
this study and was restricted to the Nourlangie Creek
system.
Arius midgleyi occurs in only two easterly flowing rivers of
Cape York Peninsula, the Olive River [571] and the
Normanby River [697, 1099, 1349]. Both rivers are notable
for the number of species present that are more typical of
rivers west of the Great Dividing Range. This species is
common in the Normanby River, contributing almost
40% to the total gill-net catch, and occurs in both floodplain lagoons and the main river channel [697].
All three ariid catfishes discussed here appear to have
disjunct or patchy distributions across the southern
105
Freshwater Fishes of North-Eastern Australia
was about 100 m wide, a maximum of 4 m deep, with a
current velocity of about 0.25 m.sec–1, with abundant
macrophyte growth in shallow areas and a dominant
substrate of fine silt. Greatest densities were recorded from
a shallow (1–2 m) backwater area with much reduced flow,
rocky substratum and little aquatic vegetation. Allen et al.
[52] suggest that brooding male A. midgleyi prefer areas of
deep water.
portion of the Gulf of Carpentaria region, in common
with a moderate number (10–13) of other species [41].
Allen and Hoese [41] speculated that this disjunction may
be a result of lower contemporary winter temperatures
relative to more northern rivers and a substantial
predicted drop in temperature during the Pleistocene.
Kailola and Pierce [677] believed that the observed distribution pattern may equally be due to inadequate sampling
effort in the region, but acknowledged that climate change
during the Pleistocene may have contributed to presentday patterns of distribution.
It is not uncommon for the three species of Arius to occur
in the same river (see Distribution section) and at least A.
leptaspis and A. midgleyi frequently occur in the same
habitat [944, 946]. Kailola and Pierce [677] suggest that A.
midgleyi may be more typical of upstream reaches and is
displaced upstream by A. leptaspis or A. graeffei. Allen et al.
[52] also state that A. midgleyi is common in upstream
reaches. Further examination of this suggestion may
provide some insight into the factors that determine abundance and distribution of these species. Comparison of
patterns of macrohabitat distribution in the Normanby
River, which contains A. midgleyi only, with those in the
Mitchell River, which contains all three species, may prove
fruitful.
Macro/meso/microhabitat use
Both Arius graeffei and A. leptaspis are reported to occur in
freshwater and estuarine habitats [52] whereas A. midgleyi
is an exclusively freshwater species occasionally occurring
near the upper tidal limit [677]. Arius graeffei may penetrate into marine waters also [52, 284, 676]. Bishop et al.
[193] report that A. leptaspis in the Alligator Rivers Region
was common or moderately common in floodplain, corridor and muddy lowland lagoons but only occasionally
occurred in perennial escarpment and sandy creek habitats. This species was widespread occurring in 20 of 26
regularly sampled study sites. Weak ontogenetic variation
in habitat use was also reported for juvenile A. leptaspis
with a shift from lowland muddy lagoons to floodplain
lagoons and then corridor lagoons with increasing size
[193]. Arius graeffei in contrast, occurred only in muddy
lowland and corridor lagoons and was uncommon.
Environmental tolerances
Data listed in Table 1 represent the range of ambient water
quality conditions in which these catfishes occur. As such
they should not be construed as representing upper and
lower tolerance limits.
The temperature ranges reported here are indicative of
tropical or subtropical conditions. The minimum value
reported here of 20.9°C for A. graeffei is lower than the
22–23°C lower limit suggested responsible for determining
the distributional limits for many species in the southern
portion of the Gulf of Carpentaria region [41]. Moreover,
winter water temperatures in the Clarence River, where A.
graeffei is reportedly common, descend as low as 15–16°C
[1140]. Juvenile A. graeffei are reported to withstand
temperatures as low as 10°C [936] but the lower temperature limits for A. leptaspis and A. midgleyi are unknown.
Kailola and Pierce [676] believed them to be lower than
22–23°C. Low winter temperatures may play some role in
determining distribution for although these catfish species
may be able to tolerate temperatures of 20–23°C, they may
not be able to breed at these temperatures.
The use of off-channel floodplain habitats seems typical of
the three catfishes as A. midgleyi has been recorded from
such habitats also [697]. The early-dry season population
of A. midgleyi in floodplain lagoons of the Normanby
River was dominated by fish between 200–300mm SL
[697]. Such fish are probably transitional between 0+ and
1+ year classes [677] and are most likely to have invaded
such habitats when water levels were high.
Elsewhere A. midgleyi has been reported from fast-flowing
rivers, billabongs, creeks, deep pools and desiccating
waterholes [677]. This species reportedly does well in
impoundments. Kailola and Pierce [677] remark that it is
rarely numerically dominant except in impounded waters
such as Lake Argyle on the Ord River, where it makes up
about 70% of the catfish population. Arius graeffei also
does well in impoundments in Queensland [1081]. Arius
graeffei and A. leptaspis have also been reported from a
similarly wide array of habitat types [586, 591, 940, 944,
946, 1046, 1098, 1140].
The dissolved oxygen concentrations listed in Table 1 are
indicative of fairly well-oxygenated waters although
hypoxic conditions may be present, especially at depth, in
floodplain habitats in which A. graeffei, A. leptaspis and A.
midgleyi occur. Arius leptaspis has been recorded in fish
kills for which low dissolved oxygen levels (<0.1 mg.L–1)
were implicated as a major cause [187].
Rimmer [1140] noted that A. graeffei was widespread in the
lower Clarence River of northern New South Wales. The
river where Rimmer undertook his study on reproduction
106
Arius graeffei, Arius leptaspis, Arius midgleyi
Table 1. Physicochemical data for Arius graeffei, A. leptaspis
and A. midgleyi. The summary provided for A. graeffei is based
on a single study undertaken in Burdekin River [1098], those
for A. leptaspis are based on two studies undertaken in the
Northern Territory [193, 944] and those for A. midgleyi are
based on two studies (data combined) undertaken in rivers of
the Northern Territory [944, 946], a study in the Normanby
River [1093] and a study undertaken in floodplain lagoons of
the Normanby River [697]. Note that the units used to
quantify water clarity differ between studies.
Parameter
Min.
Max.
Mean
31
6.5
7.0
160
190
29.3
5.3
6.6
117
33
9.4
7.8
463
2.6
26.9
7.7
7.3
196
1.7
The three ariid catfishes discussed here appear to be tolerant of a moderate range of pH values although riverine
populations tend to occur in neutral to slightly basic
waters on average. Floodplain populations of A. leptaspis
and A. midgleyi may tolerate slightly acidic conditions.
Arius graeffei occurs in slightly acidic waters on Fraser
Island [77]. Overall, these species appear to tolerate a
range of pH.
The conductivity values presented in Table 1 are all indicative of freshwaters. However, A. leptaspis and A. graeffei
have both been recorded from brackish estuaries or estuaries and near shore marine habitats, respectively [52,
356], and are therefore able to withstand more saline
conditions than reported here. All three species tolerate a
range in water clarity, although data presented in Table 1
indicate a preference for clear waters.
Arius graeffei
Alligator Rivers region
Temperature (°C)
28
Dissolved oxygen (mg.L–1)
4.4
pH
6.1
Conductivity (µS.cm–1)
10
Secchi depth (cm)
15
Burdekin River ( n = 9)
Temperature (°C)
20.9
Dissolved oxygen (mg.L–1)
10.8
pH
8.2
Conductivity (µS.cm–1)
790
Turbidity (NTU)
5.4
Reproduction
Ariid catfishes exhibit a high degree of parental care of
their young: the eggs and larvae are incubated in the
buccal cavity of the male [1143]. The eggs are large (>10
mm) and relatively few in number (Table 2), traits that are
typical of species exhibiting parental care. Reproductive
investment (in terms of GSI values) is low in A. leptaspis
but higher in A. graeffei from the Clarence River as a result
of relatively greater fecundity (Table 2). The significance
of this difference is unclear.
Arius leptaspis
Alligator Rivers region (n = ?)
Temperature (°C)
26
34
Dissolved oxygen (mg.L–1)
0.1
9.7
pH
4.8
9.1
Conductivity (µS.cm–1)
4
478
Secchi depth (cm)
1
360
Roper River (n = 4)
Temperature (°C)
25
29
Dissolved oxygen (mg.L–1)
6.0
6.7
pH
7.2
8.2
Conductivity (µS.cm–1)
Secchi depth (cm)
400
50
30.3
5.8
6.1
24.9
7.9
6.7
117.5
2.35
Prior to incubation, the epithelium of the buccal cavity,
particularly that covering the palatal tooth patches, grows
rapidly and thickens greatly, presumably to protect the
eggs. In addition, epithelial structures associated with
mucus production increase in number and activity and
serum immunoglobulins become detectable in the mucus:
both changes may confer some protective function for the
incubating eggs [1143]. Feeding ceases in males during
incubation. In many female ariids, including those
discussed here, the pelvic fin becomes enlarged and thickened in the period leading up to spawning [1143]. Rimmer
and Merrick [1143] cite several early studies in which it
was believed that these structures function either to hold
the eggs after they are extruded and prior to being taken
into the buccal cavity by the male, or they function as
‘claspers’ enabling the copulating fishes to remain in very
close proximity. The exact means by which the eggs are
fertilised prior to buccal incubation has not been
observed.
26.3
3.8
7.3
297.9
12.8
Gonadal enlargement is rapid in A. graeffei from the
Clarence River and occurs within a rapidly short period
(September to November): the spawning season appears
to be similarly contracted (November to December) and
synchronised year-to-year [1140]. Gonad development in
76
26
6.4
7.8
170
Arius midgleyi
Roper and Victoria rivers (n = 17)
Temperature (°C)
23
29
Dissolved oxygen (mg.L–1)
3.0
9.5
pH
7.0
8.7
Conductivity (µS.cm–1)
Secchi depth (cm)
50
500
Normanby River (n = 4)
Temperature (°C)
24
26
Dissolved oxygen (mg.L–1)
7.2
9.2
pH
6.2
7.16
Conductivity (µS.cm–1)
92
150
Turbidity (NTU)
0.1
5.4
Normanby River floodplain (n = 15)
Temperature (°C)
22.9
33.4
Dissolved oxygen (mg.L–1)
1.1
7.1
pH
6.0
9.1
Conductivity (µS.cm–1)
81
412
Turbidity (NTU)
2.1
120
25.8
7.2
8.1
242
107
Freshwater Fishes of North-Eastern Australia
A. leptaspis from the Alligator Rivers region [193] occurs
over a similarly well-defined period but peak GSI values
differed in incidence from year-to-year. Spawning may be
more protracted than that seen in A. graeffei however
[193]. Arius midgleyi may breed slightly earlier than A.
leptaspis or A. graeffei. In Lake Argyle on the Ord River,
stage II to IV and stage V females of A. midgleyi are present
in July and September, respectively [677]. Kailola and
Pierce [677] cite a personal communication from Hamar
Midgley that early breeding may occur in rivers also. Arius
midgleyi is reported to have a faster growth rate than other
northern ariid catfishes and may reach 200–300 mm in
length in the first year. All three species breed prior to the
onset of the wet season, perhaps stimulated by increasing
temperature and daylength, and this may allow young to
take advantage of the enhanced production, particularly
of small fish species, that occurs during the wet season. A
slightly earlier spawning season and faster growth may
enable A. midgleyi to predate other sympatric ariid species
as well as other fish species.
small-scale movement to deeper water during the incubation phase [677]. However, the fact that Kennard [697]
collected large numbers of individuals in floodplain habitats of the Normanby River soon after the cessation of the
wet season suggests that this species undertakes extensive
lateral (and probably longitudinal) movements onto the
floodplain during periods of floodplain inundation.
Moreover, movement appears to be an integral component
of the life history of other ariid catfishes [1143] and particularly of A. graeffei. This species is frequently recorded in
fishway studies and is often dominant in such studies [11,
157, 158, 159, 232, 740, 1173, 1274, 1276, 1305].
Upstream movement by A. graeffei through the fishway on
the Fitzroy River barrage occurs over a wide range of
conditions and throughout the year [1274]. Water temperature range from 18–29°C but fish mostly moved when
water temperatures exceeded 23°C and very large numbers
(>1000 fish.day–1) were observed in the fishway when
water temperature exceeded 27°C. This species migrated
upstream over a wide range of discharge (18–195 757
ML.day–1) but highest numbers were recorded at times of
low flow (1% exceedance). Stuart [1274] estimated that up
to 12.2 t of A. graeffei moved through the Fitzroy River
fishway per month and that the highest capture rates coincided with the highest tides for each month. This species
used the fishway more at night than during the day and
smaller fish were less able to ascend the fishway than larger
fish. An earlier study on this structure also reported that
upstream migration occurred throughout the year but was
greatly reduced in July/August [740].
The exact location of spawning is unknown for these ariid
species although males are reported to congregate in
deeper water during incubation. Spawning behaviour
remains undescribed but vigorous pursuit of males by
females has been reported for a related species [1143].
Coates [314] reported that an observed positive relationship between egg size and female length, and of embryo
size and male length, in New Guinean ariid catfishes, was
suggestive of non-random mating and positive assortment
on the basis of size. This seems plausible given that only
large males could accommodate very large egg masses
within their buccal cavities.
A similar study in the Burnett River revealed that A. graeffei ascended the fishway located on the tidal barrage from
January to May over a temperature range of 29°C to 22°C,
respectively, and over a range of discharge from 0 to 300
ML (mean daily flow averaged over each month). Peak
numbers were recorded in May. Fish descended the fishway over the same period [1173]. Further upstream, A.
graeffei also migrated up the fishway on the Ben Anderson
Weir [1276]. They did so over a range of flow conditions
(1–94% exceedance flows) but mostly during times of low
flow. It migrated throughout the year except in the coldest
months, July and August.
The eggs and developing young are held within the
distended male buccal cavity for an extended period: the
young to hatch at an advanced state of development with a
functional alimentary canal and feeding structures [193,
1142]. Feeding on plankton while in the parent’s mouth
commences shortly after hatching; the observation that A.
graeffei juveniles increase in weight by 20% in the interval
between hatching and the cessation of buccal incubation
suggests that substantial feeding occurs during this phase.
Hatching difficulties under in vitro culture conditions
associated with herniation of the chorion have been
reported to lead to high mortality (up to 90%) for A.
leptaspis [936] and A. graeffei [1142] but have not been
observed in naturally incubated embryos [1142] possibly
because the male frequently churns the eggs within the
buccal cavity at the time of hatching [1144].
Upstream movement of A. graeffei of between 200–350
mm length (but dominated by fish between 200–250 mm)
through the fishway on the Kolan River barrage was
attempted mostly in spring and summer over a range of
conditions [232]. A weak positive relationship between
discharge and movement was recorded (r2 = 0.103,
p<0.05), however, this relationship was dominated by two
large peaks in movement recorded at flows of 200 and
5500 ML.day–1. Ignoring these two events, more fish
moved at times of low flow.
Movement
The limited information available on the biology of A.
midgleyi does not suggest extensive migration other than
108
Arius graeffei, Arius leptaspis, Arius midgleyi
Table 2. Life history information for three species of ariid catfish. Summary information for A. graeffei is based on Rimmer [1140,
1141] and Bishop et al. [193], that for A. leptaspis is based on Bishop et al. [193], and that for A. midgleyi on Kailola and Pierce
[677] unless otherwise noted.
Age at sexual maturity (months)
A. leptaspis – 24 months
A. midgleyi – 36 months (estimate only)
Minimum length of ripe females (mm)
A. graeffei – 280–285 mm (length at first maturity, i.e. 50% of population mature)
A.leptaspis – 300 mm (length at first maturity, i.e. 50% of population mature)
A. midgleyi – 500 mm
Minimum length of ripe males (mm)
A. graeffei – 270–275 mm (LFM)
A.leptaspis – 270 mm CFL (LFM), some precocious males 187–240 mm CFL
Longevity (years)
A. leptaspis – possibly up to 5 years
Sex ratio
A. graeffei – 1:0.82, males in excess
A.leptaspis – generally 1:1, although males or females in excess on occasions
Peak spawning activity
A. graeffei – November, peak in GSI values pronounced, late wet/early dry season in
Northern Territory
A. leptaspis – late dry/early wet season, precedes flooding
A. midgleyi – September–October (estimate only)
Critical temperature for spawning
A. graeffei – 26°C
A. leptaspis – 26°C [936]
Inducement to spawning
A. graeffei – possibly temperature and increasing photoperiod (>13.7 h)
A. leptaspis – ?, not cued by flooding
Mean GSI of ripe females (%)
A. graeffei – 12–16%
A. leptaspis – 4.3 ± 2.6% (SD)
Mean GSI of ripe males (%)
A. graeffei – 0.28% maximum
A. leptaspis – <1%
Fecundity (number of ova)
A. graeffei – 40–122, average 70.5. Brood size 1–83
A. leptaspis – 26–70, average 42. Average brood size 28
A. midgleyi – 100–180, possibly as high as 400
Fecundity/length relationship
A. graeffei – F = 0.478 (SL in mm) – 81.6; n = 40, r = 0.89, p<0.001
Egg size (mm)
A. graeffei – 11–13.7 mm, average 12.2 mm, fertilised eggs 12.3–15.2 mm
A. leptaspis – 11.9–15.7 mm, average 13.8 mm
A. midgleyi – 10 mm
Frequency of spawning
A. graeffei – spawning season short, females total spawners
A. leptaspis – spawning season may be protracted
Oviposition and spawning site
A. leptaspis – unknown but ripe fish found in most lagoon habitats
Spawning migration
A. graeffei – may move into deeper water to breed
A. leptaspis - ?
A. midgleyi – may move into deeper water to breed or incubate
Parental care
A. graeffei – buccal incubation and extensive parental care
A. leptaspis – buccal incubation and extensive parental care
A. midgleyi – buccal incubation and extensive parental care
Time to hatching
A. graeffei – 4–5 weeks
A. leptaspis – 4 weeks, 2–4 weeks at 32°C [936]
Length at hatching (mm)
A. graeffei – 20–27 mm TL
A. leptaspis – 24 mm CFL, juveniles up to 60 mm CFL remain in buccal cavity
A. midgleyi – ?
Length at feeding
A. graeffei – shortly after hatching 20–27 mm TL
Age at first feeding
A. graeffei - feeding occurs shortly after hatching [1143]
A. leptaspis – feeding occurs shortly after hatching [1143]
Age at loss of yolk sac
A. graeffei – 6–8 weeks
A. leptaspis – 6–8 weeks [936]
Duration of larval development
A. graeffei – 6–8 weeks
A. leptaspis – 6–8 weeks [936]
Length at metamorphosis (mm)
A. graeffei – 50 mm
A. leptaspis – 50–60 mm
109
Freshwater Fishes of North-Eastern Australia
A consistent observation in the fishway studies cited above
is that the number of fish able to reach the top of the fishway is lower than the number entering at the bottom, and
that only the largest fish appear to be able to ascend these
structures [11, 232, 1274, 1276]. Despite the presence of
fishways on some tidal barrages and weirs, catfish migrations are impeded in some rivers [157, 1305]. A common
feature of almost all fishway studies, with the exception of
Russell [1173], is that they provide information on
upstream movement only. Complementary information
on the reproductive status of migrating fishes is rarely
gathered and there is limited potential to examine why fish
are migrating.
A. graeffei (juveniles) n = 186
Fish (4%)
Microcrustaceans (14%)
Unidentified (34%)
Macrocrustaceans (10%)
Terrestrial invertebrates (5%)
Other macroinvertbrates (25%)
Detritus (3%)
Aquatic macrophytes (5%)
Filamentous algae (1%)
A. graeffei (adults) n = 116
Fish (12.4%)
Unidentified (27%)
Macrocrustaceans (17.2%)
Rimmer [1140] cites studies [403] suggesting that estuarine or near-shore marine populations of A. graeffei
migrate upstream into freshwaters to spawn. The fishway
studies cited above contain many fishes that are, judging
by their size, large enough to reproduce. However, the fact
that migrations occur over a much longer time frame than
the short spawning period reported by Rimmer [1140]
indicates that some impetus other than reproduction
stimulates movement.
Molluscs (0.5%)
Terrestrial invertebrates (9.4%)
Aquatic insects (6.4%)
Filamentous algae (11.6%)
Aquatic macrophytes (3.8%)
Terrestrial vegetation (10.4%)
Detritus (1.4%)
A. leptaspis n = 633
Fish (15.3%)
Unidentified (26.4%)
Macrocrustaceans (13.5%)
Arius leptaspis has not been recorded from fishways and
little is known of its movement biology except that that it
disperse widely in the Alligator Rivers region [193]. Given
that this species occurs in estuarine habitats, there is probably significant movement between this habitat and
upstream areas.
Terrestrial invertebrates (6.2%)
Terrestrial vertebrates (1.3%)
Aquatic insects (20.7%)
Filamentous algae (1%)
Terrestrial vegetation (12.4%)
Detritus (0.9%)
Aquatic macrophytes (2.4%)
A. midgleyi n = 109
Trophic ecology
Information on the trophic ecology of A. graeffei, A.
leptaspis and A. midgleyi is drawn from several sources.
Sumpton and Greenwood [1279] examined the diet of
juvenile (<100 cm TL) A. graeffei in the estuary of the
Logan-Albert River. These data and dietary information
from studies undertaken in the Barker-Barambah system,
a tributary of the Burnett River, (n = 53) [1080], the
Burdekin River (n = 25) [1093] and Nourlangie Creek, in
the Alligator Rivers region (n = 38) [193] were used to
summarise the adult diet. Information on the diet of A.
leptaspis was sourced entirely from Bishop et al. [193].
Information on the diet of A. midgleyi included data from
riverine (n = 8) [1099] and floodplain lagoon populations
(n = 101) [697] of the Normanby River.
Unidentified (11.9%)
Terrestrial invertebrates (16%)
Fish (47%)
Terrestrial vertebrates (3%)
Macrocrustaceans (8.3%)
Terrestrial vegetation (4.9%)
Detritus (1.4%)
Aquatic macrophytes (1.4%)
Filamentous algae (1.4%)
Aquatic insects (4.3%)
Figure 2. The average diet of three species of fork-tailed
catfish. See text for data sources.
that piscivory is acquired early in life. Plant material is only
a minor component of the diet, as are terrestrial insects.
The diet is notable for its diversity, including plant, invertebrate and vertebrate food, the diversity of feeding styles
employed and the wide array of habitats from which it is
procured (i.e. benthos, water column and water surface).
Juvenile A. graeffei in estuarine reaches of the LoganAlbert River consume a wide variety of food types, but
particularly polychaete worms (expressed as other
macroinvertebrates in Figure 2). Planktonic microcrustacea and shrimps and prawns were also important, collectively comprising 39% of the total diet. Although fish were
only a minor component of the diet it is interesting to note
The diet of adult A. graeffei is similarly diverse but differs
from that of juveniles by an increased consumption of fish,
plant matter (both aquatic and terrestrial), macrocrustacea and terrestrial invertebrates. Such changes are not
110
Arius graeffei, Arius leptaspis, Arius midgleyi
unusual for northern Australian fishes of large size.
Geographic differences in diet were moderately large,
involving differences in the relative importance of particular food types and changes in foraging style. For example,
A. graeffei from Barker-Barambah Creek consumed
macrophytes and algae (8% and 24%, respectively)
whereas these food types were absent from, or contributed
less than 3% to, the diet of fish from the Burdekin River
[1093] or the Alligator Rivers region [193]. Similarly,
terrestrial vegetation was either absent from, or unimportant (<5%) in, the diet except in those fish from the
Alligator Rivers region where this food type contributed
22% to the total. Fish were a minor component of the diet
of fish from Barker-Barambah Creek (5%) but important
in the Burdekin River and the Alligator Rivers region (12%
and 22%, respectively). Macrocrustacea varied similarly in
importance (5%, 39.5% and 19.6% for Barker-Barambah
Creek, the Burdekin River and the Alligator Rivers region,
respectively).
of these species ensures that most populations are secure.
Some authors have expressed concern about the impact of
dams and weirs on populations of A. graeffei in south-eastern Queensland [157, 1305] and despite their abundance
in fishway structures, smaller size classes appear less able
to negotiate these structures [11, 232, 1274, 1276].
Dissociation of freshwater habitats from estuarine reaches
may have consequences for the maintenance of populations of A. graeffei and A. leptaspis populations in some
rivers. These species are clearly warm-water fishes:
impoundments that alter a river’s thermal regime are likely
to impact on this species, particularly those rivers in the
south-eastern portion of the range of A. graeffei where its
lower thermal tolerance may be just above winter minima.
River regulation reducing flood frequency and magnitude
and hence floodplain inundation, or restricting movement
between floodplain habitats and the main channel, is likely
to impact on this species. Degradation of floodplain habitats is highly likely to impact on these catfishes, and this
effect is already visible in the Burdekin River delta where
reductions in the extent and integrity of riparian forests
and poor water quality are correlated with the absence of
A. graeffei (C. Perna, pers. comm.).
The average diet of A. leptaspis is not greatly different from
that of A. graeffei (Fig. 2). However, comparison of the diet
of these species in the Alligator Rivers region suggests
more extensive partitioning of resources. For example, A.
leptaspis consumed more fish and macrocrustaceans, less
terrestrial plant material and more aquatic insect larvae
than did A. graeffei. Nonetheless both species are
macrophagic omnivorous feeders. The diversity of fish
species consumed by A. leptaspis is very high, including
neosilurid catfishes, Porochilus rendahli, Melanotaenia
spp., Ambassis spp., Leiopotherapon unicolor, Toxotes
chatareus, Glossogobius giuris, Hypseleotris compressa,
Oxyeleotris lineolatus, Strongylura krefftii, Nematalosa erebi
and conspecifics.
Despite the potential for water infrastructure to impact on
these catfishes, A. graeffei and A. midgleyi do well in
impounded waters, and in some circumstances, so well
that a commercial fishery is supported (e.g. Lake Argyle on
the Ord River). Elsewhere, ariid catfishes appear in the
bycatch of near-shore and estuarine fisheries and are
frequently amongst the most abundant species in the
bycatch. In a study of the effects of netting on non-target
fishes, comparison of relative abundance and biomass of
ariid catfishes revealed that although the relative abundance varied little (7.8% versus 9.7% for open and closed
rivers, respectively), ariid catfishes comprised 25% of the
biomass in rivers closed to fishing compared to 13% in
rivers open to commercial netting. Notably however the
total fish biomass in rivers open to commercial fishing was
greater (across all rivers, regions and seasons) than in
closed rivers [501].
Fish comprised about half of the diet of A. midgleyi in
both riverine and floodplain habitats of the Normanby
River (Fig. 2); a finding in close agreement with the observation by Kailola and Pierce [677] that this species is
primarily carnivorous. The remainder of the diet is dominated by terrestrial invertebrates and macrocrustacea,
supporting other observations that these items are important in the diet [677, 944]. Terrestrial vegetation, detritus
and aquatic plant matter are far less important in the diet
of A. midgleyi than in either A. leptaspis or A. graeffei.
The southern limit of the distribution of A. graeffei
appears to have contracted northward in the last two
decades and populations in northern New South Wales
appear to have declined in abundance, the reasons for
which are unclear but may signal a general decline in the
health of these rivers.
Conservation status, threats and management
Arius leptaspis, A. graeffei and A. midgleyi are all listed as
Non-Threatened [1353]. The wide northern distribution
111
Neosilurus hyrtlii Steindachner, 1867
Hyrtl’s tandan
37 192011
Family: Plotosidae
tapering posteriorly. Predorsal distance 24–30% of TL.
Dorsal spine stout, slightly curved, weakly serrated on
inside edge, occasionally serrate on both sides [1304].
Pungent spine on pectoral fins more strongly serrated on
inside edge. Dorsal profile straight or slightly convex.
Premaxilla with small sub-ovate patch of pointed teeth on
either side of the midline; palatine teeth only slightly larger
with mixed molariform and conical teeth arranged in a
small triangular patch; teeth in lower jaw conic anteriorly,
molariform posteriorly. Gill rakers on anterior face of first
arch slender; anterior face of second arch with large papillae-like rakers, broad at base grading into transverse
ridges; posterior face of first arch with two rows of papillae, the anterior row noticeably larger; transverse ridges on
posterior face of second arch and anterior face of third
arch longer than arch width, slightly overlapping the base
of the gill filaments.
Description
First dorsal fin: I, 5–6; Second dorsal and anal fins confluent with caudal fin, 115–135 rays; Pectoral: I, 10–11; Pelvic:
12–14; Gill rakers: 19–24 [34, 1304]. Figure: mature specimen 185 mm SL, upper Burdekin River, April 1995; drawn
2001.
A moderately large species of catfish, commonly reaching
300 mm SL but more commonly between 100–200 mm
SL. Largest specimen collected from the Burdekin River
was 454 mm SL [1093]. The largest specimens collected by
Bishop et al. in the Alligator Rivers region were about 400
mm TL [193]. Merrick and Schmida [936] list maximum
weight as 2.0 kg, far greater than maximum weight
recorded by us (920 g) [1093]. The relationship between
length (mm SL) and weight (g) for Neosilurus hyrtlii from
the Burdekin River is W = 4.786 x 10–6 L3.11, r2 = 0.990, n =
251, p<0.001. Sexual dimorphism is limited: females grow
to larger size than males and possess a thick and rounded
genital papilla, in contrast to a conical pointed papillae
characteristic of male fish [1030].
Colour in life: variable depending on location, age and
water clarity. Small specimens are frequently (although
not always) silver laterally with bright to dull yellow fins.
This colour form, frequently referred to as N. glencoensis,
is rarely observed in fish greater than 200 mm SL. Larger
specimens are most commonly a dark brown/grey dorsally
grading to white on ventral surface of body and head with
Head broad, slightly flattened, possessing four pairs of
barbels. Nasal barbels barely reaching beyond eye, mental
barbels reaching to gill opening. Snout obtusely pointed
and wider than long. Eye set in front half of head. Body
112
Neosilurus hyrtlii
Queensland estuaries and near-shore marine habitats. The
family contains approximately 31 species in 10 genera
[48]. Five genera occur in freshwaters of Australia:
Tandanus (2 spp. but see comments in appropriate
section); Neosiluroides (1 sp.); Anodontoglanis (1 sp.);
Porochilus (3 spp.) and Neosilurus (6 spp. although more
may be present) [48, 936, 1042]. Merrick and Schmida
[936] list nine species of undescribed Neosilurus, Allen
[34] lists three, and no undescribed species were included
in Allen et al. [52]. However, Allen et al. [52] remark that
further research on the many geographic populations of
N. hyrtlii is needed as there is a strong possibility that the
nominal species may be composed of more than one
taxon.
dorsal fin and joined dorsal/caudal/anal fin being dark
brown/black (rarely yellow). Pectoral and anal fin greyishwhite. Specimens from highly turbid waters show little
colour except a dull grey [1093]. During spawning, both
sexes are a bright silvery-white laterally and on the head,
and the fins are a bright vivid yellow [1030]. Colour in
preservative: yellow pigments typically lost, body
brown/grey to pale tan, white ventrally.
Neosilurus hyrtlii and N. ater are frequently syntopic in
many river systems and in some rivers other plotosid
catfishes may also be collected from the same habitat (i.e.
N. mollespiculum and P. rendahli in the Burdekin River).
These latter two species are easily distinguished due to
possession of unique morphological characters (see
respective chapters). Taylor [1304] provides a key distinguishing several species of neosilurid catfish and the
couplet separating N. ater and N. hyrtlii (listed as N. glencoensis) is reproduced here:
Neosilurus hyrtlii, the type species for the genus, was first
described by Steindachner in 1867 from material collected
in the Fitzroy River, Queensland [1262]. Synonyms are
numerous and include Silurichthys australis Castelnau,
1875; Neosilurus australis Castelnau, 1878; Eumeda elongata Castelanu, 1878; Neosilurus robustus Ogilby, 1908;
Copidoglanis glencoensis Rendahl, 1922 and N. mortoni
Whitley, 1941. Reference to this species under the names
N. glencoensis, Tandanus hyrtlii and T. robustus may be
found also, the former being the most common.
Second dorsal short, 24–37 rays to middle of caudal fin,
length from origin to tip of caudal fin 20–30% SL, head
length 17–21% SL, posterior face of first gill arch with two
rows of papillae, snout shorter than post-orbital length of
head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .N. hyrtlii
Second dorsal long, 39–52 rays to middle of caudal fin,
length from origin to tip of caudal fin 30–40% SL, head
length 21–25% of SL, posterior face of first gill arch with
only a single row of papillae, snout longer than post orbital
length of head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .N. ater
Distribution
Neosilurus hyrtlii is extremely widely distributed and can
attain high levels of abundance. It occurs in the Pilbara
region from the Ashburton River north [33, 936] and has
been recorded from most major rivers of the Kimberley
region (Charley, Lawley, Fitzroy, Meda, Isdell, Carson,
Berkely, King Edward, King George, Mitchell, Roe, Prince
Regent, Drysdale, Berkley and Ord rivers) [30, 45, 388,
619, 620]. This species is widely distributed in the
Northern Territory from the Daly River across to Arnhem
Land [193, 243, 772, 774, 1304].
Systematics
Plotosidae is a family of catfishes within the order
Siluriformes, a large group (~2500 spp.) of predominantly
freshwater species that occurs on all continents except
Antarctica. Other notable families within the Siluriformes
include the Bagridae, Clariidae, Loricariidae, Ariidae and
Siluridae. Some members of these families are among the
largest of freshwater fishes. The Ariidae and Plotosidae are
the only siluriforms that occur naturally in Australia or
New Guinea. The Plotosidae includes both marine/estuarine and freshwater forms and is distributed in the IndoWest Pacific from Japan to Australia and east to Fiji [52].
Generic boundaries and affinities remain obscure [48] and
the family is currently being revised. Marine forms are
distinguished by the presence of a dendritic organ
protruding from behind the anus. This organ is also present in one genus of New Guinean freshwater plotosid
(Oloplotosus). Australian and New Guinean genera tend to
be restricted to freshwater. Plotosus is an exception, with
three species occurring in estuarine or marine waters and
one species (P. papuensis Weber) occurring in freshwater.
Plotosus lineatus (striped catfish) is common in
Bishop et al. [193], in their extensive study of the fish
fauna of the Alligator Rivers region, found that N. hyrtlii
was widespread and abundant, occurring in escarpment
pools and streams (3/10 sites), lowland sandy creek-bed
pools (1/7 sites), back flow billabongs (10/11 sites), corridor billabongs (2/7 sites) and floodplain billabongs (2/6
sites) and contributing 11.4, 0.3, 1.3, 0.1 and 0.1% of the
total number of fish collected from these sites, respectively.
Over the period of the study, N. hyrtlii contributed 3.2%
of the total number of fish collected. Overall, it was present in all major habitat types in this region but was abundant only in escarpment habitats and in these habitats,
abundant only in the early and late dry seasons when
escarpment habitats function as important dry season
refugia. Woodland and Ward [1416] recorded N. hyrtlii
(grouped with N. ater and possibly P. rendahli as ‘plotosid
113
Freshwater Fishes of North-Eastern Australia
Tully, Maria and Herbert river drainages [583, 584, 585,
599, 643, 1085, 1087, 1096, 1179, 1184, 1187, 1349]. This
species rarely achieves high levels of abundance in these
systems however. For example, it was ranked 51st of more
than 60 species in the extensive survey of Pusey and
Kennard (comprising only 0.01% of the total number of
fish collected) [1085] and was ranked 18th and 27th in the
South Johnstone and Mulgrave rivers, respectively, where
it contributed 0.1% of the collective total from these rivers
[1096]. Neosilurus hyrtlii has also been recorded from
floodplain lagoons in the Wet Tropics region [585, 1131].
catfishes’) as moderately abundant in isolated pools in
Magela Creek. The presence of this species was persistent
through time as the pools contracted during the dry
season, and unlike some other species, local extinctions of
this species were not observed.
Castelnau [287] included Plotosus elongatus among the
fauna of the Norman River in the Gulf of Carpentaria
region. Castelnau had previously used this name for
Tandanus tandanus, however [283], a species not found in
the Gulf region. From his description, it is most likely that
he was alluding to N. hyrtlii and N. ater. We have recorded
this species from Gunpowder Creek, a tributary of the
Leichhardt River [1093]. Neosilurus hyrtlii is widely
distributed in drainages entering the Gulf of Carpentaria
[34].
Further to the south, N. hyrtlii occurs in the Black-Alice
[176, 1349], Ross [1030] and Burdekin rivers [1098]. In a
three-year study (1989–1992), this species contributed
6.1%, 1.0% and 2.9% of electrofishing, seine-netting and
gill-netting catches and was the 5th, 6th and 6th most
abundant species, respectively [1098]. It is widespread in
this river system, being recorded from the main channel,
upstream and downstream of the Burdekin River Falls; in
the northern tributary streams, such as Keelbottom Creek,
Fanning River, Star River and Running River; as well as the
turbid south-western tributaries such as the Belyando
River [256, 260, 1098, 1349, 1408] and floodplain lagoons
of the delta area (C. Perna, pers. comm.). In the Belyando
River, N. hyrtlii was recorded from four of five sites and
comprised 37.6% of the total catch (gill-, dip- and seinenetting, fish traps and electrofishing) [256].
Neosilurus hyrtlii also occurs in the internal drainages of
central Australia and has been recorded from the
Georgina, Diamantina, Cooper, Bulloo and Finke rivers
[34, 455, 456, 457, 605, 1341, 1349]. This species occurs in
the Paroo and Warrego rivers, tributaries of the Darling
River [605, 1069, 1201] and in the Condamine River
[1069]. In a recent survey of the Cooper, Barcoo, Georgina
and Diamantina drainages, N. hyrtlii was recorded from
11 of 12 sites and comprised 17.8% of the catch from these
sites [121].
Neosilurus hyrtlii has been recorded from the Embley,
Dulhunty, Jardine, Wenlock, Archer, Edward, Holroyd,
Mitchell, Palmer and Coleman rivers and Kupandhanang
Swamp near Weipa on the western side of Cape York
Peninsula [571, 643, 991, 1349]. On the eastern side of
Cape York Peninsula, this species has been recorded from
the Olive, Lockhardt, Claudie, Stewart, Massey Creek,
Rocky, Normanby, McIvor and Endeavour drainages [571,
697, 1093]. Neosilurus hyrtlii comprised 0.8% of the electrofishing catch and 1.3% of the gill-netting catch from
floodplain lagoons of the Normanby River (being
recorded from 6 of 6 lagoons), but was more abundant in
gill-netting catches from the main river channel itself
(3.4% of catch) [697]. This species is widespread in the
Normanby River, (occurring in all 13 sites examined)
extending well upstream into the headwaters. It may
achieve greater abundances in the river channel (4.4% of
the total catch [1093]) than in floodplain lagoons [697].
This species was even more abundant in the more
ephemeral Stewart River were it comprised 8.1% of the
total fish catch and was recorded from four of five sites
[1093].
Neosilurus hyrtlii has been recorded from the Pioneer
River [1081], drainages discharging into Shoalwater Bay
[1328, 1349], most tributary systems of the Fitzroy River
(its type locality) including the highly intermittent Isaacs
River [160, 283, 284, 1093, 1274, 1349], the Burnett [205,
700, 1173, 1276], Elliot [700], Isis [700, 1305], Calliope
[915] and Kolan rivers [232, 1328], Baffle Creek [826], and
even in some freshwater lakes of Fraser Island [77]. It is
not common in these southern rivers, however. For example, N. hyrtlii comprised only 0.07% of the catch from a
total of 203 samples from 63 sites in the Burnett River
[700].
Neosilurus hyrtlii has been recorded from the Mary River
[1093, 1349] but is uncommon in this system where it was
recorded from only six of 50 locations sampled over the
period 1994–1997 (a total of 225 samples) and comprised
only 0.07% of the 83 198 fish collected. It was persistent at
those sites in which it occurred however and contributed
an average relative abundance of 1.01 ± 0.15% of the total
at these sites. Mean (±SE) and maximum densities were
0.135 ±0.029 fish.10m–2, respectively. Average and maximum biomass densities at these sites were 2.25 ± 0.45
g.10m–2 and 12.4 g.10m–2, respectively, comprising on
average, 0.23 ± 0.06% of the total biomass [1093].
Neosilurus hyrtlii is widely but patchily distributed in the
high-gradient, swiftly flowing rivers of the Wet Tropics
region, being thus far recorded from the Endeavour,
Annan, Daintree, Barron, Mulgrave/Russell, Johnstone,
114
Neosilurus hyrtlii
within a single season. Use of such habitats by small juveniles may extend over several flood events.
Despite being recorded from the Brisbane River in the past
[662], it has not been detected in a recent survey of 111
separate locations (a total of 165 samples) throughout the
catchment [704, 1093]. Similarly, it has not been detected
in recent surveys in the Albert/Logan River (68 locations,
174 samples). Thus, its southern limit on the east coast
appears to be the Mary River. It was not recorded in the
extensive surveys of the northern coastal rivers of NSW
undertaken as part of the NSW Rivers Survey [1201].
While the information presented above for the Normanby
River suggests that N. hyrtlii is more abundant in riverine
rather than off-channel lentic habitats, this species has
frequently been reported from floodplain and wetland
habitats across its range.
Neosilurus hyrtlii is a benthic species found over a wide
range of water depths and most frequently observed in
close association with the substrate. During the day, adult
N. hyrtlii tend to be confined to deeper waters (>2 m)
although when cover in the form of woody debris or
undercut banks is abundant, adult fish may be found in
much shallower waters (40–60 cm). At night, the extent of
dendency on cover is much reduced and adult N. hyrtlii
may be observed foraging over sandy open reaches as shallow as 30 cm [1093]. In the Burdekin River, very small
juveniles (<60 mm) are common in sandy glides as shallow as 5 cm. In such cases, fish are invariably sheltering
under leaf litter (often single isolated leaves), macrophytes
or mats of colonial blue-green algae (Gloeotrichia sp.).
Adult N. hyrtlii are frequently observed foraging singly at
night but just as frequently observed foraging in small
shoals. It is not uncommon when gill-netting at night to
collect 20 to 30 similarly sized individuals in one net but
few in other nets. Underwater observations by us reveal
that shoaling is very common in juvenile N. hyrtlii (<20 cm
SL). Shoals may contain up to 100 individuals (although 40
to 50 is more common) and rather than being well-coordinated cohesive groups, such shoals are best characterised as
a rolling ball of fish constantly being joined or left by individuals for varying lengths of time. Although N. hyrtlii is
occasionally recorded from reaches with coarse substrates,
it is most frequently collected from areas with a muddy or
sandy substratum. It is essentially a still-water species,
although it is capable of ascending reaches with substantial
water velocities. Its benthic habit probably ensures that
velocities experienced are much less than average water
velocities. We have observed, on one occasion, an adult N.
hyrtlii moving through a rapid/run section with an average
water velocity of about 0.5 m.sec–1. Passage was affected by
a series of short bursts between isolated woody debris or
root masses. Once such cover was accessed, the pectoral fins
were extended and apparently locked in this position,
anchoring the fish in place for several minutes, after which
another upstream sortie was made.
In summary, N. hyrtlii is extremely widely distributed and
its distribution closely matches that of other very widespread species such as L. unicolor, A. percoides and N. erebi.
Although present in the perennial rivers of the Wet Tropics
region, it is rarely abundant. Neosilurus hyrtlii achieves its
greatest abundance in more seasonal, low gradient rivers
such as the Burdekin and Normanby rivers. In part, its
distribution is probably limited by its tolerance to low
water temperatures, much the same as is reported for L.
unicolor. Herbert et al. [571] include it amongst a large
group of species from Cape York Peninsula characterised
as ‘colonising species’.
Macro/meso/microhabitat use
It should be evident from the discussion above that N.
hyrtlii occurs in a wide variety of macrohabitats ranging
from small permanent or intermittent tributary streams
through large lowland low gradient seasonal rivers of Cape
York Peninsula and central Queensland, to high gradient
perennial rivers of the Wet Tropics region, to floodplain
lagoons and wetlands typical of many rivers of northern
Australia. Thus, from a macrohabitat perspective, N. hyrtlii
makes use of virtually every aquatic habitat available
within a river with the exception of the estuarine reaches.
It also use dune lakes [77].
Habitat use varies with season and age in the Alligator
Rivers region [193]. Over all sampling occasions,
Neosilurus hyrtlii was recorded from all muddy lowland
lagoons sampled, some sandy lowland creeks, and corridor and floodplain lagoons. However, this species was
recorded from sandy creeks only during the late dry season
whereas in the late wet/early dry seasons, N. hyrtlii was
recorded from lowland lagoons, floodplain lagoons and
perennial streams of the escarpment. Juveniles were
mainly found in lowland lagoons and sandy creeks.
In contrast to the downstream and lateral movements
reported by Bishop et al. [193], Orr and Milward [1030]
reported upstream spawning migrations of N. hyrtlii in
Campus Creek, a tributary of the Ross River, Townsville.
Use of such habitats by adult fishes is transitory and
limited to the spawning period, however, several spawning
runs associated with separate flood events may occur
Environmental tolerances
Experimental data concerning the environmental tolerances of this species are lacking. Data presented in Table 1
are derived from field studies and represent the range of
conditions in which N. hyrtlii has been found.
115
Freshwater Fishes of North-Eastern Australia
be more tolerant of lower temperatures as winter temperatures as low as 8°C have been recorded in the Finke River
[767]. Northern populations may not tolerate temperatures below 20°C. Low water temperatures probably play
an important role in limiting the southern distribution of
N. hyrtlii.
Neosilurus hyrtlii occurs predominantly in warm waters as
would be expected given its distribution. The maximum
water temperature in which N. hyrtlii has been recorded is
38°C (waterholes of Cooper Creek) [121] and similarly
high temperatures (36°C) have been recorded in the
Alligator Rivers region (Table 1). This species clearly tolerates temperatures in the mid-30s for extended periods.
Neosilurus hyrtlii is found over a wide range of dissolved
oxygen (DO) levels. The average dissolved oxygen concentration in the three lotic studies included above (Cape York
Peninsula, Burdekin River and Mary River) are all close to
saturation and range from 7.5 to 8.7 mg O2.L–1. In contrast
the remaining studies listed in Table 1 (Alligator Rivers
region and Normanby River floodplain lagoons) dealt
largely or entirely with lentic habitats and it can be seen
that average dissolved oxygen levels experienced by N.
hyrtlii in such habitats are substantially lower and on occasions very much lower (<1.2 mg O2.L–1). Hogan and
Graham [583] recorded N. hyrtlii in a lagoon of the Tully
floodplain in which DO was as low as 0.35 mg O2.L–1.
Perna (pers. comm.) recorded N. hyrtlii in floodplain
lagoons of the Burdekin River delta in which average DO
levels were 42% saturation but for which occasional minimum saturation levels plummeted to 0.2%. From these
data it is obvious that N. hyrtlii is tolerant of hypoxic
conditions. Nonetheless, Bishop [187] recorded N. hyrtlii
(as Neosilurus sp. B) among the dead in a large fish kill for
which hypoxia was suggested to be the primary cause. The
effects on growth and reproduction that might arise from
long-term exposure to levels of between 1.5–3.5 mg O2.L–1
or whether such profoundly depressed DO levels are inimical to eggs, larvae and small juveniles are unknown. Given
that reproduction in many areas appears concentrated in
seasonally flowing streams, it is probable that these early
life stages are intolerant of grossly depressed dissolved
oxygen levels. Johnson [666] reported large fish kills
involving N. hyrtlii in inland Queensland waters in the first
two decades of the 20th century. Such kills were invariably
associated with the winter low-flow period and Johnson
attributed the cause of these kills to infection by the fungal
pathogen Saprolegnia. It is probable that low water
temperatures and the poor water quality (particularly low
dissolved oxygen) existing at the time and remarked upon
by Johnson [666] were also important.
With the exception of the Mary River, minimum water
temperatures in sites in which it has been recorded are
between 21 and 23°C. The minimum temperature
recorded for the Mary River population is much lower
than this, as is the average temperature in this river. It is
likely that 12°C closely approximates the lower limit for
this species, although populations in inland drainages may
Table 1. Physicochemical data for Hyrtl’s tandan Neosilurus
hyrtlii. Turbidity values are listed as NTU except for the
Alligator Rivers region (ARR) where they are listed as Secchi
disc depths in cm. Data listed for the ARR were from readings
taken from the bottom of the water column. Elsewhere, they
are derived from the midpoint of the water column. n refers
to the number of samples.
Parameter
Min.
Max.
Alligator Rivers region [193]
Temperature (°C)
23
36
Dissolved oxygen (mg.L–1)
1.0
9.7
pH
5.2
7.3
Conductivity (µS.cm–1)
4
620
Turbidity (cm)
1
170
Cape York Peninsula (n = 8) [1093]
Temperature (°C)
21
28
Dissolved oxygen (mg.L–1)
7.3
11.2
pH
6.55
8.35
Conductivity (µS.cm–1)
75
420
Turbidity (NTU)
0.4
5.4
Mean
29.4
3.7
6.0
31
24.7
8.7
7.28
157.8
1.9
Normanby River floodplain lagoons (n = 6) [697]
Temperature (°C)
22.9
33.4
26.2
Dissolved oxygen (mg.L–1)
1.1
7.1
3.52
pH
6.0
9.1
7.06
Conductivity (µS.cm–1)
81
412
192
Turbidity (NTU)
2.1
120
15.5
Burdekin River (n = 33) [1080]
Temperature (°C)
21
33
Dissolved oxygen (mg.L–1)
2.6
11.0
pH
6.76
8.46
Conductivity (µS.cm–1)
56
790
Turbidity (NTU)
0.25
16.0
25.5
7.50
7.74
430.3
3.2
Mary River (n = 21) [1093]
Temperature (°C)
12.8
32.2
Dissolved oxygen (mg.L–1)
5.2
11.4
pH
7.0
8.67
Conductivity (µS.cm–1)
123
1855
Turbidity (NTU)
1.5
15
19.4
8.02
7.93
817.7
5.7
Neosilurus hyrtlii has been recorded from a wide range of
water acidity (5.2–9.1 pH units), although the pH range
within studies is considerably smaller (average range = 2.07
units) (Table 1). The greatest pH range reported in Table 1
(3.1 pH units) was recorded in studies in which floodplain
lagoons were the dominant habitat type sampled.
Neosilurus hyrtlii occurs over a wide range of water
conductivity: 4–1855 µS.cm–1; it should be considered a
freshwater species. Given that it lacks a dendritic organ to
116
Neosilurus hyrtlii
are known. Bishop et al. [193] found that length at first
maturity (the size at which 50% of the sample were
mature) was 135 mm for both male and female fish, and
that no fish below 130 mm with gonads at or greater than
stage III were present in the population. These authors
cautioned that very few fish in their sample possessed
gonads at a state of development greater than stage III.
Similarly, only 15% of a sample of 288 N. hyrtlii from the
Burdekin River possessed gonads at a state of development
of stage IV or greater [1093]. The minimum size of stage III
fish from the Burdekin River was 91 and 118 mm SL for
male and female fish, respectively. Minimum sizes for stage
V fish were 124 and 120 mm SL for male and female fish,
respectively. Sexual maturity is reached at a relatively small
size, probably at about 12 months of age. However, Orr and
Milward [1030], in their study of spawning and migration
behaviour in a tributary of the Ross River, found that
actively spawning fish were larger (and probably older)
allow osmoregulation in saline environments, it is unlikely
to tolerate conductivities in excess of 4000 µS.cm–1 for
prolonged periods.
A substantial range (0.25–120 NTU) in water clarity is
characteristic of the habitats in which N. hyrtlii occur.
Burrows et al. [256] recorded this species from the
Belyando River in which turbidity was as high as 581 NTU
and remains so for extended periods of time. Its nocturnal
habitat and possession of barbels to facilitate prey detection probably enable N. hyrtlii to forage effectively in habitats of low light availability due to elevated levels of
suspended inorganic material. The tolerance of eggs and
early life history stages to high levels of suspended sediment is unknown.
Reproduction
The reproductive biology of Neosilurus hyrtlii has not been
studied in great detail although some of the key elements
Table 2. Life history information for Neosilurus hyrtlii. Data listed are drawn primarily from a medium-term study undertaken in
the Alligator Rivers region of the Northern Territory [193], a medium term study of changes in population size structure in the
Burdekin River [1093], and a short-term study undertaken in a tributary of the Ross River in northern Queensland [1030].
Information about larval development is based on material identified to genus only, as spawning aggregations observed by Orr
and Milward contained both N. hyrtlii and N. ater. It is assumed here that early development in both species is identical.
Age at sexual maturity (months)
12 months (?)
Minimum length of ripe females (mm)
LFM = 135 mm (median length of mature fish) [193]
Minimum length of ripe males (mm)
LFM = 135 [193]
Longevity (years)
five years (?)
Sex ratio (female to male)
1:1 occasional excess of females after spawning season [193]
Occurrence of ripe fish
Stage IV in late wet to late dry, stage V early wet [193]; stage V in November [1093]
Peak spawning activity
Start of the wet season [193, 1030]
Critical temperature for spawning
Unknown but likely to be >25°C
Inducement to spawning
Rising water levels
Mean GSI of ripe females (%)
19.1% [1030], 3.6 ± 3.4% [193]
Mean GSI of ripe males (%)
Unknown
Fecundity (number of ova)
3630 eggs in one female 205 mm TL
Fecundity /length relationship
?
Egg size (mm)
1.3 ± 0.9 mm intraovarian [193], 2.6 mm water-hardened [1030]
Frequency of spawning
Unknown, may be several spawning events in one season but unknown whether single
individual spawns more than once [1030]
Oviposition and spawning site
Tributary streams [1030, 1093], spawning sites unknown in Alligator Rivers region,
gravel beds suggested to be important [193]
Spawning migration
Upstream [1030]
Parental care
None
Time to hatching
60 hours at 26–27°C [1030]
Length at hatching (mm)
5.7–6.0 mm [1030]
Length at free swimming stage
?
Length at metamorphosis (mm)
25 mm [1030]
Duration of larval development
28 days [1030]
Age at loss of yolk sack
?
Age at first feeding
?
117
Freshwater Fishes of North-Eastern Australia
reported that one female, of 205 mm TL with a GSI of
10.1%, contained an estimated 3630 eggs with an average
diameter of 1.3 mm. Water-hardened eggs are reportedly
much larger: 2.6 mm [1030]. The eggs are non-adhesive
and strongly demersal and rapidly settle amongst the
interstices of the sediment probably preventing downstream removal in the current. Egg density in the sediment
has been estimated at 2000 eggs.m-2 [1030].
than indicated above. Male fish were 170–220 mm in
length whereas female fish were 200–300 mm [1030]. The
minimum size of stage VI male N. hyrtlii in the Burdekin
River was 217 mm SL whereas the minimum size of stage
V females was 433 mm SL [1093]. Admittedly, the sample
sizes used here are very small (n = 2 for males and n = 3
for females), but collectively these data suggest that
although sexual maturation may occur in the first year,
reproduction, especially in female N. hyrtlii may be
delayed until the second year. Although ageing studies
have not been undertaken for this species, the large size
attained suggests by N. hyrtlii suggests it may live for up to
five years.
Embryonic development is rapid with hatching occurring
after about 60 hours at 26–27°C [1030]. Gastrulation
occurs 10 hours after fertilisation, myomeres and optic
vesicles are recognisable after 30 hours; heart, otic capsules
and lenses after 40 hours. The larvae are 5.7–6 mm long at
hatching and poorly developed. The medial finfold is present but the eyes are unpigmented. Barbel development
occurs 48 hours post-hatching and is complete after 10
days. Fin rays appear after 4–6 days and full fin development is complete after 28 days. The yolk is completely
absorbed after 10 days post-hatch. Metamorphosis is
complete at 25 mm length and the adult form attained
after six weeks [1030].
Spawning occurs during the summer wet season. Orr and
Milward [1030] reported several different spawning events
associated with individual flood events. It was not known
whether individual fish participated in more than one
spawning event. Gonad recrudescence in the Alligator
Rivers region commences in the late dry season (stage IV
fish present) [193]. In the Burdekin River, stage IV fish
(and greater) were present in November samples only and
absent from samples collected in May (although some
apparently spent males were present in May of one year)
[1093].
25
Beumer [176] suggested that Neosilurus spp. are dependent on increases in water level, with accompanying
changes in turbidity and temperature, to stimulate spawning. Migration and spawning are clearly linked to flooding
in north-eastern Australia [1030, 1093]. The extent to
which temperature influences spawning is questionable,
although it probably plays an important role in stimulating gonad recrudescence. Water temperature tends to
decrease during floods [1093] and is thus not likely to be a
useful cue for reproduction. However, unseasonal floods
are not uncommon across this species’ range, and may
stimulate mass migrations akin to that seen during the
spawning period [1030]. It would be instructive to know
whether rising water levels outside the summer period also
stimulate spawning and whether temperature plays some
role in determining whether spawning occurs during such
‘false runs’.
20
15
10
5
0
Standard Length (mm)
Figure 1. Size structure of Neosilurus hyrtlii populations in the
main channel of the upper Burdekin River (closed bars, n =
151) and in tributary streams of the upper Burdekin River
(open bars, n = 79).
The available information on the extent of reproductive
investment is conflicting. Bishop et al. [193] report mean
female GSI values during the spawning season of only 3.6
± 3.4% (n = 6) whereas Orr and Milward [1030] report a
mean female GSI of 19% (n = 8). This disparity can probably be reconciled by the fact that running ripe fish were
not present in the Alligator Rivers sample whereas Orr and
Milward’s sample was derived from a spawning aggregation and presumably contained stage VI fish only.
Fecundity data are lacking except Bishop et al. [193]
Movement
In the Alligator Rivers region of the Northern Territory,
substantial movements between different types of habitat
occurs (see section on macrohabitat use) but given that
Bishop et al. [193] were unable to identify spawning sites,
it is not known which movements are associated with
reproduction. This species was rarely observed migrating
118
Neosilurus hyrtlii
en masse in this region [190] as observed in north-eastern
Australia. In the Ross River near Townsville, adult fish
migrate upstream into small intermittent tributaries
[1030]. In the upper Burdekin River (i.e. above the
Burdekin Falls Dam), the great majority of small juveniles
collected over the period 1989–1992 were from tributary
streams such as Keelbottom Creek and the Fanning River
(Figure 1), suggesting that N. hyrtlii makes upstream
spawning migrations in this system also. The general
paucity of fish greater than 80 mm in length in these tributary streams suggests that dispersal from the natal to the
adult habitat occurs in the first year. The abrupt decrease in
the number of fish greater than this length in tributary
streams, coupled with the similarly abrupt increase in representation by fish greater than 80 mm SL in the main channel, suggests that emigration occurs either over a relatively
short time period or that it occurs over a narrow size range.
Queensland. These include: Arthington et al. [98] (n = 28,
Herbert and Tully rivers); Hortle and Pearson [599] (n =
1, Annan River); Pusey et al. [1097] (n = 10, Mulgrave and
Johnstone rivers); Pusey et al. [1099] (n = 36, Pascoe,
Stewart and Normanby rivers of Cape York Peninsula);
Kennard [697] (n = 32, floodplain lagoons of the
Normanby River); Bishop et al. [193] (n = 187, Alligator
rivers region); and Pusey et al. [1093] (n = 202, Burdekin
River). The latter two studies included data from both wet
and dry seasons, whereas the remainder were confined to
the dry season only.
Molluscs (6.3%)
Unidentified (18.3%)
Microcrustaceans (13.7%)
Stuart’s [1274] study of fish movements through the fishway located on the Fitzroy River barrage found that N.
hyrtlii (and P. rendahli) only contributed a very small
proportion of the fishes moving through this structure
(124 of a total of 23 000). Other studies of fishways located
on tidal barrages have also found N. hyrtlii to be a minor
component of the fauna using such structures [1173,
1276], probably because N. hyrtlii tends not to occur in
estuarine or tidal reaches. Nonetheless, these studies have
revealed significant insight into movement biology of this
species. For example, small fish seem equally able to ascend
fishways under most flow conditions as do larger fish
[1274, 1276]. However, small fish (<150 mm TL) moved
upstream during periods of low flow only (18 ML.day-1),
whereas larger fish moved upstream under a wider array of
flow conditions. Ascent occurred predominantly at night.
Very few fish moved through the Fitzroy River fishway
outside the period November to March (peak in January)
[1274]. Similarly most movement through the Ben
Anderson Barrage on the Burnett River occurred in spring
and early summer: no movement occurred in March, April,
July or August [1276]. No movement in the Fitzroy River
was recorded when water temperatures were below 22°C
[1274], whereas movement in the Burnett River occurred
over the range of 15–25°C [1276].
Detritus (15.0%)
Terrestrial invertebrates (1.0%)
Aerial aquatic insects (1.0%)
Aquatic macrophytes (1.0%)
Aquatic insects (44.3%)
Figure 2. The average diet of Neosilurus hyrtlii. Summary
based on gut contents analysis of 496 individuals derived
from seven separate studies (see text).
The average diet of N. hyrtlii is dominated by aquatic
invertebrates, principally chironomid larvae, trichopteran
larvae and ephemeropteran nymphs. Detritus comprised
15% of the diet. Microcrustacea were an important
component of the diet, comprising 14% of the total.
Molluscs (both bivalves and gastropods) were also important. The diet depicted in Figure 2 suggests a benthic feeding habit consistent with its body morphology. However,
the presence of terrestrial invertebrates and the adult
forms of aquatic insects suggests that it may occasionally
forage at the water’s surface.
There is substantial geographic variation in diet. For
example, the contribution of detritus to the diet ranged
from 0% in the Herbert/Tully River sample to 65.2% in
the sample from floodplain lagoons of the Normanby
River. Detritus was present but unimportant (3.3%) in the
diet of riverine fish of Cape York Peninsula. This difference may reflect the different availability and quality of
food sources in lentic and lotic environments. However,
the diet of Northern Territory fish, containing many individuals from lowland muddy lagoons also, did not contain
detritus to any significant degree (1%). These fish, in
contrast, consumed appreciable amounts of microcrustaceans (20.6% - principally Cladocera). Microcrustaceans
Huey [605] recently examined dispersal by N. hyrtlii in the
dryland Warrego River and Cooper Creek using electrophoretic and DNA sequencing techniques. Substantial
levels of gene flow within catchments but not between
catchments was detected suggesting that juveniles did not
disperse very widely during periods of flood.
Trophic ecology
Information on the diet of N. hyrtlii is available from seven
separate studies, six of which were conducted in
119
Freshwater Fishes of North-Eastern Australia
by large predatory fish such as barramundi, fork-tailed
catfish and tarpon [697].
contributed only 3.3% of the total diet of N. hyrtlii from
lagoons of the Normanby River. Microcrustaceans were
almost absent from riverine samples of this region (1.1%),
yet contributed 14% of the diet of N. hyrtlii from the
Burdekin River. Cladocera were present but relatively
unimportant and the bulk of this prey class for these fish
was composed of benthic ostracods.
Conservation status, threats and management
Neosilurus hyrtlii is listed as Non-Threatened by Wager
and Jackson[1353]. Given its wide distribution and generally high abundance, this species is probably secure and
likely to remain so in the future. However, it should be
recognised that the wide distribution of this species may
be partly artefactual, obscuring the existence of more
narrowly distributed, undescribed taxa that may be of
greater conservation significance. Genetic studies may
help to resolve this uncertainty. The limited data available
suggests that movement is an important feature of the
biology of this species and access to tributary streams
appears to be important for reproduction, in north-eastern populations at least. Accordingly, the development of
water infrastructure that inhibits upstream movement, or
which captures high flow events and therefore removes the
probable stimulus for spawning migrations, is likely to
negatively impact on this species. Finally, the ecology of
this species is not well understood. For example, the information concerning reproduction is limited as is information on the movement biology of this species. Effective
management is hampered by these knowledge deficits.
Small bivalve molluscs were present in the diet of N. hyrtlii
from the Burdekin River (11.4%), lagoons of the
Normanby River (4.9%), the Mulgrave/Johnstone rivers
(3.2%) and the Herbert/Tully River (2%). Small
gastropods contributed more than 1% of the diet only in
the Mulgrave/Johnstone River (25.3%) and Normanby
River lagoons (8.6%).
Overall, the diet of N. hyrtlii is composed primarily of
very small prey items such as chironomid and
trichopteran larvae, Cladocera, ostracods and detritus.
Larger prey such as fish or macrocrustaceans were
absent from the diet. This species forages on much
smaller prey than might be expected on the basis of body
and mouth size [1097, 1099] and the extent of ontogenetic variation in diet is not great as a consequence
[1099]. Such a diet is not unexpected for a nocturnally
feeding benthic species. Neosilurus hyrtlii is preyed upon
120
Neosilurus ater (Perugia, 1894)
Black catfish, Butter Jew, Narrow-fronted tandan
37 192009
Family: Plotosidae
extending to or almost to base of caudal rays; canals of
head opening through a moderate number of pores; a
cluster of about 5–25 temporal pores between eyes, axillary pore present. Premaxilla with a small rectangular
patch of tiny pointed teeth on each side of midline; teeth
on palate about four times as large, with rounded crowns,
arranged in a large semicircular to triangular, posteriorly
truncated patch. Teeth in lower jaw pointed anteriorly,
molariform posteriorly. Maxillary and nasal barbels reaching to or very slightly behind eye; outer mental barbel
longest, extending to base of pectoral fin. Slender gill
rakers present on anterior faces of first and second arches,
those of first arch about half length of gill filaments, those
of second arch shorter, about as long as arch width; posterior face of first arch with a row of enlarged papillae along
anterior edge; posterior faces of second to fourth arches
and the anterior face of third to fifth arches with transverse, low, adnate, opposing ridges [34, 52, 1304].
Description
First dorsal fin: I, 5–7; Second dorsal fin and anal fin
confluent with caudal fin; Upper procurrent dorsal rays:
39–52; Anal plus lower caudal rays: 84–103; Pectoral: I,
1–13; Pelvic: 12–15, outer ray simple or very shallowly
branched; Gill rakers: 24–30, 18–23 on lower limb [34, 52].
Figure: mature specimen, 202 mm SL, upper Burdekin
River, April 1995; drawn 2002.
A large catfish commonly reaching 400 mm in length, but
more commonly around 250 mm. Allen et al. [52] list a
maximum length of 470 mm, Bishop et al. [193] list 508
mm TL as maximum size in the Alligator Rivers region,
and we have recorded one individual in the Burdekin River
of 700 mm SL [1093]. The relationship between weight (in
g) and length (TL in cm) for N. ater from the Alligator
Rivers region is W = 7.3 x 10–3 L3.04; r2 = 0.947, n = 106,
p<0.001. The relationship between weight (g) and length
(SL in mm) for N. ater from the Burdekin River is W =
5.07 x 10-6 L3.109; r2 = 0.99, n =224, p<0.001. Note the differences in unit length.
Colour in life: usually mottled grey to black, often
yellow/tan ventrally in region between head and origin of
anal fin. During spawning the colour of this region may
intensify to an intense orange/gold [1030]. Colour in
preservative: almost uniformly brown to black, sometimes
mottled.
Post-orbital length of head markedly shorter than snout
length; head length 21–25% of SL. Second dorsal fin
long, length from origin to tip 30–40% SL. Lateral line
121
Freshwater Fishes of North-Eastern Australia
ater to be present in four of six lagoons examined and both
main channel sites located on the Normanby River, where
it comprised 1.2% and 0.6% of the electrofishing catch
and 0.3% and 1.5% of the gill-netting catch, respectively.
Systematics
Neosilurus ater was originally described as Lambertia atra
by Perugia in 1894, from material collected in Inawi, Papua
New Guinea. Formal placement within Neosilurus as N.
ater was by Weber and de Beaufort in 1913 [1372]. This
species has also been described as N. mediobarbis by
Ogilby in 1908 [1017]. No other synonyms are known but
reference to this species as Lambertichthys ater [1398] or
Tandanus ater [1304] may be found.
Neosilurus ater is similarly widespread in the Wet Tropics
region although apparently patchily distributed in the
northern section of the region. This species has been
recorded from the Daintree River [643, 1085, 1185], being
present in four of 15 sites surveyed by Russell et al. [1185],
but is apparently absent from the Mossman and Mowbray
rivers and Saltwater Creek to the immediate south [1185].
This species is widespread and abundant in the Barron
River being recorded from over half of all sites surveyed
[1187], including those upstream of the Barron Falls. Its
presence upstream of the Falls is probably due to translocation [1186] although separation of the upper Mitchell
and Barron rivers is topographically minor and anecdotal
accounts of connection during periods of extremely high
rainfall exist [229]. Whether interbasin movement occurs
at these times is unknown. Neosilurus ater is present in the
following drainages: Mulgrave River (20/45 sites) [1184],
Johnstone River (6/73 sites) [1177], Liverpool Creek (6/29
sites), Maria Creek (2/17) and Hull River (1/5) [1179],
Moresby River (3/17 sites) [1183], the Tully/Murray rivers
[585, 1085], and Herbert River (7/11 wetland sites) [584,
643]. It is not overly abundant and is limited to lowland
reaches of these rivers. The abundance of this species may
be underestimated if daytime electrofishing is the sole
means of sampling. Recent studies examining the trophic
ecology of lowland fishes of the Mulgrave River have
revealed N. ater to be abundant and dominant in nocturnal gill-net catches (T. Rayner, pers. comm.).
Distribution and abundance
Neosilurus ater occurs in northern Australia and southern
Papua New Guinea and Irian Jaya [36, 42, 52, 576].
Although recorded as present in the Sepik River in northern New Guinea [316], a subsequent taxonomic survey of
this river did not include N. ater [46]. This species is very
patchily distributed in the Kimberley region, being
recorded from the Lawley, King Edward, Carson and
Drysdale rivers only [620], but its distribution across the
Northern Territory appears to be continuous [193, 772,
774, 1304], extending to some of the larger off-shore
islands [1353].
With the exception of the Gregory River [643] there are
very few records of N. ater in rivers draining into the
southern portion of the Gulf of Carpentaria. Further to
the east, N. ater has been recorded from the Mitchell River
[571, 643] and is widespread in this system, being recorded
from its major tributaries the Walsh and Palmer rivers
[571] and extending up into the headwaters [1186]. This
species has also been recorded from the Coleman, Archer,
Holroyd, Wenlock and Jardine rivers [41, 571] and
Kupandhanang Swamp near Weipa [571] on the western
side of Cape York Peninsula. Whether the absence of N.
ater from Gulf rivers between the Mitchell and Gregory
rivers represents a real and significant disjunction in
distribution, or is simply due to inadequate sampling,
remains to be demonstrated. However, given the widespread distribution detailed here, it is most probable that
the distribution of N. ater is continuous across most of
northern Australia.
Beumer [176] recorded a number of species of neosilurid
catfishes from the Black-Alice River north of Townsville
but did not distinguish between species. There is little
doubt that N. ater was one of the species recorded in this
river. It has been recorded from the Ross River also [1030].
Neosilurus ater is both widespread and abundant in the
Burdekin River, having been recorded from every major
tributary system (i.e. Cape/Campaspe, Belyando/Suttor,
Broken/Bowen) [256, 586, 591, 1098], from the headwaters
to the freshwater/estuarine interface, including wetlands
of the Burdekin River delta (C. Perna, pers. comm.) and
Baratta Creek [1045]. In a three-year study of the fishes of
the Burdekin River [1098], this species was the seventh
most frequently collected species in gill-netting catches
and 13th most frequently collected species in both electrofishing and seine-netting catches. In another study in
that drainage but restricted to the Belyando/Suttor River,
N. ater comprised 2.5% of the total number of fishes
collected by a range of methods including gill-, seine- and
dip-netting, traps and electrofishing [256].
The distribution of N. ater in rivers of north-eastern
Queensland is nearly continuous from the Claudie River
of Cape York Peninsula, south to the Pioneer River. This
species has been recorded from the Claudie, Lockhart,
Pascoe, Stewart, Rocky, Starke, McIvor, Normanby,
Endeavour and Annan rivers [571, 599, 697, 974, 1099,
1223] as well as a number of small creek systems such as
Harmer, Black, Massey and Scrubby creeks [571]. It is
notable that N. ater has been recorded from dystrophic
dunelake systems (both Shelburne Bay and Cape Flattery)
[571, 1101]. In a study of the fish fauna of floodplain
lagoons of the Normanby River, Kennard [697] found N.
122
Neosilurus ater
be observed foraging over sandy open reaches as shallow
as 30 cm. Adult N. ater are frequently observed foraging
singly at night but just as frequently are observed foraging
in small shoals. It is not uncommon when gill-netting at
night to collect 20–30 similarly-sized individuals in one
net but few in other nets. Although occasionally recorded
from reaches with coarse substrates, this species is most
frequently collected from areas with a muddy or sandy
substratum. It is essentially an inhabitant of still to slowlyflowing waters, although it is capable of ascending reaches
with substantial water velocities. Its benthic habit probably ensures that focal velocities experienced are much less
than average water velocities. Woody debris and undercut
banks provide important daytime cover for N. ater and it
is unusual to observe this species not in association with
such microhabitat elements. Juvenile N. ater make use of
smaller cover elements such as leaf litter or aquatic macrophytes.
The southern range limit of N. ater is the Pioneer River
[1081]. It has not been collected from the Fitzroy or the
Burnett rivers despite extensive survey and fishway work
in these rivers.
Macro/meso/microhabitat use
From the discussion above, it should be evident that N.
ater inhabits a wide array of aquatic habitats ranging from
acidic, dystrophic lakes, through to large rivers and their
floodplain wetlands. It has been recorded from small
permanent tributary streams [41] and intermittent tributary streams [1030]. In the latter case, use of such streams
is restricted in adult fishes to the spawning season only,
and in juveniles to the period required to achieve metamorphosis (see Table 1).
Neosilurus ater is widespread in the Alligator Rivers region.
Bishop et al. [193] recorded this species in 24 of 26 regularly sampled sites, occurring in floodplain lagoons, corridor lagoons, escarpment main channel water bodies and
perennial streams, and most lowland muddy lagoons and
sandy creek-bed habitats. Habitat use varied seasonally.
During the dry season, N. ater was most common in
escarpment habitats, floodplain lagoons and main channel
corridor lagoons, and was absent from lowland habitats.
At the commencement of the wet season, N. ater moved
out of these refugial habitats and colonised all available
lowland habitats. Return migrations to refugial habitats
occurred in the late wet season. This pattern of habitat use
is in contrast to that reported for N. ater in the Ross River
of north-eastern Queensland. During the dry season, N.
ater were confined to permanent water in the lowland
sections of the river and made short migrations upstream
for spawning at the commencement of the wet season
[1030].
Environmental tolerances
Experimental data concerning the environmental tolerances of this species are lacking. Data presented in Table 1
are derived from field studies and represent the range of
conditions in which Neosilurus ater has been found.
Neosilurus ater occurs predominantly in warm waters. The
maximum water temperature in which N. ater has been
recorded is 33.4°C (Table 1). The maximum water temperature recorded for the Alligator Rivers region was accompanied by a surface water temperature of 36°C [193]. This
species clearly tolerates temperatures in the low to mid30s for extended periods. Minimum water temperatures in
which N. ater has been recorded are between 21 and 23°C.
Low water temperatures probably play an important role
in limiting the southern distribution of N. ater.
Neosilurus ater is found over a wide range of dissolved
oxygen levels. The average dissolved oxygen concentration
in the two lotic studies included above (Cape York
Peninsula and Burdekin River) range from 8.0 to 8.5 mg
O2.L–1 and are both close to saturation. In contrast, the
remaining studies listed in Table 1 (Alligator Rivers region
and Normanby River floodplain lagoons) dealt largely or
entirely with lentic habitats and it can be seen that average
dissolved oxygen levels experienced by N. ater in such
habitats were substantially lower and on occasions very
much lower (<1 mg O2.L–1). Hogan and Graham [585]
recorded N. ater in lagoons of the Tully/Murray River
floodplain with DO levels of 1.3 mg O2.L–1. Perna (pers.
comm.) recorded N. ater in floodplain lagoons of the
Burdekin River delta in which average DO levels were 42%
saturation but for which occasional minimum saturation
levels plummeted to 0.2%. From these data it is obvious
that N. ater is tolerant of hypoxic conditions. Nonetheless,
River gradient appears to be an important determinant of
macrohabitat use by N. ater. In rivers of low gradient such
as the Mitchell, Normanby or Burdekin rivers (notwithstanding the presence of the Burdekin River Falls), N. ater
occurs over the full length of the river. In rivers of higher
gradient, such as those of the Wet Tropics region, this
species is restricted to the lowland reaches. Allen [33]
comments that N. ater prefers areas of faster flowing water
in main channels.
Neosilurus ater is a benthic species and is most commonly
observed in close association with the substrate. It may be
found over a wide range of water depths [1093]. During
the day, adult N. ater tend to be confined to deeper waters
(>2 m) although when cover in the form of woody debris
or undercut banks is abundant, adult fish may be found in
much shallower waters (40–60 cm). At night, the extent of
dendency on cover is much reduced and adult N. ater may
123
Freshwater Fishes of North-Eastern Australia
Neosilurus ater occurs over a wide range of water conductivity: 2–790 µS.cm–1; it should be considered a freshwater
species. Given that it lacks a dendritic organ to allow
osmoregulation in saline environments it is unlikely to
tolerate conductivities in excess of 4000 µS.cm–1 for
prolonged periods.
Table 1. Physicochemical data for the Black catfish Neosilururs
ater. Turbidity values are listed as NTU except for the Alligator
Rivers region where they are listed as Secchi disc depths in
cm. Data listed for this region were taken from the bottom of
the water column. Elsewhere, readings were taken from the
midpoint of the water column. n refers to the number of
samples upon which summaries are based.
Parameter
Min.
Max.
Alligator Rivers region [193]
Temperature (°C)
23
32
Dissolved oxygen (mg.L–1)
0.6
6.2
pH
4.5
6.8
Conductivity (µS.cm–1)
2
70
Turbidity (cm)
2
360
Cape York Peninsula (n = 6) [1093]
Temperature (°C)
21
26
Dissolved oxygen (mg.L–1)
7.3
11.2
pH
6.2
7.2
Conductivity (µS.cm–1)
80
200
Turbidity (NTU)
0.1
5.4
A substantial range (0.3–120 NTU) in water clarity is characteristic of the habitats in which N. ater occur. Burrows et
al. [256] recorded this species from the Belyando River in
which turbidity may be as high as 581 NTU and remains
so for extended periods of time. Its nocturnal habitat and
possession of barbels to facilitate prey detection probably
enable N. ater to forage effectively in habitats of low light
availability due to elevated levels of suspended inorganic
material. The tolerance of eggs and early life history stages
to high levels of suspended sediment is unknown.
Mean
27.2
3.4
5.9
95
24.3
8.5
6.8
125.7
1.9
Bishop [187] recorded N. ater among the dead in a large
fish kill for which hypoxia was suggested to be the primary
cause. The effects on growth and reproduction that might
arise from long-term exposure to levels of between 1.5–3.5
mg O2.L–1 or whether such profoundly depressed DO
levels are inimical to eggs, larvae and small juveniles are
unknown. Given that reproduction in many areas appears
concentrated in seasonally flowing streams, it is probable
that these early life stages are intolerant of extremely low
levels of dissolved oxygen.
Reproduction
As is the case for N. hyrtlii, the reproductive biology of N.
ater is poorly documented and what little is known is
derived primarily from research undertaken in the
Alligator Rivers region [193] and in an intermittent tributary of the Ross River in Townsville [1030] (Table 2).
Bishop et al. [193] determined that length at first maturity
(length at which 50% of the sample is mature) was 260 and
280 mm TL for male and female fish, respectively. This is
approximately twice the size at which male and female N.
hyrtlii mature [193]. Maturation at lengths in excess of 200
mm SL occurs in the Burdekin River also [1093]. Gonad
recrudescence commences in the mid-dry to early wet
season, peaking in the early wet season in the Alligator
Rivers region. Average GSI values during the breeding
season were estimated to be 6% ± 2.5% and 1.7% ± 0.9,
for female and male fish, respectively. GSI values decreased
rapidly after a short breeding season that occurred during
the wet season. Running ripe fish were found in a variety
of habitats, both lentic and lotic. Bishop et al. [193] cite
unpublished observations by H. Midgley of running ripe
plotosid catfishes congregating in large numbers in Magela
Creek soon after flow commenced. This observation parallels that of Orr and Milward [1030] who describe
upstream spawning migrations by N. ater (and N. hyrtlii)
in the Ross River.
Neosilurus ater has been recorded from a wide range of
water acidity (4.5–9.1 pH units), although the pH range
within studies is considerably smaller (average range = 1.9
units) (Table 1). This species has been recorded from
acidic dune lakes in which pH was 5.01 [1101]. This
species most frequently occurs in waters of near-neutral
acidity although some populations, such as those occurring in dune lakes [1101] and floodplain wetlands [193]
tolerate much lower pH levels.
The fact that N. ater and N. hyrtlii make simultaneous
spawning migrations into the same habitats [1030]
suggests the existence of very strong mechanisms for reproductive isolation. Orr and Milward [1030] observed
that these species assume substantially different body
and fin colouration during the spawning run (see descriptions), and this may help to prevent inappropriate mate
choice. Moreover, N. ater apparently swim together in pairs
immediately prior to spawning with the head pointed
Normanby River floodplain lagoons (n = 6) [697]
Temperature (°C)
22.9
33.4
26.3
Dissolved oxygen (mg.L–1)
2
6.3
3.4
pH
6.4
9.1
7.3
Conductivity (µS.cm–1)
81
412
120
Turbidity (NTU)
3.4
120
22.6
Burdekin River (n = 29) [1093]
Temperature (°C)
21.5
33
Dissolved oxygen (mg.L–1)
4.2
11.0
pH
6.8
8.5
Conductivity (µS.cm–1)
56
790
Turbidity (NTU)
0.3
16
26.0
8.0
7.7
426.3
3.565
124
Neosilurus ater
season is short in duration. Greater research effort is
required to assess whether individual females spawn more
than once, a life history tactic that may be advantageous
in areas where spawning is restricted to intermittent
streams in which discharge is unpredictable in incidence
and duration.
downward coupled with frequent tumbling and intertwining, whereas in N. hyrtlii, the male follows the female, holding the snout adjacent to the female’s flank, followed by a
short dart ahead to arch the body around the female’s snout
[1030].
Neosilurus ater is moderately fecund for its size, producing
between 2540 and 26 070 (average = 7890) small eggs with
an intraovarian diameter of about 1.6 mm. Water-hardened
eggs are apparently slightly larger. The eggs are demersal
and non-adhesive. Bishop et al. [193] report that in addition to the presence of well-developed eggs in the ovaries
of mature fish, many clusters of small, undeveloped eggs
of about 0.16 mm diameter could be found. This raises the
possibility that N. ater is a serial spawner. However, the
steep decline in average GSI values through time observed
in the Alligator Rivers region suggests that the spawning
Ripe N. ater were collected from a variety of habitats in the
Alligator Rivers region but the exact site of spawning was
unknown [193], in contrast to reports by Orr and Milward
[1030], who observed spawning in an intermittent stream
with a gravel/sand bed.
Limited evidence concerning the location of spawning
sites for the neosilurid catfishes of the Burdekin River,
although far from comprehensive, suggests that both
N. ater and N. hyrtlii migrate upstream into tributaries
(Fig. 1) whereas N. mollespiculum remains in the main
Table 2. Life history information for Neosilurus ater. Data listed are drawn primarily from a medium-term study undertaken in
the Alligator Rivers region of the Northern Territory [193], a medium term study of changes in population size structure in the
Burdekin River [1093], and a short-term study undertaken in a tributary of the Ross River in northern Queensland [1030].
Information about larval development is based on material identified to genus only, as spawning aggregations observed by Orr
and Milward contained both N. hyrtlii and N. ater. It is assumed here that early development in both species is identical. LFM =
length at first maturity.
Age at sexual maturity (months)
24 months (?)
Minimum length of ripe females (mm)
LFM = 280 [193]
Minimum length of ripe males (mm)
LFM = 260 [193]
Longevity (years)
5 years (?)
Sex ratio (female to male)
1:1 [1030], variable excess of females after spawning season
Occurrence of ripe fish
Stage IV in late wet to late dry, stage V early wet [193]; stage V in November [1093]
Peak spawning activity
Start of the wet season
Critical temperature for spawning
Unknown but likely to be >25°C
Inducement to spawning
Rising water levels
Mean GSI of ripe females (%)
10.5% [1030], 6.0 ± 2.5% [193]
Mean GSI of ripe males (%)
1.7 ± 0.9% [193]
Fecundity (number of ova)
Average = 7890 (n = 13), range = 2540–26 070 [193]
Fecundity /length relationship
?
Egg size (mm)
1.4 mm intraovarian (range = 0.85–1.64) [193], 2.0 mm water-hardened [193], 2.6 mm
water-hardened [1030]
Frequency of spawning
May be several spawning events in one season but unknown whether single individual
spawns more than once [1030]
Oviposition and spawning site
Tributary streams [1030, 1093], main channel [1093] – gravel beds
Spawning migration
Upstream [1030]
Parental care
None
Time to hatching
60 hours at 26-27°C [1030]
Length at hatching (mm)
5.7–6.0 mm [1030]
Length at free swimming stage
?
Length at metamorphosis (mm)
25 mm [1030]
Duration of larval development
28 days [1030]
Age at loss of yolk sack
?
Age at first feeding
?
125
Freshwater Fishes of North-Eastern Australia
5, Annan River; Pusey et al. [1097], n = 49, Mulgrave and
Johnstone rivers; Pusey et al. [1099], n = 50, Pascoe, Stewart
and Normanby rivers of Cape York Peninsula; Kennard
[697], n = 21, floodplain lagoons of the Normanby River;
Pusey et al. [1093], n = 164, Burdekin River; Bishop et al.
[193], n = 260, Alligator Rivers region. The latter two studies included data from both wet and dry seasons whereas
the remainder were confined to the dry season.
channel [1093] (see pp. 129–132). Separation of spawning
grounds of at least one species and differences in mating
behaviour of the remaining two may be sufficient to maintain reproductive isolation in these catfish species.
Embryonic and larval development are assumed to follow
the same pattern as described for N. hyrtlii.
Figure 1. Size structure of Neosilurus ater populations in the
main channel of the upper Burdekin River (closed bars, n
=108) and in tributary streams of the upper Burdekin River
(open bars, n = 51) [1093].
Figure 2. The average diet of Neosilurus ater. Summary based
on stomach contents analysis of 549 individuals derived from
six separate studies (see text).
30
Molluscs (9.5%)
Microcrustaceans (5.3%)
Unidentified (29.0%)
20
10
Detritus (12.0%)
0
Aquatic insects (39.8%)
Terrestrial vegetation (1.5%)
Aquatic macrophytes (2.2%)
Fish (0.7%)
Length (mm)
The average diet of N. ater is dominated by aquatic invertebrates (~40%), detritus (12%), molluscs (~10%) and
microcrustacea (~10%). Other items were unimportant
overall, although each may have been significant in each
individual study. For example, fish comprised one-third of
the diet of N. ater from the Annan River but did not
contribute more than 1% in any other study.
Movement
Other than the study by Orr and Milward [1030] demonstrating upstream migrations associated with spawning,
little is known of the movement biology of N. ater. This
species has not been recorded in studies undertaken in fishways. Clearly, upstream migrations by adults for spawning
must be followed by a return migration by spent individuals, followed later by downstream dispersion of juveniles.
The data presented in Figure 1 suggests that the juveniles
return to the main channel at relatively small size, as juveniles between 120–240 mm SL are absent from tributary
streams. In the Alligator Rivers region, substantial movements between expanded wet season habitats (principally
in the lowlands) and dry season refugia (principally in
upstream escarpment habitats) have been reported [193].
Ontogenetic and geographic variation in diet is
pronounced in N. ater. Pusey et al. [1099] provided information on the diet of small (<150 mm SL, n = 31) and
large (>150 mm SL, n =19) N. ater in rivers of Cape York
Peninsula. Small fish relied more on aquatic invertebrates
than did large fish (62% versus 38%, respectively),
consumed more filamentous algae (6.6% versus 0%,
respectively), consumed less microcrustaceans (almost
entirely ostracods) (5.9% versus 22%, respectively) and
much less molluscs (0% versus 20%, respectively).
Although the consumption of larger prey items such as
molluscs increased with increasing fish size (undoubtedly
as a result of an increased ability to handle and process
such prey), increasing body size was not necessarily associated with increasing size for all prey items. For example,
very small ostracods were an important food source for N.
ater in rivers of Cape York Peninsula. Notably, these small
Neosilurus ater, like N. hyrtlii, is most active at night. Most
movement probably occurs at night, with the exception of
spawning runs, which have been observed during daylight
hours.
Trophic ecology
Information on the trophic ecology of N. ater is available
from six separate studies, five of which were conducted in
Queensland. These include: Hortle and Pearson [599], n =
126
Neosilurus ater
prey items were not ingested incidentally along with
organic detritus, as detritus was not recorded in the diet of
fish from Cape York rivers.
Table 3. Comparative importance (% of total for each region)
of selected food items in the diet of N. hyrtlii and N. ater.
Items are included only if substantial differences in
proportional contribution occurred.
Detritus was very important in the diet of N. ater from
some of the other study areas. This food source
contributed 60% of the total diet of fish from the Mulgrave
and Johnstone rivers of the Wet Tropics region (n = 49)
and 48% of the diet of catfish from floodplain lagoons of
the Normanby River (n = 21) but did not contribute more
than 7% of the diet in any other study area. Notably,
microcrustaceans contributed very little to the diet in these
studies, further emphasising the fact that when benthic
microcrustaceans occur in the diet at appreciable levels,
this is a result of active selection and processing rather
than inadvertent ingestion as a by-product of detrivory. In
addition, the type of microcrustacean eaten by N. ater
varied between studies. For example, Cladocera (and to a
lesser extent Conchostraca) were the dominant microcrustacean in the diets of fish from the Alligator Rivers region
and from the floodplain of the Normanby River, reflecting
the abundance of these taxa in lentic waters. The microcrustacean component of the diet of fish from riverine
study areas (Burdekin River and rivers of Cape York
Peninsula) was dominated by ostracods. The amount and
type of molluscs eaten by N. ater varied between studies
also. For example, in the Mulgrave and Johnstone rivers,
small gastropods were twenty times more important than
were bivalve molluscs (12.5% versus 0.6%, respectively).
In contrast, bivalve molluscs were ten times more important than were gastropods (20.6% versus 2%, respectively)
in the Burdekin River, and approximately equal contributions were recorded in the diet of fish from lagoons of the
Normanby River (7.7% versus 6.9% for bivalve and gastropod molluscs, respectively). Molluscs were either absent or
unimportant (<1%) in the diet of fish from the Annan
River and the Alligator Rivers region.
Dietary item
N. hyrtlii
N. ater
Alligator Rivers region
Microcrustaceans (Cladocera)
20.6
7.6
Normanby River floodplain
Detritus
Terrestrial invertebrates
Aquatic insects
65.0
10.4
6.0
48.0
1.5
25.4
Cape York Peninsula
Microcrustaceans (ostracods)
Molluscs
3.3
0
12.1
7.6
Wet Tropics region
Detritus
Molluscs
32.0
28.5
60.0
12.8
Burdekin River
Detritus
Microcrustaceans (ostracods)
Molluscs
22.0
14.0
11.4
5.6
1.4
22.6
between studies. Similarly, interspecific differences in the
proportional contribution of detritus, molluscs and
microcrustacea occur in the Wet Tropics region and the
Burdekin River also. These data suggest that these two
morphologically similar species do indeed partition the
available food resources.
Significantly however, this apparent partitioning is not
consistent across the various studies. For example, while
microcrustaceans are an order of magnitude more important in the diet of N. hyrtlii from the Burdekin River than
in N. ater, and three times more important in the Alligator
Rivers region, the reverse condition was observed in rivers
of Cape York Peninsula where microcrustacea were more
important in the diet of N. ater. Similarly, molluscs were
more important in the diet of N. ater from Cape York and
the Burdekin River whereas this food item was more
important in the diet of N. hyrtlii from the Wet Tropics
region. Contrasting patterns of partitioning with respect to
detritus are also evident in Table 3. The mechanisms or
factors responsible for these variable patterns of dietary
segregation are unknown but the data serve to illustrate
that these two morphologically similar, frequently
sympatric and syntopic, catfishes are able to partition food
resources effectively. Moreover, these data suggest that both
species are able to employ a range of foraging strategies
when circumstances dictate. Investigation of the mechanisms allowing the coexistence of these two species, and
additional species such as N. mollespiculum and Porochilus
rendahli, is warranted.
The average diet of N. ater, taken across all studies, is
extremely similar to that of N. hyrtlii: both being dominated by aquatic invertebrates, molluscs, microcrustaceans
and detritus. However, when comparison of the diet of
each species is restricted to individual studies, it can be
seen that substantial dietary segregation occurs (Table 3).
For example, microcrustaceans were more important in
the diet of N. hyrtlii in the Alligator Rivers region than N.
ater from this region. In lagoons of the Normanby River,
N. ater consumed less detritus, less terrestrial insects and
more aquatic invertebrates than did N. hyrtlii, whereas in
rivers of this region, N. ater consumed more microcrustacea and molluscs than did N. hyrtlii. Note that the type
(Cladocera versus Ostracoda) and location (planktonic
versus benthic) of the microcrustacean food differed
127
Freshwater Fishes of North-Eastern Australia
important for reproduction, in north-eastern populations at least. Accordingly, the development of water
infrastructure that inhibits upstream movement, or
which captures high flow events and therefore removes
the probable stimulus for spawning migrations, is
highly likely to negatively impact on this species.
Finally, the ecology of N. ater is poorly documented. For
example, the information concerning reproduction is
limited as is information on movement biology and the
mechanisms allowing coexistence of closely related
species. Effective management is hampered by these
knowledge deficits.
Conservation status, threats and management
Neosilurus ater is listed as Non-threatened [1353].
Given its wide distribution and generally high abundance, this species is probably secure and likely to
remain so in the future. However, available information
suggests the existence of two disjunct populations, one
restricted to north-western Australia and the other to
north-eastern Australia. Whether this represents a true
separation of these populations and whether significant
genetic differentiation has occurred is unknown.
Movement is an important feature of the biology of this
species and access to tributary streams appears to be
128
Neosilurus mollespiculum Allen & Feinberg, 1998
Soft-spined catfish
37 192023
Family: Plotosidae
of eye; inner mental barbel slightly shorter. Teeth slender,
conical, arranged in several rows on upper and lower jaw;
lunate patch of larger teeth on palate. Dorsal profile of head
strongly convex in adult specimens. Dermal fold on chin
forming deep groove across region between lower lip and
ventral gill opening; branchiostegal membranes broadly
united to each other and partly free from isthmus.
Description
First Dorsal fin: I, 4 (spine flexible and last ray consisting
of 2–3 small closely clustered rays arising from the same
pterygiophore); Second dorsal and anal fin confluent with
caudal fin: Upper procurrent caudal rays 28–33; Caudal
rays: 8–9; Anal: 71–82; Pectoral: I, 13; Pelvic: 13–14. Gill
rakers on lower limb of first arch: 12–16. Dorsal and
pectoral fin spines weak, flexible and generally lacking
serrations except occasionally in juveniles. Figure:
composite, drawn from photographs of adult specimens,
one of which is the paratype depicted in Allen and
Feinberg [48]; drawn 2002.
Colour in life: variable, ranging from dark charcoal-grey
or nearly black through to yellowish-grey brown dorsally
and lighter ventrally. Young individuals tend to be darker
than adults. Colour in preservative: pale grey to yellowish
or tan, often darker grey on back and top of head.
Neosilurus mollespiculum is a moderate-sized to large catfish
that may reach 410 mm SL (440 mm TL [52]) but is most
commonly 150–200 mm SL. The relationship between
length (SL in mm) and weight (g) is W = 5.31 x 10–6 L3.085: r2
= 0.98, n = 99, p<0.001 [1093]. The following description is
drawn largely from the original description [48]. Head
length about one-quarter of SL (22–24% SL); eye small
(13–20% of HL), set in middle of head (snout length =
45–53% of HL) and close to dorsal profile. Nasal barbel
21–34% of HL usually reaching about 2/3 distance between
snout and anterior margin of eye; maxillary and outer
mental nasal about equal, reaching to below level of middle
Systematics
Neosilurus mollespiculum has only recently been described
[48] although it has long been recognised as a distinct
taxon – Allen’s Neosilurus sp. C. [34]. This taxon was
composed of two species, both lacking rigid spines in the
dorsal and pectoral fins, namely N. mollespiculum and N.
pseudospinosus. Prior to the description of two separate
species, Allen [34] figured the distribution of Neosilurus
sp. C. (p. 63) as extending across the Northern Territory,
the Gulf of Carpentaria in Queensland, Cape York
Peninsula and south to the Burdekin River. Neosilurus
129
Freshwater Fishes of North-Eastern Australia
Burdekin Falls. In the upper Burdekin River, this species
occurs in tributary rivers as well as the main channel
[1082, 1098]. It has also been collected from the Bowen
River, the major lowland tributary of the Burdekin River
[1098]. The only major tributary system of the Burdekin
River in which this species has not been recorded is the
Cape River and Belyando/Suttor system in the south-western portion of the catchment. Burrows et al. [256] did not
collect this species from the turbid waters of the Belyando
River despite collecting N. ater, N. hyrtlii and P. rendahli.
Neosilurus mollespiculum probably does occur in the
south-western tributaries of the upper Burdekin River and
its apparent absence is probably due to misidentification.
Despite its widespread distribution, few researchers working in the catchment have recognised this species.
pseudospinosus has been recorded from rivers of the
Kimberley region and from the Victoria and Daly River
systems of the Northern Territory only, whereas N. mollespiculum is limited to the Burdekin River [48]. The two
species are closely related and superficially resemble N.
ater, which contrastingly possesses rigid spines on the
dorsal and pectoral fins, and a higher gill raker count on
the lower limb of the first brachial arch (18–23 versus
12–16 for N. ater and N. mollespiculum, respectively) [48].
Neosilurus mollespiculum differs from N. pseudospinosus in
having a smaller average number of procurrent caudal rays
(31 versus 37), a slightly shorter dorsal fin base (13–19%
of SL versus 19–26% SL) and shorter nasal barbels
(24–32% of HL versus 33–58% HL) [48].
The etymology of the species epithet is from the combination of the Latin for soft spine in reference to the characteristic soft, flexible dorsal spine.
Neosilurus mollespiculum is frequently sympatric with
both N. hyrtlii and N. ater and appears to have almost
identical habitat requirements. Reference to the
meso/microhabit requirements of these species will
adequately cover those of N. mollespiculum. However, this
raises the interesting question of how such closely related
species are able to coexist in the Burdekin River.
Distribution and abundance
Neosilurus mollespiculum is endemic to the Burdekin River
drainage. Allen and Feinberg [48] examined several specimens in the Australian Museum that were supposedly
collected from Lillesmere Lagoon in the Fitzroy River and
from the Mary River in the early 1900s. The paucity of
additional collecting data associated with these specimens
led Allen and Feinberg to conclude that the locations were
in error and that the distribution of this species does not
extend outside the Burdekin River. Lillesmere Lagoon is,
in fact, located in the Burdekin River drainage. An extensive series of freshwater fishes was collected from the Mary
River and the Burdekin River, including Lillesmere
Lagoon, in 1883; the description of which was published
the following year by Macleay [847]. Although plotosid
catfishes were not mentioned in Macleay’s paper, several
other errors in labelling and attribution are associated
with this collection (M. McGrouther, pers. comm.) and it is
most likely that the specimens of N. mollespiculum labelled
as being from the Fitzroy River and the Mary River were
indeed part of this collection.
Environmental tolerances
Information on the environmental tolerances of
Neosilurus mollespiculum are drawn from water quality
measurements at sites in which this species has been
collected.
Table 1. Physicochemical data for the soft-spined catfish
Neosilururs mollespiculum. n refers to the number of site
sampling occasion combinations for which data were
available.
In a study of the Burdekin River undertaken by Pusey et al.
[1098] N. mollespiculum was the 15th, 10th and 9th most
abundant species in electrofishing, seine-netting and gillnetting samples, respectively and contributed 1.0%, 0.1%
and 1.1% of the catches by these methods, respectively. It
was the second most abundant of the catfishes (total standardised catch over study period for N. hyrtlii, N. mollespiculum, N. ater, P. rendahli and T. tandanus = 1431, 226,
111, 30 and 7, respectively).
Parameter
Min.
Max.
Burdekin River (n = 23) [1080]
Temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
21.5
4.2
6.76
56
0.25
33
10.0
8.46
790
6.0
Mean
25.7
7.73
7.71
408.8
2.7
Neosilurus mollespiculum occurs in warm, relatively welloxygenated, fresh waters of near neutral acidity and low
turbidity. Tolerance to high levels of suspended sediment
appears limited given the data presented in Table 1 and the
fact that this species appears to be absent from the more
turbid tributaries in the south-west of the Burdekin River
catchment. However, as discussed above, this latter finding
may have more to do with a failure to distinguish between
this species and N. ater or N. hyrtlii than an apparent
avoidance of turbid waters. The data listed in Table 1 for
N. mollespiculum are almost identical to the values listed
Macro/meso/microhabit use
Neosilurus mollespiculum occurs throughout the Burdekin
River system, both upstream and downstream of the
130
Neosilurus mollespiculum
for N. ater and N. hyrtlii (see respective chapters), a finding that is not wholly unexpected given the similarity in
distribution and habitat requirements of these species in
the Burdekin River. The extent to which the tolerances of
N. mollespiculum match the broad range seen for N. hyrtlii
are unknown however.
15
10
Reproduction
Very little is known of the reproductive biology of N.
mollespiculum. It is likely that many aspects of its reproductive biology parallel those observed for N. hyrtlii and
N. ater. For example, spawning probably occurs during the
wet season. The only occasion that we have detected
mature stage V or VI females was in November 1991 (Fig.
1), prior to the period in which elevated flows are normally
expected to occur [1093]. Note however, that similarly
mature fish were not recorded in November of the preceding year.
5
0
Length (mm)
I
II
III
IV
Figure 2. Population size structure of Neosilurus mollespiculum
in the main channel (closed bars, n = 53) and tributary
streams (open bars, n = 33) of the upper Burdekin River.
V
40
Movement
Nothing is known of this aspect of the biology of N. mollespiculum. Data presented in Figure 2 suggests that spawning migrations into tributary streams do not occur, but
such a conclusion is definitely provisional until more
information is available.
30
20
Trophic ecology
Information on the trophic ecology of N. mollespiculum is
drawn from a single study, composed of three sampling
occasions, conducted over the period November 1990 to
November 1991 (n = 114) [1093].
10
0
Nov. 90
May 91
The diet of N. mollespiculum is extremely similar to the
average diet of both N. hyrtlii and N. ater. It is primarily
composed of benthic invertebrates, particularly insects
such as chironomid larvae, mayfly nymphs and caddisfly
larvae. This species consumes less detritus (3.5%) than
either N. hyrtlii (14.4%) or N. ater (11.4%) but more filamentous algae (7.1% versus 0.7% and 1.1%, respectively).
Molluscs comprise only 1.6% of the diet of N. mollespiculum as opposed to 6.3% and 9.5% in N. hyrtlii and N. ater.
Nov. 91
Figure 1. Temporal changes in maturation in populations
of Neosilurus mollespiculum in the upper Burdekin River
[1093].
Neosilurus mollespiculum may not migrate upstream into
tributary streams to spawn as occurs in N. hyrtlii and N.
ater. Comparison of population size structure in the
main channel of the upper Burdekin River with that of
tributary systems, such as Keelbottom Creek and the
Fanning and Running rivers, reveals that small juveniles
(<80 mm SL) were present in the main channel only.
Separation of spawning and juvenile habitats may be an
important mechanism allowing coexistence of these
species.
This comparison is based on the average diet of N. hyrtlii
and N. ater determined by pooling dietary information
from a number of different regions. Comparison of the
diet of these species from the Burdekin River, whilst
revealing that the generalisations made above still hold
true to an extent, also reveal a much finer dietary segregation in these three species when in sympatry. For example,
131
Freshwater Fishes of North-Eastern Australia
Microcrustaceans (7.7%)
Molluscs (1.6%)
Macrocrustaceans (0.9%)
Unidentified (34.0%)
Detritus (3.5%)
Aerial aq. Invertebrates (1.0%)
Aquatic insects (43.4%)
Algae (7.1%)
Fish (0.9%)
the diet of N. ater (1.4%) but more important in the diet
of N. mollespiculum (7.7%) and N. hytlii (13.9%). Dietary
partitioning may be another mechanism allowing the
coexistence of these three closely-related species. It should
be added however, that no N. mollespiculum were collected
in May 1992 after the commencement of a prolonged
drought in the Burdekin catchment, although N. ater and
N. hyrtlii remained present, albeit at reduced densities.
These species may compete intensely for resources when
they are limited: this assertion remains untested however,
as do most inferences about the biology of this species.
Conservation status, threats and management
Neosilurus mollespiculum is listed as a Poorly Known
Species by Wager and Jackson [1353] and remains unlisted
by ASFB [117]. Listing by Wager and Jackson was for the
taxon known as Neosilurus sp. C., prior to the recognition
of N. mollespiculum and M. pseudospinosus as distinct
species. Its status should be revised in view of its restricted
distribution. This species appears currently secure within
the Burdekin River but any proposed development of
water infrastructure in the catchment, and changes in flow
regime associated with regulation, may impact on this
species in the future. Much greater research effort is
needed to define the biology of this narrowly endemic
species.
Figure 3. The average diet of the soft-spine catfish Neosilurus
mollespiculum (n =114 individuals) [1093].
detritus comprised only 5.6% and 3.5% of the diet of N.
ater and N. mollespiculum but accounted for 22% of the
diet of N. hyrtlii. Macrocrustacea (shrimps and prawns)
were completely absent from the diet of N. hyrtlii but present, although relatively unimportant (~1%) in the diet of
N. ater and N. mollespiculum. Molluscs were relatively
unimportant in the diet of N. mollespiculum (1.6%),
important in the diet of N. hyrtlii (11.5%) and very important in the diet of N. ater (22.6%). In contrast, microcrustaceans (mainly ostrocods) were a minor component of
132
Porochilus rendahli (Whitley, 1928)
Rendahl’s catfish
37 192012
Family: Plotosidae
than post-orbital head length; profile often deeply
concave; dorsal spine short; lateral line continuous
(discontinuous in P. obbesi); canals of head opening from
relatively few pores; temporal pores, between the eyes, few
in number, usually one on each side of the midline, axillary pore present. Branchiostegal membranes rather
broadly united, premaxilla with small rectangular patch of
tiny pointed teeth on each side of the midline; teeth on
palate large, rounded and arranged in semicircular to shallowly crescentic patch. Teeth in lower jaw pointed in front,
molariform behind. Nasal barbel extending to, or beyond,
posterior end of head; maxillary barbel reaching well
behind eye; outer mental barbel reaching to, or beyond,
base of pectoral fin base; the inner mental barbel, slightly
shorter. Gill rakers on anterior face of first gill raker slender, those of middle of anterior face of second arch short,
chubby, broad at the base, grading above and below into
transverse ridges; posterior face of first arch with two rows
of papillae along arch near margins, the anterior row
slightly larger; second arch posteriorly with papillae more
or less connected transversely across arch into ridges.
Anterior nares on end of snout, above upper lip (in P.
obbesi the nostril is situated on the upper lip), anterior to
and slightly lateral to nasal barbel, without vestige of
projecting tubule.
Description
First dorsal fin: I, 5–7 (most commonly 5), spine pungent,
weakly serrate or roughened; Second dorsal fin and anal
fin confluent with caudal fin; Upper procurrent dorsal
rays: 24–31; Anal plus lower caudal rays: 79–97 (Allen et
al. [52] list a total of 104–127 rays); Pectoral: I, 9–11, spine
pungent, serrae straight to slightly recurved; Pelvic: 10–13,
Gill rakers on first arch: 22–26, of which 5–7 are on upper
limb [52, 1304]. Figure: composite, drawn from photographs and after Taylor [1304]; drawn 2003.
Porochilus rendahli is a small catfish that may achieve a
maximum size of about 240 mm TL [1304]. Specimens
this large are rare and P. rendahli is more commonly less
than 150 mm in length. For example, the maximum length
(SL) in a sample of 292 fish from Arnhem Land and
Groote Eylandt was 187 mm and 96% of this sample was
less than 127 mm SL [1304]. Bishop et al. [193] recorded a
maximum size of 195 mm (TL) in a sample of 328 fish.
These authors provide the following relationship between
weight (W in g) and length (TL in cm): 4.4 x 10–3 L3.16; r2 =
0.98, n = 328, p<0.001.
The following description is drawn largely from Taylor
[1304]. Head length (17.5–20.8% SL), usually shorter than
maximum body depth (19.3–22.2% SL); snout shorter
133
Freshwater Fishes of North-Eastern Australia
River [1349] suggests it may be more widespread in the
region. The distribution on the western side of Cape York
Peninsula is more or less continuous. The Mitchell River
and its tributaries, the Walsh and Palmer rivers [571, 643,
1186], and the Edward, Holroyd, Archer, Wenlock and
Jardine rivers [41, 52, 571, 1349] all contain P. rendahli.
The related species P. obbesi also occurs in the Jardine and
Olive rivers [41, 571].
Colour in life: variable, ranging from light grey to nearblack, sometimes with mottling, to yellow/tan with golden
sheen [52]. Colour in preservative: dark grey to brown
dorsally, grading lighter ventrally, lower head and
abdomen pale.
Taylor [1304] commented on the extent of variation in
some characters within the series he examined. Specimens
from Groote Eylandt differed from mainland specimens
(Roper River area) in having fewer gill rakers on the first
arch, more vertebrae, a crescentic to shallowly triangular
palatal tooth patch rather than semicircular to deeply
triangular palatal tooth patch and longer barbels. In addition, the number of temporal pores on the head varied
from two to eight across the series. Given the wide distribution of this species (see below), it is probable that even
greater variation exists. It is our belief that this species is
frequently confused with juveniles of other plotosid
catfishes and as a consequence, its distribution and macrohabitat requirements are not fully documented.
It is patchily distributed on the east coast of Australia, with
P. rendahli being recorded only from the Pascoe, Stewart,
Normanby and Endeavour rivers [52, 182, 697, 1349],
Three Quarter Mile/Scrubby Creek [571] and the Cape
Flattery region [1101] of Cape York Peninsula. It is broadly
sympatric but not syntopic with P. obbesi in the dune fields
of Cape Flattery [1101].
Porochilus rendahli is apparently absent from the northern
part of the Wet Tropics region, being present in the Barron
[608, 1085, 1349], Mulgrave [1093], Johnstone [643,
1093], Tully [1085] and Herbert rivers [643] only. This
species is widely distributed in the Burdekin River, occurring throughout the catchment [586, 1098, 1349] including the highly turbid Belyando/Suttor River [256] and
floodplain lagoons of the Burdekin River delta (C. Perna,
pers. comm.).
Systematics
Porochilus was erected by Weber in 1913 to contain the
type species P. obbesi from the Lorenze River in southern
Papua New Guinea [1042]. The genus was originally
thought to be monotypic but is now known to contain
four species: P. obbesi (northern Australia and southern
Papua New Guinea), P. maraukensis (southern Papua New
Guinea), P. argenteus (central Australia) and P. rendahli
(northern Australia) [37, 52]. Porochilus rendahli was first
described as Copidoglanis obscurus by Rendahl in 1922
[1127]. This name had however been proposed for
another catfish, now recognised as Plotosus limbatus
Valenciennes, 1840, by Günther in 1864. Whitley then
proposed the name Copidoglanis rendahli in 1928 [1042].
Since then, this species has been referred to as Tandanus
rendahli [1304] and most commonly as Neosilurus
rendahli [936, 1042]. The first reference to this species
being placed within the genus Porochilus appears to be
Allen and Hoese [41], who state that ‘Feinberg and Nelson,
who are revising the freshwater Plotosidae, include this
species in the genus Porochilus’. Subsequent publications
by Allen [52, 1304] have consistently employed the name
Porochilus rendahli.
Further to the south, P. rendahli has been reported from
the Fitzroy River and streams of the Shoalwater Bay area
[1349], Burnett [700, 1349], River [701], Mary [701,
1349], Pine [1349] and Brisbane rivers [1349]. It is
extremely uncommon in these southern rivers and it is
unlikely that the distribution extends further south than
the Brisbane River.
Porochilus rendahli is usually uncommon in the east-coast
river systems in which it has been recorded. For example,
this species was the 16th (of 22) most frequently collected
species in electrofishing samples in the Burdekin River
[1098]. Porochilus rendahli contributed only 13 of a total
of 35 851 fishes collected from 281 samples in the
Mulgrave/Russell, Johnstone and Tully rivers [1093]. In a
more extensive survey of the Wet Tropics region, only 12
specimens from a total of 7325 fish were collected [1085].
This species contributed 0.1% only of the total electrofishing catch in floodplain lagoons of the Normanby River
[697].
Distribution and abundance
Porochilus rendahli is widely but patchily distributed across
northern Australia. This species occurs in a few rivers of
the Kimberley region (Yeeda, Fitzroy, Drysdale and Ord
rivers) [52] and in coastal rivers of the Northern Territory
including Groote Eylandt [52, 193, 772, 774, 1304].
Records from rivers of the southern portion of the Gulf of
Carpentaria are scant but its presence in the Leichhardt
High levels of abundance do occur occasionally. For example, this species comprised 10.5% of the total number of
fishes collected from highly turbid waterholes of the
Belyando/Suttor River [256]. Bishop et al. [193] described
P. rendahli as being common to moderately abundant in
the Alligator Rivers region.
134
Porochilus rendahli
Table 1. Physicochemical data for Porochilus rendahli.
Turbidity values are listed as NTU except for the Alligator
Rivers region (ARR) where they are listed as Secchi disc depths
in cm. Data listed for the Alligator Rivers region were
recorded from the bottom of the water column. Elsewhere,
they are derived from the midpoint of the water column.
Macro/meso/microhabitat use
Porochilus rendahli has been recorded from a variety of
habitats including both riverine and off-channel. This
species is widely distributed in the Burdekin River, inhabiting the main channel both upstream and downstream of
the Burdekin Falls, floodplain lagoons of the delta, intermittent tributary streams of the upper Burdekin river and
low gradient in-channel lagoons of the Belyando River, but
rarely occurs in the higher gradient Bowen/Broken River
[1082]. In the Normanby River, it has been recorded from
both the main channel and floodplain lagoons [697, 1099].
In the Alligator Rivers region, P. rendahli was collected
from 17 of 26 regularly sampled sites and occurred in all
muddy lowland lagoons and floodplain lagoons, and some
corridor lagoons and perennial escarpment streams [193].
Juvenile P. rendahli were collected from lowland muddy
and floodplain lagoons.
Parameter
Min.
Max.
Alligator Rivers region [193]
Temperature (°C)
23
34
Dissolved oxygen (mg.L–1)
2
9.5
pH
5.2
7.3
Conductivity (µS.cm–1)
2
620
Turbidity (cm)
1
170
Mean
28
3.8
6
31
Normanby River, river and floodplain lagoon (n = 2) [1093]
Temperature (°C)
22.9
26
Dissolved oxygen (mg.L–1)
2.0
7.3
pH
6.9
7.2
Conductivity (µS.cm–1)
80.9
152
Turbidity (NTU)
3.4
5.4
Porochilus rendahli is a benthic species that prefers habitats
with low water velocities, and is most common in reaches
with a muddy substrate [52, 193]. This species is
frequently associated with aquatic vegetation [52] and
achieves greatest abundance in areas with dense
submerged macrophytes [193].
Cape Flattery (n = 1) [1101]
Temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
Environmental tolerances
The data presented in Table 1 are drawn from measurements of ambient conditions in sites in which P. rendahli
occurs. As such, the usual caveats concerning extrapolation of this data to indicate upper and lower tolerance
levels apply. Moreover, summaries based on more than one
sample are restricted to the Alligator Rivers region and the
Burdekin River. However, as the information available for
this species is very limited, we have included data from
several individual sites from other basins also.
Burdekin River (n = 7) [1093]
Temperature (°C)
15
28
Dissolved oxygen (mg.L–1)
4.2
11
pH
7.22
8.3
Conductivity (µS.cm–1)
258
435
Turbidity (NTU)
1.3
4.75
32
7.4
5
385
22.9
7.3
7.7
339
3.0
the Belyando River in which high levels of very fine
suspended sediment maintained very high turdidity levels
(mean = 397 NTU) for extended periods.
Porochilus rendahli occurs in warm waters (Table 1) as
would be expected given its distribution. The southern
limit of this species is probably determined by low water
temperature. The data presented in Table 1 suggest that P.
rendahli is tolerant of low levels of dissolved oxygen.
Indeed, levels of dissolved oxygen saturation in floodplain
lagoons of the Burdekin River delta average 47% saturation only and may drop to as little as 0.4% overnight (C.
Perna, pers. comm.). A well-developed tolerance to hypoxia
is not unexpected for species inhabiting tropical lagoons
with abundant macrophyte growth.
Reproduction
What little is known about the breeding biology of P.
rendahli is drawn entirely from the work of Bishop et al.
[193] in the Alligator Rivers region. This species matures
at small size: length at first maturity (LFM) reported to be
100 mm and 110 mmTL for male and female fish, respectively, although stage IV or V fish as small as 99 mm TL
were observed in some populations. The breeding season
is limited to the early wet season although gonad recrudescence commences in the mid dry season when temperatures exceed 28°C. Spawning apparently occurred in
muddy lowland lagoons. Average GSI values for male and
female fish during the spawning season were 0.7 ± 0.1%
and 5.2 ± 1.7%, respectively. Estimated fecundity from a
sample of eight fish was about 900 eggs (range =
240–3465) with an average diameter of 1.3 mm.
Porochilus rendahli has been recorded across a wide range
of pH (5–8.3). Again, a tolerance to low pH levels is not
unexpected given this species’ pattern of macro and mesohabitat use. Porochilus rendahli has been recorded from
very fresh and moderately clear waters. However, Burrows
et al. [256] found P. rendahli to be abundant in lagoons of
135
Freshwater Fishes of North-Eastern Australia
Movement
Little is known about this aspect of the biology of P.
rendahli, except that migration into lowland muddy
lagoons for spawning has been reported in the Alligator
Rivers region [193].
Trophic ecology
Information on the trophic ecology of P. rendahli
presented in Figure 1 is drawn from three separate studies:
Bishop et al. [193] in the Alligator Rivers region (n = 397);
Pusey et al. [1099] in rivers of Cape York Peninsula (n = 3)
and Pusey et al. [1082] in the Burdekin River (n = 10).
The diet of P. rendahli is relatively simple, being dominated by aquatic invertebrates and microcrustaceans. The
aquatic invertebrate component is dominated by chironomid midge larvae and small ephemeropteran nymphs.
Microcrustaceans varied in importance and composition
across the three studies, being absent from the Cape York
sample, contributing 10% in the Burdekin River sample
(comprised mainly of ostracods), and contributing 31% of
the total in the Alligator Rivers sample (dominated by
Cladocera) [193].
Fish (0.4%)
Other microinvertebrates (0.4%)
Unidentified (20.8%)
Microcrustaceans (30.1%)
Terrestrial invertebrates (0.1%)
Aerial aq. Invertebrates (0.5%)
Detritus (3.2%)
Terrestrial vegetation (0.1%)
Algae (0.2%)
Macrocrustaceans (0.5%)
Molluscs (0.8%)
Aquatic insects (43.1%)
Figure 1. The average diet of Porochilus rendahli. Summary
drawn from three separate studies (see text) and a combined
total of 410 individuals.
Conservation status, threats and management
Porochilus rendahli is classified as Non-Threatened by
Wager and Jackson [1353]. Given the paucity of information on this species, it is difficult to identify specific threats
to this species. Broad issues of relevance include reclamation, isolation and degradation of off-channel wetlands,
and the imposition of barriers to movement. An increased
effort to document the biology of this species, and of
plotosid catfishes in general, is needed.
Such a simple diet clearly reflects the constraints imposed
by a benthic habitat and small size. Of importance in this
regard is that the diet of P. rendahli is almost identical to
that of the juvenile forms of the larger plotosid catfishes
Neosilurus ater, N. hyrtlii and N. mollespiculum.
136
Tandanus tandanus Mitchell, 1838
Eel-tailed catfish
37 192006
Family: Plotosidae
Description
First dorsal fin: I, 6; Second dorsal fin and anal fin confluent with caudal fin: 140–150 rays; Pectoral: I, 10; Pelvic: I,
5; Scaleless; Gill rakers on first arch: 23–32 [34, 270, 936,
1069]. Figure: mature specimen, 175 mm SL, Little
Mulgrave River, November 1994; drawn 1995.
Wet Tropics [1093]: W = 1.18 x 10–4 L2.645, r2 = 0.554, p<
0.001, n = 215, range = 86–323 mm SL (but note the low
exponent and low r2 value);
Tandanus tandanus is a large, robust fish. A maximum
length of around 900 mm TL and weight of 6.8 kg has been
recorded but this species is more common to 500 mm and
1.8 kg [270, 748, 749]. Of 529 specimens collected by electrofishing and seine-netting in streams of the Wet Tropics
region over the period 1994–1997 [1093], the mean and
maximum length of this species was 171 and 400 mm SL,
respectively. The modal length of 191 fish collected largely
from gill-netting samples in the Burnett River was 420 mm
SL [99]. Of 2349 specimens collected by electrofishing and
seine-netting in streams of south-eastern Queensland over
the period 1994–2000 [1093], the mean and maximum
length of this species were 107 and 500 mm SL, respectively, with the majority (80% of individuals) 150 mm SL
or less.
Burnett River [205]: W = 4.4 x 10–6 SL3.244, r2 = 0.997,
p<0.001, n = 242, range = 33–474 mm SL;
Burnett River [99]: W = 4.0 x 10–3 SL3.329, r2 = 0.953,
p<0.001, n = 199, range = 190–520 mm SL;
Gwydir River (and elsewhere in the Murray-Darling
Basin) [359, 362]: W = 2.96 x 10–6 TL3.223, r2 = 0.992,
p<0.001, n = 858, range = ~30–590 mm TL. Note that this
equation tended to underestimate the weight of large fish
and a parabolic relationship was more suitable for fish
greater than 350 mm TL. This equation takes the form W
= 0.0225 TL2 – 11.278 TL + 1637.8, r2 = 0.941, p<0.001, n
= ~397.
All of the above studies recorded little difference in lengthweight relationships between the sexes.
Tandanus tandanus has a broad, slightly flattened head and
posteriorly tapering and compressed body. The mouth is
relatively small and inferior, with thick, fleshy lips
surrounded by four pairs of barbels. Anteriorly pointing
tubular nostrils are located on front border of upper lip.
Equations describing the relationship between length (SL
or TL in mm) and weight (W in g) are available for the
following populations:
137
Freshwater Fishes of North-Eastern Australia
Vomerine teeth are small, conical and arranged in a semicircular patch. The first dorsal fin is positioned anteriorly
on the body and preceded by a pungent, serrated spine.
The second dorsal and anal fins are confluent with caudal
fin, originating on the middle of the back. Pectoral fins are
located ventrally and also preceded by a pungent, serrated
spine. The entire body is scaleless with smooth, slimy skin;
the lateral-line is well-defined and straight. This species is
sexually dimorphic with the urinogenital papilla of
females triangular and that of males longer and cylindrical. Colour may vary from olive-green to brown, dark grey
or purplish on back and sides and fading to creamy-white
on ventral surface. Also ontogenetic colour variation, with
juveniles and subadults usually grey or brown with dark
brown mottling on sides; mottling is less prominent in
adult specimens. Preserved colouration brown to dark
grey, sides with lighter mottling [4, 21, 59, 76, 79, 81, 97].
Systematics
The genus Tandanus, originally proposed as a subgenus of
Plotosus, was erected by Mitchell [955] in 1838 to contain
T. tandanus. Tandan is an aboriginal word [797]. The two
nominal species Tandanus are endemic to Australia and
have disjunct distributions. Tandanus bostocki Whitley,
1944 [1389] is confined to coastal drainages of south-western Australia and T. tandanus is widely distributed
throughout eastern and inland Australia.
The taxonomy and phyletic structure of T. tandanus is
complicated and remains unresolved despite recent investigation. Lake [754] speculated that the Tandanus species
present in the Daintree River may be a distinct species due
to its extreme isolation from other populations of T.
tandanus. Merrick and Schmida [936] noted that northern
populations did show some differences in growth and
habitat preference but considered them conspecific with
the nominal form. Musyl [980], using electrophoretic
techniques, identified several genetically distinct populations: the nominal form in the Murray-Darling Basin and
the Hunter, Mary and Brisbane rivers; a subspecific form
of T. tandanus in the Fitzroy River of central Queensland;
and an undescribed species in the Bellinger and Nymboida
rivers (a tributary of the Clarence River). A fourth distinct
form from the Tully River was identified electrophoretically by Keenan et al. [682], confirming Lake’s initial suspicions that the Wet Tropics region may harbour an
undescribed species of Tandanus. This taxon exhibits
significant differences at 50% of loci examined (C.
Keenan, pers. comm. cited in [310]). Additional electrophoretic examination of populations of T. tandanus in
northern New South Wales also emphasised the distinctiveness of the Bellinger River catfish (fixed differences
between it and Murray-Darling and Nymboida River
138
catfish at 17% of allozyme loci surveyed) [982]. Further,
this study demonstrated that the catfish present in the
Nymboida River were sufficiently distinct from Murray/
Darling stocks (fixed differences at 8% of allozyme loci
surveyed) to warrant species level elevation, although
there was evidence of past, although not recent, hybridisation between these stocks [982]. Importantly, these
authors found little accompanying morphological variation between stocks and interpreted this as indicative of
cryptic speciation. Note however, that the Wet Tropics
population was not included in the morphometric analysis in this study, although they are superficially very similar in external morphology and colouration [1093]. Jerry
and Woodland [651] examined genetic differentiation
within the catfish populations of northern New South
Wales at a finer spatial scale than that of Musyl and Keenan
[982]. They found that the Bellinger River form also
occurred in the Macleay, Hastings and Manning rivers and
exhibited very little genetic differences across these rivers.
They confirmed that the Nymboida River form was indeed
a separate species and that it occurred in the Tweed,
Clarence and Richmond rivers. In contrast, significant
genetic structuring was evident in these populations, and
genetic similarities between them, particularly those in the
Tweed and Clarence rivers, and the population present in
the Namoi River (the type locality of T. tandanus) may
have arisen from hybridisation with Murray/Darling
stocks of T. tandanus translocated into the area in the early
1900s [651]. Collectively, these studies indicate the presence of several distinct taxa: 1) the nominal form in the
Murray Darling Basin and rivers of south-east
Queensland; 2) the Bellinger River form; 3) the Nymboida
or Clarence River form (including putative hybrids); 4) a
subspecies of T. tandanus in the Fitzroy River; and 5) the
Tully River form of the Wet Tropics region. Obviously,
further research is required to fully resolve the systematics
of this species, especially those populations of central and
northern Queensland, particularly in light of the widespread present practice of translocation of this species
throughout Queensland [982]. It is possible however, that
the extent of translocation undertaken in the past may be
so great (see below) as to obscure any definitive resolution
of the systematics and biogeography of this species
complex.
Whilst mindful of the existence of distinct forms of T.
tandanus in Queensland, and of the fact that no formal
description or allocation of names has yet occurred for any
such distinct forms, the present discussion retains this
name as applicable to all populations in north-eastern
Australia.
Tandanus tandanus
Queensland. Tandanus tandanus was the eighth most
abundant species collected in an extensive survey of the
Wet Tropics region and occurred in eight of 10 major
drainage basins, being absent from the Bloomfield River
and short coastal streams of the Cardwell area only [1085,
1087]. Subsequent survey work has confirmed its presence
in all major drainages of the region from the Daintree
River south to the Murray River [1093, 1096, 1177, 1179,
1183, 1184, 1185, 1187]. It is apparently absent from the
Mowbray River [1185] but probably occurs in this
drainage. This species has not been recorded from the
Herbert River [584, 643]. This species is widespread within
rivers of the Wet Tropics region. It was recorded from 36%
of all sites examined by Pusey and Kennard [1085, 1087]
and a similarly widespread distribution was recorded by
Russell and co-workers [1177, 1179, 1183, 1184, 1185,
1187] and in recent investigations in the Mulgrave and
Johnstone rivers (Table 1). It is apparently slightly more
widespread in the Mulgrave River than the Johnstone
River but this more properly reflects the greater proportion of sites in the latter river located at high elevation. It is
only moderately abundant in the Mulgrave and Johnstone
rivers, being the 12th most abundant species overall (7th
and 14th in the Mulgrave and Johnstone rivers, respectively). This species is a major component of the biomass
present within streams of the Wet Tropics region being the
second most important species overall (behind A. reinhardtii). Across both rivers, average and maximum numerical density estimates were 0.21 ± 0.03 fish.10m–2 and 3.91
fish.10m–2, respectively. Average and maximum biomass
density estimates were 27.2 ± 3.5 g.10m–2 and 80.6 g.10m–2
[1093]. Tandanus tandanus most commonly occurs with
(in decreasing order of abundance) M. s. splendida,
Distribution and abundance
Tandanus tandanus is a widespread species occurring in
coastal and inland drainages of eastern Australia from
Cape Tribulation in the Wet Tropics region of northern
Queensland south to the Shoalhaven River in central New
South Wales. Inland, it was once present throughout much
of the Murray-Darling Basin. In eastern Queensland it is
native to most coastal drainages from Myall Creek (just
north of Cape Tribulation) south to the border with New
South Wales, but there appears to be a 400 km gap in the
natural distribution of this species between (and including) the Herbert River and the O’Connell River in central
Queensland [1069, 1085, 1349]. It is also present in lakes
and streams on Fraser Island [1349] and North Stradbroke
Island off the south-eastern Queensland coast. In coastal
New South Wales it is native to most drainages from the
Queensland border south to the Manning River [553,
814]. There have been many introductions and translocations of hatchery-reared and wild fish to rivers within and
beyond the natural distribution of T. tandanus [95, 1350].
In northern Queensland, fish (some from Enoggera Dam
in the Brisbane River basin) have been translocated to Lake
Tinaroo impoundment in the Barron River basin where
they have become established in small numbers. They have
also been stocked in Freshwater Creek and the Lake Morris
impoundment (Barron River), the Atherton Tablelands
section of the North Johnstone River including tributaries
such as the Beatrice River and above Millaa Millaa Falls
[310, 582, 908]. Hundreds of fish bred in 1984/85 at the
Walkamin Research Station hatchery were released into
unspecified streams on the upper Atherton Tablelands
(Fisheries Research Branch (1985), cited in Clunie and
Koehn [310]); these streams could potentially include
those flowing into the Barron, Johnstone, Tully or Herbert
River basins. In central Queensland, catfish have been
successfully introduced into the Burdekin River, a catchment in which they do not naturally occur [1082]. This
species has also been stocked in impoundments in the
Fitzroy River basin [823].
Table 1. Distribution, abundance and biomass data for
Tandanus tandanus in the Wet Tropics region. Data
summaries for a total of 572 individuals collected from rivers
in the Wet Tropics region over the period 1994–1997 [1093].
Data in parentheses represent summaries for per cent and
rank abundance and per cent and rank biomass, respectively,
at those sites in which this species occurred.
On the basis of genetic evidence it has been suggested that
T. tandanus populations in the Brisbane River, south-eastern Queensland, may have been introduced from the
Murray-Darling Basin [682]. In coastal New South Wales,
successful introductions of T. tandanus into the Hunter,
Hawkesbury and Shoalhaven rivers have extended the
southerly range of this species [442, 443, 859, 860, 1069],
although this species may be indigenous to the latter two
rivers [437]. Clunie and Koehn [310] document numerous other introductions and translocations of this species
in New South Wales, ACT, Victoria and South Australia.
% locations
% abundance
Rank abundance
% biomass
Rank biomass
Tandanus tandanus is widely distributed and relatively
common in the Wet Tropics region of northern
139
Total
Mulgrave
River
Johnstone
River
43.3
50
41
1.6 (5.4)
2.6 (8.5)
1.3 (3.8)
12 (7)
7 (5)
14 (10)
13.1 (31.7)
2 (2)
20.1 (27.2) 10.4 (31.7)
2 (2)
2 (2)
Mean numerical density
(fish.10m–2)
0.21 ± 0.03
0.33 ± 0.08 0.15 ± 0.02
Mean biomass density
(g.10m–2)
41.4 ± 8.5
27.2 ± 3.5
19.6 ± 2.6
Freshwater Fishes of North-Eastern Australia
P. signifer, M. adspersa, C. rhombosomoides and H.
compressa. Anguilla reinhardtii is frequently abundant
(2nd most abundant) when syntopic with T. tandanus in
the Mulgrave River [1093].
and formed 1.0% of the total number of fishes collected
(12th most abundant). It has not been collected from the
Elliott River but is present and moderately common in
rivers of the Burrum Basin [157, 491, 736, 987, 1305]. With
the exception of small coastal streams of the Tin Can Bay
region, T. tandanus is present in most other streams south
to the Queensland–New South Wales border. Surveys
undertaken by us between 1994 and 2003 in south-eastern
Queensland [1093] collected a total of 3050 individuals of
T. tandanus and it was present at 61.7% of all locations
sampled (Table 2). Overall, it was the 14th most abundant
species collected (1.9% of the total number of fishes
collected) and was the 11th most abundant species at sites
in which it occurred (2.6%). In these sites, T. tandanus
most commonly occurred with the following species
(listed in decreasing order of relative abundance):
Psuedomugil signifer, Retropinna semoni, Melanotaenia
duboulayi, Craterocephalus marjoriae and Gambusia
holbrooki. It was most widespread in the Mary River where
it occurred at 78% of locations surveyed, but was also relatively widespread in streams of the Moreton region, the
Brisbane River and the Albert-Logan Basin (present at
60% or more of all locations surveyed). This species
achieved the highest relative abundances in the Brisbane
River where it formed 2.4% of the total catch and 4.2% of
the catch at those sites in which it occurred. It was also
moderately common in other basins of the south-eastern
Queensland region. By virtue of the relatively large size
attained by this species, T. tandanus formed a high proportion of the total biomass of fishes collected. It was the 2nd
most important species, forming 15.4% of the total
biomass of fish collected and 26.8% of the biomass at
those sites in which it was present. The greatest relative
biomass was observed in the streams of the Moreton Coast
and in the Brisbane River. Across all rivers, average and
Tandanus tandanus is very patchily distributed in rivers
and streams of coastal central Queensland. It has been
translocated to the Burdekin River where it is essentially
restricted to the site of introduction (Valley of Lagoons)
[1082]. We have collected only two individuals outside this
area over the period 1989–1997 [1093]. It is uncommon
and contributed 0.2% of the total electrofishing catch (and
was absent from seine-netting and gill-netting catches)
over the period 1989–1992 [1098]. This river has a high
diversity of plotosid catfishes (three species of Neosilurus
and Porochilus rendahli) and T. tandanus may compete
with these species and be limited in the extent to which it
may expand its distribution. This situation may not persist
if more impoundments are located on the upper Burdekin
River as neosilurid catfishes appear unable to spawn in
standing waters whereas T. tandanus may (see below).
This species is present but uncommon in the Pioneer River
[658, 1081]. It appears to be uncommon in short coastal
streams between Sarina and Yepoon, having been collected
only in Plane Creek [779], some streams of the Shoalwater
Bay area and in Water Park Creek [1328]. It is widespread
and generally moderately common in the Fitzroy River
basin [156, 160, 404, 405, 658, 659, 942, 1173, 1180, 1351],
Calliope River [915], Boyne River (possibly translocated)
[593], Baffle Creek [826] and the Kolan River [232, 658].
This species is widespread and generally common in
south-eastern Queensland. In a review of existing fish
sampling studies in the Burnett River, Kennard [1103]
noted that it had been collected at 30 of 63 locations
surveyed (7th most widespread species in the catchment)
Table 2. Distribution, abundance and biomass data for Tandanus tandanus. Data summaries for a total of 3050 individuals
collected from rivers in south-eastern Queensland over the period 1994–2003 [1093]. Data in parentheses represent summaries
for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Rank biomass
Mary River Sunshine Coast Moreton Bay
rivers and
rivers and
streams
streams
Brisbane
River
Logan-Albert
River
South Coast
rivers and
streams
61.7
78.0
37.9
60.0
59.5
67.6
50.0
1.87 (2.63)
1.69 (2.07)
0.78 (3.04)
1.30 (2.80)
2.44 (4.22)
2.04 (3.03)
1.18 (3.42)
14 (11)
13 (11)
10 (9)
11 (11)
11 (8)
9 (7)
15.35 (26.78) 12.66 (26.89)
11 (9)
0.79 (14.83)
47.44 (63.72) 37.77 (41.45) 16.32 (22.21) 13.38 (28.53)
2 (2)
2 (2)
4 (2)
1 (1)
2 (2)
3 (3)
2 (2)
Mean numerical density
(fish.10m–2)
0.24 ± 0.02
0.22 ± 0.02
0.06 ± 0.01
0.14 ± 0.03
0.33 ± 0.06
0.26 ± 0.03
0.09 ± 0.02
Mean biomass density
(g.10m–2)
19.03 ± 1.44
16.18 ± 1.74
3.61 ± 0.00 102.02 ± 41.04 33.20 ± 6.44
18.13 ± 2.10
9.52 ± 4.93
140
Tandanus tandanus
The widespread distribution within rivers of the Wet
Tropics region presented above is reflected in the wide
range of macrohabitat conditions detailed in Table 3. This
species occurs in small second order streams of small
catchment area (1 km2) through to fifth order streams of
several hundreds of square kilometres (Table 3). Such
streams range in size from about 2 to 40 m in width and
occur at elevations ranging up to 722 m.a.s.l. Note
however, that populations occurring at high elevation (i.e.
the Atherton Tablelands) are probably translocated.
Although this species occurs in streams with very little
riparian cover, the mean and weighted mean values
(34.7% and 41.7%, respectively) suggest that it occurs
most commonly and is most abundant in streams with an
intact riparian zone.
maximum numerical densities recorded in 600 hydraulic
habitat samples (i.e. riffles, runs or pools) were 0.24 individuals.10m–2 and 4.66 individuals.10m–2, respectively.
Average and maximum biomass densities at 451 of these
sites were 19.03 g.10m–2 and 208.79 g.10m–2, respectively.
Highest numerical densities and biomass densities were
recorded from the Brisbane River and streams of the
Moreton Coast, respectively. Juvenile and subadult fish
(≤150 mm SL, corresponding to two years or younger
[359, 362]; hereafter termed juveniles) were present in
greater densities (mean and maximum density of 0.26 and
4.66 individuals.10m–2, respectively) than adult fish (>150
mm SL, 2+ years [359, 362]) (mean and maximum density
of 0.09 and 0.75 individuals.10m–2, respectively) in
hydraulic habitat units where this species occurred in
south-eastern Queensland (n = 408 and 282 samples for
juveniles and adults, respectively) [1093]. Conversely,
adult fish formed greater biomass densities (mean and
maximum biomass of 27.64 and 208.79 g.10m–2, respectively) than juveniles (mean and maximum biomass of
3.04 and 41.10 g.10m–2, respectively) (n = 266 and 399
samples for adults and juveniles) [1093].
This species occurs in streams of a wide range of gradient
from lowland channels with a gradient less than 0.1% to
cascade sections of streams with a gradient exceeding 7%.
It most commonly occurs in and is most abundant in
Table 3. Macro/mesohabitat use by Tandanus tandanus in the
Wet Tropics region (juveniles and adults combined). Data
summaries for 223 individuals collected from 54 locations in
the Mulgrave/Russell, Johnstone and Tully rivers between
1994 and 1997 [1093]. W.M. refers to the mean weighted by
abundance to reflect preference for particular conditions.
Tandanus tandanus is widespread and moderately
common in coastal rivers of northern and central New
South Wales [282, 437, 438, 441, 484, 553, 814]. This
species was once present throughout much of the MurrayDarling Basin [1069] where it was historically very
common [778], being rare or absent only upstream of
Wagga in the Murrumbidgee River and upstream of
Mulwala in the Murray River. Recent surveys [553, 807]
and reviews by Morris et al. [965] and Clunie and Koehn
[310] reveal that since the late-1970s and early-1980s, it
has undergone dramatic declines in distribution and
abundance throughout much of the basin, although it is
still present and locally common in some parts of the
Queensland section of the upper Darling River
(Condamine River) and in many impoundments in New
South Wales and Victoria. Refer to Morris et al. [965] and
Clunie and Koehn [310] for more details on the present
distribution and population status of this species in southern Australia.
Parameter
2
Catchment area (km )
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
Min.
Max.
Mean
W.M.
1.0
1.5
8.1
10
1.9
0
334.9
67
104
722
39.1
85
71.4
16
40.2
74
10.9
34.7
80.9
17.6
41.9
59.6
11.2
41.7
Gradient (%)
0.05
Mean depth (m)
0.19
Mean water velocity (m.sec–1) 0
Juveniles of this species have been reported to form loose
schools but adults are usually solitary, except when breeding [270].
Macro/mesohabitat use
Tandanus tandanus is found in a variety of lotic and lentic
habitats including small coastal streams, rainforest
streams, large rivers and in dune lake and stream systems.
It is also common in some artificial lakes and impoundments.
141
7.33
0.87
0.45
0.84
0.40
0.17
0.75
0.42
0.17
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
48.0
52.0
72.0
56.0
41.0
76.0
98.0
5.6
15.3
21.1
14.1
13.1
21.9
9.1
2.8
12.4
24.2
14.8
14.9
23.8
7.3
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
7.0
6.8
33.0
75.0
10.0
47.6
12.5
11.4
35.0
75.0
0.4
0.2
2.1
7.1
0.5
7.9
2.0
1.8
8.0
16.4
0.4
0.1
1.4
6.7
0.6
10.8
1.7
1.8
11.4
21.5
Freshwater Fishes of North-Eastern Australia
streams of a gradient less than 1% (Table 3). Such streams
tend to be about 0.40 m deep and with current velocities
of 0.17 m.sec–1 and are best typified as riffle/runs.
Although this species may be found in stream reaches
dominated by mud and sand, the average substrate
composition in sites in which it occurs tends to be highly
diverse containing approximately equal proportions of
sand gravel and cobbles and a slightly elevated proportion
of fine gravel and rocks. These latter two substrate types
are proportionally more important in sites in which this
species is abundant.
Table 4. Macro/mesohabitat use by Tandanus tandanus in
rivers of south-eastern Queensland (juveniles and adults
combined). Data summaries for 3050 individuals collected
from samples of 600 mesohabitat units at 183 locations in
south-eastern Queensland streams between 1994 and 2003
[1093]. W.M. refers to the mean weighted by abundance to
reflect preference for particular conditions.
Parameter
Catchment area (km2)
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
Tandanus tandanus occurs in streams with moderately
abundant in-stream cover (Table 3). It is not common in
streams with abundant introduced para grass, however.
Leaf litter is moderately abundant in sites in which this
species is common and the disparity between the mean
and weighted mean values for undercut banks and root
masses, suggest that this species is more abundant in sites
in which these microhabitat elements are common.
Min.
5.6 10 211.7
4.0
270.0
0.5
335.0
0.0
460
1.8
46.8
0.0
91.1
Gradient (%)
0
Mean depth (m)
0.05
Mean water velocity (m.sec–1) 0
In rivers and streams of south-eastern Queensland, T.
tandanus is widely distributed, ranging between 0.5 and
335 km from the river mouth and at elevations up to 460
m.a.s.l. (Table 4). It most commonly occurs within 200 km
of the river mouth and at elevations around 110 m.a.s.l. It
is present in a wide range of stream sizes (1.8–46.8 m
width) but is more common in streams of intermediate
width (6–10 m) and with low to moderate riparian cover
(<40%). There is little ontogenetic difference in the
macrohabitat use of T. tandanus, possibly suggesting that
juveniles do not disperse far from the natal habitat [1093].
However, some ontogenetic variation in mesohabitat use
is evident, with juvenile fish collected more frequently in
relatively shallow, moderately flowing runs and adults
more commonly collected in deeper runs and pools
(weighted mean velocity = 0.14 m.sec–1 and 0.12 m.sec–1
for juveniles and adults, respectively; weighted mean depth
= 0.34 m and 0.41 m for juveniles and adults, respectively)
[1093]. Adults and juveniles were collected over a similarly
wide range of substrate conditions, but both age-classes
were most common in mesohabitats dominated by sand,
fine gravel, coarse gravel and cobbles. Juveniles and adults
were especially common in mesohabitats with abundant
aquatic macrophytes, filamentous algae, leaf litter undercut banks and root masses (Table 4). However, adults
appear to prefer mesohabitats with a greater availability of
undercut banks (weighted mean 16.1% versus 8.9% for
adults and juveniles, respectively) and root masses (18.7%
versus 13.9% for adults and juveniles, respectively) [1093].
Max.
3.02
1.10
0.87
Mean
W.M.
796.8 1216.7
46.6
56.8
146.6 175.7
97
110
8.9
7.6
38.6
38.5
0.38
0.41
0.13
0.31
0.35
0.13
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
57.1
100.0
72.4
78.2
66.8
57.1
76.0
4.5
16.9
21.1
26.8
21.3
7.8
1.6
3.8
14.9
20.4
30.3
21.8
7.6
1.3
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
69.6
65.9
45.0
65.7
39.1
92.6
37.6
22.5
96.3
100.0
11.0
8.4
1.5
4.8
1.3
12.9
3.7
3.3
13.9
19.0
12.2
10.8
1.3
4.9
1.6
10.5
3.2
3.3
10.4
15.0
benthic pool-dwelling species [553] and it has been
reported to occur over sand or gravel substrates in billabongs, ponds, lakes and turbid slow-flowing streams and
rivers, and where aquatic and fringing vegetation is
common [270, 310, 814, 1069]; it has also been reported to
be more abundant in lakes and backwaters than in flowing
water [749]. Richardson [1133] reported that juvenile fish
in the Tweed River, northern New South Wales, were more
common in deep, slow flowing sites with mud-gravel
substrates, aquatic plant cover and deposits of organic
detritus. Adults had similar habitat preferences but were
more common in areas with bedrock substrates.
Microhabitat use
Both juvenile and adult T. tandanus in the Wet Tropics
region occur most frequently in water velocities of less
than 0.3 m.sec–1 although juveniles are more frequently
found in faster flowing water than adults (Fig. 1a). Both
Tandanus tandanus has been reported to occur at elevations greater than 600 m.a.s.l. in the Condamine River
[310]. Harris and Gehrke classified T. tandanus as a
142
Tandanus tandanus
aquatic macrophytes and leaf litter than are juveniles (Fig.
1). Very small juveniles (<60 mm SL) are frequently found
in very swiftly flowing water, sheltering under the straplike leaves of Aponogeton spp. In summary, adult T.
tandanus in the Wet Tropics region tend to occur most
frequently in deeper, slow waters over a mixed substrate
with a high proportion of mud and sand, and in association with root masses, undercut banks and woody debris,
whereas juveniles tend to occur more commonly in
shallow, swiftly flowing waters associated with the
substrate, leaf litter or macrophytes.
age classes are benthic in habitat occupying the lower onethird of the water column and often in direct contact with
the substratum (Fig. 1d); they consequently experience
reduced focal velocities compared to average current
velocity (Fig. 1b). Adult and juvenile T. tandanus partially
segregate with respect to depth and substrate composition
with juveniles being more frequently collected from
shallow areas (10–40 cm) (Fig. 1c) with coarse substrates
(Fig. 1e) whereas adults prefer deeper areas with slightly
finer substrates. Adults are more frequently collected from
large woody debris, root masses and undercuts and less
frequently from amongst the substrate, associated with
(a)
60
(b)
(a)
40
30
60
40
40
20
20
0
0
40
20
20
10
0
0
Mean water velocity (m/sec)
(c)
Focal point velocity (m/sec)
60
(d)
25
30
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
80
20
60
40
15
20
10
20
0
0
25
(b)
60
(e)
Total depth (cm)
40
20
40
10
(f)
5
20
0
0
Total depth (cm)
Relative depth
30
30
(e)
10
20
10
5
10
0
0
Substrate composition
20
15
20
15
Relative depth
(f)
10
5
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Tandanus tandanus juveniles
(solid bars) and adults (open bars) in the Wet Tropics region.
Summaries derived from capture records for 76 juvenile (≤150
mm SL) and 89 adult (>150 mm SL) individuals from the
Johnstone and Mulgrave rivers, northern Queensland, over the
period 1994–1997 [1093].
Microhabitat structure
Figure 2. Microhabitat use by Tandanus tandanus juveniles
(solid bars) and adults (open bars) in south-eastern
Queensland. Summaries derived from capture records for
550 juvenile (≤150 mm SL) and 167 adult (>150 mm SL)
individuals from the Mary and Albert rivers, south-eastern
Queensland, over the period 1994–1997 [1093].
143
Freshwater Fishes of North-Eastern Australia
(1996), cited in [310]) and may explain anecdotal accounts
of fish kills following snow melts [310]. Laboratory experiments [749, 752] revealed that juvenile fish (60–80 mm,
probably sourced from the Murray-Darling Basin) became
motionless and lay on their sides at very low temperatures
(4°C), and did not recover if exposed to this temperature
for more than a few days. Fish did however, survive shortterm (~1 hour) exposure to temperatures as low as 1°C
[749, 752]. The deaths of adult catfish (up to 1.8 kg) were
observed in artificial outdoor ponds exposed to winter
temperatures around 4°C [749, 752]. When gradually
acclimated, fish in the laboratory survived for several days
at temperatures greater than 35°C but became very
distressed and lost their equilibrium at 38°C, surviving
when temperatures were subsequently reduced [749, 752].
In rivers of south-eastern Queensland, T. tandanus was
most frequently collected from areas of low water velocity
(usually less than 0.2 m.sec-1) (Fig. 2a and b). Juveniles
(≤150 mm SL) have been recorded at maximum mean and
focal point water velocity of 1.44 and 1.01 m.sec-1, respectively. Adults (>150 mm SL) have been recorded at lower
maximum mean and focal point water velocities (0.66 and
0.48 m.sec–1, respectively) than juveniles. This species was
collected over a wide range of depths but juveniles were
common in water depths between 10 and 50 cm; adults
were collected more frequently in deeper water (Fig. 2c).
Both age classes are benthic in habit and most commonly
occupy the lower water column or occur in direct contact
with the substrate (Fig. 2d). It is found over a wide range
of substrate types but most often over sand, gravel and
cobbles, with little difference in substrate use between age
classes (Fig. 2e). Adult T. tandanus were more commonly
collected close to the stream-banks (within 1 m) than juveniles (75% of adults versus 49% of juveniles) [1093], and
almost always in close association with some form of
submerged cover (Fig. 2f). Substantial ontogenetic variation in the use of microhabitat structures was evident:
juveniles were most frequently collected in close association with the substrate, aquatic macrophytes (especially
Vallisneria nana and Potomogeton spp.), filamentous algae
and leaf litter beds; adults were more commonly collected
in undercut banks, root masses and large woody debris
(Fig. 2f).
Tandanus tandanus appears to tolerate a wide range of
dissolved oxygen concentrations, fish in south-eastern
Queensland having been collected in waters ranging from
0.3–17.1 mg.L–1 (Table 5). Field experiments revealed that
subadult fish (200–300 mm) introduced to saline pools in
the Wimmera River, western Victoria, showed acute LD50s
at dissolved oxygen concentrations of 0–2% saturation
(Ryan et al. (1999), cited in [310]). In contrast, T. tandanus
in the Wet Tropics region has been recorded from welloxygenated streams only (Table 5). Significant fish kills
involving this species in the upper North Johnstone River
downstream of Malanda have been associated with
organic contamination and high levels of BOD. It is possible that substantial variation in tolerance to hypoxia
occurs across this species’ range.
Several workers have reported a strong association
between T. tandanus and aquatic vegetation in the
Murray-Darling Basin and elsewhere, but a reliance on this
habitat component is not universal; Clunie and Koehn
[310] concluded that the significance of aquatic macrophytes to this species was unclear and warranted further
investigation.
This species has been collected in acidic and basic conditions in streams of south-eastern Queensland (range
4.8–9.1) and the Wet Tropics region (range 5.1–8.4) (Table
5). Southern populations also appear tolerant of high
levels of suspended sediment. The maximum turbidity at
which this species has been recorded in south-eastern
Queensland is 250 NTU, but it appears to prefer less turbid
waters (mean 6.3 NTU). This species is also relatively
common in the naturally turbid waters of the upper
Darling River, where it has been recorded at turbidities up
to 910 NTU (D. Moffat, pers. comm., cited in [310]).
Streams of the Wet Tropics in which this species occurs are
generally very clear and the high value reported in Table 5
(29.7 NTU) was associated with a summer thunderstorm
and was transient only.
Environmental tolerances
Tandanus tandanus is reputedly a hardy species [748, 749],
an observation supported by some limited experimental
and field evidence of the environmental tolerances of this
species. In Queensland rivers it has been collected over a
relatively wide range of physicochemical conditions (Table
5). Populations from south-eastern Queensland appear
tolerant of a relatively wide range of temperatures
(8.4–33.6°C), whereas those of rainforest streams of the
Wet Tropics have been collected over a smaller range
(17–29.9°C). In the Murray-Darling Basin, low water
temperatures due to cold water discharges from impoundments have been implicated in fish kills and a decline in
range in the upper Murray and Murrumbidgee rivers [270,
310, 749, 1069, 1224]. The stress of low water temperatures
may predispose T. tandanus to infection (Bowmer et al.
We have collected T. tandanus in streams with relatively
high conductivities (up to 3580 µS.cm-1) (Table 5). This
species is able to tolerate relatively high salinities: experimental acute and chronic LD50s have been observed
as 13.6 ppt and 17.8 ppt, respectively [311, 641]. Field
experiments revealed that subadult fish (200–300 mm)
144
Tandanus tandanus
Reproduction
The reproductive biology and early development of southern populations of T. tandanus is comparatively well studied but there is little information available for this taxon in
the Wet Tropics region (Table 6). This species spawns and
completes its entire life cycle in freshwater and will breed
in outdoor ponds [750, 751, 809] and impoundments [99,
310, 359]. Eggs fertilised in outdoor ponds have also been
reared in aquaria [751].
introduced to saline pools in the Wimmera River, western
Victoria, showed acute LD50s at salinities between 23.4
ppt and 26.4 ppt (Ryan et al. (1999), cited in [310]).
Juvenile fish were reported by Ryan et al. to be significantly
less tolerant than adults to elevated salinities, these authors
speculating that young fish had poorly developed
osmoregulatory abilities and insufficient time to acclimatise to elevated salinities through their life history. Waters
of the Wet Tropics region where this species occurs are
very dilute (Table 5).
Sexual maturity is reached within five years of age. Davis
[359, 361], in his study of T. tandanus from the Gwydir
River, observed that fish of both sexes commenced gonadal
development (reproductive stage III) at two years of age.
Fifteen per cent of male fish examined were sexually
mature (reproductive stage V) at three years of age and at
weights between 600–700 g (equivalent to about 380–395
mm TL); all males were mature by five years of age and at
weights over 1.2 kg (equivalent to about 460 mm TL or
greater). Some females in this study tended to mature at a
slightly smaller size (27% of females were of reproductive
stage V at weights of 400–500 g, equivalent to 335–355 mm
TL) but all females examined had reached sexual maturity
at the same age and size as males [359, 362]. Bluhdorn and
Arthington [205] observed that female fish in the Burnett
River, south-eastern Queensland, also mature at a slightly
smaller size than males; the smallest mature female (reproductive stage V) was 299 mm SL and the smallest mature
male was 384 mm SL. Richardson [1133] reported that
male fish in the Tweed River, northern New South Wales,
matured at 370 mm TL and females matured at 390 mm
TL. Sexually precocious females (~150 mm, 50–80 g) have
been reported from a small overcrowded dam in New
South Wales (P. and J. Norman, pers. comm., cited in
Clunie and Koehn [310]).
There have been several large fish kills in eastern
Queensland waters that have included T. tandanus [10, 16,
1093]. Despite investigation by the Queensland
Environmental Protection Agency in some cases, the
cause(s) of these fish kills could not usually be established
with any certainty, although hypoxic or anoxic conditions
associated with large accumulations of organic matter
following flow events were often implicated [10, 16, 1093].
Several instances of fish kills have been reported from
agricultural areas in the Murray-Darling Basin and elsewhere, although the causes are usually unclear [81, 221,
310]. Pesticide runoff from cotton growing areas has been
implicated in some fish kills [81]. Tandanus tandanus
sampled from tributaries of the Darling River in central
New South Wales have been found to contain endosulfan
residues up to 0.31 mg/kg wet weight [998, 1002]. These
levels lie within the concentration range shown to cause
ultrastructural changes in the gills and liver of T. tandanus
exposed to endosulfan under experimental laboratory
conditions [999, 1000, 1001]. Olsen [1026] detected relatively high residues of organochlorine insecticides (DDT
= 1090 µg.kg-1 and Dieldrin = 280 µg.kg-1) in T. tandanus
from South Australia.
Tandanus tandanus has an extended breeding season
during spring and summer in south-eastern Queensland;
ripe (stage V) and spent fish in the Burnett River were
present between October and March [99]. Similar temporal patterns in GSI values were observed with peak
monthly mean GSI values occurring in October for
females (~6.2%) and remaining elevated until about
January. Male GSI values showed a similar temporal
pattern but were much lower (<1%, but note that these
were estimated from maturing fish of stage IV only) [99].
Peak GSI levels for female fish in the Tweed River, northern New South Wales were also recorded in October
[1133], with spawning suspected to occur through to
February [1135]. The phenology of spawning in southern
Australia is generally similar (if slightly more concentrated
and later in the year) in Queensland rivers. Females from
Murray-Darling populations were reported to have the
highest standardised ovarian weights and the largest
Table 5. Physicochemical data for Tandanus tandanus in the
Wet Tropics region and south-eastern Queensland over the
period 1994 to 2003 [1093].
Parameter
Min.
Max.
Wet Tropics region (n = 133)
Water temperature (°C)
17
Dissolved oxygen (mg.L–1)
4.9
pH
5.1
Conductivity (µS.cm–1)
6
Turbidity (NTU)
0.2
Mean
29.9
11.6
8.4
62
29.7
23.1
7.0
7.2
33.9
3.4
South-eastern Queensland (n = 380)
Water temperature (°C)
8.4
33.6
Dissolved oxygen (mg.L–1)
0.3
17.1
pH
4.8
9.1
Conductivity (µS.cm–1)
19.5
3580.0
Turbidity (NTU)
0.2
250.0
19.5
7.6
7.7
488.9
6.3
145
Freshwater Fishes of North-Eastern Australia
intraovarian eggs in November and December, and ripe
fish were most abundant in January and February, leading
Davis [359, 361] to conclude that spawning was concentrated in summer from January to March. Note however
that a small number of ripe fish were present as early as
September [359, 361]. Overall sex ratios for 2+ fish (n =
976) from the Gwydir River have been reported as 0.94
females for every male [361]. Sex ratios for adult fish
(minimum 250 mm TL, n = 191) from the Burnett River
were reported as 0.78 females for every male [99].
areas, elevated discharges may occur during the summer
breeding period and it has been suggested that the consequent inundation of floodplains and shallow backwaters
may encourage food production and facilitate growth of
fish larvae and juveniles [361]. However, it appears that
this species may require stable low flows for spawning and
nest-building. In artificial ponds, fluctuating water levels
that expose nests before the eggs are laid can result in the
abandonment of nests and although another nest may be
built, a sequence of several interruptions will result in a
resorption of oocytes and the failure of a female to breed
in a particular year [750].
The spawning stimulus for T. tandanus is unknown but
Davis [361] suggested that increasing temperature was the
primary factor stimulating spawning. The October peak in
reproductive activity in Burnett River populations
occurred at surface water temperatures of 23°C and ripe
females were not recorded at temperatures below 20°C
[99]. This species (possibly the male [1158]) constructs a
nest in which the female deposits the eggs. Nest building
may occur between one and four weeks prior to actual
spawning [310]. Critical temperatures for the commencement of nest-building and spawning in southern populations have been reported as 24°C [361, 750], running ripe
males have been observed at 18°C (Raadik, pers. comm.,
cited in Clunie and Koehn [310]), fish have been observed
on nests at bottom temperatures of 13.8°C and the first
eggs were laid at water temperatures of around 21°C [310].
Spawning cues are probably not associated with rising
water levels or flooding [361] but this may hasten spawning for fish in artificial outdoor ponds [750]. In southern
In the Wet Tropics region, nest construction commences
in late September or October [1093] and very small individuals are present in November or December (Figure 3).
In south-eastern Queensland, we have observed nests in
early September [1093] and the peak spawning period in
spring and early summer in this region coincides with
increasing water temperatures, increasing day length and a
reduced likelihood of elevated discharges. However,
length-frequency data (Figs. 3 and 4) indicate that very
small juvenile fish (<30 mm SL) were present in streams of
both northern and south-eastern Queensland for an
extended period from spring through summer in the Wet
Tropics region and spring to autumn in south-eastern
Queensland. Juveniles from 30–60 mm SL were most
common in south-eastern Queensland streams in the
summer months, suggesting that the development of
30
40
Spring
(n = 445)
30
Summer
(n = 735)
Aug. - Dec.
(n = 244)
20
Jan. - April
(n = 92)
May - July
(n = 193)
AutumnWinter
(n = 1169)
20
10
10
0
0
Standard Length (mm)
Figure 3. Temporal variation in length-frequency distributions
of Tandanus tandanus, from sites in the Mulgrave and
Johnstone rivers of the Wet Tropics region sampled between
1994 and 1997 [1093]. The number of fish from each period
is given in parentheses.
Standard length (mm)
Figure 4. Seasonal variation in length-frequency distributions
of Tandanus tandanus, from sites in the Mary, Brisbane, Logan
and Albert rivers, south-eastern Queensland, sampled
between 1994 and 2000 [1093]. The number of fish from
each season is given in parentheses.
146
Tandanus tandanus
T. tandanus in the upper Noosa River, south-eastern
Queensland: ‘… we noticed a violent commotion in the
water under an overhanging bank, and on investigation
with a paddle we had the good luck to pick up four large
and healthy River Jewfishes (Tandanus tandanus), the
marriage ceremonies of which we had thus cruelly and
wantonly interrupted.’
larvae and juveniles occurred not only during low-flow
conditions normally experienced during spring and early
summer in this region, but also during higher flows
normally occurring in mid- to late summer [1093]. A
prolonged spawning season is not evident in streams of
the Wet Tropics region (Fig. 3). It is noteworthy that southeastern populations are dominated by individuals less than
90 mm SL whereas the northern is skewed towards larger
individuals.
The abundance of adult males in individual runs or pools
in streams of the Wet Tropics region often seems to be in
excess of the number of nests particularly if nests are
located close to areas of undercut banks or extensive root
masses [1093]. It is unknown whether males compete for
nest sites, whether they assess potential mates or indeed
whether females assess the suitability of males and their
nests, or whether small males have alternative mating
strategies when faced with a shortage of potential nesting
sites.
Nesting occurs in a wide range of habitats including runs
and pools in small to medium sized stream in south-eastern Queensland [1093], flooded and shallow portions of
large streams and still backwaters in southern Australia
[751, 933, 1093], and also in shallow impoundments (e.g.
Wivenhoe Dam and North Pine Dam [1093]). Merrick
and Midgley [933] observed a nest in water depths of 0.6
m and mean water velocities of 0.05–0.07 m.sec–1 in the
Mary River, south-eastern Queensland. However, microhabitat characteristics of nest sites do vary widely and we
have observed active nests in south-eastern Queensland
streams in water depths ranging from 0.2–1.8 m and velocities ranging from 0–0.1 m.sec-1 [1093]. Clunie and Koehn
[310] have reported nests in water depths ranging from
0.35–1.6 m in a Victorian Lake. Nest location in streams of
the Wet Tropics region appears to be non-random and
associated with the thalweg track. Nests are more
frequently situated at the downstream end of a run than in
the upper half and their location may be associated with
areas of downwelling. The extensive engineering that takes
place during nest construction may even create areas of
greater exchange between surface and hyporheic waters.
Demersal, non-adhesive eggs are deposited in the nest and
these settle within the interstices of the substrate. It is
unknown whether fertilisation occurs in the water column
before egg settlement within the nest or subsequently as
the male swims over and inspects the nest after each bout
of egg deposition by the female [749, 933, 936]. After
spawning, the female moves away and the male guards and
maintains the nest [310, 933]. Males have been observed
aggressively chasing away intruders (including alien
species such as redfin – Perca fluviatilis [310]) and fanning
the nest with their fins to clear away sediment and debris.
This possibly also facilitates egg settlement within the
substrate [310, 748, 1093, 1158]; however, both sexes may
guard the nest in artificial ponds [749]. We have also
observed single adult fish periodically making forays onto
the nest after taking refuge in adjacent undercut banks and
root masses (usually within 3 m of the nest) in the
Daintree and Mary rivers [1093]. The same nest may be
used in consecutive years, although it is unclear whether
by the same pair of fish [310, 933]. Three separate size
classes of larvae sampled within a nest in a Victorian lake
[310] indicate that multiple spawnings may also occur in
the same nest, with the male possibly attracting a number
of females to the nest over a breeding season [310]. It is
also possible that several males used the same nest over the
breeding season [310].
The nest is usually characterised by a circular, saucershaped depression in the substrate, 0.5 to 2 m in diameter,
and made of coarse sand or gravel with a central depression, usually of coarser material such as coarse gravel and
sometimes rocks and sticks [270, 310, 750, 933]. Human
refuse such as bottles and cans have been recorded in the
central portion of some nests [310]. Some nests are simply
slight depression in beds of aquatic charaphytes (Chara
spp. and Nitella spp.) with very little exposed substrate
[310, 1093]. Larger fish are reported to construct larger
nests [310]. Nests can also be oval or U-shaped (nest shape
may depend on locality, with fish in the Bellinger River,
northern New South Wales, usually constructing U-shaped
nests (Bishop, cited in [982]). In an artificial outdoor pond,
spawning has also been reported in the absence of a nest
but instead occurred directly on gravel [749].
Descriptions of gonad morphology and histology are
available in Davis [359, 360] and Machin [831]. Fecundity
for T. tandanus varies with fish size, linearly with weight
and exponentially with length for fish from the Gwydir
River [359, 361] (Table 4). In this study, estimates of total
fecundity for mature and ripe fish ranged from 2000 eggs
for fish of 675 g to 20 600 eggs for fish of 2275 g [359, 361].
In artificial ponds fish ranging in weight from 1250 to
Elaborate courtship and spawning displays have been
reported to occur directly above or near the nest [283,
933, 1158, 1387]. In 1917, Ogilby [1023] published the
following observations of reproductive behaviour of
147
Freshwater Fishes of North-Eastern Australia
Incubation periods appear relatively short and have been
reported to range from 8 to 11 days (at 15–21°C) [748]
and 6 to 7 days (at 19–25°C) in southern Australia [749,
751]; the duration of egg development is likely to be
shorter in warmer water temperatures in northern rivers.
Photographic images and brief descriptions of larval
development are available in Lake [749, 751]. Larvae are
comparatively poorly developed at hatching, ranging in
size from 7.0 to 7.4 mm TL and lacking barbels and
pectoral fins. Barbels appear as tiny buds three days after
hatching [751]. At seven days larvae were reported to be 12
mm and had distinguishable barbels [749, 752] but larvae
at 12 days have also been reported to attain lengths of only
10.5–11.0 mm TL [751]. Larvae were free swimming at
2000 g were estimated to contain between 18 000 and
26 000 eggs [750] suggesting they were more fecund than
wild fish of equivalent size (9000 to 15 000 eggs for fish
from the Gwydir River [359, 361]). Intraovarian eggs are a
clear dark amber colour and range in size from about
2.0–3.0 mm diameter, increasing with the size and also
fecundity of the fish [361, 751]. Eggs range from 3.1–3.4
mm in diameter when water-hardened [749, 751]. The
developing eggs are spherical, light green to yellow in
colour, the perivitelline space is small, the yolk is granular
in appearance without major oil globules and the chorion
is thick (0.15–0.2 mm), slightly rough and transparent
[749, 751]. Photographic images of egg development are
available in Lake [749, 751].
Table 6. Life history information for Tandanus tandanus.
Age at sexual maturity
4–5 years [359, 361]
Minimum length of gravid (stage V)
females (mm)
335–355 mm TL [359, 361]; 299 mm SL [205]; 390 mm TL [1133]; 150 mm TL [310]
Minimum length of ripe (stage V) males (mm)
380–395 mm TL [359, 361]; 384 mm SL [205]; 370 mm TL [1133]
Longevity
At least 8 years (may be considerably longer) [359, 362]; 11–12 years [310, 1209]
Sex ratio (female to male)
0.94:1 [361]; 0.78:1 [99]
Occurrence of ripe (stage V) fish
September–March; slightly later in cooler southern states [99, 270, 359, 361]
Peak spawning activity
October–January in the Burnett River [99]; October in the Tweed River [1133];
January–March in the Murray-Darling Basin [359, 361]
Critical temperature for spawning
? >20°C [99, 361, 750]
Inducement to spawning
? Increase in water temperatures; water level rise may hasten spawning [361, 750]
Mean GSI of ripe (stage V) females
Maximum 6.2% [99]
Mean GSI of ripe (stage V) males
Maximum <1% (stage IV only) [99]
Fecundity (number of ova)
Maximum total instantaneous fecundity = 26 000 (increases with fish size) [359, 361,
750]
Total fecundity (TF)/Length (mm TL) or
Weight (g) relationship
TF = 5.2 x 10–8 L4.19, r = 0.593, n = ~37, p<0.001 [359, 361];
TF = 7.947 W – 1156, r = 0.547, n = ~37, p<0.001 [359, 361]
Egg size (diameter)
Intraovarian eggs from ripe fish 2.0–3.0 mm, eggs size increasing with size and
fecundity of the fish [359, 361]; Water-hardened eggs 3.1–3.4 mm [749, 751]
Frequency of spawning
Annually [732]
Oviposition and spawning site
Non-adhesive, demersal eggs deposited in an oval or U-shaped gravel nest and settle
within interstices of substrate. Nest usually circular, saucer-shaped depressions (0.5–2
m diameter), composed of fine - coarse gravel (maximum substrate size 5 cm). Nest
constructed by male 1–2 weeks prior to spawning. [750, 933, 936]
Spawning migration
None known
Parental care
Usually male but both sexes may guard, clean and fan nest until eggs hatch. Nestguarding adults observed to take refuge in adjacent undercut banks and root masses
in the Daintree River, northern Queensland and the Mary River, south-eastern
Queensland [750, 933, 936, 1093]
Time to hatching
6–7 days (at 19–25°C) [750, 751]; 8–11 days (at 15–21°C) [748]
Length at hatching (mm)
7.0–7.4 mm TL [751]
Age at free swimming stage
12–14 days [751]
Age at loss of yolk sack
?
Age at first feeding
19 days [751]
Length at first feeding
?
Length at metamorphosis
14–16 mm TL [751]
Age at metamorphosis
23–24 days [749, 751]
148
Tandanus tandanus
and adult fish in pool-overfall type fishways in the
Brisbane River basin (details on abundance, timing or
direction of movements unclear). Small numbers of adults
have been recorded in fishways on tidal barrages in the
Kolan [11, 232], Burnett [1173, 1276, 1277] and Mary
rivers [158, 159]. Fish appeared to be making upstream
movements as they were reported to be ascending the fishways in the Fitzroy, Kolan and Burnett River studies [232,
1173, 1276, 1277]. Stuart and Berghuis [1276, 1277]
recorded low numbers of adult T. tandanus migrating
upstream in May and August and throughout the spring
months. These authors suggested that these fish were
moving upstream after being displaced downstream of the
tidal barrage by flood events [1276, 1277]. Reynolds
[1131] speculated that the lack of a distinct spawning or
dispersal migration indicates that local populations of this
species are likely to be susceptible to local anthropogenic
disturbances.
12–14 days and fed at 19 days, with the pectoral fin buds
visible by this time [751]. Larvae reached 15 to 19 mm by
17–21 days and larval development was almost complete
at 23 days [749, 751]. Following metamorphosis, growth is
rapid, reaching 90 mm TL in the first winter, 300–400 mm
TL by 16 months, 170–360 mm by 30 months, 250–480 by
42 months and 500 mm by the sixth year [362, 752, 936].
The lifespan of T. tandanus is unknown and estimates vary
depending on the method of age determination used; lifespan may also vary among populations due to genetic and
environmental factors [310, 1209]. Estimates of fish from
the Gwydir River using dorsal spine annuli validated with
fish of known age and tagging data, recorded a maximum
age of eight years [359, 362]. Elsewhere, maximum ages
based on otolith analysis have been estimated as 11–12
years [1209] and 12 years (T. Raadik, pers. comm., cited in
Clunie and Koehn [310].
Movement
Limited information on the movement patterns of T.
tandanus is available. This species has been suggested to be
generally sedentary with a small home range [359, 362,
1133]. Adults are mainly active at night with peak activity
occurring during dusk and early evening [359]. Adults
may be territorial, especially during breeding season [933].
Adult fish have been reported to usually remain within the
one locality and return to within 100 m if displaced from
it [359, 362]. Tagging return data from adult fish in the
Tweed River revealed that of the 8% of fish recaptured,
none had moved more than 50 m after being at liberty for
almost six months [1133]. This species does not usually
undergo long distance movements although a downstream movement of approximately 14 km was documented for an individual fish tagged during a low flow
period and recaptured following a large flood in the
Murray River, South Australia [1128, 1131]. In this study
of 425 tagged fish, 60% of 85 recaptured fish had not
moved from the original tagging location and 37% moved
less than 10 km up or downstream throughout the study
period. During low flow periods only, the maximum
movements upstream and downstream were 4 and 8 km,
respectively. One individual was recaptured five times over
a 27-month period [1128, 1131]. Upstream movements
have also been documented during floods in the Namoi
River, New South Wales [143]. Larvae and juveniles probably emigrate from the adult nesting habitat and colonise
adjacent areas [1131]. Five small juveniles (15–20 mm SL)
were collected in an overnight drift-net set downstream of
riffle and located at least 100 m upstream or downstream
from the closest nest site in a tributary of the Mary River
[1093]. There are several instances where juveniles and
adults of this species have been recorded using fishways on
weirs and tidal barrages. Johnson [658] collected juvenile
Trophic ecology
Diet data for T. tandanus juveniles (≤~150 mm SL) and
adults (>~150 mm SL) is available for individuals sampled
from rivers and streams in the Wet Tropics region of
northern Queensland [1097] and central Queensland
[1080], and from rivers, streams and impoundments in
south-eastern Queensland [80, 99, 100, 103, 205], coastal
central New South Wales [555], and the Murray-Darling
Basin [359, 363]. Tandanus tandanus is a carnivorous
species, juveniles relying on generally small-sized food
items, switching to larger food items with growth (Fig. 5).
The diet of juvenile fish is dominated by aquatic insects
(61.9%), fish (13.6%), microcrustaceans (10.4%) and
terrestrial invertebrates (9.5%). Small amounts of detritus, molluscs and macrocrustaceans are also consumed
(Fig. 5). Spatial variation in the diets of juvenile fish is
apparent, with microcrustaceans, fish and terrestrial invertebrates occurring in the diets of juvenile fish collected
during the filling phase of an impoundment in the Gwydir
River (Murray-Darling Basin) [359, 363]. The diets of
juveniles from streams in south-eastern Queensland [80]
and the Wet Tropics region [1097] were composed primarily of aquatic insects (>83% in both studies). Adult fish
consume a wide range of food types including large crustaceans (27.2%), aquatic insects (25.5%), particulate detritus (16.4%), molluscs (14.9%), terrestrial invertebrates
(7.3%) and fish (4.7%).
The role of detritus in the diet of T. tandanus is unclear: it
may simply be ingested incidentally during benthic foraging, or intentionally as some workers report it to be
composed of particulate organic matter as well as benthic
algae (e.g. filamentous algae, diatoms and desmids) [917],
all of which may be assimilated by this species. Anatomical
features of T. tandanus suggest specialisation for benthic
149
Freshwater Fishes of North-Eastern Australia
We can find no published information on the feeding ecology of T. tandanus larvae, although 27-day-old larvae in
aquaria are reported to consume cladocerans, copepods
and chironomid larvae [751].
T. tandanus (juveniles), n = 290
Terrestrial invertebrates (9.5%)
Fish (13.6%)
Detritus (2.2%)
Microcrustaceans (10.4%)
Conservation status, threats and management
Recent detailed reviews of the conservation status, threats
and management requirements of T. tandanus are available in Morris et al. [965] and Clunie and Koehn [309,
310]. These reports highlight the fact that despite longheld concerns about the declining distribution and abundance of T. tandanus, particularly in the southern
Australia, this species has generally received little formal
recognition as a threatened species until very recently. As
early as 1971, Lake [754] identified T. tandanus as a
species whose distribution and/or abundance had been
considerably reduced. In 1984, Cadwallader et al. [273]
listed this species as Indeterminate – Possibly Threatened
in Victoria but this classification was upgraded to
Vulnerable in 1990 [731, 1004] and T. tandanus is now
listed under the Flora and Fauna Guarantee Act 1988
[310]. In 1991, Lloyd et al. [816] considered T. tandanus
to be Vulnerable in the Murray-Darling Basin. In 1993,
Wager and Jackson [1353] listed Tandanus sp. A from the
Bellinger River as Rare, but T. tandanus was listed as Non
Threatened. In 1997, T. tandanus was declared a protected
fish in South Australia by regulations under the Fisheries
Act 1982 [310]. In 2001, this species was listed as a
member of an Endangered Ecological Community in the
lower Murray River [1005] and in the lowland catchment
of the Darling River [329] under the New South Wales
Fisheries Management Act 1994. This species is not listed
for protection under Queensland legislation. Size limits
and bag limits are in place for this species in all states
[616].
Macrocrustaceans (0.9%)
Molluscs (1.4%)
Aquatic insects (61.9%)
T. tandanus (adults), n = 962
Fish (4.7%)
Microcrustaceans (0.1%)
Macrocrustaceans (27.2%)
Unidentified (2.1%)
Terrestrial invertebrates (7.3%)
Aerial aq. Invertebrates (0.1%)
Terrestrial vertebrates (0.1%)
Terrestrial vegetation (1.0%)
Detritus (16.4%)
Aquatic macrophytes (0.6%)
Algae (0.3%)
Molluscs (14.9%)
Aquatic insects (25.5%)
Other macroinvertebrates (0.1%)
Figure 5. The mean diet of Tandanus tandanus juveniles
(≤~150 mm SL) and adults (>~150 mm SL) (sample sizes for
each age class are given in parentheses). Data derived from
stomach contents analysis of fish from the Wet Tropics region
of northern Queensland [1097], central Queensland [1080],
south-eastern Queensland [80, 99, 100, 103, 205], coastal
New South Wales [555, 1133], and the Murray-Darling Basin
[359, 363].
foraging, enabling the ingestion of macroscopic food items
together with particulate matter containing small invertebrates. These features include a broad, flattened head, inferior mouth, presence of barbels, grinding dental
apparatus, fleshy gill rakers and long, convoluted intestine
[917]. Chemoreception and the high density of sensory
papillae around the head and mouth might play an important role in food location [270, 917]. Davis [359, 363]
reported however, that there was little evidence of
mechanical breakdown of ingested food items in his study
and attributed this to the small, poorly developed teeth of
T. tandanus, and the lack of significant modification of the
gill rakers for grasping or crushing. Davis [359, 363]
concluded that this species is an opportunistic carnivore
capable of open foraging for large mobile prey and ‘grubbing’ in the substrate, enabling it to exploit a wide range of
food sources (see also Clunie and Koehn [310] and references therein).
Morris et al. [965] and Clunie and Koehn [310] recommended that the conservation status of T. tandanus be
upgraded. These authors specifically recommended that
T. tandanus be listed as Endangered under the IUCN Red
List, Vulnerable under the National Environment and
Protection and Biodiversity Act 1999, Vulnerable under the
Australia Society for Fish Biology listing of the conservation status of Australian Fishes [117], Vulnerable under
the New South Wales Fisheries Management Act 1994, but
no change to the current listing in other States. The most
recent (2003) listing of the conservation status of
Australian Fishes by the Australia Society for Fish Biology
[117] includes Tandanus n. sp. from the Bellinger River as
Data Deficient. However, as at December 2003, we are not
aware if the conservation status of this species has been
upgraded according to the recommendations of Morris et
al. [965] and Clunie and Koehn [309].
150
Tandanus tandanus
T. tandanus and the significance of the threats.
Nevertheless, it was clear that certain factors such as those
associated with water infrastructure development have
contributed to the decline of catfish over large spatial
scales, whereas other factors such as interactions with alien
fish and the impacts of agricultural chemicals are likely to
have affected this species at more localised scales [310]. A
recovery plan [309] has been prepared for T. tandanus in
which a detailed list of recovery and management actions
is recommended.
Clunie and Koehn [310] thoroughly reviewed existing and
potential threats to T. tandanus, particularly for populations in the Murray-Darling Basin. Potential threats to this
species included those associated with water infrastructure development (changes to flow regimes, changes to
thermal regimes and barriers to fish movement), introduced species (particularly carp and redfin), water quality
and habitat degradation (due to sedimentation, salinity,
algal blooms, agricultural chemicals, riparian vegetation
degradation, removal of woody debris, and declines in
abundance of aquatic vegetation), diseases and other
potential impacts associated with the aquaculture industry and translocations (e.g. genetic implications), and
commercial and recreational fishing pressures. Clunie and
Koehn [310] cautioned that many of the threats faced by
T. tandanus were potentially synergistic and complex, and
this together with lack of detailed information on many
aspects of the ecology of this species, made it difficult to
accurately diagnose the specific causes of decline of
Similar threatening processes as those described above
probably occur throughout much of the range of T.
tandanus in Queensland, however this species is not obviously in decline yet. Greater effort is needed to define the
phyletic structure of T. tandanus populations in Queensland
in order to identify stocks that may be of enhanced conservation significance and to provide a more rigorous
underpinning for any future translocation activities.
151
Retropinna semoni (Weber, 1895)
Australian smelt
37 101001
Family: Retropinnidae
origin just before and opposite to anal fin base on posterior half of body. Small adipose fin located above posterior
anal rays. Slender caudal peduncle and moderately forked,
round-lobed caudal fin. Ventral keel extending along
abdomen from behind pelvic fins to vent. Nuptial tubercles present on body and head, larger in males and also
occurring on fins. Colour variable but usually olive-green
to orange with fine black spots (melanophores) on dorsal
surface. Minimal fin pigmentation and body often translucent with silvery peritoneum and vertebral column externally visible. Silvery spot on operculum, dark patch on
caudal peduncle and occasionally, a purplish sheen along
sides. Male specimens from south-east Queensland rivers
often bright orange-red during spring reproductive
period, particularly in tannin-stained waters. Specimens
from some tributaries of the Mary River in south-eastern
Queensland are often infested with numerous small (<2
mm diameter) encysted trematode metacercaria which
appear as brownish-black spots beneath the skin. Dove
[1432] provided a list of parasite taxa recorded from R.
semoni in south-eastern Queensland. Emits a distinct
cucumber odour when freshly caught. Preserved colouration usually opaque silvery, tan, or yellow-brown [34, 270,
887, 893, 936, 1093].
Description
Dorsal fin: 7–11 rays; Anal: 13–19; Pectoral: 8–12; Caudal:
18–19 segmented rays; Pelvic: 6; Vertical scale rows: 50–70;
Gill rakers on first arch: 16–25; Vertebrae: 45–53 [34, 270,
887, 893].
Retropinna semoni is a small fish known to reach 100 mm
TL but more common to 50–60 mm TL [270, 893]. Fish in
northern populations are commonly smaller than those in
more southern areas [893]. Of 10 963 specimens collected
in streams of south-eastern Queensland, the mean and
maximum length of this species were 37 and 68 mm SL,
respectively. The equation best describing the relationship
between length (SL in mm) and weight (W in g) for 475
individuals (range 21–63 mm SL) sampled from the Mary
River, south-eastern Queensland, is W = 0.5 x 10–5 SL3.227,
r2 = 0.956, p<0.001 [1093].
Retropinna semoni is an elongate species with compressed
body, relatively large eyes and rounded snout. Moderately
large, terminal mouth extending back to below middle of
eye. Small, cycloid and easily dislodged scales present on
body but not head; extent of scale coverage on body varies
among populations and may be reduced in populations
from southern inland areas. Lateral line absent. Dorsal fin
152
Retropinna semoni
Systematics
Retropinnidae contains four species from two genera
Retropinna and Stokellia, occurring in coastal marine and
freshwaters of south-eastern Australia, New Zealand and
the Chatham Islands. Although phylogenetic relationships
are unclear, the family Retropinnidae is thought to be
closely related to other Southern Hemisphere salmoniformes including Protroctidae, Aplochitonidae and
Galaxiidae [887, 889].
of the Murray River in eastern South Australia. Retropinna
semoni is also present on Fraser and Moreton islands off
the south-eastern Queensland coast. Inland, it occurs
throughout much of the Murray Basin and northern tributaries of the Darling Basin. It is also present in Cooper
Creek in the Lake Eyre drainage basin [52, 270, 507, 733,
814, 893, 1113, 1201, 1340]. Attempted introductions of R.
semoni to Tasmania and Papua New Guinea have reportedly not been successful [887].
The systematics of the Retropinnidae has a very confused
history, probably due largely to the high degree of variability in morphologic and meristic characters frequently
observed within and among taxa [887]. Aspects of the
taxonomy and relationships of members of the family have
been discussed by McCulloch [877], Stokell [1268], Woods
[1417] and McDowall [885, 887]. In the most recent and
complete revision of the Retropinnidae, McDowall [887]
provided a detailed history of the taxonomic problems of
the family, listed the numerous generic and specific
synonyms, and included full descriptions of all recognised
species.
In central Queensland, R. semoni has been reported as far
north as the Fitzroy River [754] but it has not been
collected during numerous subsequent surveys of this
basin [160, 404, 405, 823, 942]. The next most northerly
record for this species is approximately 150 km further
south in Baffle Creek [1349] and it is also present in the
Kolan River [1349]. It appears to be quite uncommon in
both rivers and has not been reported from fishway studies or riverine surveys of these basins [232, 658, 826].
Retropinna semoni is widely distributed in south-eastern
Queensland and is present in most major rivers and
streams from the Burnett River south to the border with
New South Wales. It is generally very common in this
region and often locally abundant, forming schools of
thousands of individuals [1093]. In a review of existing
fish sampling studies in the Burnett River, Kennard [1103]
noted that it has been collected at 22 of 63 locations
surveyed (10th most widespread species in the catchment)
and formed 5.2% of the total number of fishes collected
(fourth most abundant). It has not been recorded from the
Elliott River and appears to be uncommon in the Burrum
Basin [701, 736].
Retropinna Gill, 1862 [448] contains three species, two of
which occur in Australia; the remaining members of the
family occur in New Zealand [887, 893]. The Australian
retropinnids have disjunct distributions with Retropinna
semoni (Weber, 1895) [1370] present on the mainland and
R. tasmanica McCulloch, 1920 [877] confined to
Tasmania.
Distribution and abundance
Retropinna semoni is a relatively widespread and common
species occurring in coastal and inland drainages of eastern and southern Australia. This species occurs in coastal
catchments from central Queensland, south through New
South Wales and west through Victoria to near the mouth
Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New
South Wales border [1093] collected a total of 21 615 individuals from 52% of all locations sampled (Table 1).
Table 1. Distribution, abundance and biomass data for Retropinna semoni in rivers of south-eastern Queensland. Data summaries
for a total of 21 615 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries for per
cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Rank biomass
51.7
Mary River Sunshine Coast Moreton Bay
rivers and
rivers and
streams
streams
70.0
13.23 (20.02) 11.15 (14.72)
13.8
15.0
2.03 (38.24)
0.58 (12.26)
Brisbane
River
Logan-Albert
River
42.3
77.9
3.52 (8.84) 25.08 (34.15)
South Coast
rivers and
streams
60.0
14.05 (21.13)
3 (1)
3 (2)
9 (1)
14 (3)
9 (2)
1 (1)
2 (2)
1.10 (1.39)
0.77 (0.94)
0.04 (0.51)
—
0.43 (0.68)
2.02 (2.57)
0.59 (0.64)
7 (5)
6 (5)
13 (5)
—
14 (7)
5 (4)
5 (5)
Mean numerical density
(fish.10m–2)
2.23 ± 0.48
2.48 ± 1.01
0.29 ± 0.10
0.43 ± 0.37
0.93 ± 0.15
2.64 ± 0.32
0.69 ± 0.17
Mean biomass density
(g.10m–2)
1.54 ± 0.19
1.39 ± 0.29
0.15 ± 0.11
—
0.56 ± 0.12
2.10 ± 0.29
0.42 ± 0.18
153
Freshwater Fishes of North-Eastern Australia
Table 2. Macro/mesohabitat use by Retropinna semoni in
rivers of south-eastern Queensland. Data summaries for
21 615 individuals collected from samples of 532 mesohabitat
units at 153 locations between 1994 and 2003 [1093].
W.M. refers to the mean weighted by abundance to reflect
preference for particular conditions.
Overall, it was the third most abundant species collected
(13.2% of the total number of fishes collected) and was
very common at sites in which it occurred (20.2% of total
abundance). In these sites, R. semoni most commonly
occurred with the following species (listed in decreasing
order of relative abundance): P. signifer, M. duboulayi, C.
marjoriae and G. holbrooki. Retropinna semoni was the 7th
most important species in terms of biomass, forming 1.1%
of the total biomass of fish collected. This species was most
widespread and abundant in the Mary, Brisbane, LoganAlbert and South Coast basins, where it occurred in over
40% of locations sampled and formed more than 3.5% of
the total number of fish collected in each basin. It was less
common or widespread in the short coastal streams of the
Sunshine Coast or Moreton Coast. Across all rivers, average and maximum numerical densities recorded in 532
hydraulic habitat samples (i.e. riffles, runs or pools) were
2.23 individuals.10m–2 and 246.54 individuals.10m–2,
respectively (the latter being recorded in a small (47.7 m2),
isolated tributary pool of the Mary River) [1093]. Average
and maximum biomass densities at 441 of these sites were
1.54 g.10m–2 and 61.96 g.10m–2, respectively.
Parameter
Min.
Max.
Mean
W.M.
5.0
5.0
9.0
0
1.4
0
10 211.7
270.0
300.0
300
46.8
93.4
965.1
53.7
142.9
87
9.2
39.2
621.9
45.8
159.4
94
6.2
31.1
Gradient (%)
0
Mean depth (m)
0.05
Mean water velocity (m.sec-1) 0
3.02
1.04
0.87
0.62
0.37
0.19
0.77
0.23
0.20
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
74.0
100.0
70.7
78.2
66.8
65.0
70.0
3.6
13.2
18.9
27.9
24.7
9.9
1.7
1.3
11.5
22.3
27.0
24.4
10.9
2.6
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
86.1
63.6
20.0
40.9
50.0
90.0
37.6
22.5
85.0
100.0
9.4
7.4
1.4
4.2
1.2
11.2
3.6
3.0
10.9
16.7
13.0
14.3
0.7
3.7
1.0
7.4
1.8
1.8
4.0
8.5
2
Catchment area (km )
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
Macro/mesohabitat use
Retropinna semoni is found in a variety of habitats including still or slow-flowing aquatic habitats in large lowland
floodplain rivers (e.g. backwaters, swamps and billabongs), upland rivers and streams, small coastal streams,
dune systems (Fraser and Moreton islands), lakes (including inland salt lakes) river impoundments (dams and
weirs) and brackish river estuaries [52, 270, 814]. In New
South Wales this species has been classified as a riffledwelling species [553, 1200].
Retropinna semoni can be widespread within river systems,
occurring from estuaries to headwaters. An altitudinal
range of 0 to 760 m.a.s.l. has been recorded for this species
in eastern Victorian rivers [1111, 1112]. In south-eastern
Queensland we have collected this species between 9–300
km upstream from the river mouth and at elevations up to
300 m.a.s.l. (Table 2), but it more commonly occurs within
160 km of the river mouth and at elevations less than 100
m.a.s.l. It is present in a wide range of stream sizes
(1.4–46.8 m width) but is most common in streams
around 6 m width and with low riparian cover (~31%).
This species has been recorded in a range of mesohabitat
types but it most commonly occurs in high gradient
(weighted mean = 0.77%) riffles and runs characterised by
shallow depth (weighted mean = 0.23 m) and high mean
water velocity (weighted mean = 0.20 m.sec-1) (Table 2). It
is more commonly found in deeper slow-flowing pools
during extended periods of low flow, when the availability
of riffle and run habitats is diminished and longitudinal
connectivity is restricted [1093]. Retropinna semoni is
most abundant in mesohabitats with intermediate to
coarse-sized substrates (fine gravel, coarse gravel and
cobbles) and often where submerged aquatic macrophytes
and filamentous algae are common.
Microhabitat use
In rivers of south-eastern Queensland, microhabitat use of
R. semoni is strongly influenced by discharge-related variations in habitat availability. During periods of high flow,
individuals use moderate to high-flow environments with
maximum mean and focal point water velocity of 1.35
m.sec–1 (Fig. 1a and b). We have also frequently observed
aggregations of fish in slackwater eddies within areas of
high flow [515, 1093]. During periods where habitat
choice is restricted by low flows, this species is frequently
collected in areas with water velocities less than 0.05
m.sec–1. This species was collected over a wide range of
154
Retropinna semoni
(a)
20
15
15
10
10
5
5
0
0
Mean water velocity (m/sec)
40
Larvae are reported to be planktonic, usually congregating
at the water surface [951, 952]. King [718] sampled larvae
in major tributaries of the lower Murray River and
reported their presence in a range of habitat types including anabranch and floodplain billabongs, and on the
floodplain proper during flood periods, but reported their
preference for deeper billabong habitats.
(b)
20
(c)
40
30
30
20
20
10
10
0
0
(d)
Total depth (cm)
(e)
30
Environmental tolerances
Harris and Gehrke [553] classified R. semoni as tolerant of
poor water quality and habitat degradation, but this
species is widely reported as being fragile and intolerant of
handling [270, 797, 893]. In south-eastern Queensland
this species has been collected over a relatively wide range
of water quality conditions (Table 3). Temperatures at sites
in which this species was collected ranged between 8.4 and
31.7°C, some sites had very low dissolved oxygen concentrations (minimum 0.6 mg.L–1), mildly acidic to basic
waters (range 6.0–9.1), and moderately high conductivity
(maximum 1624.2 µS.cm–1). The maximum turbidity at
which this species has been recorded in south-eastern
Queensland is 144.0 NTU.
Focal point velocity (m/sec)
Relative depth
40
(f)
30
20
20
10
Table 3. Physicochemical data for Retropinna semoni. Data
summaries for 20 852 individuals collected from 339 samples
in south-eastern Queensland streams between 1994 and
2003 [1093].
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Retropinna semoni. Data derived
from capture records for 3603 individuals from the Mary and
Albert rivers, south-eastern Queensland, over the period
1994–1997 [1093].
depths but usually less than 60 cm (Fig. 1c) and frequently
less than 30 cm during low flows. A pelagic schooling
species, it most commonly occupies the mid to upper
water column or near the water surface (Fig. 1d) [515]. It
is found over a wide range of substrate types but most
often over coarse gravel and cobbles (Fig. 1e). Retropinna
semoni often schools in mid-stream and in open water:
64% of individuals sampled in south-eastern Queensland
rivers and streams were collected in areas greater than 1 m
from the stream-bank and 14% of fish were collected in
areas greater than 0.2 m from the nearest available cover
(Fig. 1f) [1093]. This species was more commonly
collected in open water during periods of high flow and
was most frequently found in close association with coarse
substrates, aquatic vegetation and leaf litter during low
flows (Fig. 1f) [1093].
Parameter
Min.
Max.
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
8.4
0.6
6.0
51.0
0.4
31.7
16.2
9.1
1,624.2
144.0
Mean
19.7
8.0
7.7
387.4
5.5
Hume et al. [607] collected R. semoni over a wide range of
water quality conditions in their extensive survey of fish in
the Goulburn River, a tributary of the Murray River in
central Victoria. Sites in which this species was collected
were characterised by the following water quality conditions: dissolved oxygen 3.6–16.8 mg.L–1, pH 3.7–9.8,
conductivity 50.4–7800 µS.cm–1 and turbidity 0.4–680.0
NTU [607].
Retropinna semoni is euryhaline and has frequently been
recorded at the base of tidal barrages (refer to section on
Movement) and in brackish and estuarine waters. It has
also been recorded in saline lakes in inland Victoria at salinities up to 8.8 ppt [301]; juveniles have been recorded at
salinities ranging between 0.04 to 2.8 ppt [300]. Studies of
salinity tolerances of adult R. semoni revealed that experimental chronic (four-day) LD50s have been observed as
58.7 ppt [1405, 1406]. Death occurred between 50 and 66
ppt, but fish showed no signs of distress and continued to
155
Freshwater Fishes of North-Eastern Australia
[1093] and the Brisbane River [951] were generally similar
in size at equivalent reproductive stages. Length at first
maturity (equivalent to reproductive stage III) for fish
from the Tweed River, northern New South Wales was
reported as 30 and 32 mm LCF for males and females,
respectively [1133]. The smallest ripe fish reported from
the lower Goulburn River in inland Victoria were 36 mm
LCF [607]. Fish in aquaria are reported to breed at lengths
between 40–60 mm TL [797].
swim and feed normally until death. Williams [1406]
cautioned that salinity tolerance information derived from
experiments on adult fish may not necessarily be transferable to other life stages, and that the tolerances of eggs and
larvae are likely to be much lower than those observed for
adult fish.
Ham [502] conducted lower temperature tolerance experiments on R. semoni from south-eastern Queensland. Fish
acclimated for seven days at 15°C were observed to lose
orientation at temperatures of about 2.5°C, move spasmodically at 1.5°C and cease movement completely at
about 1°C [502]. Fish acclimated for seven days at 10°C
were reported to have a significantly greater tolerance of
low water temperatures, losing orientation at temperatures of about 2.2oC and ceasing movement completely at
about 0.7°C [502]. Based on the results of a series of experiments on the upper thermal tolerances of R. semoni from
the Latrobe River in coastal eastern Victoria, Harasymiw
[537] established that the minimum LD50 temperature for
fish acclimated over varying periods and temperatures was
31°C. It was concluded that fish could tolerate exposure to
a maximum temperature of 29°C for extended periods
[537].
50
Males
45
Females
40
35
30
25
20
Retropinna semoni appears to be intolerant of elevated
concentrations of suspended sediments. Tunbridge (cited
in Doeg and Koehn [386]) reported dead and dying fish at
sites in the Thomson River affected by sediment concentrations of 190–200 mg.L–1.
I
II
III
IV
V
Reproductive stage
Figure 2. Mean standard length (mm SL ± SE) for male and
female Retropinna semoni within each reproductive stage. Fish
were collected from the Mary River, south-eastern
Queensland, between 1994 and 1998 [1093]. Samples sizes
can be calculated from the data presented in Figure 3.
Reproduction
Quantitative information on the reproductive biology of R.
semoni is available from field and aquarium studies [607,
749, 797, 951, 952, 1093, 1133]. Details are summarised in
Table 4. Although facultative anadromy has been reported
in some retropinnids [887, 893], R. semoni spawns and can
complete its entire life cycle in freshwater and it has been
bred in captivity in freshwater [515, 797, 952].
Retropinna semoni commences spawning in winter and
may continue through to summer, but spawning appears
to be concentrated in late winter and spring. In the Mary
River, immature and early developing fish (stages I and II)
were most common between October and May (Fig. 3).
Developing fish (stages III and IV) of both sexes were present almost year-round. Gravid males (stage V) were present from May through to October and gravid females were
present from May through to February, however gravid
fish from both sexes were most abundant between July and
September (Fig. 3). The temporal pattern in reproductive
stages generally mirrored that observed for variation in
GSI values. Peak monthly mean GSI values (9.4% ± 0.8 SE
for males, 12.4% ± 1.3 SE for females) occurred in August
for both sexes and GSIs remained elevated for longer in
females than in males (Fig. 4). The mean GSI of ripe (stage
V) fish was 7.8% ± 0.4 SE for males and 11.8% ± 0.5 SE for
females [1093]. Reproductive activity and GSIs for fish
from tributaries of the Brisbane River [951] and the Tweed
In both sexes only the left gonad develops [887].
Maturation commences at a relatively small size.
Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary River, south-eastern
Queensland, were 29.8 mm SL and 39.7 mm ± 0.7 SE,
respectively for males and 25.8 and 38.2 mm ± 0.7 SE,
respectively for females (Fig. 2). Gonad maturation in
both sexes was commensurate with somatic growth up
until stage III, after which the mean length did not differ
substantially between each reproductive stage (Fig. 2).
Gravid (stage V) females were slightly larger than males of
equivalent maturity (minimum 33.2 mm SL, mean 45.8
mm ± 0.6 SE for females; minimum 32.3 mm SL, mean
42.5 mm ± 0.8 SE for males). Fish from the Mary River
156
Retropinna semoni
River, northern New South Wales [1133, 1135], were
generally very similar to values observed for fish from the
Mary River [1093]. Sex ratios during the breeding season
for populations from the Brisbane River have been
reported as 2–4 females for every male [951].
14
Males
12
Females
10
Reproductive stage
I
II
III
8
IV
V
6
Males
100
4
(12) (10) (7) (11) (44) (16) (8) (12) (35) (8) (10) (18)
2
80
0
60
40
Month
20
Figure 4. Temporal changes in mean Gonosomatic Index
(GSI% ± SE) of Retropinna semoni males (open circles) and
females (closed circles) in the Mary River, south-eastern
Queensland, during 1998 [1093]. Samples sizes for each
month are given in Figure 3.
0
Females
100
(14) (15) (6) (8) (53) (17) (13) (14) (53) (18) (14) (8)
80
Retropinna semoni has an extended spawning period but it
is unknown whether this species is a protracted, serial or
repeat spawner [614]. In south-eastern Queensland, the
peak spawning period in winter and early spring usually
coincides with pre-flood periods of low and relatively
stable discharge. However, breeding may also continue
through the months of elevated discharge at the
commencement of the wet season in December/January.
In southern Australia, the peak spawning period of R.
semoni during spring also often coincides with elevated
river flows. However, Humphries et al. [615] demonstrated
that larvae in the Campaspe River were present for up to
nine months of the year, indicating that spawning can take
place over a wide range of flow conditions. Hume et al.
[607] reported that spawning success in the Goulburn
River was independent of flooding and greater in years of
comparatively low flows during spring. Furthermore, King
[718] reported high larval abundances in major tributaries
of the lower Murray River during years of high and low
flow and found no evidence for greater spawning or
recruitment success during flooding. Milton and
Arthington [951] suggested that low flow conditions
during the reproductive period are likely to increase the
potential of larvae to encounter high densities of small
prey, avoid physical flushing downstream due to high flows
and thereby maximise the potential for recruitment into
juvenile stocks. A similar low-flow recruitment hypothesis
has been proposed for this species in the Murray-Darling
60
40
20
0
Month
Figure 3. Temporal changes in reproductive stages of
Retropinna semoni in the Mary River, south-eastern
Queensland, during 1998 [1093]. Samples sizes for each
month are given in parentheses.
The spawning stimulus is unknown but the winter reproductive period in south-eastern Queensland corresponds
with low water temperatures, possibly reflecting the
salmoniform affinities and largely temperate distribution
of this species [951]. Spawning appears to occur earlier in
the year in south-eastern Queensland [951, 1093] than in
southern Australia [607, 749], reflecting the latitudinal
gradient in temperature. Studies from both regions reveal
that spawning commences at temperatures exceeding
about 15°C [607, 951, 952]. In aquaria, spawning has been
reported to occur at water temperatures between 21 and
24°C [1210].
157
Freshwater Fishes of North-Eastern Australia
hardened [952]. The demersal eggs are spherical, transparent, amber in colour, and strongly adhesive [797, 952]. The
perivitelline space is large and several large and many small
oil droplets are present in the yolk [952]. Details of embryological development are available in Milward [952]. Eggs
are reported to hatch after six to 10 days at 21 to 24oC [797]
and after nine days at 15.5 to 18.0°C [952]. Details of larval
morphology and photographs of larval stages can be found
in Serafini and Humphries [1218] and Milward [952].
Newly hatched larvae are small (4.61 mm TL), elongate and
eel-like, and are capable of swimming at this stage [952].
Three days after hatching, the yolk sac is completely
absorbed and larvae range between 5.29–5.51 mm TL
[952]. The mean length of flexion and post-flexion larvae is
reported as 9.6 mm (measured to end of notochord) and
11.9 mm SL, respectively [1218].
Basin [614, 615, 718]. Length-frequency data indicate that
small juvenile fish (less than 20 mm SL) were most
common in streams of south-eastern Queensland during
spring, further suggesting that the development of a larval
cohort occurred during low-flow conditions usually experienced during this time (Fig. 5) [1093].
30
Spring
(n = 2178)
25
Summer
(n = 2819)
20
AutumnWinter
(n = 5966)
15
Length at age data using evidence from scale annuli from
fish in the Brisbane River [951] indicate that 1+ fish (males
and females) were 44–45 mm SL and 2+ fish were greater
than 51.5 mm SL, with females slightly larger than males
in this age group. Milton and Arthington [951] reported
that R. semoni reached sexual maturity within one year of
age (estimated at six to nine months). Growth rates for
populations from inland Victoria were similar with Hume
et al. [607] reporting that R. semoni reached 36–42 mm in
one year and that this age class dominated the breeding
population in this region. Pollard [1059] estimated that
fish in a western Victorian saline lake grew to approximately 50 mm in the first year. The maximum length of
fish collected in south-eastern Queensland was 68 mm SL
[1093], suggesting an age of 3+ years, but given that this
species is thought to attain a larger size in southern populations (possibly up to about 100 mm TL), it is likely that
this species lives even longer in southern parts of its range.
10
5
0
Standard length (mm)
Figure 5. Seasonal variation in length-frequency distributions
of Retropinna semoni from sites in the Mary, Brisbane, Logan
and Albert rivers, south-eastern Queensland, sampled
between 1994 and 2000 [1093]. The number of fish from
each season is given in parentheses.
Total fecundity for fish from the Mary River is estimated
to range from 106–1203 eggs (mean 530 ± 41 SE, n = 99
fish) [1093]. Fecundity for fish from the Brisbane River
ranges from 98–1050 eggs (mean 362 ± 36 SE, n = 115
fish) [949]. Milton and Arthington [951] reported significant relationships between body length, body weight and
fecundity (Table 4). Fish of 35 mm SL produced about 160
eggs, whereas fish of 55 mm SL produced about 600 eggs
[951]. In aquaria, R. semoni is reported to deposit up to
120 eggs [797]. It is uncertain whether this species spawns
only once during the breeding season or whether multiple
batches of eggs are produced.
Movement
There is limited quantitative data available concerning the
movement biology of R. semoni. Unlike R. tasmanica,
which is probably anadromous [52, 893], R. semoni
appears to undertake facultative amphidromous and
potomadromous movements [893]. Movements between
estuaries, brackish lowland rivers and freshwaters do
occur, but probably not for the purposes of reproduction.
Although it has been recorded in estuarine areas and small
numbers of individuals have been collected in fishways
located on tidal barrages, spawning in estuarine waters has
not been reported for this species. Russell [1173] collected
10 individuals descending a tidal barrage fishway on the
Burnett River over a 2½-year period. Johnson [658]
reported small numbers of juvenile and adult R. semoni
moving upstream through a tidal barrage fishway in the
Mary River. Berghuis [158, 159] observed aggregations of
In the wild, spawning may occur in aquatic vegetation
[270] whereas fish in aquaria have been observed scattering
eggs onto the gravel substrate [515, 797]. No parental care
of eggs has been reported. Eggs are relatively small. The
mean diameter of 818 intraovarian eggs from stage V fish
from the Mary River was 0.73 mm ± 0.01 SE [1093]. The
diameter of newly-laid eggs is reported as 0.80 mm and the
eggs swell to an average diameter of 0.95 mm when water-
158
Retropinna semoni
fish (often in large numbers) below tidal barrages in the
Mary River system, although few individuals were
collected at the top of fishways on these structures suggesting limited upstream movement through these fishways.
way on the Barwon River in the Darling Basin was
reported to occur during low flows in October and
November [1334]. Young-of-the-year fish (15–45 mm TL)
in the Murray River were observed attempting to ascend a
vertical-slot fishway on the Torrumbarry Weir during
daylight hours between November and February, a period
of relatively low discharge. Fish were probably attempting
to disperse to upstream habitats but apparently had difficulty ascending the fishway [854, 858]. Upstream migrations of R. semoni do not appear to be limited to periods of
low flow. Upstream movement of approximately 2500 subadults was recorded through a fishway in the Nepean
River, central New South Wales, in March during a period
of elevated flows (discharge of 140 ML.day-1) [483]. No
fish were observed moving at lower flows [483]. Small
aggregations of R. semoni have also been reported below a
weir spillway on the Lerderderg River, Victoria, between
June and July, a period of relatively high discharge [182].
During periods of reduced flows, individuals in rivers of
Facultative potamodromy appears a common feature of
the movement biology of R. semoni and probably serves as
a dispersal mechanism for juveniles and subadults. Mass
migrations within freshwater have frequently been documented and very large aggregations downstream of barriers to movement have been reported. In the Mary River,
south-eastern Queensland, a large aggregation of youngof-the-year fish (at least 5000–10 000 individuals estimated
to be around 20–25 mm TL) were observed immediately
downstream of small barrier to movement (disused road
culvert) in the main river channel. These fish were
presumed to be attempting to move upstream during a
period of stable low flows in spring (mid-September).
Upstream movement of juveniles through a barrage fishTable 4. Life history information for Retropinna semoni.
Age at sexual maturity
6–9 months [951]
Minimum length of gravid (stage V)
females (mm)
33.2 mm SL [1093]; spawning fish in aquaria 40 mm TL [797]
Minimum length of ripe (stage V) males (mm) 32.3 mm SL [1093]
Longevity
2+ years [951], possibly 3+ [1093]
Sex ratio (female to male)
2:1–4:1 [951]
Occurrence of ripe (stage V) fish
Winter through to summer (May to February) [1093]
Peak spawning activity
Winter and spring (July–September) [951, 1093]
Critical temperature for spawning
15°C (field) [607, 951, 952], 21–24°C (aquaria) [797]
Inducement to spawning
? Probably temperature [951]
Mean GSI of ripe (stage V) females (%)
11.8% ± 0.5 SE [1093]
Mean GSI of ripe (stage V) males (%)
7.8% ± 0.4 SE [1093]
Fecundity (number of ova)
Total fecundity = 106–1203, mean = 530 [1093]; 98–1050, mean = 362 [951]
Total Fecundity (TF) / Length (mm SL) or
Weight (g) relationship
TF = 0.005 L2.92, r2 = 0.74, p<0.001, n = 47 [951]
TF = 385.3 W0.09, r2 = 0.79, p<0.001, n = 47 [951]
Egg size (diameter)
Intraovarian eggs 0.73 mm [1093]; newly laid eggs 0.80 mm [952]; water-hardened
eggs 0.95 mm [952]
Frequency of spawning
?
Oviposition and spawning site
Adhesive, demersal eggs scattered over gravel substrate or attached to aquatic
vegetation [270, 515, 797]
Spawning migration
None known
Parental care
None known
Time to hatching
Varies with temperature. 6–10 days (at 21–24°C) [797]; 9 days (at 15.5–18.0°C) [952]
Length at hatching
Newly hatched prolarvae 4.61 mm TL [952]
Length at free swimming stage
Capable of swimming at hatching [952]
Age at loss of yolk sack
3 days
Age at first feeding
Approximately 3 days [614]
Length at first feeding
?
Age at metamorphosis
?
Length at metamorphosis
Flexion larvae 9.6 mm; post-flexion larvae 11.9 mm [1218]
Duration of larval development
? Possibly 14 days [718]
159
Freshwater Fishes of North-Eastern Australia
Conservation status, threats and management
The conservation status of R. semoni was listed as NonThreatened by Wager and Jackson [1353] in 1993 and this
species remains generally common throughout most of its
range in eastern Australia. Potential threats to R. semoni in
south-eastern Queensland are similar to those identified
for many other small-bodied fish species in this region, for
example Atherinidae, Melanotaeniidae, Pseudomugilidae
and Eleotridinae.
south-eastern Queensland appear to retreat to refugia
(pools) or less transitory habitats within the main river
channel. Occasionally, large numbers of fish have been
observed trapped in small isolated tributary pools during
extended periods of low flow in this region [1093].
Feeding ecology
Diet data for R. semoni is available for 1277 individuals
from coastal rivers of south-eastern Queensland [80, 205]
and New South Wales [1133, 1134], floodplain waterbodies of Cooper Creek [246] and inland rivers and floodplain
lakes of the Murray-Darling Basin [267, 396, 607, 805,
1062]. This species is a microphagic carnivore. Aquatic
insects comprised mostly of drifting larval stages of
Diptera, Ephemeroptera and Trichoptera formed 44.2% of
the total mean diet and planktonic microcrustaceans
comprised a further 21.7% (Fig. 6). A substantial proportion of the diet is composed of allochthonous material,
mostly terrestrial invertebrates (15.0%) and winged adult
forms of aquatic insects (4.1%). Small amounts of fish
(unidentified fish eggs) and algae are also consumed occasionally. Some spatial variation in the diet of R. semoni is
evident, apparently related to habitat type and hence food
availability. For example, in studies of lentic and floodplain habitats (e.g. lowland rivers and floodplain lakes and
billabongs [246, 396, 607, 805, 1062]) fish were observed
to consume large amounts (>30% in each study) of microcrustaceans (zooplankton) in comparison to fish collected
from lotic habitats [80, 205, 267, 1133, 1134] (<2.5% in
each study). The diets of fish in lotic habitats were dominated by aquatic insects (>53% in each study). Retropinna
semoni has been observed foraging during the daytime
[1093] and also nocturnally [858]. This species is reputedly an important forage fish for other larger fish and
avian predators [270, 887].
Fish (0.8%)
Unidentified (12.8%)
Microcrustaceans (21.7%)
Terrestrial invertebrates (15.0%)
Other macroinvertebrates (0.2%)
Aerial aq. Invertebrates (4.1%)
Terrestrial vegetation (0.7%)
Algae (0.5%)
Aquatic insects (44.2%)
Figure 6. The mean diet of Retropinna semoni. Data derived
from stomach contents analysis of 1277 individuals from
coastal south-eastern Queensland [80, 205], coastal New
South Wales [1133, 1134], floodplain waterbodies of Cooper
Creek [246] and inland rivers and floodplain lakes of the
Murray-Darling Basin [267, 396, 607, 805, 1062].
160
Alien fish species (particularly Gambusia holbrooki and
other poeciliids) threaten many small native species with
similar habitat and dietary requirements in south-eastern
Queensland streams. Retropinna semoni may be particularly at risk in degraded stream habitats supporting large
populations of G. holbrooki, also an inhabitant of the
upper water column and a microphagic carnivore [78, 80,
92, 94, 96]. Riparian and in-stream habitat degradation
(e.g. riparian clearing, native and alien weed infestations
and sedimentation) may affect terrestrial and aquatic food
supplies of importance to small stream species such as R.
semoni. Extensive infestations of introduced para grass,
Brachiaria mutica, may also constrain the foraging behaviour of this surface-feeding species in degraded urban
streams [94]. Several aspects of in-stream habitat degradation can affect the availability of suitable spawning
substrates; for instance, aquatic weeds can out-compete
native submerged macrophytes used for spawning, and
excessive sedimentation may clog the interstices of gravel
substrates and smother the demersal eggs of R. semoni
[108, 1092]. Many field observations suggest that the natural movements of this species between estuaries, brackish
lowland rivers and freshwaters, and within river systems
may be severely constrained by in-stream barriers (e.g.
dams, weirs, tidal barrages, even road culverts). The dispersal movements of both juvenile and adult fish may be
affected. Flow modifications (particularly rapid fluctuations in water levels or aseasonal flow releases) during the
months of spawning and larval development may have
severe impacts on recruitment by damaging or exposing
fish eggs attached to submerged vegetation, or flushing eggs
and larvae downstream. Microscopic invertebrate prey are
also likely to be reduced in abundance by flow-related habitat disturbances, or flushed downstream during spates and
aseasonal flow releases. The environmental tolerances of
R. semoni are so poorly documented that the effects of
degraded water quality, such as low dissolved oxygen levels
and increased turbidity, are difficult to evaluate. In some
respects this species is known to be hardy (e.g. it is euryhaline and tolerates a wide thermal range) yet it is physically
fragile and intolerant of handling.
Arrhamphus sclerolepis Günther, 1866
Snub-nosed garfish
37 234006
Family: Hemiramphidae
subspecies, A. s. sclerolepis and A. s. krefftii. Arramphus sclerolepis sclerolepis has fewer anal rays than A. s. krefftii
(modal count = 15 versus 16), fewer vertebrae (46 or 47
versus 49), more gill rakers (23 or 24 versus 19–21) and a
proportionally shorter jaw at larger sizes [320].
Description
Dorsal fin: 13–16; Anal: 14–17; Pectoral: 12–14; Vertical
scale rows: 45–50; Gill rakers on first arch: 18–25; Gill
rakers on second arch: 15–20 [320]. Arramphus sclerolepis
is commonly between 150–250 mm SL but may attain a
length of 360 mm SL (about 400 mm TL) and a weight of
255 g [37, 936]. Figure: composite, drawn from photographs of adult specimens 180–220 mm SL, Bowen River,
May 1991; drawn 2002.
Collette [320] initially believed these differences to be
clinal on the east coast of Australia, but evidence for clinal
variation was no longer apparent when specimens from
other northern Australian population were considered.
Significant differences between adjacent populations are
evident for some meristic characters however, but the
pattern of variation is not consistent across all characters
except for the ratio of lower jaw length to head length
[320].
Arrhamphus sclerolepis is a long slender fish (although
relatively stout bodied compared with other garfishes)
with a protruding lower jaw: lower jaw proportionally
longer in smaller individuals, particularly in the subspecies
A. s. krefftii (see Figure 114 in Merrick and Schmida
[936]). Caudal fin forked with lower lobe slightly longer
than the upper lobe. Colour in life: silvery-white laterally
grading to an olive-green dorsally and white ventrally. A
metallic midlateral stripe extends from the opeculum to
the base of the caudal fin. The margins of the dorsal scales
may be darkened at their dorsal and ventral extremities,
thus imparting a regular spotting to the dorsal surface. The
extremity of the lower jaw may be a vivid orange in colour.
Two points are of interest here. First, very few of the fish in
the series upon which A. sclerolepis sclerolepis is based were
collected from freshwater (possibly one individual from
Rollingstone Creek in Queensland and another from the
Gascoyne River in Western Australia) [320]. Second, there
is a substantial overlap in meristic counts for the two
subspecies. Furthermore, subspecific differences in head
morphology are only evident in larger fish: both subspecific forms appear to belong to the same statistical population with respect to the rate of increase with increasing size
Significant geographical variation in meristics and
morphometry led Collette [320] to erect the two
161
Freshwater Fishes of North-Eastern Australia
and distribution). No synonyms are known for the former
whereas the latter was originally described as
Hemirhamphus kreftii Steindachner (note incorrect
spelling of species epithet) and subsequently as
Hemiramphus breviceps Castelnau [1042], and incorrectly
identified or listed as H. argenteus, H. sclerolepis, A. schei or
A. brevis (=Melapedalion breve (Seale)) [320].
of the head to lower jaw ratio when less than 100 mm long.
Importantly, approximately 85% of the Queensland
sample of A. s. sclerolepis examined by Collette [320] were
below this length. The larger size classes (>100 mm SL) for
the A. s. sclerolepis series were dominated by fish from east
of the Great Dividing Range (80%). It would be instructive to apply modern genetic techniques such as DNA
sequencing to examine geographic variation in this
species. It would also be instructive to determine the
extent to which variations in water temperature or salinity
during the early larval phase affect body meristics and
morphology (i.e. spatial variation may be phenotypic and
developmental rather than genetic).
Distribution and abundance
Arramphus sclerolepis is widely but patchily distributed
across southern New Guinea, and northern and northeastern Australia. The subspecies A. s. sclerolepis is said to
occur in Australia from the Gascoyne River in Western
Australia to the Pioneer River in Queensland [52]. Within
this range, it has been infrequently collected from freshwaters however: occurring predominantly in near-shore
marine or estuarine habitats. This species was not
collected from freshwater reaches of 13 rivers in the
Kimberley region [45, 620] nor were any of the Northern
Territory specimens examined by Collette from freshwaters [320]. Many other studies undertaken in freshwaters
of the Northern Territory, some very intensive, and collectively covering an area extending from the Daly River to
Arnhem Land, have also failed to collect this species from
freshwater [193, 262, 772, 944, 946, 1197, 1304].
Systematics
Hemiramphidae (halfbeaks or garfishes) is a moderately
large family with a circumglobal distribution, inhabiting
marine, estuarine and, to a lesser extent, freshwaters. It is
composed of 12 genera containing 85 species [254]. A large
number of species (34) are contained with a single genus,
Hyporhamphus. Cladistic relationships of the genera and
species of halfbeaks have not been fully resolved [254]
although the family is known to be the sister group of the
Exocoetidae (flying fishes) [322]. Approximately 18 species
of Hemiramphidae in seven genera are known from
Australian waters: Arramphus (1 sp.), Euleptorhamphus (1
sp.), Oxyporhamphus (1 sp.), Rhyncorhampus (1 sp.),
Hemirhamphus (2 spp.), Zenarchopterus (5 spp.) and
Hyporhamphus (7 spp.) [1042]. Of these genera, only two
(Arrhamphus and Zenarchopterus) contain species that are
occasionally or principally freshwater in habit.
Arramphus s. sclerolepis occurs in the near-shore environment and estuaries of the Gulf of Carpentaria [197, 320,
356, 1349]. Cyrus and Blaber [356] found it relatively
common but restricted to the lower reaches of the Embley
Estuary during the wet season (28th most abundant of
>100 species, CPUE = 1.5 x 10–4 fish.m.hr–1). It was more
abundant (8th, CPUE = 10.8 x 10–4 fish.m.hr–1) by the start
of the following dry season but still restricted to the lower
estuary. By the late dry A. s. sclerolepis was still common
(15th, CPUE = 2 x 10–4 fish.m.hr–1) in the lower estuary
but also abundant (8th, CPUE = 5.3 x 10–4 fish.m.hr–1) in
the middle reaches of the estuary. The extent of upstream
movement was claimed to be limited by low salinity and
high turbidity during the wet season [356].
The halfbeaks are, in general, characterised by an elongate
lower jaw and short upper jaw. Arramphus however, differs
from all other Australian halfbeaks in that the lower jaw is
shortened also. In addition, it differs from Zenarchopterus
in having a non-elongated nasal papilla, forked caudal fin
(as opposed to rounded) and unmodified anal fin rays;
characters it shares with all other Australian half beaks
[320]. Two other halfbeak genera also share the greatly
reduced lower jaw condition with Arramphus:
Melapedalion (Seale) in the Philippines and Chriodorus
Goode and Bean in the western Atlantic.
Freshwater populations have been recorded in the lower
Mitchell River, but not its upper reaches [1186], and in the
Mitchell River tributary systems, the Walsh (2602), Palmer
[569] and Lynd [1349] rivers. Other rivers of western Cape
York Peninsula in which this species has been recorded
include the Wenlock [571], Norman [320] and Watson
[1349] rivers .
The genus Arramphus was first described by Günther in
1866 with A. sclerolepis as the type species (by monotypy).
The lectotype, held in the British Museum of Natural
History, was incorrectly listed as coming from ‘? New
Zealand’. Collette [320] believed it came from the
Northern Territory or Western Australia as this species
does not occur in New Zealand.
No freshwater populations of A. s. sclerolepis in rivers of
the east coast of Cape York Peninsula are known despite
substantial survey work. The most northern samples
included in the analysis of Collette [320] were from
marine near-shore habitats in the Cooktown area. The
Two subspecies are known; the nominal subspecies A. s.
sclerolepis, and A. s. krefftii (but see sections on description
162
Arrhamphus sclerolepis
most northern freshwater populations on the east coast
appear to be those in Saltwater Creek north of Cairns
[583] and the Barron River [1085, 1087, 1187]. Other
rivers in the Wet Tropics region in which A. s. sclerolepis
has been recorded include the Mulgrave/Russell [1184],
Moresby [1183] and Herbert rivers [584]. In all cases, A. s.
sclerolepis is restricted to the very lower reaches of these
rivers and in some cases, the subspecific status is assumed.
It has been translocated into Lake Tinaroo on the Atherton
Tablelands [593].
the Burnett River barrage. Arramphus s. krefftii has been
recorded from the Mary River [660, 1234] and the Noosa
River (at Trewontin and in Lake Cooroibah) [320]. This
species has also been recorded from the Brisbane [320,
593, 907, 1349] and the Albert/Logan rivers [1349]. This
species occurs naturally in the Wivenhoe Dam approximately 150 km upstream of the river mouth and has been
translocated into Somerset Dam on the Stanley River. It is
apparently abundant in Wivenhoe Dam and dominates
recreational angling catches [593]. Although historically
present in the lower reaches of the Brisbane River [320], it
was not amongst those species shown to be able to negotiate the fishway located at the Mt Crosby Weir [1238].
Further south, this species has been collected from freshwater reaches of the Ross River [1349] and the Burdekin
River [586, 940, 1098, 1349]. Within the Burdekin River, it
has been recorded from as far upstream as the Gorge Weir
(approximately 128 km upstream from the delta) [940]
and the lower reaches of the Bowen River (approximately
140 km from the delta) [1098]. Most texts put the distribution of A. s. sclerolepis as extending to the Bowen area.
South of this supposed limit, Arramphus sclerolepis
(subspecific differentiation not noted) has been recorded
from freshwaters of the Pioneer River (Marsden unpubl.
data cited in Pusey [1081]) and from estuarine waters of
the Murray/St Helens creeks (Lunow unpubl. data cited in
Pusey [1081]).
Arrhamphus sclerolepis is a common inhabitant of estuaries and the near-shore environment of south-east
Queensland [968, 969, 970]. This species has been
recorded from artificially created canal systems but is not
as abundant as in adjacent natural systems [968].
Although its marine distribution extends to the Sydney
area, there are few records of A. s. krefftii occurring in
freshwaters in New South Wales. Collette’s sample
included one specimen from the Clarence River [320].
Only four individuals were collected from two short
coastal rivers of northern New South Wales (the
Richmond and Hastings Rivers) during the New South
Wales Rivers Survey [553, 554]. It has also been recorded
from the Hawkesbury River [553].
Midgley [942] recorded A. sclerolepis (subspecific differentiation not noted) from three locations in the Fitzroy River
catchment: the Fitzroy river itself approximately 70 km
from the river mouth, the Don River approximately 200
km upstream and the Isaac River approximately 300 km
upstream of the mouth. These records were later included
as being within the distribution of A. s. sclerolepis [1349]
but the basis for doing so is obscure. Johnson and Johnson
also noted that A. sclerolepis was common and abundant
in the Fitzroy River [659]. Berghuis and Long [160] state
that A. sclerolepis is frequently observed in the lower
reaches of the Fitzroy River also, and Stuart [1274] noted
this species at the base of the fishway located on the
barrage near the river mouth.
It may seem that a great deal of attention has been
focussed above on establishing the distributional limits of
this species and on the meristic and morphometric basis
for subspecies differentiation. Our intent in doing so is to
illustrate how infrequently A. sclerolepis has been recorded
from freshwater habitats and further, when it has been
recorded in freshwater, it has usually been from lowland
reaches close to the river mouth. Exceptions to this observation include the inland populations present in the
Brisbane, Boyne, Fitzroy, Burdekin and Mitchell rivers;
notably, with the exception of the Boyne River, all are large
river systems with relatively low average gradient (i.e. a
large proportion of total length exists below 50 m elevation). Furthermore, we believe it important to point out
how very few of the series used by Collette [320] were
collected from freshwaters. Researchers should perhaps be
more critical in allocating populations to different
subspecies based solely on distribution in the future.
The Fitzroy River has traditionally been considered to be
within the range of A. s. krefftii, however only two of the
27 Queensland fish included in the series upon which A. s.
krefftii is based [320] were from this drainage.
Further south, A. sclerolepis has been recorded from estuarine waters of the Shoalwater Bay area [1328] and from
freshwaters of the Boyne River where it has established a
self-sustaining population in the impounded reaches of
Awonga Dam [943]. Freshwater populations have been
recorded in the Burnett, Kolan and Elliott rivers but it was
not common nor widely distributed in these systems
[700]. Russell [1173] recorded A. sclerolepis moving downstream in small numbers through the fishway located on
Macro/meso/microhabitat use
Freshwater populations of A. sclerolepis tend to be
restricted to the lower reaches of rivers, although there are
some reports (see above) of this species penetrating many
kilometres upstream. Such examples typically occur in
163
Freshwater Fishes of North-Eastern Australia
Maturation occurs by at least 215–225 mm TL (both males
and females) [943]. Breeding apparently occurs only after
surface water temperatures have reached 28°C [52],
however the basis for this observation remains obscure.
Allen et al. [52] suggest that under normal conditions this
species moves to estuaries to breed and the spatio-temporal variation in abundance reported by Cyrus and Blaber
[356] and detailed above, suggests that spawning occurs
during the wet season.
large low gradient rivers. When located far upstream, the
typical habitat is one of large waterholes or open river. No
information is available on microhabitat use except that A.
sclerolepis is mostly observed close to the water’s surface.
Environmental tolerances
Environmental tolerance data for A. sclerolepis in freshwaters is extremely scant, being restricted to water quality
data for four site/sampling occasions in the Burdekin River
[940, 1098] and three sites in the Fitzroy River basin [942].
Given the small number of fish collected and sites
involved, we consider it prudent to list maximum and
minimum values only in Table 1.
Movement biology
No quantitative information is available on this aspect of
the biology of A. sclerolepis in freshwaters although it is
frequently implied that this species does indeed make
substantial migratory movements between fresh and
saline waters. The appearance of A. sclerolepis in fishways
[1173, 1274] or congregated below such structures [586]
supports this notion. Moreover, the observation that
instream barriers such as weirs and dams result in strict
discontinuities in disitribution also supports other
evidence that A. sclerolepis moves extensively within the
lower reaches of rivers. Cyrus and Blaber [356] included it
among a group of species that moved upstream only when
turbidity decreased and salinity increased. This observation implies that any movement upstream must be accompanied by some degree of physiological acclimation.
These values are not indicative of a great range in water
chemistry. In the Embley Estuary, A. sclerolepis was
recorded occurring in waters ranging from 17.2 to 39 ppt
salinity and 1.2 to 9.2 NTU turbidity [356]. Cyrus and
Blaber [356] classified A. sclerolepis as a marine species
that, along with a number of other species (their Group
B), was prevented from accessing the upper reaches of the
estuary during the wet season by low salinity and high
turbidity. This observation however does not accord well
with other observations of this species in completely freshwater. Arramphus sclerolepis may be capable of slowly
acclimating to low salinity although it is tempting to speculate that some freshwater populations (not including
those landlocked by impoundments) rarely, if ever, come
into contact with saltwater.
Trophic ecology
Information on the diet of A. sclerolepis is limited to
frequency of incidence data for a sample of 20 individuals
(19 freshwater, 1 estuarine) collected from the Brisbane
River [917], volumetric data for a sample of 23 individuals
from the Burdekin River [705], and anecdotal accounts
[52, 320, 936]. Collectively, these data suggest a predominantly herbivorous habit. McMahon [917] noted that filamentous algae and diatoms were each present in all of the
fish examined. Fish in the Burdekin River [1093]
consumed filamentous algae exclusively. Vascular plants
were observed in 13 of the fish examined by McMahon
[917] and Merrick and Schmida [936] detail an observation of A. sclerolepis grazing on Vallisneria fronds.
Estuarine populations of A. sclerolepis are also herbivorous
[194]. Insect larvae were recorded in only two of the individuals examined by McMahon [917] but 14/20 individuals contained mature insects (presumably terrestrial
insects taken from the water’s surface). Zooplankton may
also occur in the diet [936]. Interestingly, like many other
herbivorous or omnivorous Australian fish (see Scortum
parviceps or Nematalosa erebi), juveniles appear to totally
microcarnivorous [1322].
Table 1. Physicochemical data for the snub-nosed garfish
Arramphus sclerolepis. Minimum and maximum values only
are presented. Units of measurement vary between studies;
conductivity is given in either µS.cm–1 or ppm of Total
Dissolved Solids* and turbidity is given in either NTU or
Secchi disc depths (m)**.
Parameter
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity
Turbidity
Min.
24.5
5.6
7.3
198
145*
3.3
0.9**
Max.
29.0
8.3
8.2
235
770*
5.3
1.0**
Reproduction
Information on this aspect of the biology of A. sclerolepis
is limited except that it is evidently able to spawn in freshwaters. Midgley [943] reported that A. sclerolepis was able
to reproduce successfully in Awonga Dam, an impoundment of the Boyne River. A self-sustaining population is
also present in Wivenhoe Dam on the Brisbane River.
The morphology of the feeding apparati of A. sclerolepis
was described by McMahon [917]. Numerous small (<0.5
164
Arrhamphus sclerolepis
addition, A. sclerolepis may be directly involved in the
export of aquatic production from freshwaters to estuarine systems or the indirectly involved in the export of
aquatic production out of the aquatic food web completely
(filamentous algae → garfish → piscivorous birds).
mm), tricuspid teeth, directed postero-medially, are present on margins of the upper and lower jaws. Similarly
numerous and small, but predominantly molariform,
teeth are located in patches within the pharynx forming a
pharyngeal mill. Highly numerous mucous producing
cells are located throughout the digestive system including
the pharynx. The gut is simple in structure, lacking a stomach or pyloric caecae. It is short, being only about half as
long as the body (i.e. Relative Gut Length (RGL) = 0.5)
[917, 1322], but it has a large volume [1322]. In general,
the gut of herbivorous fishes is long; RGL varying between
3.7 and 4.2 [1322]. The absence of a stomach is important
for it means that acid hydrolysis of ingested material
cannot occur and this typically results in low assimilation
efficiencies (i.e. ~38%). Maceration of ingested material is
achieved in A. sclerolepis by the pharyngeal mill. Tibbetts
[1322] suggested that the copious mucus (AGP type – acid
glyciproteins) produced by this species has three functions. First, it binds food together and acts to lubricate the
occluding surfaces of the paryngeal mill. Second, it lubricates the movement of the ingesta through the gut. Third,
it plays some role in the assimilation of plant nutrients.
This last point may explain why high assimilation rates
have been observed in other hemiramphid species (see
Tibbett [1322]).
Conservation status, threats and management
Arramphus sclerolepis is listed as Non-Threatened by
Wager and Jackson [1353]. Potential threats to this species
include barriers to movement such as sand dams (in the
Burdekin River, for example) and tidal barrages and weirs.
Hemiramphids have been included in fish kills associated
with exposure of Potential Acid Sulphate soils and A. sclerolepis may also be intolerant of low pH [1180]. Activities
which increase water turbidity may affect this species by
negatively impacting on its major food source (aquatic
plants). Elevated turbidity in estuaries and consequent
effects on seagrass production is also likely to impact on
this species as many hemiramphids are dependent on this
food source [320].
Halfbeaks have traditionally been of commercial value
[320] and 1990 landings approached 1000 t [678].
Although A. sclerolepis has traditionally been included
within halfbeak landings [320, 936], Kailola et al. [678] do
not list it as an important commercial species. It is of
recreational significance however, being a fine table fish
(although bony) and favoured as live bait for barramundi.
Some research effort should be focused on better defining
the genetic or environmental basis for subspecific differentiation in this species, particularly in view of the recent
increase in interest in this species with respect to its suitability for translocation and the stocking of reservoirs.
Arramphus sclerolepis occurs in the diet of many species of
piscivorous birds such as cormorants and sea eagles, and
of fish such as barramundi [1093]. Thus, this species may
be an important component of aquatic food webs in that
they may accelerate the passage of primary production
through different trophic levels (filamentous algae →
garfish → top level predator such as barramundi). In
165
Strongylura krefftii (Günther, 1866)
Freshwater longtom
37 235009
Family: Belonidae
Estimates of maximum size for this species vary from 750
mm [754] to 850 mm [52]. The maximum size recorded
by Hortle [596] in a New Guinean sample of 75 individuals was 630 mm SL. A maximum size of 640 mm CFL from
a sample of 224 individuals was recorded by Bishop et al.
[193]. Taylor [1304] recorded a maximum length of 635
mm SL from lagoons in the Oenpelli region of Arnhem
Land. Obviously, very large individuals approaching the
maximum length cited by Allen et al. [52] are uncommonly encountered and fish of lengths below 500 mm SL
are more common. The size distribution of the sample
examined in Bishop et al. [193] was weakly bimodal with a
strong peak at around 300 mm CFL and a second weaker
peak at about 420-430 mm CFL. The mean length in this
sample was 316 mm CFL. The equation: W = 0.00987 x
L3.197, n = 224, r2 = 0.938, was found to best describe the
relationship between length (CFL in cm) and weight (in g)
for S. krefftii from the Alligator Rivers region [193].
Description
First dorsal: 16–18; Anal: 19–21; Pectoral: 11–12; spines
absent. Figure: composite, drawn from photographs of
adult specimen, Burdekin River, November 1990; drawn
2002.
Strongylura krefftii, or long tom, is distinctive and unlikely
to be confused with any other species. The body is long and
slender with the dorsal and anal fins set well back on the
body. The head is large, comprising up to one quarter of
total length, and is dominated by a set of elongated jaws
(both upper and lower) armed with numerous sharp teeth.
Development of the jaw apparatus commences with the
lower jaw followed by the upper jaw, such that small specimens pass through a halfbeak phase and may resemble
juvenile hemiramphids. The eye is large, particularly in
juvenile specimens. Colour in life is typically dark green
dorsally grading through silver on the flanks to white
ventrally. A faint orange midlateral stripe occurs in the
posterior half of the body in some specimens and faint
spots occur on the opercula and the dorsal two-thirds of
the body [596]. Sexual dimorphism has been reported for
Papua New Guinean specimens: large males (>400 mm SL)
develop a dorsal hump at about the midpoint of the body
and large black blotches on the opercula and flanks [596].
Systematics
The Belonidae is a circum-tropical family containing
marine, estuarine and freshwater species and a number of
species that may be found across, and even breed in, all
three habitats [254]. The family has repeatedly invaded
166
Strongylura krefftii
Holroyd [571], Wenlock [571, 1349], Ducie [1349], Jardine
[41, 771]; and it has been collected from swamps and
lagoons near Weipa [571]. These records indicate a seemingly continuous distribution across northern Australia.
freshwaters, particularly rivers discharging into the western Atlantic [321, 1435]. Phylogenetic relationships
among the Belonidae (excluding S. krefftii) have recently
been examined by Lovejoy and Collette [1435] and
Banford et al. [1429]. There are about 11–12 freshwater
and 20 marine species. Collette et al. [322] demonstrated
that the family is monophyletic and a sister group of the
marine planktivorous Scomberesocidae (king gars). The
genus Strongylura was suggested to be paraphyletic
however [211]. Accordingly, there has been some debate
about the number and identity of species within the genus
and the family as a whole [322].
In sharp contrast, S. krefftii was not collected from a single
river of the eastern portion of Cape York Peninsula [571]
during the comprehensive CYPLUS surveys undertaken in
the early 1990s and the only record of its presence in this
region is that of Kennard [697] for the Normanby River.
Other fish species more typical of western Cape York
Peninsula also occur in the Normanby River (e.g. Arius
midgleyi Kailola and Pierce). We could find no further
reference to its presence in any river south of the
Normanby until the Herbert River [643, 1349]. This range
of latitude encompasses the otherwise highly diverse rivers
of the Wet Tropics region. Significantly, these rivers are
among the most thoroughly surveyed rivers of north-eastern Australia. Other belonids such as Tylosurus crocodiles
(Péron and Lesueur), T. gavialoides (Castelnau) and T.
strongylura (van Hasselt) have been recorded from the
estuarine reaches of these rivers [1187]. Strongylura krefftii
may have once been present in some rivers of the Wet
Tropics in recent times. Long-time residents of the upper
Russell River have recounted to the senior author that a
species of long tom was present in this river but was extirpated by an outbreak of redspot disease in the 1970s.
Strongylura was first described by van Hasselt in 1824
based on the type species S. caudimaculata from SouthEast Asia. The genus contains both freshwater and marine
representatives and is circum-tropical in distribution.
Australian strongylurids include S. krefftii (Günther), S.
incisa (Valenciennes), S. leiura (Bleeker), S. strongylura
(van Hasselt) and S. urvillii (Valenciennes), of which only
the former is found in freshwater. Other Australian
belonid genera include Ablennes Jordan and Fordice,
Platybelone Fowler and Tylosurus Cocco. Members of the
latter genus are frequently observed in the lower estuary of
Queensland’s northern rivers.
Strongylura krefftii was first described as Belone krefftii by
Günther in 1866. Synonyms are otherwise limited to
misspellings of the species epithet and S. perornatus (first
described as Stenocaulus perornatus by Whitley, 1938).
Hortle [596] demonstrated that S. perornatus from the
Sepik River fitted the description of male S. krefftii.
Strongylura krefftii occurs in the Ross River [1349] and in
the Burdekin River [587, 591, 940, 1098], also penetrating
far upstream into its tributary, the Bowen River [1098];
despite the difficulties posed by such barriers as the Clare
Weir [587]. Strongylura krefftii (as Belone krefftii) was
collected from Lillesmere Lagoon, a large floodplain
lagoon of the Burdekin River in the late 1800s in a very
intensive survey [847] but it has not been collected from
floodplain habitats of the Burdekin delta (C. Perna, pers.
comm.) or the wetlands of Baratta Creek [1046] in more
recent times. Off-channel wetland habitats of this river can
no longer be described habitats of even moderate condition: Lillesmere Lagoon, for example, is a weed-infested
bog devoid of any riparian vegetation and with abysmal
water quality. This species has not been collected from the
Houghton River [255].
Distribution and abundance
Strongylura krefftii is confined to northern Australia and
New Guinea. The New Guinean distribution includes
rivers of southern Papua New Guinea and of Irian Jaya [37,
42, 495] and the Sepik Ramu system of northern Papua
New Guinea [46, 51, 316, 596].
Strongylura krefftii occurs in the Fitzroy, Carson and Ord
rivers of the Kimberley region in Western Australia [388,
620] and is probably widespread in this region. Its range
extends across the Northern Territory from the Victoria
[946] and Daly rivers [945], through the Alligator Rivers
region [193, 772, 1064, 1416] to drainages of Arnhem
Land (Rosie Creek and the Limmen Bight River [944], and
the Roper River [1304]). Rivers of the Gulf of Carpentaria
region of Queensland from which it has been collected
include the Leichhardt [1090, 1349], Gregory [643, 755]
and Gilbert [755]. This species has been recorded from
most rivers draining the western portion of Cape York
Peninsula including the Embley [356], Mitchell [571, 643,
1186, 1349] (including its tributary systems the Walsh and
the Palmer rivers), Coleman [571, 1349], Edward [571],
The distribution of S. krefftii extends further to the south
to include the Pioneer [1081] and the Fitzroy River
drainages [659, 942, 1274] and the latter’s tributary
systems, the McKenzie, Don and Dawson rivers [942]. This
species’ distribution includes the Boyne [1349], Kolan
[1349], Burnett [661], Burrum [701] and Mary [701]
rivers but does not extend south of the Mary River.
Strongylura krefftii seldom achieves high levels of abundance. This species comprised less than 0.01% of seine-
167
Freshwater Fishes of North-Eastern Australia
netting catches and about 2% of the gill-netting catch in a
three-year study of the fishes of the Burdekin River [1098].
It was absent from the electrofishing catch in this study.
This species was similarly absent from electrofishing
catches in lagoons of the Normanby River and comprised
under 1% of the gill-netting catch [697]. In contrast,
Bishop et al [193] found S. krefftii abundance in the
Alligator Rivers region to be in the upper-middle quartile.
Pollard [1064] found it similarly abundant in Magela
Creek, in the Alligator River drainage.
have also been recorded moving through the fishway
located on the barrage of the Fitzroy River.
The use of lentic floodplain waterbodies by S. krefftii
appears little reported for eastern rivers in contrast to
reports for rivers of north-western Australia. The extent to
which this difference reflects real differences in biology,
regional differences in hydrology (i.e. flooding regime),
regional differences in sampling effort in different habitats, or regional differences in the extent, accessibility and
quality of off-channel habitats is not known; a knowledge
gap of some significance.
Macro/meso/microhabitat use
Strongylura krefftii has been recorded from a range of
habitats. Pollard [1064] found this species to be widely
distributed in Magela Creek in the Northern Territory. In a
larger study of the freshwater fishes of the Alligator Rivers
region, in which Magela Creek occurs, S. krefftii was
recorded from 23/26 sites regularly sampled by Bishop et
al. [193] encompassing floodplain, corridor and muddy
lagoons, creeks with a sandy bed, escarpment main channel waterbodies and perennial escarpment streams. This
study revealed that habitat use changed with age: small
individuals (50–200 mm CFL) were recorded from floodplain lagoons and in sandy creeks and corridor lagoons;
the latter two habitats were suggested to provide routes of
dispersal. Fish between 200–360 mm CFL were rarely
collected from floodplain lagoons and were more common
in lowland muddy lagoons, as were fish larger than this
size range, despite being widely distributed. Taylor [1304]
reported both very small (50 mm) and large (635 mm)
specimens in a lowland freshwater billabong that was
occasionally tidally influenced during extreme wet
seasons. It was also recorded in the main channel of the
Roper River [1304]. We have recorded small numbers in
the upper reaches of the Leichhardt River where the habitat was dominated by still, moderately deep (approx. 2 m)
water over a gravel-cobble bottom.
Bishop et al. [193] detected an association between presence of S. krefftii and the extent of vegetated cover present
in lagoons, with lagoons containing submerged macrophytes being favoured over lagoons with emergent or
floating macrophytes and those without any vegetative
cover. These authors suggested that aquatic macrophytes
may be important spawning sites, citing Lake’s [754] assertion that the eggs of this species have tendrils which adhere
to submerged vegetation. Pollard [1064] reports frequent
observations of S. krefftii lurking under overhanging vegetation and amongst tree roots, particularly those of
Pandanus species. This habit has been observed also in the
Bowen River, where overhanging Melaleuca foliage is used
as cover from which to launch ambush attacks on other
fishes (BJP, pers. obs.). Just as frequently however, S. krefftii
can be observed cruising open waters a few centimetres
from the water’s surface. None of the accounts from which
this summary is drawn suggest that S. krefftii occurs in
reaches with appreciable current velocities despite the fact
that this species is a powerful swimmer and able to move
exceedingly quickly when alarmed.
Environmental tolerances
Few data are available on this aspect of the biology of S.
krefftii except data describing ambient conditions in sites
in which it has been collected (Table 1).
Kennard [697] recorded this species in both the main river
channel and a floodplain lagoon of the Normanby River but
it was not abundant in either habitat. In the Burdekin River,
this species has been collected throughout the main river
channel below the Burdekin Falls (now the site of a very
large dam) and in the main river channel of its major
lowland tributary, the Bowen River [1082, 1098] but
currently appears absent from lagoonal habitats of the
Burdekin River delta (C. Perna, pers. comm.). Strongylura
krefftii appears limited to the lowland reaches of the Pioneer
River although may have once been far more widespread in
this system [1081]: three weirs along its lower length have
probably impacted on this species. It has been recorded
moving upstream through the fish lift on Dumbleton Weir
(T. Marsden, pers. comm. cited in Pusey [1081]). Long tom
Strongylura krefftii has been collected from across a wide
range of temperatures (22.9–38oC), nonetheless this range
is typical of those temperatures expected for northern
Australia. Although S. krefftii has been recorded most
commonly from moderately well-oxygenated waters, it is
evident from the conditions experienced in the Normanby
River that hypoxic conditions may be tolerated. However,
S. krefftii was recorded among the dead in a large fish kill
in the Northern Territory for which hypoxia was implicated as the major cause.
This species has been recorded from acidic and basic
waters although the average conditions tend to be within
one pH unit of neutrality. In all cases, S. krefftii was
collected from waters of low conductivity and moderately
168
Strongylura krefftii
season. We have collected a ripe female (380 mm SL)
containing ovulated eggs in the lower Burdekin River in
November, an observation also consistent with a
wet season spawning season [1093]. Although measurement of fecundity were not made, the eggs were about 2
mm in diameter.
Table 1. Physicochemical data for Strongylura krefftii.
Summaries are derived from average site data from three
studies: 1) Bishop et al. [193] in the Alligator Rivers region, n =
23 sites; 2) Pusey et al. [1098], n = 5 site/sampling occasions
in the Burdekin River drainage, and 3) Kennard [894], two
sites on the Normanby River and its floodplain. Note the
difference in units used to describe turbidity. Temperature,
dissolved oxygen and pH for the Alligator Rivers region and
the Normanby River were taken at the water’s surface.
Parameter
Alligator Rivers region (n = 23)
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (cm)
Mean
Max.
Reproductive investment does not appear to be great as
Bishop et al. [193] report mean female wet season GSI
values of 2.2 ± 1.6% only. These data suggest that S. krefftii
is iteroparous. The spawning location is unknown but in
the Norethern Territory ripe females have been collected
from escarpment streams, lowland sandy creeks and shallow lagoons, whereas small individuals are recorded from
floodplain lagoons and corridor habitats. The eggs of some
other belonids have numerous tendrils which allows
attachment to vegetation. If this spawning mode also
occurs in S. krefftii, then delivery to juvenile habitats by the
current must occur after hatching. Egg development is
apparently protracted (one to five weeks) in many
belonids [224, 225].
Min.
30.0
6.3
6.4
–
72
38
9.1
8.6
98
1
24
3.7
4.6
6
360
Normanby River (n = 2)
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
–
–
–
–
–
23
2.8
7.4
263
7.1
22.9
2.4
6.0
252
2.0
Burdekin River (n = 5)
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
30.0
8.9
7.99
394
2.76
33
12.1
8.80
790
5.30
23
7.2
7.27
131
1.76
Movement
There is little published information on this aspect of the
biology of S. krefftii. Bishop et al. [193] implied that
spawning occurred in lowland sandy creeks and shallow
lagoons and that eggs or larvae were passively delivered to
floodplain lagoons, the fish dispersing out of these habitats as they grew. Strongylura krefftii has been recorded in
fishways [1274], congregated below such structures [587]
or congregated below weirs lacking an effective fishway
[942]. Unfortunately, the number of fish observed in these
studies has been too few to draw any meaningful conclusions with respect to timing of, and conditions which stimulate, movement. Lateral movement into off-channel
habitats clearly occurs in some rivers. Salinity tolerance is
unknown in this species, however it has not been recorded
in marine environments. It therefore appears unlikely that
this species would be able to move easily between river
basins: a characteristic that may be of importance if populations are catastrophically affected by drought, disease or
human disturbance (see Environmental Tolerance section
above).
high clarity. It is noteworthy that the range of conditions
experienced across the three studies is not greatly different
from that recorded within the Alligator Rivers region
alone.
Reproductive biology
The reproductive biology of S. krefftii in Australia remains
largely unstudied. Bishop et al. [193] reported that
although gender could be determined at small size (133
and 195 mm CFL for females and males, respectively) and
that stage III gonads were present in female fish at 317 mm
and male fish at 267 mm, length at first maturity (i.e.
length at which 50% of the sample is reproductively
mature) was substantially greater, particularly for females:
420 mm and 290 mm for females and males, respectively.
Based on estimated growth rates, Bishop et al. estimated
that such fish were in the 2+ and 1+ age classes, respectively [193].
Trophic ecology
The diet summary depicted in Figure 1 is drawn from two
studies. The first is that by Bishop et al. [193] (n = 132) for
the Alligator Rivers region, and the second is our own
unpublished data for four fish collected from the Burdekin
River. Mean contribution by each category has been
weighted by sample size: accordingly the data provided by
Bishop et al. [193] dominates the summary. Fish were the
only item found in fish from the Burdekin River.
In the Alligator Rivers region, mature fish (stage V) were
recorded in the mid-dry to early wet seasons whereas ripe
fish (stage VI) were only collected in the late dry and early
wet seasons only [193]. These observations suggest a
spawning season coincident with the monsoonal wet
169
Freshwater Fishes of North-Eastern Australia
contained a wide range of fish sizes. It is probable that
piscivory increases in importance with increasing size such
that adult fish are exclusively piscivorous. Very small individuals, particularly those in the halfbeak stage, may be
planktivorous.
Strongylura krefftii is predominantly piscivorous but also
consumes smaller amounts of surface dwelling invertebrates and terrestrial insects and prawns. The consumption of terrestrial vegetation and algae is probably
accidental. The prey consumed by S. krefftii is diverse and
includes chandids, melanotaeniids, plotosid catfishes,
terapontid grunters, atherinids and clupeids.
Unidentified (11.3%)
Terrestrial invertebrates (1.0%)
Terrestrial vegetation (3.6%)
Algae (4.2%)
Aquatic insects (5.5%)
Macrocrustaceans (3.0%)
Fish (71.4%)
Figure 1. The mean diet of Strongylura krefftii. Information
sources upon which this figure is based are discussed in the
text.
Bishop et al. [193] did not provide a breakdown of changes
in diet with size but the sample examined in the study
170
Conservation status, threats and management
Strongylura krefftii is listed as Non-Threatened by Wager
and Jackson [1353], however the general paucity of biological information concerning this species makes it difficult
to ascertain the existence and severity of potential threats.
However, it is clear that S. krefftii make substantial movements within river systems and that different life history
stages utilise different habitats. Consequently structures
that impede movement are potentially threatening. The
observation that juvenile S. krefftii in the Northern
Territory use off-channel habitats suggests that the quality
and availability of such habitats may impact on the viability of long tom populations. Moreover, since such habitats
are frequently only accessible during periods of high flow,
water resource development which reduces the frequency
and duration of large flow events may also impact on this
species. The absence of information on this species is of
concern, particularly given that it is not uncommonly
encountered in fishways. Greater research effort to elucidate the biology of this species is needed.
Craterocephalus marjoriae Whitley, 1948
Marjorie’s hardyhead
37 246025
Family: Atherinidae
upper jaw overhangs lower jaw when mouth closed [350,
635, 936]. Body scales large and dorsoventrally elongated
with prominent circuli; large, irregularly-shaped scales on
top of head. Opercles and preopercles scaled. First dorsal
fin originating behind tips of pectoral fin rays, second
dorsal fin originating above or slightly behind origin of
anal fin [350, 635]. In the second dorsal, pectoral, pelvic
and anal fins of this species, a single unsegmented ray
sometimes separates the fin spine and the segmented rays
(the unsegmented ray is counted together with the
segmented rays in the meristics listed above). Caudal fin
forked.
Description
First dorsal fin: IV–VII; Second dorsal: I, 6–8; Anal: I, 6–9;
Pectoral: 12–16; Caudal: 14–17 segmented rays; Pelvic: I, 5;
Vertical scale rows: 27–30; Horizontal scale rows: 5–7;
Predorsal scales: 10–14, Gill rakers on lower branch of first
arch: 10–13; Vertebrae: 30–32 [34, 52, 350, 635, 1093,
1391].
Craterocephalus marjoriae is a small hardyhead known to
reach 97 mm TL but more common to 50 mm [34, 635].
Of 9199 specimens collected in streams of south-eastern
Queensland [699, 704, 709, 1093], the mean and maximum length of this species were 36 and 74 mm SL, respectively. The equation best describing the relationship
between length (SL in mm) and weight (W in g) for 650
individuals (range 17–70 mm SL) sampled from the Mary
River, south-eastern Queensland is W = 0.2 x 10–4 SL3.062, r2
= 0.980, p<0.001 [1093].
Body golden to sandy-yellow in colour, ventral surface and
opercles silvery, top of head and snout darker. Fins clear or
straw coloured. Prominent iridescent silver-gold midlateral stripe extending as far forward as pectoral fins. A dark,
triangular blotch lateral to vent sometimes visible in populations from the Clarence River. In northern populations,
rows of tiny black spots sometimes present on scales
directly above mid-lateral stripe and on head [34, 350, 635,
936]. During the breeding season, pigmentation of male
intensifies with gold mid-lateral stripe becoming more
pronounced and the white testis becoming visible through
the body wall. The single (left) ovary of the female also
Craterocephalus marjoriae is a robust species with a
moderately deep, elongate body. The head is blunt and
slightly flattened, sloping towards snout. The mouth is
small, not reaching eye, and is oblique and protrusible.
Two rows of small, sharp, inwardly pointed teeth present
on medial third of upper jaws, single row in dentary. The
171
Freshwater Fishes of North-Eastern Australia
becomes more apparent as the black mesovarium develops
and the urinogenital papilla becomes transparent and
dorsoventrally flattened. Preserved colouration darker
than described above, specimens becoming light browntan with silvery or black mid-lateral stripe [34, 350, 635,
936, 949].
represent distinct species: C. helenae and C. marianae in
the Northern Territory and C. munroi in the Gulf of
Carpentaria [345, 350, 637].
Distribution and abundance
Craterocephalus marjoriae is patchily distributed in coastal
drainages between central Queensland and northern New
South Wales. The central core of its range is from the
Burnett River, south-eastern Queensland, south to the
Nerang River. In this region it appears generally restricted
to the larger river basins: the Burnett, Mary, Noosa, Pine,
Brisbane, Logan, Albert, Coomera and Nerang rivers. With
the exception of Hilliards Creek, it does not appear to be
present in any of the smaller coastal streams of the region.
There are isolated records of this species occurring further
north in the Fitzroy River [658], small coastal streams near
Sarina [779] and in the Burdekin River [350]. It is possible
that these highly disjunct records are due to misidentification, the result of chance dispersal or translocation [350,
1093]. A disjunct population also occurs to the south in
the Clarence River, northern New South Wales [635]. This
species has not been recorded from the sand islands off the
south-eastern Queensland coast.
Craterocephalus marjoriae is similar in general appearance
to the largely sympatric congener C. stercusmuscarum
fulvus, especially juveniles. Distinguishing characteristics
of C. marjoriae include a more robust and deeper body,
the distinctive protrusion of the upper jaw over the lower
jaw when the mouth is closed, and prominent iridescent
silver-gold mid-lateral stripe extending as far forward as
pectoral fins [350].
Systematics
The family Atherinidae contains approximately 173
species from about 25 genera worldwide, occurring mainly
in marine and estuarine waters [422, 632, 637, 671, 1207].
In Australia, freshwater representatives comprise approximately 15 species from three genera [52, 637]. The genus
Craterocephalus McCulloch, 1912 [876] is generally
restricted to freshwaters and is present in New Guinea and
Australia. The systematics of the genus have been thoroughly reviewed and revised in recent years by Ivantsoff,
Crowley and Allen [343, 345, 346, 347, 348, 350, 352, 632,
633, 637, 638]. The genus is currently thought to contain
24 species, 14 of which occur in Australia [37, 52, 422,
637]. The etymology of the genus epithet is from the
combination of the Greek for bowl or mixing vessel and
head, possibly referring to the strong or sturdy head of
species in the genus [422, 797], from which the common
name hardyhead is also derived. Craterocephalus can be
divided into three distinct groups or species complexes
[635]. Two of these groups, the ‘eyresii’ (including C.
marjoriae) and ‘stercusmuscarum’ groups, contain freshwater species while the third (‘honoriae’) contains estuarine and marine species [343, 635]. Electrophoretic
evidence indicates that members of the ‘eyresii’and ‘stercusmuscarum’ groups are so dissimilar as to almost constitute separate genera [343]. Species radiation within the
genus Craterocepahalus was considered by Crowley et al.
[352] ‘to be a recent phenomenon’ in New Guinea (occurring from the Pliocene-Pleistocene epochs) but Crowley
[343] considered ‘hardyheads at least ... are not the result
of recent speciation’ in Australia.
Craterocephalus marjoriae is relatively uncommon at the
northern extent of its range (e.g. north of the Burnett
River). It is however, very common and widely distributed
within the major rivers of south-eastern Queensland and
is often locally abundant, forming schools of hundreds of
individuals [1093]. In a review of existing fish sampling
studies in the Burnett River, Kennard [1103] noted that it
has been collected at 15 of 63 locations surveyed (13th
most widespread species in the catchment) and formed
1.5% of the total number of fishes collected (12th most
abundant). Surveys undertaken by us between 1994 and
2003 in catchments from the Mary River south to the
Queensland–New South Wales border [1093] collected a
total of 16 017 individuals from 33% of all locations
sampled (Table 1). Overall, it was the fifth most abundant
species collected (9.8% of the total number of fishes
collected) and was present in relatively high abundances at
sites in which it occurred (15.3% of total abundance, third
most common species). In these sites, C. marjoriae most
commonly occurred with the following species (listed in
decreasing order of relative abundance): P. signifer, R.
semoni, M. duboulayi and G. holbrooki. In freshwaters of
south-eastern Queensland, C. marjoriae co-occurs with its
congener, C. s. fulvus, reasonably often. Both species
occurred together at 47 of the 127 locations in which
either species was sampled [1093]. Craterocephalus marjoriae was the 5th most important species in terms of
biomass, forming 1.3% of the total biomass of fish
collected. It was most common in the Mary and the
Craterocepahalus marjoriae, first described by Whitley in
1948 [1391], is confined to coastal rivers of south-eastern
Queensland and northern New South Wales. However, it
was once thought to have a wide and disjunct distribution
in eastern and northern Australia. It is now recognised that
populations previously identified as C. marjoriae actually
172
Craterocephalus marjoriae
Table 1. Distribution, abundance and biomass data for Craterocephalus marjoriae. Data summaries for a total of 16 017
individuals collected from rivers in south-eastern Queensland over the period 1994-2003 [1093]. Data in parentheses represent
summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species
occurred.
Total
% locations
% abundance
Rank abundance
Mary River Sunshine Coast Moreton Bay
rivers and
rivers and
streams
streams
Brisbane
River
Logan-Albert
River
South Coast
rivers and
streams
32.6
66.0
–
15.0
29.7
39.7
5.0
9.81 (15.25)
13.20 (15.73)
–
0.44 (4.39)
3.89 (10.69)
9.22 (16.03)
0.06 (0.73)
5 (3)
2 (2)
–
16 (4)
8 (4)
4 (3)
21 (8)
1.27 (1.95)
1.60 (2.39)
–
–
0.79 (1.35)
0.73 (1.11)
–
5 (5)
4 (4)
–
–
8 (8)
8 (6)
–
Mean numerical density
(fish.10m–2)
1.88 ± 0.31
2.14 ± 0.49
–
0.23 ± 0.05
1.27 ± 0.44
1.67 ± 0.28
0.05 ± 0.00
Mean biomass density
(g.10m–2)
1.97 ± 0.32
2.44 ± 0.51
–
–
1.56 ± 0.63
1.11 ± 0.18
–
% biomass
Rank biomass
present in a wide range of stream sizes (range = 0.7–44.2
m width) but is more common in streams of intermediate
Albert-Logan rivers where it was the second and fourth
most abundant species, respectively. It was comparatively
widespread throughout these catchments, being present at
66% and 42% of locations sampled in the Mary and
Albert-Logan rivers, respectively. This species is comparatively rare or absent from the remaining catchments of
south-eastern Queensland sampled by us. Across all rivers,
average and maximum numerical densities recorded in
435 hydraulic habitat samples (i.e. riffles, runs or pools)
were 1.88 individuals.10m–2 and 124.02 individuals.10m–2,
respectively. Average and maximum biomass densities at
367 of these sites were 1.97 g.10m–2 and 105.0 g.10m–2,
respectively. Highest numerical densities and biomass
densities were recorded from the Mary River. In New
South Wales, C. marjoriae has only been recorded from the
Clarence River [282, 814, 1201] where it is apparently very
common. For example, in a survey of 11 sites in the
Clarence River in 1991, this was the most abundant species
sampled, forming 37% of the total number of fish
collected [282]. In a later survey of six sites in the Clarence
River, only 10 individuals were collected from a single
location [553].
Table 2. Macro/mesohabitat use by Craterocephalus marjoriae.
Data summaries for 16 017 individuals collected from 435
mesohabitat units at 97 locations in south-eastern
Queensland streams between 1994 and 2003 [1093]. W.M.
refers to the mean weighted by abundance to reflect
preference for particular conditions.
Parameter
Catchment area (km2)
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
Min.
5.6
4.0
0.5
0
0.7
0
Gradient (%)
0
Mean depth (m)
0.05
Mean water velocity (m.sec–1) 0
Macro/mesohabitat use
Craterocephalus marjoriae is found in a variety of lotic
habitats, but generally only in the larger river systems
within it range. It is usually widespread within river
systems but appears to be restricted to freshwaters. In
south-eastern Queensland, C. marjoriae has generally
similar macro/mesohabitat use patterns as its congener, C.
stercusmuscarum. This species occurs throughout the
major length of rivers, ranging between 0.5 and 335 km
from the river mouth and at elevations up to 400 m.a.s.l.
(Table 2). It most commonly occurs within 200 km of the
river mouth and at elevations around 110 m.s.a.l. It is
173
Max.
Mean
W.M.
4850.6
211.0
335.0
400
44.2
80.0
477.5
45.4
188.5
114
9.4
33.2
361.9
37.9
196.8
110
6.7
32.4
3.02
1.08
0.84
0.47
0.39
0.14
0.34
0.29
0.10
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
76.4
100.0
58.5
78.2
66.8
65.0
41.4
4.3
16.1
20.2
26.2
22.6
9.5
1.2
3.9
15.1
20.3
26.1
25.6
7.9
1.1
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
69.6
65.9
20.0
62.7
50.0
92.6
29.9
15.5
88.3
100.0
13.0
9.7
1.0
5.7
1.5
11.7
2.9
2.7
11.1
15.7
11.3
12.6
0.6
4.8
1.3
9.5
1.7
2.0
5.7
8.3
Freshwater Fishes of North-Eastern Australia
this species has been classified as a pool-dwelling species
[553] and has been reported to prefer well-vegetated, clear,
flowing streams with sand and gravel substrates [34, 635,
814, 936].
width (5–10 m) with low to moderate riparian cover
(usually <40%).
In rivers of south-eastern Queensland, this species has
been recorded in a range of mesohabitat types but it most
commonly occurs in runs characterised by moderate
gradient (weighted mean = 0.34%), moderate depth
(weighted mean = 0.39 m) and low to moderate mean
water velocity (weighted mean = 0.1 m.sec–1) (Table 2). It
also occurs in shallow riffles with high gradient (maximum = 3.02%) and high water velocity (maximum = 0.84
m.sec–1). This species is most abundant in mesohabitats
with substrates of intermediate size (fine gravel, coarse
gravel and cobbles) and particularly where submerged
aquatic macrophytes, filamentous algae, leaf litter beds,
undercut banks and root masses are common. Elsewhere,
50
(a)
50
40
40
30
30
20
20
10
10
0
0
30
Microhabitat use
In rivers of south-eastern Queensland, C. marjoriae was
most frequently collected from areas of low to moderate
water velocity (usually less than 0.4 m.sec–1) (Fig. 1a and
b). It has been recorded at maximum mean and focal point
water velocity of 1.09 and 0.96 m.sec–1, respectively.
Aggregations also often observed in slack-water eddies
(e.g. behind rocks and debris) within high velocity riffle
habitats [1093]. This species was collected over a wide
range of depths, but most often between 10 and 60 cm
(Fig. 1c). A pelagic schooling species, it most commonly
occupies the mid water column (Fig. 1d). It is found over a
wide range of substrate types but most often over fine
gravel, coarse gravel and cobbles (Fig. 1e). Although often
collected in areas greater than 1 m from the stream-bank
(53% of individuals sampled) and in open water (Fig. 1f),
the majority (90% of individuals) were collected in areas
less than 0.2 m from the nearest available cover. It was
frequently collected in close association with filamentous
algae, aquatic macrophytes and the substrate, but was also
found close to leaf-litter beds and submerged marginal
vegetation (Fig. 1f). Nothing is known of larval habitat
use. In the Mary River during January, large aggregations
of juveniles 10–15 mm were often observed in slack-water
areas among submerged marginal vegetation adjacent to
areas of high water velocities (riffles and runs) [1093].
(b)
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
30
20
20
10
10
0
0
Total depth (cm)
30
Environmental tolerances
Little quantitative data is available concerning environmental tolerances, although laboratory experiments
revealed that adult C. marjoriae lost orientation and were
unable to control lateral movement or remain upright at
5.4°C, and moved only spasmodically at 4.4°C [95].
Craterocephalus marjoriae has been collected over a relatively wide range of physicochemical conditions (Table 3)
including sites with low dissolved oxygen concentrations
(minimum 0.3 mg.L–1), mildly acidic to basic waters
(range 6.3–9.1), and high conductivity (maximum 5380
µS.cm-1). The maximum turbidity at which this species has
been recorded in south-eastern Queensland is 144 NTU.
Despite the wide range of physicochemical conditions
reported above, this species is not common in degraded
urban streams of the Brisbane region [94, 95, 704, 707,
709], suggesting that it may be sensitive to habitat and
water quality degradation. Harris and Gehrke [553] classified C. marjoriae as intolerant of poor water quality. It has
been reported to thrive in impounded waters (e.g. Lake
Barambah in the Burnett River) [205], possibly because of
Relative depth
(e)
(f)
20
20
10
10
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Craterocephalus marjoriae. Data
derived from capture records for 2582 individuals from the
Mary and Albert rivers, south-eastern Queensland, over the
period 1994–1997 [1093].
174
Craterocephalus marjoriae
[1093] than in the Brisbane River [949], suggesting reproduction may occur at a smaller size for fish in the Mary
River. For example, the minimum and mean lengths of
stage III females from the Mary River were 28.4 and 41.1
mm SL, respectively ([1093], Fig. 2), and those from the
Brisbane River were 35.2 and 47.5 mm SL, respectively
[949]. Gonad maturation in both sexes was commensurate with somatic growth, the mean length at each reproductive stage being different from all other stages (Fig. 2).
Gravid (stage V) females were slightly larger than males of
equivalent maturity (minimum 32.8 mm SL, mean 48.2
mm ± 0.6 SE for females; minimum 31.7 mm SL, mean
44.3 mm ± 0.6 SE for males). The minimum size of spawning female fish in aquaria is reported as 38 mm SL and the
first fertile eggs were observed when males were 39.5 mm
SL [1210].
the prevalence of shallow, clear water areas with sandy
substrates and abundant aquatic vegetation in this lake
[12, 205].
Table 3. Physicochemical data for Craterocephalus marjoriae.
Data summaries for 15 274 individuals collected from 285
samples in south-eastern Queensland streams between 1994
and 2003 [1093].
Parameter
Min.
Max.
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
8.4
0.3
6.3
19.5
0.2
31.7
19.5
9.1
5380.0
144.0
Mean
19.8
8.0
7.8
496.8
5.1
Reproduction
Quantitative information on the reproductive biology of
C. marjoriae is available from two field studies [949, 1093]
and one aquarium study [1210]; details are summarised in
Table 4. This species spawns and completes its entire life
cycle in freshwater and has been bred in captivity [1210].
Maturation commences at a relatively small size.
Minimum and mean lengths of early developing (reproductive stage II) fish from the Mary River, south-eastern
Queensland, were 27.6 mm SL and 36.7 mm ± 1.5 SE,
respectively for males and 21.3 and 34.2 mm ± 1.0 SE,
respectively for females (Fig. 2). Fish of equivalent reproductive stage were slightly smaller in the Mary River
Reproductive stage
I
II
III
IV
V
Males
(49) (14) (8) (11) (28) (7)
(12) (56) (39 ) (7) (14)
100
80
60
40
20
50
Males
45
0
Females
Females
100
40
(44) (28) (19) (19) (43) (12)
(3 6) (82) (38) (13) (37)
80
35
60
30
40
25
20
0
20
I
II
III
IV
V
Reproductive stage
Figure 2. Mean standard length (mm SL ± SE) for male and
female Craterocephalus marjoriae within each reproductive
stage. Fish were collected from the Mary River, south-eastern
Queensland, between 1994 and 1998 [1093]. Samples sizes
can be calculated from the data presented in Figure 3.
Month
Figure 3. Temporal changes in reproductive stages of
Craterocephalus marjoriae in the Mary River, south-eastern
Queensland, during 1998 [1093]. Samples sizes for each
month are given in parentheses.
175
Freshwater Fishes of North-Eastern Australia
post-breeding months (March–May) and amongst mature
fish (>45 mm SL) [949].
Craterocephalus marjoriae has an extended breeding
season from late winter through to summer but spawning
appears to be concentrated in late winter and spring. In
the Mary River, immature and early developing fish (stages
I and II) were most common between January and May
(Fig. 3). Developing fish (stages III and IV) of both sexes
were present year-round. Gravid males (stage V) were
present from June to March and gravid females were present from June through to January, however gravid fish
from both sexes were most abundant between August and
November (Fig. 3). The temporal pattern in reproductive
stages mirrored that observed for variation in GSI values.
Peak monthly mean GSI values (8.4% ± 0.7 SE for males,
7.2% ± 0.5 SE for females) occurred in August for both
sexes and remained elevated through to December (Fig.
4). The mean GSI of ripe (stage V) fish was 7.4 % ± 0.3 SE
for males and 6.3% ± 0.2 SE for females [1093].
Reproductive activity for fish in the Brisbane River [949]
generally matched that observed for fish from the Mary
River [1093], except that peak reproductive activity
occurred slightly later in the year. Ripe fish (equivalent to
stage V) were present between September and January and
peak monthly mean GSI values (7.0% for males, 8.5% for
females) were observed in September for females and
October for males, remaining elevated in both sexes until
January [949]. Overall sex ratios for populations from the
Brisbane River have been reported as 1.3 females for every
male, and significantly more females were present during
The spawning stimulus is unknown but corresponds with
increasing water temperatures and photoperiod. In
aquaria, spawning occurred at water temperatures
between 25 and 29°C [1210]. Milton and Arthington [949]
observed that the peak spawning period for fish in the
Brisbane River in September–October coincided with
surface water temperatures between 19 to 23°C, and day
length from 11 to 11.5 hours. The peak spawning period
generally coincides with pre-flood periods of low and
stable discharge in rivers of south-eastern Queensland.
However, breeding may also continue through the months
of elevated discharge at the commencement of the wet
season in December/January. This species is thought to
spawn repeatedly during the breeding season and it has
been suggested that multiple spawning over an extended
period is an adaptation to the relatively unpredictable
timing of the onset of wet season flooding [949]. The
spawning of adults and presence of larvae can occur when
the likelihood of flooding is low, but the predictability of
high temperatures and low flows are higher. These conditions are likely to increase the potential of larvae to
encounter high densities of small prey, avoid physical
flushing downstream due to high flows and thereby
maximise the potential for recruitment into juvenile
25
Spring
(n = 2217)
10
Males
8
20
Summer
(n = 2552)
Females
15
AutumnWinter
(n = 4429)
6
10
4
5
2
0
0
Month
Figure 4. Temporal changes in mean Gonosomatic Index
(GSI% ± SE) stages of Craterocephalus marjoriae males (open
circles) and females (closed circles) in the Mary River, southeastern Queensland, during 1998 [1093]. Samples sizes for
each month are given in Figure 3.
Standard length (mm)
Figure 5. Seasonal variation in length-frequency distributions
of Craterocephalus marjoriae, from sites in the Mary, Brisbane,
Logan and Albert rivers, south-eastern Queensland, sampled
between 1994 and 2000 [1093]. The number of fish from
each season is given in parentheses.
176
Craterocephalus marjoriae
year-round and may not necessarily be related solely to
prevailing temperature and/or discharge regime but may
also involve other physical or biological factors.
stocks, as has been hypothesised for other small-bodied
fish species in the Murray-Darling Basin [614, 615].
Milton and Arthington [949] reported that juvenile fish in
the Brisbane River were present between October and
February and these authors were able to discern a clear
cohort that could be tracked through to the following
breeding season. In contrast, subsequent sampling in
rivers of south-eastern Queensland [1093] revealed that
juvenile fish less than 20 mm SL were present year-round
and no obvious seasonal peak in juvenile abundance (i.e.
no clear cohort of juvenile fish) was observed (Fig. 5). The
latter data support the suggestion made earlier that this
species has an extended spawning period. The data further
suggest that suitable conditions for recruitment of larvae
through to the juvenile stage and beyond may persist
In the wild, spawning probably occurs in aquatic macrophytes and submerged marginal vegetation. Spawning
observations in aquaria suggest that pre-spawning behaviour is initiated adjacent to aquatic vegetation whereby the
male swims beneath and behind the female, nudging the
anterior rays of the anal fin and posterior belly region of
the female with the interorbital or snout area of his head
[1210]. Adhesive, demersal eggs are attached to aquatic
macrophytes. The male follows within 5 cm of female and
then releases milt onto the eggs when swimming adjacent
to her. In aquaria, males and conspecifics have been
observed to eat eggs during and following deposition
Table 4. Life history information for Craterocephalus marjoriae.
Age at sexual maturity (months)
<12 months [949]
Minimum length of gravid (stage V)
females (mm)
32.8 mm SL (field) [1093], 38 mm SL (aquaria) [1210]
Minimum length of gravid (stage V)
males (mm)
31.7 mm SL (field) [1093], 39.5 mm SL (aquaria) [1210]
Longevity (years)
2+ [949]
Sex ratio (female to male)
1.3:1 [949]
Occurrence of ripe (stage V) fish
Late-winter, spring and summer. June–March [1093], September–January [949]
Peak spawning activity
Late-winter and spring. Elevated GSI between August and December [1093], Elevated
GSI between September and January [949]
Critical temperature for spawning
? 19–23°C (field) [949]; 25–29°C (aquaria) [1210]
Inducement to spawning
? possibly temperature and day length
Mean GSI of ripe (stage V) females (%)
6.3% ± 0.2 SE (maximum mean GSI in August = 7.2% ± 0.5 SE) [1093]; (maximum
mean GSI in September = 8.5%) [949];
Mean GSI of ripe (stage V) males (%)
7.4% ± 0.3 SE (maximum mean GSI in August = 8.4% ± 0.7 SE) [1093]; (maximum
mean GSI in October = 7.0%) [949]
Fecundity (number of ova)
Total fecundity = 30–484, mean = 196 ± 8 SE [1093]; Batch fecundity = 48–259, mean =
137 ± 10 SE [949], In aquaria 2–15 eggs deposited in 3–5 day period [1210]
Total Fecundity (TF) and Batch Fecundity
(BF)/length relationship (mm SL)
Log10 TF = 1.671 Log10 L – 0.575, r2 = 0.283, p<0.001, n = 146 [1093]. Log10
BF = Log10 (6.1 x 10–4) + 2.52 Log10 L, r2 = 0.58, p<0.001, n = 61 [949].
Egg size (diameter)
Intraovarian eggs from stage V fish = 1.02 mm ± 0.01 SE [1093]. Water-hardened eggs
1.15–1.25 mm [1210].
Frequency of spawning
Extended spawning period, probably repeat spawner [949]
Oviposition and spawning site
In the wild, spawning probably occurs in aquatic macrophytes and submerged marginal
vegetation. In aquaria, adhesive, demersal eggs are attached to aquatic macrophytes
[1210]
Spawning migration
None known
Parental care
None known
Time to hatching
After fertilisation, hatching takes 6.5 to 7 days in aquaria at 25–29°C [1210]
Length at hatching (mm)
Newly hatched prolarvae 5.7 mm SL [1210]
Length at free swimming stage
Postlarvae 7.25 mm SL [1210]
Age at loss of yolk sack
?
Age at first feeding
?
Length at first feeding
Postlarvae 7.25 mm SL [1210]
Length at metamorphosis (days)
?
Duration of larval development
?
177
Freshwater Fishes of North-Eastern Australia
35–36 mm SL, 1+ fish were 46–47 mm SL and 2+ fish
(females only) were greater than 56 mm SL. These data
(together with stage-length and sex ratio data presented
earlier) collectively suggest that sexual maturity is reached
at one year of age, males appear to die after their first
breeding season and females live for over two years. In
aquaria, fish have been reported to live for up to 18
months [1210].
[1210]. No parental care of eggs has been reported.
Total fecundity for fish from the Mary River is estimated
to range from 30–484 eggs (mean 196 ± 8 SE, n = 146 fish)
[1093]. Batch fecundity for fish from the Brisbane River
ranges from 48–259 eggs/batch (mean 137 ± 10 SE, n = 61
fish) [949]. In the aquarium, C. marjoriae was observed to
deposit 2–15 eggs in a 3–5 day period followed by a rest
period of 6–9 days [1210]. Fecundity is significantly
related to fish size. The relationship between length (SL in
mm) and total fecundity (TF) for 146 fish from the Mary
River is Log10 TF = 1.671 Log10 SL – 0.575, r2 = 0.283,
p<0.001 [1093]. Fish of 40 mm SL produced about 150
eggs in total, whereas fish of 60 mm SL produced about
350 eggs [1093]. The relationship between length (SL in
mm) and batch fecundity (BF) for 61 fish from the
Brisbane River is Log10 BF = Log10 (6.1 x 10-4) + 2.52 Log10
SL. r2 = 0.58, p<0.001 [949]. Fish of 40 mm SL produced
about 80 eggs per batch, whereas fish of 60 mm SL
produced about 240 eggs [949]. Milton and Arthington
[949] suggested that Craterocephalus marjoriae invests
more into reproductive effort than its congener C. stercusmuscarum, with higher GSI values throughout the breeding season (particularly males) and higher mean batch
fecundity, although both species have similar sized eggs
(see also chapter on C. stercusmuscarum).
Movement
There is no quantitative information on the movement
patterns of C. marjoriae. This species has not been
observed to use fishways on weirs or tidal barrages in the
Burnett [658, 828, 1276, 1277], Mary [158, 159, 658] and
Brisbane rivers [658], nor were large numbers of individuals found to be congregating below these structures,
despite being abundant in the latter two rivers. However, it
is likely that this species is able to undertake local dispersal
and/or recolonisation movements. It is particularly abundant in streams that periodically become disconnected by
extended periods of low flows, when surface waters recede
to a series of isolated pools (e.g. in tributaries of the Mary
and Brisbane rivers). In these streams, rapid recolonisation of previously dry river reaches has been observed
soon after flows resumed in summer and longitudinal
connectivity was re-established (i.e. within 48 hours
[1093]).
Eggs are relatively large. The mean diameter of 1337
intraovarian eggs from stage V fish from the Mary River
was 1.02 mm ± 0.01 SE [1093]. The diameter of waterhardened eggs has been reported to range from 1.15 to
1.25 mm [1210]. Eggs are characterised by a smooth nonadhesive chorion and 10 adhesive filaments (1 mm or
longer) originating in a cluster at the animal pole of the
egg [1210]. Oil droplets in the yolk were 0.01 to 0.1 mm
diameter at spawning and were initially concentrated at
the animal pole, later migrating in a bunch to the vegetal
pole. Eggs hatch after 6.5 to 7 days at 25 to 29°C.
Illustrations of larval stages can be found in Semple [1210].
The mean length of prolarvae three hours after hatching
was 5.7 mm SL. At this stage the top of the head, preoperculum and lateral line were spotted and the eyes, swimbladder and surface pigments were black. Paired contour
melanophores were visible on the dorsal surface and
dendritic melanophores were present on the belly, caudal
and ventral contours. Postlarvae were 7.25 mm SL and, by
this stage, the anal and dorsal fin buds were developing, the
caudal fin was rayed, rows of small punctate melanophores
were visible on the caudal fin and anal finfold, and larvae
had commenced swimming and feeding. Juveniles began to
school once the fins were fully rayed [1210].
Trophic ecology
Diet data for C. marjoriae is available for 224 individuals
from studies in the Burnett and Albert rivers, south-eastern Queensland (Fig. 6). This species is a microphagic
omnivore. Algae (filamentous and unicellular) comprised
the largest proportion of the total mean diet (26.9%) and
small amounts of aquatic macrophytes (2.0%) were also
consumed. Microcrustaceans (23.6%) and aquatic insects
(14.6%) were relatively important components of the diet
and small amounts of fish (primarily fish eggs), molluscs
and terrestrial invertebrates were also consumed. The high
degree of herbivory in C. marjoriae is greater than that
observed for other similarly sized and/or closely related
species (e.g. C. stercusmuscarum) in south-eastern
Queensland streams. A number of anatomical features
make C. marjoriae well suited to benthic foraging and
herbivory [917]. These characteristics include a small
mouth with protrusible jaws that form an anteroventrally
directed tube, potentially facilitating benthic grazing. This
species also has an extra loop to the gut and the ratio of
intestine length to standard length is over 2.5 times greater
than that of C. stercusmuscarum and other similarly-sized
sympatric species that consume less aquatic plant matter
([917] this study). In aquaria, adults will consume a range
of food types including small anuran tadpoles, mosquito
Length at age data using evidence from scale annuli [949]
indicate that 0+ fish (males and females) were around
178
Craterocephalus marjoriae
[95] observed that hardyheads (Craterocephalus spp.) in
the Brisbane region were rarely present or abundant where
the alien fish species Gambusia was present. These authors
speculated that similarities in diet increased the potential
for competition among these species. In contrast, our
recent, more extensive sampling of rivers and streams in
south-eastern Queensland [1093] indicates that C. marjoriae and G. holbrooki frequently occur together, often in
large numbers. Co-occurrence data such as these provide
no evidence for the impact of alien fish species such as G.
holbrooki on C. marjoriae.
larvae and other common aquarium foods such as Calanus
and Artemia nauplii, Tubifex worms and commercial flake
foods [1210]. Even finely minced animal meats are eaten.
Postlarvae will consume similar items to those listed above
as well as infusoria made from lettuce [1210].
Fish (4.0%)
Microcrustaceans (23.6%)
Unidentified (29.4%)
Molluscs (2.4%)
Terrestrial invertebrates (1.1%)
Aquatic macrophytes (2.0%)
Aquatic insects (14.6%)
Algae (26.9%)
Figure 6. The mean diet of Craterocephalus marjoriae. Data
derived from stomach contents analysis of 224 individuals
from the Burnett River [205] and Albert River [1421], southeastern Queensland.
Conservation status, threats and management
The conservation status of Craterocephalus marjoriae is
listed as Non-Threatened by Wager and Jackson [1353].
Although listed by Wager [1349] as having a restricted
distribution, it is generally very common and widely
distributed within the major rivers of south-eastern
Queensland and in the Clarence River, northern New
South Wales. It is relatively uncommon at the northern
extent of its range (e.g. north of the Burnett River).
Like many other native species, siltation arising from
increased erosion rates and sediment transport in catchments may be a threat to the spawning habitats of C.
marjoriae and may also affect aquatic invertebrate food
resources. Interactions with alien fish species (e.g. competition for resources and predation on eggs, larvae and juveniles) is another other potential threat. Arthington et al.
Very little is known of movement patterns, however,
limited upstream dispersal movements of young-of-theyear probably occur, suggesting that C. marjoriae is likely
to be sensitive to barriers to movement caused by structures such as dams, weirs, barrages, road crossings and
culverts. River regulation, independent of the imposition
of barriers, may also impact on C. marjoriae populations.
Changes to the natural discharge regime and hypolimnetic
releases of unnaturally cool waters from large dams may
interrupt possible cues for movement, or de-couple optimal temperature/discharge relationships during critical
phases of spawning, larval movement and development.
Unseasonal flow releases during naturally low flow periods
in September and October appear likely to negatively
affect reproductive success as this coincides with the
period of peak spawning activity and larval development.
The availability of aquatic macrophyte beds, the likely
spawning habitat of C. marjoriae, may be maximised
during low flow periods. Scouring actions of elevated
discharges at the onset of the wet season may reduce or
remove aquatic macrophyte beds. Larval development is
also likely to be favoured during low flow periods, during
which time phytoplankton and invertebrate abundances
are also high [949].
Fish in aquaria have been reported to be susceptible to
intestinal worm infestations [1210] and a species of
Craterocephalus (possibly C. marjoriae) from the Brisbane
catchment was infected by the digenetic trematode
Opecoelus variabilis (Opecoelidae) [338, 339].
179
Craterocephalus stercusmuscarum (Günther, 1867)
Fly-specked hardyhead
37 246029
Family: Atherinidae
Description
First dorsal fin: IV–VIII; Second dorsal: I, 5–10; Anal: I,
7–10; Pectoral: 11–15; Caudal: 15–18 segmented rays;
Pelvic: I, 5; Vertical scale rows: 32–35; Horizontal scale
rows: 6–8; Predorsal scales: 11–18, Gill rakers on lower
branch of first arch: 9–13; Vertebrae: 31–38 (C. s. fulvus:
31-36, C. s. stercusmuscarum: 35–38) [352, 486, 635, 637].
Figure: mature male specimen of C. s. stercusmuscarum, 51
mm SL, North Johnstone River at Malanda, September
1994; drawn 1998.
Craterocephalus stercusmuscarum is a moderate-sized
hardyhead commonly reaching 50–60 mm. The northern
subspecies C. s. stercusmuscarum is known to grow to a
larger size (maximum 108 mm LCF) [635] than C. s. fulvus
(maximum 78 mm SL) [52, 635]; specimens from the
Wenlock River may reach 125 mm TL [69]. Of 2555 specimens collected in streams of south-east Queensland, the
mean and maximum length of this species were 34 and 73
mm SL, respectively. The equation best describing the relationship between length (SL in mm) and weight (W in g)
for 306 individuals of C. s. fulvus (range 20–73 mm SL)
sampled from the Mary River, south-eastern Queensland
is W = 0.7 x 10–5 L3.217, r2 = 0.985, p<0.001 [1093]. The
northern subspecies is known to consist of at least two
25
Upper Johnstone (n = 620)
20
Lower Johnstone (n = 165)
15
Mulgrave
(n = 59)
10
5
0
Standard length (mm)
Figure 1. Size frequency distributions for Craterocephalus
stercusmuscarum stercusmuscarum populations in the upper
Johnstone River (n = 620, open bars), lower Johnstone River
(n = 165, hatched bars), and Mulgrave River (n = 59, closed
bars). Specimens were collected over the period 1994–1998
[1093].
180
Craterocephalus stercusmuscarum
sides of C. s. stercusmuscarum, less evident or absent in
small individuals or populations from southern and
inland areas (i.e. C. s. fulvus). Minor colour variation
between sexes. Running ripe females with dark blotch
around vent; males with bright yellow or gold coloured
ventral surface during breeding season. Colour in preservative: white to brown, with midlateral stripe as described
above [486, 635, 637].
distinct lineages (see below) [899], with a lineage present
on the Atherton Tablelands of the Wet Tropics region
growing to larger size than that occurring in the lowland
rivers of this area (Fig. 1). The population size structure of
C. s. stercusmuscarum in the Burdekin River (n = 295)
closely resembles that of lowland Wet Tropics populations
depicted in Figure 1, with a maximum length (SL) of 70
mm, and a slightly bimodal distribution with modal peaks
for the 35–40 and 50–55 mm size classes [1082].
The equation best describing the relationship between
length (SL in mm) and weight (W in g) for 288 individuals
of C. s. stercusmuscarum (range 21–82 mm SL) from the
Atherton Tablelands section of the Johnstone River is W =
1.6 x 10–5 L2.952, r2 = 0.969, p<0.001. The equivalent relationship for 134 individuals (range 17–63 mm SL) from
the lower Johnstone River and the Mulgrave River (elevation less than 50 m.a.s.l.) is W = 0.9 x 10–5 L3.108; r2=0.968,
p<0.001 [1093]. Bishop et al. [193] report a length/weight
relationship of W (in g) = 0.011 L2.880; r2 = 0.949, p<0.001
where L = CFL in cm.
Larval C. s. stercusmuscarum are diffusely pigmented
throughout larval development. A few punctate
melanophores occur on the head behind the level of the
eyes and nape. Stellate melanophores are irregularly and
diffusely distributed down the mid-line of the dorsal
surface. Stellate melanophores are present on the opercula
and abdomen of some specimens, however they seldom
extended forward through the isthmus. The peritoneum
along the dorsal surface of the swim bladder is heavily
pigmented. Stellate melanophores are always present along
the lateral line but are unevenly distributed along its length
[1093].
Craterocephalus stercusmuscarum is an elongate and slender species. The head of larger specimens often slopes
towards snout and possesses an interorbital trough. The
mouth is small, protrusible and bordered with thick lips;
mouth not reaching anterior margin of eye. The mouth
gape is restricted by fusion of lips. Teeth are small, in two
or three rows in medial third of each jaw. Body scales relatively large, dorsoventrally oval, with concentric and
complete circuli; scales arranged in distinct rows along
body. Scales present on preopercle and opercle. First dorsal
fin originating behind tips of pectoral rays; second dorsal
fin originating in line with origin of anal fin. Pectoral fin
inserted forward of pelvic fin. Caudal fin forked with
rounded tips [486, 635, 637].
The two subspecies of C. stercusmuscarum can be separated
on the basis of the following characters: Craterocephalus s.
fulvus (sometimes referred to as the un-specked hardyhead
or Mitchellian hardyhead) is generally less vividly coloured
than C. s. stercusmuscarum, the lateral black spots are absent
[637] or present but not as readily apparent [1093], and it
has fewer vertebrae (31–36 in C. s. fulvus, 35–38 in C. s. stercusmuscarum) [637]. Craterocephalus s. fulvus in coastal
south-eastern Queensland is similar in general appearance
to the sympatric C. marjoriae, especially juveniles.
Distinguishing characteristics of C. s. fulvus include a more
slender, elongate body, a dark stripe running though eye and
parallel rows of faint dark spots sometimes present along
sides of body.
The larvae are typically elongate and narrowly fusiform in
body plan. The eyes are heavily pigmented with a welldeveloped and slightly dorsoventrally compressed lens.
The mouth is functional immediately after hatching and
the gut is either simple or coiled but always non-striated in
newly hatched larvae. A coiled and striated gut is present
in flexion larvae. A yolk sac is present in early preflexion
larvae but no longer so by flexion [1093]. More detail on
larval morphology is presented in the section on reproduction (below).
Systematics
Craterocephalus stercusmuscarum was originally described
by Günther in 1867 [486] as Atherina stercus muscarum,
the species epithet (and common name) referring to the
pattern of black dots along the side of the body. Other
synonyms of C. stercusmuscarum include Atherinichthys
maculatus Macleay, 1883 [847] and C. worrelli Whitley
1948 [1391]. Ivantsoff et al. [637] showed that some populations of a species from the Murray-Darling Basin, previously recognised as C. fluviatilis McCulloch, 1913 [876],
and populations of C. stercusmuscarum from south-eastern Queensland coastal rivers were morphologically indistinguishable, but differed from northern Australian
populations of the latter species. Consequently, the subspecies C. stercusmuscarum fulvus and C. s. stercusmuscarum were recognised [352, 637]. Although differing in
colouration and vertebral counts, their conspecific status
Colour varies between localities and subspecies. Dorsal
surface green-grey, lower sides and ventral surface silvery.
A dark stripe runs from snout and across eye, becoming
black, gold or silver in colour and continuing to base of
caudal fin. Dorsal surface of head often black; body scales
stippled on edges. A single black spot at the base of each
scale forms a series of longitudinal parallel rows along
181
Freshwater Fishes of North-Eastern Australia
was justified on the basis that preliminary electrophoretic
analysis revealed no differences between C. s. fulvus and C.
s. stercusmuscarum, and juveniles of both species could not
be separated on the basis of external characteristics [352,
637]. Further information on the relationships between C.
s. fulvus, C. fluviatilis and other hardyhead species can be
found in Crowley and Ivantsoff [347]. Craterocephalus s.
stercusmuscarum has been confused with C. randi [41,
1304], a closely related and almost indistinguishable
species confined to Papua New Guinea [37, 343, 352].
Herbert and Peeters [569] speculated that there may be
several undescribed species closely related to C. stercusmuscarum in rivers of north-western Cape York Peninsula
on the basis that these populations have different scale
patterns and usually lack black spots.
insufficient time for divergence since eastern and western
flowing rivers had been separated. In contrast to the
absence of morphological divergence, McGlashan and
Hughes [899] detected high levels of genetic differentiation in eastern flowing rivers of the Wet Tropics region,
identifying two highly divergent lineages and further
divergence within one of these lineages. The first lineage
was restricted to lowland sections of the Herbert,
Mulgrave, Liverpool and Johnstone drainages. The second
occurred in the high elevation Atherton Tableland sections
of the Herbert, Johnstone and Barron rivers. Within this
group, significant divergence between the Barron River
(and one Johnstone River population) and the Johnstone
and Herbert rivers was also detected. Additional preliminary analysis revealed that the high elevation populations
of the Johnstone River were more closely related to
Northern Territory populations of C. s. stercusmuscarum
than they were to lowland populations within the same
region. McGlashan and Hughes [899] argued that the
upland population was derived from western flowing
rivers. It is interesting to note that C. s. stercusmuscarum
from the Northern Territory and high elevation sites from
the Johnstone River are both less robust for a given length
than lowland populations (see above). The Atherton
Tablelands has a very complex geomorphic history with
substantial recent vulcanism and drainage rearrangement
[618].
Crowley [343] proposed that the phylogenetic structure of
the Australasian craterocephalids (i.e. a single, highly
distinct clade known as the ‘eyresii’ group and another
clade separating into two subgroups, one composed of
freshwater species and referred to as the ‘stercusmuscarum’
group and the other composed of marine or estuarine
species referred to as the ‘honoriae’ group) could be
explained by a series of separate invasions of freshwater.
The initial invasion of the ancestral Craterocephalus
species was postulated to be from the north or north-west
and occurred during the mid-Cretaceous (95–110
m.y.b.p.) marine transgression when much of central
Australia was flooded. As sea levels once more receded,
peripheral populations also retreated whereas more inland
populations become isolated and gave rise to the ‘eyresii’
group. Invasions associated with the later Oligocene/earlyMiocene marine transgression gave rise to the ‘stercusmuscarum’ group. Most New Guinean craterocephalids are
closely related to C. stercusmuscarum and speciation
within this clade appears to be relatively recent [352].
Crowley [343] suggested that the current distribution of
the subspecies C. s. fulvus (see below) implied that it must
have been present on the east coast prior to the uplift of the
Tweed volcanic shield some 20–23 m.y.b.p. However, more
recent allozyme electrophoretic data did not support this
hypothesis and analysis of mtDNA sequence divergence
suggested a more recent (approximately one million years)
separation of these two populations [901]. McGlashan and
Hughes [901] suggested that coastal populations of the two
subspecies had been independently derived.
Crowley [343], based on osteological evidence, noted that
C. s. stercusmuscarum populations on either side of the
Great Dividing Range in northern Queensland are almost
identical and concluded that either this species had
recently entered these rivers from both the Gulf of
Carpentaria and the Coral Sea or that there had been
182
Distribution and abundance
Craterocephalus stercusmuscarum is a very widespread
species occurring in coastal and inland drainages of eastern and northern Australia. This species occurs in Timor
Sea drainages of the Northern Territory, the Gulf of
Carpentaria and western Cape York, coastal catchments
throughout most of eastern Queensland and was historically present throughout much of the Murray-Darling
Basin [52, 635]. In north-western Queensland, it is present
in most major drainages in the Gulf of Carpentaria region
[41, 571, 643, 1349]. This species is patchily distributed in
north-eastern Queensland, and with the exception of the
Annan River, it appears to be absent between southern
Cape York Peninsula (south of the Normanby Basin) and
the northern Wet Tropics region (north of the Barron
River). It is present in most major drainages from the
Barron River south to about the New South Wales border
but appears absent from short coastal streams near
Cardwell, Proserpine, Tin Can Bay and the Sunshine
Coast. This species has also been recorded from Fraser
Island off the coast of south-eastern Queensland. As far as
we are aware, the eastern Australian distribution of C. s.
fulvus extends only as far south as the Nerang River in
south-eastern Queensland. However, Llewyllen [814] indicated that it was occasionally reported from the ‘extreme
Craterocephalus stercusmuscarum
north coast of New South Wales’ and Faragher and Harris
[407] list this species as being present there. It is unclear
whether these records are erroneous or whether the presence of this species has been confused with C. marjoriae,
which occurs in the Clarence River.
The distribution of the two subspecies of C. stercusmuscarum in Queensland was once thought to be separate. The
southern limit of the distribution of C. s. stercusmuscarum
was originally suggested to be the Dee River (Fitzroy
Basin) [352] and C. s. fulvus was thought to occur only as
far north as Maryborough [637]. More recently, Wager
[1349] and Allen et al. [52] suggested that both subspecies
were sympatric in the Mary River. Recent genetic analysis
of populations of C. stercusmuscarum from eastern
Queensland and the Murray-Darling Basin [899, 901]
supported the notion that the two putative subspecies
were genetically distinct (on the basis of mtDNA data) but
indicated that C. s. fulvus is present at least as far north as
the Elliott River and no populations of C. s. stercusmuscarum were present south of the Calliope River. It is
unclear whether the subspecies are sympatric in the 250
km span between these rivers [901].
Craterocephalus s. stercusmuscarum is relatively common
in northern Australia. It was the 4th most abundant
species collected in extensive sampling of the Alligator
Rivers region in the Northern Territory [193] and was also
observed to be common and widespread in other studies
of the region [189, 262, 1064]. In some habitats however,
such as pools in sandy creek-beds, this species may by relatively rare and replaced by C. marianae [1416].
apparently absent from smaller drainages such as the
Maria and Moresby rivers [583, 1183]. The absence from
these drainages may be artefactual as this species has been
recorded from small coastal drainages south of the
Herbert River [1053]. This species was the 9th most widely
distributed and the 10th most abundant species in an
extensive survey of the region [1087]. In more recent
sampling in the Johnstone and Mulgrave rivers, C. stercusmuscarum was the 15th most widely distributed and the
15th most abundant species but was only the 25th most
abundant species by biomass (Table 1). This species is
more abundant in the Johnstone River than in the
Mulgrave River and occurs at greater biomass density in
the former river, partly because it occurs at greater numerical density and partly because C. stercusmuscarum grow
to larger size in the Johnstone River.
Table 1. Distribution, abundance and biomass data for
Craterocephalus s. stercusmuscarum in two rivers of the Wet
Tropics region. Data summaries for a total of 461 individuals
collected over the period 1994–1997 [1093]. Data in
parentheses represent summaries for per cent and rank
abundance and per cent and rank biomass, respectively, at
those sites in which this species occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Rank biomass
Johnstone Mulgrave
River
River
22.6
19.6
22.7
1.3 (9.5)
1.5 (11.3)
0.8 (6.6)
15 (3)
13 (3)
13 (6)
0.1 (2.2)
0.1 (2.6))
0.5 (1.4)
25 (7)
20 (6)
23 (12)
The subspecies C. s. stercusmuscarum is moderately
common and widespread in some rivers of the Gulf of
Carpentaria and western Cape York Peninsula including
the Gregory, Gilbert, Mitchell (including the Walsh and
Palmer rivers), Coleman, Edward, Archer, Holroyd, Ducie,
Watson and Jardine drainages [571, 643, 1186, 1349]. In
eastern Cape York Peninsula, it is widespread but patchily
distributed, and often locally common [571, 697, 787,
1094]. Kennard [697] found C. s. stercusmuscarum
contributed, on average, 8.2 ± 1.6% to the total electrofishing catch in aquatic habitats of the Normanby
River: relative abundance was slightly greater in floodplain
(9.7 ± 1.9%) than riverine (4.8 ± 2.6%) habitats. Temporal
variation in abundance may be substantial. For example,
we collected only seven individuals from the Pascoe,
Stewart and Normanby rivers one year prior to Kennard’s
study [179]. This species is present in the Annan and River.
This species is common and widely distributed in central
Queensland drainages including the Black-Alice, Ross,
Pioneer and Fitzroy rivers [176, 408, 586, 591, 658, 942,
1046, 1081, 1098]. In the Burdekin River, it is widely
distributed in both upland and lowland portions of the
river [586, 591, 1046, 1098] but is apparently absent or
uncommon in the more turbid drainages of the Cape/
Campaspe and Belyando/Suttor rivers [255, 256] and is
uncommon in the upper reaches of the Broken River [956].
This species contributed 1.4% and 2.1% of electrofishing
and seine-netting catches, respectively in a study conducted
in this river over the period 1989-1992 [1098].
Craterocephalus s. stercusmuscarum is widely distributed in
the Wet Tropics region, occurring in all major drainages
south of, and including, the Barron River [98, 230, 584,
585, 599, 643, 1087, 1096, 1177, 1184, 1223, 1349], but is
Craterocephalus s. stercusmuscarum is common to very
common in the Pioneer River [658, 1081] and in short
coastal streams near Sarina [779] and Shoalwater Bay
[1328]. It is widespread and generally common in the
183
Mean numerical density
(fish.10m–2)
0.37 ± 0.11
0.42 ± 0.02 0.29 ± 0.12
Mean biomass density
(g.10m–2)
1.37 ± 0.99 0.37 ± 0.15
1.02 ± 0.65
Freshwater Fishes of North-Eastern Australia
Fitzroy River [160, 658, 659, 942, 1272, 1274, 1275],
Calliope River [915], Baffle Creek [826] and the Kolan
River [11, 232, 658] (possibly also C. s. fulvus in the latter
two rivers).
and maximum numerical densities recorded in 232
hydraulic habitat samples (i.e. riffles, runs or pools) were
0.99 individuals.10m–2 and 16.40 individuals.10m–2,
respectively. Average and maximum biomass densities at
184 of these sites were 0.68 g.10m–2 and 13.27 g.10m–2,
respectively. Highest numerical and biomass densities
were recorded from the Mary River.
Craterocephalus s. fulvus is moderately common in southeastern Queensland. In a review of existing fish sampling
studies in the Burnett River, Kennard [1103] noted that it
had been collected at 27 of 63 locations surveyed (ninth
most widespread species in the catchment) and formed
2.7% of the total number of fishes collected (seventh most
abundant). It is present but apparently relatively uncommon in the Elliott River [825] and rivers of the Burrum
Basin [157, 736, 1305]. Surveys undertaken by us between
1994 and 2003 in catchments from the Mary River south
to the Queensland–New South Wales border [1093]
collected a total of 4608 individuals and it was present at
25.8% of all locations sampled (Table 2). Overall, it was
the 10th most abundant species collected (2.8% of the
total number of fishes collected) and was present in
moderate abundances at sites in which it occurred
(7.96%). In these sites, C. s. fulvus most commonly
occurred with the following species (listed in decreasing
order of relative abundance): C. marjoriae, G. holbrooki, P.
signifer, R.semoni and H. klunzingeri. It was the 19th most
important species in terms of biomass, forming only 0.2%
of the total biomass of fish collected. It was most common
in the Mary River and the Brisbane River where it was the
ninth and sixth most abundant species, respectively. It was
comparatively widespread throughout these catchments,
being present at 62% and 36% of locations sampled in the
Mary and Brisbane rivers, respectively. This species is
comparatively rare in the remaining catchments of southeastern Queensland sampled by us and was not collected
in the Albert-Logan Basin, although it is known to occur
in the Albert River [719, 1421]. Across all rivers, average
Craterocephalus stercusmuscarum was once present
throughout much of the Murray-Darling Basin [635]
where it was patchily distributed but historically common
[778, 1200]. Recent surveys reveal that it is present but
uncommon in the Queensland section of the upper
Darling River (Condamine River) [643, 807, 957, 958,
1310]. In the New South Wales portion of the MurrayDarling Basin it is also very patchily distributed and
uncommon [807, 1201]. It is thought to be rare and possibly absent from southern parts of the Murray-Darling
Basin [635], although surveys in the last 20 years have
revealed that it is patchily distributed but locally common
in some parts of the lower Murray Basin in Victoria and
South Australia [56, 507, 807, 817].
Macro/mesohabitat use
Craterocephalus stercusmuscarum is found in a variety of
habitats including large floodplain rivers and billabongs,
small rainforest streams, volcanic crater lakes (Atherton
Tablelands), dune lakes (Fraser Island), river impoundments (dams and weirs) and brackish river estuaries.
In northern Australia, Craterocephalus s. stercusmuscarum
is reportedly widely distributed in the Alligator Rivers
region, occurring in 25 of 26 regularly sampled sites [193].
Habitats occupied by this species and in which it was relatively common included corridor lagoons, sandy creekbed habitats and floodplain lagoons. Other habitats used
Table 2. Distribution, abundance and biomass data for Craterocephalus s. fulvus in rivers of south-eastern Queensland. Data
summaries for a total of 4608 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent
summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species
occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Rank biomass
Mary River Sunshine Coast Moreton Bay
rivers and
rivers and
streams
streams
Brisbane
River
Logan-Albert
River
25.8
62.0
3.4
15.0
36.0
—
2.82 (7.96)
3.82 (6.90)
0.04 (2.27)
1.55 (14.47)
5.05 (11.90)
—
South Coast
rivers and
streams
10.0
0.59 (40.39)
10 (6)
9 (7)
22 (5)
9 (2)
6 (2)
—
14 (1)
0.21 (0.69)
0.27 (0.63)
0.01 (0.03)
0.24 (0.41)
0.63 (1.24)
—
0.11 (0.43)
19 (10)
14 (10)
14 (6)
10 (7)
10 (7)
—
13 (3)
Mean numerical density
(fish.10m–2)
0.99 ± 0.13
1.06 ± 0.17
0.03 ± 0.03
0.51 ± 0.16
0.88 ± 0.18
—
0.39 ± 0.37
Mean biomass density
(g.10m–2)
0.68 ± 0.32
0.71 ± 0.14
0.03 ± 0.03
0.25 ± 0.03
0.58 ± 0.15
—
0.34 ± 0.34
184
Craterocephalus stercusmuscarum
have moderate current velocities (i.e. exposed runs). This
species is found across a wide array of substrate types. The
disparity between arithmetic and weighted means reflects
the greater abundance of this species in sites located on the
Atherton Tablelands where the stream-bed tends to be
dominated by rocks and bedrock. In-stream cover is
reasonably abundant in mesohabitats in which this species
occurs. The disparity between arithmetic and weighted
means indicates that it tends to be slightly more abundant
in mesohabitats with macrophyte beds and less abundant
in areas with large amounts of leaf litter and woody debris,
perhaps because such physical structures support greater
numbers of piscivorous fishes (Table 3, [1093]). Reaches
infested with para grass (a component of submerged vegetation in Table 3) also tend to support lower numbers of
this species. It is noteworthy that the habitat use described
in Table 3 for C. s. stercusmuscarum is in stark contrast to
the lentic environments used by this species across its
northern range and serve to illustrate the extreme adaptability of this species.
included muddy lowland lagoons and escarpment main
channel waterbodies, but it was only rarely encountered in
perennial escarpment streams.
The use of floodplain lagoon habitats appears common
for this species in northern Australia, having been reported
for populations in Cape York Peninsula [571, 894], the Wet
Tropics region [584, 585, 1085] and the Burdekin River
drainage [1046, 1125]. This species reaches high levels of
abundance in the weirs located on the Pioneer River
[1081].
In rivers of the Wet Tropics region, C. s. stercusmuscarum
(including individuals from both lineages described by
McGlashan and Hughes [899]) occurs across a wide range
of stream types, from small adventitious lowland streams
close to the river mouth, through to the main river channel both at high and low elevation (Table 3). Such habitats
tended on average to have a moderately open riparian
canopy, a width of about 15 m, a mean depth 0.5 m, and
Table 3. Macro/mesohabitat use by Craterocephalus s.
stercusmuscarum in rivers of the Wet Tropics region. Data
summaries for 393 individuals collected at 24 locations
between 1994 and 1997 [1093]. W.M. refers to the mean
weighted by abundance to reflect preference for particular
conditions.
Parameter
Min.
Max.
Mean
W.M.
Catchment area (km2)
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
2.8
3.0
30.0
15
5.2
0
515.5
67.0
104.0
750
53.7
100.0
142.8
24.6
54.8
196
14.9
32.9
109.2
20.8
77.3
458
12.8
29.5
Gradient (%)
0
Mean depth (m)
0.22
Mean water velocity (m.sec–1) 0
2.26
0.91
0.45
0.4
0.51
0.19
The macro/mesohabitat use of C. s. fulvus in south-eastern
Queensland differs to that described above for northern
Queensland populations of C. s. stercusmuscarum, probably reflecting differences in river geomorphology and
hydraulics between regions. Habitat use of C. s. fulvus is
however, generally similar to the congener, C. marjoriae, a
species with which it co-occurs throughout much of
south-eastern Queensland. Craterocephalus s. fulvus occurs
throughout the major length of rivers, ranging between 4
and 311 km from the river mouth and at elevations up to
240 m.a.s.l. (Table 4). It most commonly occurs within 220
km of the river mouth and at elevations less than 100
m.a.s.l. and is present in a wide range of stream sizes
(range = 0.7–46.8 m width) but is more common in
streams greater than 10 m width and with low riparian
cover (<30%). This subspecies has been recorded in a
range of mesohabitat types but it most commonly occurs
in low gradient (weighted mean = 0.17%) runs and pools
characterised by moderate depth (weighted mean = 0.43
m) and low mean water velocity (weighted mean = 0.09
m.sec–1) (Table 4). This is a substantially lower water velocity than that recorded for C. s. stercusmuscarum in rivers of
the Wet Tropics region (Table 3), but note that C. s. fulvus
also occurs in shallow riffles with high gradients (maximum
= 2.86%) and high velocity (maximum = 0.85 m.sec-1) on
occasions. This subspecies is most abundant in mesohabitats with fine to intermediate sized substrates (sand,
fine gravel and coarse gravel) and particularly where
submerged aquatic macrophytes, filamentous algae and
submerged marginal vegetation are common. Elsewhere,
this species has been classified as a pool-dwelling species
[553] and has been reported to occur in still or slow-
0.43
0.55
0.20
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
48.0
51.0
72.0
35.0
49.0
81.0
68.0
4.9
12.8
22.6
13.5
17.0
25.0
4.6
3.7
6.1
19.7
7.2
8.1
31.0
24.4
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
15.0
6.7
33.0
61.0
10.0
35.8
8.4
7.2
45.0
50.0
1.6
0.4
3.6
14.8
0.9
7.2
1.3
1.1
13.2
7.1
3.1
0.7
3.1
5.8
0.7
4.7
2.5
0.8
9.8
5.0
185
Freshwater Fishes of North-Eastern Australia
revealed however that this species will position itself very
close to the substrate when negotiating sections of elevated
water velocity [1093]. This species was infrequently
collected over very fine substrates, and most commonly
over rocks and bedrock, reflecting the distribution of
substrate types in those sites in which it occurred (Table
3). This species is an open water schooling species occasionally making use of such cover elements as macrophyte
beds and emergent vegetation (Fig. 2f).
flowing rivers, small streams, swamps, billabongs, lakes,
ponds and reservoirs and in fast-flowing creeks [34, 52,
270].
Table 4. Macro/mesohabitat use by Craterocephalus s. fulvus
in rivers of south-eastern Queensland. Data summaries for
4608 individuals collected from samples of 232 mesohabitat
units at 76 locations between 1994 and 2003 [1093]. W.M.
refers to the mean weighted by abundance to reflect
preference for particular conditions.
Parameter
Min.
Catchment area (km2)
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
19.3
9.0
4.0
0
0.7
0
Gradient (%)
0
Mean depth (m)
0.05
Mean water velocity (m.sec–1) 0
Max.
10211.7
270.0
311.0
240
46.8
80.0
2.86
1.08
0.85
Mean
W.M.
1540.1
73.5
193.1
83
12.3
28.9
996.0
56.1
220.8
89
11.5
24.1
0.30
0.43
0.14
60
40
20
20
0
0
Mean water velocity (m/sec)
40
0
0
0
0
0
0
0
99.6
100.0
56.7
70.9
65.8
41.1
76.0
8.4
18.4
21.9
30.1
16.8
3.0
1.4
7.5
31.8
22.6
24.7
12.1
0.9
0.4
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
64.5
65.9
26.7
65.7
43.3
43.3
31.0
15.5
50.0
58.8
19.8
11.8
1.5
8.6
2.3
9.1
3.8
3.0
8.5
12.1
23.2
15.5
0.9
15.0
3.5
6.9
2.9
2.4
3.9
6.9
60
40
0.17
0.43
0.09
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
(a)
(c)
(b)
Focal point velocity (m/sec)
40
30
30
20
20
10
10
0
0
(d)
Relative depth
Total depth (cm)
40
(e)
(f)
40
30
30
20
Microhabitat use
Craterocephalus s. stercusmuscarum in the Wet Tropics
region occurs over a range of water velocities up to 0.6
m.sec–1 although the great majority occur in flows less
than 0.3 m.sec–1 (Fig. 2a). This preference for areas of low
water velocity is also reflected in the focal point velocity
(Fig. 2b); most fish collected from average water velocities
greater than 0.20 m.sec–1 were either located low in the
water column or associated with some form of cover (Fig.
2f) and thus experienced reduced flows. Most fish were
collected from depths of 30–60 cm (Fig. 2c) and distributed throughout the water column although less
commonly in the upper 20% of the water column or close
to the substrate (Fig. 2d). Underwater observations have
20
10
10
0
0
Substrate composition
Microhabitat structure
Figure 2. Microhabitat use by Craterocephalus s.
stercusmuscarum in the Wet Tropics region (solid bars) and
C. s. fulvus in south-eastern Queensland (open bars).
Summaries derived from capture records for 78 individuals
from the Johnstone and Mulgrave rivers in the Wet Tropics
region and for 558 individuals from the Mary River, southeastern Queensland, over the period 1994-1997 [1093].
Pusey et al. [1109] examined the habitat use of larval C. s.
stercusmuscarum in the Johnstone River and found that
186
Craterocephalus stercusmuscarum
However, the data suggests that populations of this species
in the Northern Territory rarely experience temperatures
below 25°C, whereas temperatures below 20°C are experienced by populations occurring in rainforest streams at
high elevation and by those in inland locations on the
Burdekin River. It is likely that some degree of geographic
variation exists, perhaps even with a genetic basis, in tolerance to temperature extremes.
larvae (pooled across all development stages) showed no
preference for particular depths but were strongly
restricted to water velocities less than 10 cm.sec–1. In addition, larvae were more frequently found in association
with some form of cover than was predicted by the availability of cover within the study site. Pre-flexion and flexion larvae were particularly constrained by the need for
low flow environments and cover, but post-flexion were
found in slightly higher water velocities and more distant
from cover and the stream bank. Fin development in this
species is minimal until after flexion and thus pre-flexion
and flexion larvae are constrained by high water velocities
to remain close to the natal habitat (i.e. bank-associated
root masses).
Riverine locations in which C. s. stercusmuscarum occurs
appear to be moderately well-oxygenated, whereas
Table 5. Physicochemical data for Craterocephalus
stercusmuscarum. Data summaries are from a number of
studies conducted in a range of rivers and habitats across
northern and north-eastern Australia (the number of sites
from each study is given in parentheses).
In rivers of south-eastern Queensland, C. s. fulvus was
most frequently collected from areas of low to moderate
water velocity (usually less than 0.4 m.sec–1) (Fig. 2a and
b), however, it has been recorded at maximum mean and
focal point water velocity of 0.87 and 0.76 m.sec–1, respectively. Aggregations also occasionally observed in slackwater eddies (e.g. behind rocks and debris) within high
velocity riffle habitats [1093]. This species was collected
over a wide range of depths, but most often between 10
and 60 cm (Fig. 2c). A pelagic schooling species, it most
commonly occupies the mid-water column (Fig. 2d). It is
found over a wide range of substrate types but most
frequently used sand, fine gravel and coarse gravel (Fig.
2e). It was often collected in areas greater than 1 m from
the stream bank (67% of individuals sampled) and in open
water greater than 0.2 m from the nearest available cover
(18% of individuals). It was also frequently collected in
close association with aquatic macrophytes, filamentous
algae and submerged marginal vegetation (Fig. 2f). Other
workers have reported that C. stercusmuscarum is generally found in shallow water over mud, sand and gravel, and
near aquatic vegetation [52], and it has been reported to
congregate where streams flow into still water [936].
Parameter
Min.
Max.
Alligator Rivers Region (n = 25) [193]
Water temperature (°C)
25
43
Dissolved oxygen (mg.L–1)
0.9
8.2
pH
4.0
8.1
Conductivity (µS.cm–1)
2
110
Turbidity (cm)
190
2
Normanby River floodplain (n = 13) [697]
Water temperature (°C)
22.9
29.4
Dissolved oxygen (mg.L–1)
1.1
7.1
pH
6.0
8.2
Conductivity (µS.cm–1)
98
391
Turbidity (NTU)
2.1
8.6
Environmental tolerances
Little quantitative data concerning environmental tolerances is available. Craterocephalus s. stercusmuscarum has
been collected over a wide range of physicochemical
conditions (Table 5). Average water temperature recorded
at sites in which this species occurred ranged from 22.6°C
to 30.9°C, reflecting its tropical distribution. The maximum temperature experienced was 43oC but note that this
was measured at the surface and stream-bed temperatures
were 7°C lower [193]. None-the-less, this species appears
able to tolerate temperatures in excess of 30°C. Minimum
temperatures recorded varied between studies, and
depended on whether the temporal sampling regime of
these studies included periods of low temperature.
187
Mean
30.9
5.7
6.1
48
25.5
3.7
7.1
212.1
5.5
Wet Tropics (n = 35) [1093]
Water temperature (°C)
17.1
29.7
Dissolved oxygen (mg.L–1)
5.1
11.4
pH
6.2
8.2
Conductivity (µS.cm–1)
7.8
55.9
Turbidity (NTU)
0.2
9.3
22.6
7.8
7.4
36.6
2.2
Burdekin River (n = 25) [1093, 1098]
Water temperature (°C)
15
33
Dissolved oxygen (mg.L–1)
2.6
11.9
pH
6.8
8.3
Conductivity (µS.cm–1)
50
790
Turbidity (NTU)
0.3
8.0
24.9
7.9
7.6
375.2
2.8
Fitzroy River (n = 10) [942]
Water temperature (°C)
22
28
Dissolved oxygen (mg.L–1)
4.8
11.0
pH
7.3
8.2
Conductivity (µS.cm–1)
Turbidity (cm)
190
5
70
South-east Queensland (n = 142) [1093]
Water temperature (°C)
12.4
33.6
Dissolved oxygen (mg.L–1)
2.9
19.5
pH
6.1
9.1
Conductivity (µS.cm–1)
19.5
5380.0
Turbidity (NTU)
0.2
62.3
21.5
8.1
7.7
626.4
4.7
25.8
7.4
7.9
Freshwater Fishes of North-Eastern Australia
on reproduction and early development of C. s. stercusmuscarum is available from six studies [193, 306, 630, 1106,
1109, 1416], C. s. fulvus from three studies [949, 1093, 1412],
and another report [1211] was concerned with a mix of both
subspecies (hereafter reported with C. s fulvus). An additional account by Llewellyn [809, 811] on the spawning and
embryology of a species of hardyhead from the MurrayDarling Basin (identified as C. fluviatilis but now considered
[630, 635, 1211] to be C. s. fulvus) is not addressed here.
floodplain populations may experience periods of extreme
hypoxia. In lagoons on the Tully River floodplain, C. s. stercusmuscarum was collected in waters with very low
dissolved oxygen (minimum 0.2 mg.L-1) and low pH
(minimum pH 5.38) [585]. With the exception of the
Alligator Rivers population, this species occurs, on average, in waters of neutral to slightly basic pH but it is
evident that it may tolerate moderately acidic conditions
[193, 585]. The range of conductivity shown in Table 5
indicates that C. s. stercusmuscarum occurs most
frequently in very dilute freshwaters. McGlashan and
Hughes (1814) reported significant genetic differences
between populations in the North and South Johnstone
rivers separated only by a short estuarine confluence and
interpreted this result as an indication of very low gene
flow between drainages. Whether high conductivity in the
estuary provided a chemical barrier was unknown, but if
true, would be in contrast to that observed for C. s. fulvus
(see below). Craterocephalus s. stercusmuscarum is most
frequently found in waters of reasonable clarity, although
both Midgley [942] and Bishop et al. [193] report its presence in highly turbid waters. It is notable however, that this
species is widespread in the Burdekin River but is very
uncommon or absent from those sub-catchments with
persistent turbidity levels above 100 NTU [255, 256].
Craterocephalus stercusmuscarum spawns and completes
its entire life-cycle in freshwater and has been bred in
captivity [630, 797, 1211, 1412]. In the Alligator Rivers
region, Bishop et al. [193] found that C. s. stercusmuscarum matured at a small size (27–29 mm CFL). In the Wet
Tropics region, maturation commences at slightly greater
size (stage II) and reproductive development is commensurate with increasing body size (Fig 3). The upland and
lowland lineages present in the Johnstone River differ in
the size at which attainment of each separate reproductive
stage is attained: the upland population matures at greater
size than does the lowland population. In addition,
whereas lowland males were generally smaller than
females across stages III to V, upland males tended to be
larger than females except for those fish at maturity stage
V. It is unknown whether upland fish live to a greater age
than do lowland fish or whether faster growth is experienced by the upland lineage, however, the size distribution
presented in Figure 1 does not suggest the presence of a
pronounced 1+ cohort in either lineage.
Craterocephalus s. fulvus has been collected over a relatively
wide range of physicochemical conditions also (Table 5),
including sites with moderately low dissolved oxygen
concentrations (minimum 2.9 mg.L–1), mildly acidic to
basic waters (range 6.1–9.1), and high conductivity (maximum 5380 µS.cm–1). The maximum turbidity at which this
species has been recorded in south-eastern Queensland is
62.3 NTU.
80
Males
70
44
35
Females
25
78
60
Given the marine affinities of the family Atherinidae, it is
perhaps not surprising that C. stercusmuscarum is able to
tolerate elevated salinities. It is frequently recorded at the
base of tidal barrages (refer to section on movement) and
in brackish and estuarine waters [1314]. Studies of salinity
tolerances of C. s. fulvus revealed that experimental
chronic LD50s have been observed as 43.7 ppt [1406].
Death occurred between 28 and 52 ppt, fish stopped
feeding and showed signs of distress at salinities >30 ppt
and fish were unable to swim in a coordinated fashion or
maintain balance at salinities >44 ppt [1406]. In aquaria,
larvae of C. s. fulvus have been exposed to temperatures
between 23.5 and 36.0°C with no apparent adverse effects
[1211]. Harris and Gehrke [553] classified C. s. fulvus as
intolerant of poor water quality.
14
50
44
15
24
40
25
58
3
5
11
6 17
3
3
2
3
30
20
10
0
L
U
I
Reproduction
The reproductive biology of both subspecies of C. stercusmuscarum is relatively well-studied (Table 6). Information
L
U
II
L
U
L
III
IV
Reproductive stage
U
L
U
V
Figure 3. Mean standard length (mm SL ± SE) within each
reproductive stage for male and female Craterocephalus s.
stercusmuscarum of the Wet Tropics region. Fish were
collected from lowland (L) and upland (U) reaches of the
Johnstone River over the period 1994–1998 [1093]. Sample
sizes are given above each bar.
188
5
Craterocephalus stercusmuscarum
region entered a prolonged drought, conditions likely to
favour larvae of this species. There was little evidence of
pronounced recruitment associated with a very large flood
in early 1991 as the population size distribution four
months later contained very few fish less than 35 mm SL
and was skewed towards fish of 45–55 mm SL [1082].
Craterocephalus s. stercusmuscarum has an extended breeding season in both the Alligator Rivers [193] and in the
Wet Tropics regions [1093]. Breeding phenology is apparently variable from year to year in the former region, with
Bishop et al. [193] recording peak mean GSI values in the
mid-wet of one year and the mid-dry of the following year.
Kennard [697] recorded very small fish of 10–15 mm SL in
both early (May) and late dry season (November) samples
in floodplain lagoons of the Normanby River, although the
greater number of small fish collected in the late dry
season suggested that spawning was concentrated in the
mid-dry season. In the Burdekin River [1082], fish of
10–15 mm SL were absent from samples collected in
November 1990 and May 1991 and present in November
1991 and May 1992. The latter two sampling occasions
corresponded to a dramatic decrease in discharge as the
I
120
100
II
III
IV
In the Wet Tropics region, reproductively mature fish were
present in all months sampled except May and July (Fig. 4)
when water temperatures are at their minimum [1108].
The majority of fish collected between September and
November were either fully mature or nearly so. Larvae
were present throughout the year but occurred in very low
numbers from May to August [1109].
The phenology depicted in Figure 4 is reflected in temporal changes in mean GSI values (Figure 5). Female GSI
values were lowest during the winter months but increased
rapidly to maximum levels by September or October,
declining thereafter to intermediate levels over the
summer wet season due to the presence of a small number
of reproductively active fish in the population. Females
from both upland and lowland lineages followed a similar
pattern in GSI variation except that peak GSI values
occurred in September in the former as opposed to
October. Male maturation and gonad development was
synchronised with that of females (Figs. 4 and 5). Bishop
et al. [193] reported very similar mean GSI values as those
presented here.
V
Males
(6)
(11) (12) (16) (9)
(9)
(46)
(5)
(7) (13) (10)
80
60
40
20
10
0
Females - upland
120 Females
100
Males - upland
(12 (28) (17) (22) (9)
8
(14) (50) (28) (25) (44) (24)
)
6
Males - lowland
Females - lowland
80
4
60
40
2
20
0
0
Month
Month
Figure 4. Temporal changes in reproductive stages of
Craterocephalus s. stercusmuscarum in the Johnstone River, Wet
Tropics region during 1998 [1093]. Samples sizes for each
month are given in parentheses. Data for upland and lowland
lineages have been pooled.
Figure 5. Temporal changes in mean Gonosomatic Index
(GSI% ± SE) stages of Craterocephalus s. stercusmuscarum
males (open symbols) and females (closed symbols) in the
Johnstone River during 1998 [1093]. The upland lineage is
denoted by circles and the lowland lineage by squares.
Samples sizes for each month are given in Figure 3.
189
Freshwater Fishes of North-Eastern Australia
are heavily pigmented, the top of the head is spotted in a
circular patch, and the abdomen, opercle and midlateral
stripes are pigmented [630]. Upon hatching, prolarvae
swim independently of one another for the first 12 hours,
schooling thereafter in the upper water column of aquaria
[630]. At 30 days post-hatching, larvae were 8.4 mm TL on
average and, by this stage, the anal and dorsal fins were well
developed. The remnant of the fin fold persists at the
origin of first dorsal fin, but the fin bud is visible. The
ventral fin fold also persists between the anus and the anal
fin [630]. The rate of larval development appears to be
relatively rapid. Metamorphosis occurs at a small size
(9–11 mm) [1093] and fish in aquaria were observed to
approximately treble their size in the first 40 days (from
4.54 mm TL to 14.3 mm TL) [630]. After 3.5 months, these
fish had approximately doubled their size, after which time
the rate of growth slowed [630].
Craterocepahlus s. stercusmuscarum is a moderately fecund
batch spawner, producing on average 200–400 small eggs
in batches of about 70 eggs. The two lineages present in
the Wet Tropics region differ in fecundity (Fig. 6). Females
of the upland lineage produces more eggs by virtue of their
greater size than do lowland females, however the rate of
increase in fecundity with increasing weight is less, as is
the number of eggs produced when females of equivalent
size are compared (the regression equations for relationships between weight and total fecundity for these populations are given in Table 4). By contrast, the eggs of upland
fish are slightly larger than those of lowland fishes (1.08 ±
0.02 mm versus 0.98 ± 0.04 mm; n = 117 and 37, respectively). Bishop et al. [193] report an intraovarian egg size
of about 1 mm for fish from the Alligator Rivers region
also.
800
Maturation of C. s. fulvus commences at a relatively small
size. Minimum and mean lengths of early developing
(reproductive stage II) fish from the Mary River, southeastern Queensland, were 26.3 mm SL and 38.3 mm ± 1.6
SE, respectively for males, and 28.5 mm SL and 36.4 mm ±
1.6 SE, respectively for females (Fig. 7). Fish of equivalent
reproductive stage were generally similar in size for populations from the Mary (Fig 7) and Brisbane rivers [949],
south-eastern Queensland. Gonad maturation in both
sexes was commensurate with somatic growth, the mean
length at each reproductive stage being different from all
other stages (Fig. 7). Gravid (stage V) females were slightly
700
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
55
Males
8
9
50
Females
Weight (gm)
45
Figure 6. The relationship between body size (weight in g)
and fecundity for upland (■
■, thick regression line) and
lowland ( , coarsely dashed regression line) lineages of
Craterocephalus s. stercusmuscarum in the Wet Tropics region
and C. s. fulvus (▲
▲, finely dashed regression line) in southeastern Queensland [1093]. See text for regression equations.
40
35
30
The duration of embryo development for C. s. stercusmuscarum has been reported to be 13 days (at 25–27°C) [630].
Illustrations and descriptions of larval stages of this subspecies can be found in Invantsoff et al. [630]. The larvae
of C. s. stercusmuscarum hatch at small size but rapidly
become mobile and feed exogenously (Table 6). The mean
length of prolarvae one to three days after hatching was
4.0 mm TL [630]. At this stage the dorsal and ventral fin
folds are continuous but the ventral fin buds are not
apparent, the eyes and dorsal surface of the swim-bladder
25
I
II
III
IV
V
Reproductive stage
Figure 7. Mean standard length (mm SL ± SE) for male and
female Craterocephalus s. fulvus within each reproductive
stage. Fish were collected from the Mary River, south-eastern
Queensland, between 1994 and 1998 [1093]. Sample sizes
can be calculated from the data presented in Figure 3.
190
Craterocephalus stercusmuscarum
were present for longer (August to April) and were relatively abundant throughout most of this period (Fig. 8).
Temporal patterns in reproductive stages mirrored those
observed for variation in GSI values. Peak monthly mean
GSI values (5.1% ± 0.3 SE for males, 6.5% ± 0.5 SE for
females) occurred in November for males and September
for females (Fig. 9). GSI vales remained elevated for longer
in females but were highest for both sexes between August
and December (Fig. 9). The mean GSI of ripe (stage V) fish
was 5.3 % ± 0.2 SE for females and 5.5 % ± 0.3 SE for
males [1093]. Reproductive activity for fish in the Brisbane
River [949] generally matched that observed for fish from
the Mary River, although peak monthly mean GSI values
for males were lower (4.3%) and peak GSI values for
females were higher (8.5%) [949]. Overall sex ratios for
populations from the Brisbane River have been reported
as 1.2 females for every male and significantly more
females were present amongst mature fish (>45 mm SL)
[949].
larger on average than males of equivalent maturity (mean
53.6 mm SL ± 0.8 SE for females; mean 49.8 mm SL ± 1.4
SE for males), although the minimum recorded size for a
gravid female was substantially smaller (24.3 mm SL) than
that of a male (37.3 mm SL ([1093], Fig. 7). The minimum
size of spawning fish in aquaria is reported as 32 mm SL
(approximately five months of age) [1211].
Craterocephalus s. fulvus has an extended breeding season
from late winter through to summer but spawning appears
to be concentrated in late winter and spring. In the Mary
River, immature and early developing fish (stages I and II)
were most common between January and August (Fig. 8).
Developing fish (stages III and IV) of both sexes were
generally present year-round. Gravid males (stage V) were
present for a relatively short period and were most abundant between September and November. Gravid females
Reproductive stage
I
II
III
IV
V
8
Males
Males
(8) (6) (6) (9) (10) (9)
(13) (23) (10) (5) (4)
100
6
Females
80
60
4
40
20
2
0
Females
100
(36) (27) (10) (18) (18) (4)
(24) (19) (10) (7) (25)
0
80
Month
60
Figure 9. Temporal changes in mean Gonosomatic Index
(GSI% ± SE) stages of Craterocephalus s. fulvus males (open
circles) and females (closed circles) in the Mary River, southeastern Queensland, during 1998 [1093]. Sample sizes for
each month are given in Figure 8.
40
20
0
The spawning stimulus is unknown but corresponds with
increasing water temperatures and photoperiod. Milton
and Arthington [949] observed that the peak spawning
period for C. s. fulvus in the Brisbane River in SeptemberOctober coincided with surface water temperatures
between 19 to 23°C, and day length from 11 to 11.5 h.
In aquaria, spawning occurred at water temperatures
Month
Figure 8. Temporal changes in reproductive stages of
Craterocephalus s. fulvus in the Mary River, south-eastern
Queensland, during 1998 [1093]. Sample sizes for each
month are given in parentheses.
191
Freshwater Fishes of North-Eastern Australia
small-bodied fish in south-eastern Queensland streams
(e.g. 207]) and in the Murray-Darling Basin (see
Humphries et al. [614]).
between 25 and 29°C, with the majority of spawning activity occurring at 26°C [1211]. As summarised in the chapter on C. marjoriae, the extended spawning period of
Craterocephalus spp., but with a peak in spring and early
summer, may facilitate successful recruitment as the presence of eggs and larvae usually occurs when the likelihood
of flooding is low, but the predictability of high temperatures and low flows are higher. Milton and Arthington
[949] reported that juvenile fish in the Brisbane River were
present between October and February and these authors
were able to discern a clear cohort that could be tracked
through to the following breeding season. A similar
pattern is evident from more recent sampling [1093]
where individuals less than 25 mm SL were most common
in spring and summer (Fig. 10).
25
In the wild, spawning probably occurs in aquatic macrophytes and submerged marginal vegetation. Spawning
observations in aquaria suggest that pre-spawning behaviour is initiated adjacent to aquatic vegetation whereby the
male swims beneath and behind the female, nudging and
nipping the anterior rays of the anal fin, the vent and the
belly of the female [1211]. Upon reaching a suitable
spawning site within the bed of aquatic vegetation, the
male and female simultaneously shed sperm and eggs, all
the while touching constantly along their lateral lines.
Adhesive, demersal eggs are attached to aquatic macrophytes, the entire batch resting within a radius of 10 cm of
the release point. In aquaria, both sexes have been
observed to eat eggs following deposition [1211]. No
parental care of eggs has been reported.
Spring
(n=451)
20
Summer
(n=1285)
15
AutumnWinter
(n=817)
10
5
0
Standard length (mm)
Figure 10. Seasonal variation in length-frequency distributions
of Craterocephalus s. fulvus, from sites in the Mary and
Brisbane rivers, south-eastern Queensland, sampled between
1994 and 2000 [1093]. The number of fish from each season
is given in parentheses.
Schiller and Harris [1200] suggested that C. s. fulvus was a
member of a guild of species in the Murray-Darling Basin
whose spawning success was flood-related. Although these
authors cautioned that the mechanism was unclear, they
postulated that floods may benefit larvae by transporting
them to nursery areas (e.g. freshly inundated wetlands) or
larvae may benefit from the increased productivity of
main channel and backwater areas. This view is contrary
to the hypothesis that low flow periods during the reproductive season facilitate successful recruitment in smallbodied species such as hardyheads as suggested earlier for
192
Total fecundity for C. s. fulvus from the Mary River has
been estimated as ranging from 58–432 eggs (mean 219 ±
12 SE, n = 60 fish) [1093], slightly higher than that of
lowland lineages of C. s. stercusmsucarum from the Wet
Tropics region, but substantially lower than that of upland
populations in this regions (Figure 6). Batch fecundity for
fish from the Brisbane River ranges from 5–126 eggs/batch
(mean 71 ± 5 SE, n = 70 fish) [949]. In the aquarium, fish
were observed to deposit 2–85 eggs over a 5–35-second
period, with spawning occurring on two to three successive days followed by a rest period of several days [1211].
Fecundity is significantly related to fish size; the regression
equations for relationships between weight and fecundity
are given in Table 4. Fish of 40 mm SL from the Mary River
produced about 130 eggs in total, whereas fish of 60 mm
SL produced about 270 eggs [1093]. Fish of 1 g from the
Mary River produced about 130 eggs in total, whereas fish
of 4 g produced about 340 eggs [1093]. Fish of 40 mm SL
from the Brisbane River produced about 40 eggs per batch,
whereas fish of 60 mm SL produced about 140 eggs [949].
The eggs are relatively large. The mean diameter of 496
intraovarian eggs from stage V fish from the Mary River
was 1.17 mm ± 0.01 SE [1093]. The diameter of waterhardened eggs has been reported to range from 1.3 to 1.7
mm [1211]. Eggs are characterised by a finely sculptured
chorion with 50 adhesive filaments (0.5–3.0 mm in
length). Eight to thirteen oil droplets were present over the
surface of the egg at spawning; these were 0.03 to 0.15 mm
diameter, and were initially concentrated at the animal
pole, later migrating in a bunch to the vegetal pole. The
duration of embryo development has been reported to
vary from 4 to 7 days (at 25 to 29°C) [1211] and from 8 to
10 days (at 29°C) [1412]. Illustrations and descriptions of
Craterocephalus stercusmuscarum
Table 6. Life history information for Craterocephalus s. fulvus (C.s.f.) and Craterocephalus s. stercusmuscarum (C.s.s.).
Age at sexual maturity (months)
C.s.f. <12 months [949]
C.s.s. <12 months [193, 1093]
Minimum length of gravid (stage V)
females (mm)
C.s.f. 24.3 mm SL (field) [1093], 32 mm SL (aquaria) [1211]
C.s.s. 46 mm SL (lowland lineage), 55 mm SL (upland lineage) in Wet Tropics region
[1093], length at first maturity – 29 mm CFL in Alligator Rivers region [193]
Minimum length of ripe (stage V) males (mm) C.s.f. 37.3 mm SL (field) [1093]
C.s.s. 36 mm SL (lowland lineage), 58 mm SL (upland lineage) [1093], length at first
maturity – 27 mm CFL in Alligator Rivers region [193]
Longevity (years)
C.s.f. 2+ [949]
C.s.s. unknown but unlikely to exceed two years [1093]
Sex ratio (female to male)
C.s.f. 1.2:1 [949]
C.s.s. 1:1 with females slightly in excess in dry season in Alligator Rivers region [193]
Occurrence of ripe (stage V) fish
C.s.f. Late winter, spring and summer. August - April [1093], October–January [949]
C.s.s. present all year except from May to July in the Wet Tropics [1093], mid-dry
season to mid-wet in Alligator Rivers region, variable across years [193]
Peak spawning activity
C.s.f. Late winter, spring and summer. Elevated GSI between August and December
[1093], elevated GSI between September and February [949]
C.s.s. September to November in Wet Tropics region [1093], early wet season and
mid-dry season, variable across years [193]
Critical temperature for spawning
C.s.f. ? 19–23°C (field) [949]; 25–29°C (aquaria) [1211]
C.s.s. no spawning observed when temperatures below 20°C [1093]
Inducement to spawning
C.s.f. ?
C.s.s. ?
Mean GSI of ripe (stage V) females (%)
C.s.f. 5.3% ± 0.2 SE (maximum mean GSI in September = 6.5% ± 0.5 SE) [1093];
(maximum mean GSI in October = 8.5 %) [949]
C.s.s. 7.9 to 8.1%, little difference between lineages; maximum mean GSI of 6.2%
recorded in Alligator Rivers region [193]
Mean GSI of ripe (stage V) males (%)
C.s.f. 5.5 % ± 0.3 SE (maximum mean GSI in November = 5.1 % ± 0.3 SE) [1093];
(maximum mean GSI in September = 4.3%) [949]
C.s.s. 4.7–5.0%, little difference between lineages; 4.2% for Alligator Rivers region
[193]
Fecundity (number of ova)
C.s.f. Total fecundity = 58–432, mean = 219 ± 12 SE [1093]; Batch fecundity 5–126,
mean = 71 ± 5 SE [949], In aquaria 2–85 eggs deposited in 5–35-second period, with
spawning occurring on 2 to 3 successive days [1211]
C.s.s. Total fecundity = 50–832, mean = 312 ± 85 for upland lineage, 45–390, mean =
240 ± 6 for lowland lineage of the Wet Tropics region; total (large eggs only) 55–90,
mean = 71
Total Fecundity (TF) and Batch Fecundity
(BF) / Length (mm SL) or Weight (g)
relationship (mm SL)
C.s.f. Log10 TF = 0.017 L + 1.422, r2 = 0.370, P<0.001, n = 60 [1093]. Log10 BF = Log10
(7.2 x 10-3) + 3.01 Log10 L, r2 = 0.59, p<0.001, n = 70 [949]. TF = 67.65 W + 60.62, r2
= 0.454, p<0.001, n = 60 [1093]
C.s.s. TF = 81.0 W – 49.8, r2 = 0.60, p<0.001, n = 87 for upland lineage;
TF = 141.6 W - 33.9, r2= 0.84, p<0.001, n =19 for lowland lineage
Egg size (diameter)
C.s.f. Intraovarian eggs from stage V fish = 1.17 mm ± 0.01 SE [1093]. Waterhardened eggs 1.3–1.7 mm [1211]
C.s.s. Intraovarian eggs from stage V fish = 1.08 ± 0.02 mm (SE ) for upland lineage
and 0.93 ± 0.04 mm (SE) for lowland lineage of the Wet Tropics region; 1.0 mm
(range = 0.9–1.0 mm)
Frequency of spawning
C.s.f. extended spawning period, probably repeat spawner [949]
C.s.s. extended spawning , eggs release in batches [1093]
Oviposition and spawning site
C.s.f. In the wild, spawning probably occurs in aquatic macrophytes and submerged
marginal vegetation [1093]. In aquaria, adhesive, demersal eggs are attached to
aquatic macrophytes [1211]
C.s.s. Aquatic rootmasses in Wet Tropics streams [1109]
Spawning migration
C.s.f. none known
C.s.s. none known
Parental care
C.s.f. none known
C.s.s. none known
Time to hatching
C.s.f. After fertilisation, hatching takes 4 to 7 days in aquaria at 25–29°C [1211]. 8–10
days in aquaria at 29°C [1412]
C.s.s. 13 days at 25–27°C [630]
193
Freshwater Fishes of North-Eastern Australia
Table 6 (continued). Life history information for Craterocephalus s. fulvus (C.s.f.) and Craterocephalus s. stercusmuscarum (C.s.s.).
Length at hatching (mm)
C.s.f. Newly hatched prolarvae 5.0 mm SL [1211]
C.s.s. 4.8–6.4 [1093]
Length at free swimming stage (mm)
C.s.f. Postlarvae 7.7 mm SL [1211]
C.s.s. 6.3–7.7 mm at flexion [1093]
Length (mm) at loss of yolk sack
C.s.f. ?
C.s.s. 6.3–7.7 mm [1093]
Age at first feeding
C.s.f. ?
C.s.s. ?
Length at first feeding
C.s.f. Postlarvae 7.7 mm SL [1211]
C.s.s. 6.3–7.7 mm [1093]
Length at metamorphosis (mm)
C.s.f. ?
C.s.s. 9–11 mm [1093]
Duration of larval development
C.s.f. ?
C.s.s. ?
larval stages can be found in Semple [1211]. The mean
length of prolarvae at hatching was 5.0 mm SL. At this
stage the top of the head, preoperculum and lateral line
were spotted and the eyes, swim-bladder and surface
pigments were black. Paired contour melanophores were
visible on the dorsal surface and dendritic melanophores
were present on the belly. Upon hatching, prolarvae swam
randomly at the surface of aquaria. Postlarvae were 7.7
mm SL and, by this stage, the anal and dorsal fin buds were
developing, the caudal fin was rayed, rows of small punctate melanophores were visible on the caudal fin and
larvae had commenced swimming and feeding in midwater [1211]. King [718] speculated that the period of time
from spawning to the juvenile phase was possibly 14 days
for fish in the Murray-Darling Basin.
There are several instances where juveniles and adults of
this species have been recorded using fishways on weirs
and tidal barrages. Johnson [658] collected C. stercusmuscarum in pool-overfall type fishways on Bingara Weir in
the Burnett River during December 1979 and in the
Brisbane River catchment at Mt. Crosby Weir and
Brightview Weir (timing unclear). Johnson [658] collected
C. stercusmuscarum in the tidal barrage on the Kolan River
during winter, spring and summer. He also observed
hardyheads in that portion of the barrage subject to tidal
influence and in which salinities ranged between 15–30
ppt. An experimental fish lift on the Kolan River Barrage
was also used by this species [658]. Juveniles and adults
have been collected from the fishway on the Mary River
barrage and both age classes were recorded as being
common in the fishway and outwash of the Tinana Creek
Barrage. Other studies of fishways located on tidal
barrages in Queensland Rivers [11, 158, 159, 232, 1173,
1272, 1274, 1275, 1276, 1277] documented relatively small
numbers of fish using these structures in the Fitzroy,
Kolan, Burnett and Mary river catchments. Results from a
Burnett River study [1276] indicate that upstream migrations of small numbers of individuals occurred during
August, December and February. Results from a Fitzroy
River study [1274] indicate that the main period of migration occurred in November but upstream migrations of
small numbers of individuals also occurred during July
and December. The highest flow through the fishway at
which this species was recorded using the fishway was
18 305 ML.day–1, this discharge being exceeded around
10% of the time in the Fitzroy River [1274]. Another study
at the same location documented that fish used the fishway between November and February [739, 740].
Downstream migrations through fishways have also been
observed: Russel [1173] recorded low numbers of fish
descending the tidal barrage on the Fitzroy River (timing
of movement not stated).
Length at age data using evidence from scale annuli [949]
indicate that 0+ fish (males and females) grow to around
33 mm SL, 1+ fish to 49 mm SL and 2+ fish to 45 and 57
mm SL for males and females, respectively. These data
(together with stage-length and sex ratio data presented
earlier) collectively suggest that sexual maturity is reached
within one year of age, and that fish live for over two years.
Movement
Some information is available on the movement biology
of C. stercusmuscarum. Relatively large numbers of this
species have been observed moving in Magela Creek in the
Alligator Rivers region of the Northern Territory [190].
Bishop et al. [193] reported that C. s. stercusmuscarum
dispersed widely on the floodplain of the Alligator Rivers
region, moving from dry season refuges (escarpment habitats, sandy lowland creek-bed habitats) to occupy all available habitat types during the wet season. Little is known of
the movement biology of this species in the Wet Tropics
region but the existence of discrete lineages and of fixed
allelic differences between lowland populations suggests
that movement is limited in this region.
194
Craterocephalus stercusmuscarum
fulvus) has been recorded as having been transported in a
‘tornado-type cloud’ in south-western New South Wales
[878, 1400].
This small-bodied species, particularly smaller individuals, apparently has difficulty ascending pool-weir type
fishways, a design ill-suited to many small-bodied native
fishes. Johnson [658] found that juveniles and adults were
common downstream and upstream of Marian Weir in the
Pioneer River, but were not actually collected in the fishway, which he regarded as inefficient. A large proportion
of fish were unable to negotiate the full length of the fishway on a tidal barrage in the Fitzroy River, and those that
did were comparatively larger in size [1274, 1275]. No
significant difference was observed between the size distribution of fish collected at the bottom and top of the Kolan
River barrage fishway, but substantially fewer small-sized
individuals were present at the top of this fishway [232].
Trophic ecology
Diet data for C. stercusmuscarum is available for 1639 individuals from studies in the Alligator Rivers region of the
Northern Territory [193], Cape York Peninsula [697,
1099], the Wet Tropics regions of northern Queensland
[599, 1097], central Queensland [1080], south-eastern
Queensland [80, 205, 1421] and from a lake on the Murray
River floodplain in north-western Victoria [396]. This
species is a microphagic carnivore. Aquatic insects
(35.6%), and microcrustaceans (29.6%) were the most
important items in the total mean diet (Fig. 11). Aquatic
algae (11.2%) and aquatic macrophytes (1.6%) were also
consumed but contributed less to the total mean diet than
observed for the congener C. marjoriae. Other food types
of aquatic origin were relatively unimportant in the diet of
C. stercusmuscarum and only small amounts of terrestrially derived prey were consumed.
Although C. stercusmuscarum has often been sampled
downstream of tidal barrages or at the bottom of fishways
on these structures (see references cited above), access to
estuarine areas is not an obligatory component of the life
cycle. Hence the movement pattern of this species may be
classified as facultative potamodromy.
The results described above collectively suggest that low
numbers of fish move almost year-round but a peak in
upstream migration possibly occurs in early summer.
There is no quantitative data on the stimulus for movement of this species. Cotterell and Jackson [333] suggested
that C. stercusmuscarum in the Fitzroy River, central
Queensland, would move ‘anytime there is a flow between
August and April’, although the source of this information
was not given. Fish have been observed migrating in the
Fitzroy River during high flows [1274] and fish downstream of Clair Weir in the Burdekin River were suggested
to be migrating upstream during relatively high discharges
in January and February [586].
Fish (0.1%)
Other microinvertebrates (0.2%)
Unidentified (14.8%)
Terrestrial invertebrates (0.6%)
Aerial aq. Invertebrates (0.8%)
Terrestrial vegetation (0.2%)
Detritus (0.4%)
Aquatic macrophytes (1.6%)
Microcrustaceans (29.6%)
Algae (11.2%)
Macrocrustaceans (0.2%)
Molluscs (4.2%)
Other macroinvertebrates (0.4%)
Aquatic insects (35.6%)
It is likely that this species is able to undertake local dispersal and/or recolonisation movements. It is particularly
abundant in streams that periodically become disconnected by extended periods of low flow, when surface
waters recede to a series of isolated pools (e.g. tributaries
of the Mary and Brisbane rivers). In these streams, rapid
recolonisation of previously dry river reaches has been
observed soon after flows resumed in summer and longitudinal connectivity was re-established (i.e. within 48
hours [1093]). In the Burnett and Mary rivers, south-eastern Queensland, tens to hundreds of fish have been
observed in pools immediately downstream of obstructions to movement (e.g. culverts and weirs) soon after a
rise in discharge during late spring, suggesting that C. stercusmuscarum undergoes upstream dispersal/recolonisation movements cued by elevated flows [1093]. A similar
phenomenon was observed for this species in the Fitzroy
River [1351]. A species of small hardyhead (probably C. s.
Figure 11. The mean diet of Craterocephalus stercusmuscarum.
Data derived from stomach contents analysis of 1639
individuals from the Alligator Rivers region of the Northern
Territory [193], Cape York Peninsula [697, 1099], the Wet
Tropics region of northern Queensland [599, 1097], central
Queensland [1080], south-eastern Queensland [80, 205,
1421] and from a lake on the Murray River floodplain in
north-western Victoria [396].
Some spatial and temporal variation in the diet of C. stercusmuscarum is evident. For example, in studies of lentic
floodplain habitats (e.g. billabongs, lakes and wetlands
[193, 396, 697]) fish were often observed to consume
greater amounts of microcustaceans (zooplankton) than
fish collected from lotic habitats (e.g. [80, 205, 1097]). In
contrast, the diets of fish from riverine habitats [80, 599,
1080, 1097] were often dominated by aquatic insects.
195
Freshwater Fishes of North-Eastern Australia
Ecological Community in the lower Murray River [1005]
and in the lowland catchment of the Darling River [329].
In Victoria, this species was once considered to be of
restricted distribution, and/or rare [273], it was subsequently upgraded to indeterminate [731], but it was not
included in a 2000 listing of threatened vertebrate fauna in
Victoria [1004]. It is however, listed under the Victorian
Flora and Fauna Guarantee Act 1998 [1040, 1189].
The extent of herbivory and planktivory appears to vary
with age and size of the fish, and probably according to the
availability of other food sources. For example, the diet of
0+, 15–20 mm SL fish (n = 32) in floodplain habitats of
the Normanby River [697] contained 56% algae (diatoms
and desmids), whereas the diet of fish between 21–45 mm
SL (n = 69) contained 24% algae. Temporal variation in
dietary composition of these fishes was also evident. Soon
after the end of the wet season, herbivory and planktivory,
contributed 4% and 59% of the diet, respectively. By the
late dry season however, fish of equivalent size consumed
less planktonic crustaceans (34%) whereas herbivory had
increased in importance to 26%. Notably, fish collected
from the river itself consumed no planktonic microcrustaceans [1099].
Like many other native species, siltation arising from
increased erosion rates and sediment transport in catchments may be a threat to the spawning habitats of C. stercusmuscarum, and may also affect aquatic invertebrate
food resources. Interactions with alien fish species (e.g.
competition for resources and predation on eggs, larvae
and juveniles) is another potential threat to C. stercusmuscarum [95].
No information on the trophic ecology of larvae is available, however larvae from other members of the genus
Craterocephalus have been recorded feeding on rotifers
and microcrustaceans.
Craterocephalus stercusmuscarum has been shown to
undertake facultative movements although the purpose of
these movements is unclear. Nevertheless, it is likely to be
sensitive to barriers to movement caused by structures
such as dams, weirs, barrages, road crossings and culverts.
River regulation, independent of the imposition of barriers, may also impact on C. stercusmuscarum populations.
Changes to the natural discharge regime and hypolimnetic
releases of unnaturally cool waters from large dams may
interrupt possible cues for movement or de-couple optimal temperature/discharge relationships during critical
phases of spawning, larval movement and development.
Unseasonal flow releases during naturally low flow periods
in September and October are likely to negatively affect
reproductive success as this coincides with the period of
peak spawning activity and larval development. The availability of aquatic macrophyte beds, the likely spawning
habitat of C. stercusmuscarum, may be maximised during
low flow periods. Scouring actions of elevated discharges
at the onset of the wet season may reduce or remove
aquatic macrophyte beds. Larval development is also likely
to be favoured during low flow periods, during which time
phytoplankton and invertebrate abundances are also high
[949]. High discharge rates were shown to reduce larval
abundance in streams of the Wet Tropics region [1109]
In aquaria, adults will consume a range of food types
including small anuran tadpoles, mosquito larvae and
other common aquarium foods such as Calanus and
Artemia nauplii, Tubifex worms and commercial flake
foods [1210]. Even finely minced animal meats are eaten.
Postlarvae will consume similar items to those listed above
as well as infusoria made from lettuce [1211].
Conservation status, threats and management
The conservation status of Craterocephalus stercusmuscarum is listed as Non-Threatened by Wager and Jackson
[1353]. It is generally common throughout most of its
coastal distribution in northern and eastern Australia. In
the southern parts of the Murray-Darling Basin it is
thought to have undergone declines in distribution and
abundance [635] although recent surveys reveal that is still
locally common in some areas [56, 507, 807, 817]. In 2000,
Morris et al. [965] included C. s. fulvus in an assessment of
threatened and near-threatened freshwater fish in New
South Wales, on the basis that this species was considered
rare in the southern parts of the Murray-Darling Basin
and due to possible taxonomic confusion with other
hardyhead species. It was recommended in this assessment
that C. s. fulvus be listed as ‘Data Deficient’ under the
IUCN Red List of Threatened Species to promote further
investigation into its conservation status. However this
species had not been listed as at December 2003. In an
assessment of the status of freshwater fish in the MurrayDarling Basin in 2002, C. s. fulvus was considered to be
widespread but declining in the basin [15]. This species
has also been listed as a member of an Endangered
Craterocephalus stercusmuscarum is known to act as a
second intermediate host to the digenetic trematode
Stegodexamene callista (Lepocreadiidae) [339] and a
species of Craterocephalus (possibly C. s. fulvus) from the
Brisbane catchment was shown to be infected by the digenetic trematode Opecoelus variabilis (Opecoelidae) [338,
339]. Dove [1432] provided a list of parasite taxa recorded
from C. s. fulvus in south-eastern Queensland.
196
Rhadinocentrus ornatus Regan, 1914
Ornate rainbowfish, Soft-spined rainbowfish
37 245022
Family: Melanotaeniidae
Description
First dorsal fin: III–V; Second dorsal: I, 11–15; Anal: I,
18–22; Pectoral: 11–13; Caudal: 16 segmented rays. Pelvic:
I, 5; Vertical scale rows: 31–37; Horizontal scale rows: 8–9;
Predorsal scales: 14–16; Cheek scales: 2–6; Gill rakers on
first arch: 11–12; Vertebrae: 31–37 [32, 34, 38, 39, 52, 631,
936]. Figure: adult specimen, 44 mm SL, Mellum Creek,
November 1993; drawn 2003.
Scales large and cycloid, extending to cheek but excluding
jaws and inter-pelvic region. Two dorsal fins separated by
small gap, the second elongated. Origin of first dorsal fin
approximately midway between snout tip and tail base,
usually above fifth to sixth ray of anal fin [39, 1015].
Elongated anal fin originates in anterior half of body.
Usually only last few anal and dorsal fin rays are branched.
Caudal fin slightly forked. Sexually dimorphic [39]. Males
exhibit more elongate rays in the second dorsal fin and
anal fins than females; rear tips of the second dorsal and
anal fins are pointed in males, rounded in females [39].
Males tend to be deeper-bodied and exhibit brighter body
and fin colours, particularly during courtship and spawning [38, 39, 52, 517, 936]. The body is semi-transparent
with dark scale margins forming a network pattern [38,
52].
Rhadinocentrus ornatus is a small species reaching a maximum size of 65 mm TL (females) and 80 mm TL (males),
commonly 40 mm or less in the wild [52, 82, 84, 631, 783,
978]. Fish grown in aquaria can reach 100 mm TL [978].
No length–weight relationship is available for this species
but it is generally similar in shape to small and mediumsized M. duboulayi.
Rhadinocentrus ornatus is a slender, relatively elongate
species with laterally compressed body, deepening with age
[631]. Mouth very oblique, upper jaw protruding slightly.
Conical to caniniform teeth in jaws; outer row at front of
jaw enlarged but not separated from inner rows [978]; one
or more rows extending outside mouth; vomer and
palatines toothless [39]. Moderate-sized head and relatively large eyes; upper edge of eye located at or near upper
head profile [39, 936, 978]. Open pores on head [978].
Colour and pattern vary spatially among populations and
the various colour forms are a continuing source of fascination among many aquarists. Hansen [517] suggested
that three general colour forms of R. ornatus exist and
provided detailed descriptions of these: a widespread type
form, a blue form confined to streams draining into Tin
Can Bay and on Fraser Island, south-eastern Queensland,
and a pink form confined to a very restricted area near Tin
197
Freshwater Fishes of North-Eastern Australia
external ramus on the maxilla and a reduced number of
interdorsal pterygiophores [631]. Rhadinocentrus ornatus
is distinguished from Cairnsichthys by the absence of a
basisphenoid, a straight rather than curved caudilateral
margin of the lateral ethmoid, a deep lateral urohyal, and a
narrow supracleithrum [32]. A phylogenetic analysis of
the family by Aarn and Ivantsoff [23] identified Iriatherina
as being distinct from all other melanotaeniids and placed
Rhadinocentrus and Cairnsichthys in a subclade within a
larger group containing the two rainbowfish genera
(Bedotes and Rheocles) from Madagascar.
Can Bay [517]. In the type form, the body is translucent
light brown with fine reticulated scale pattern.
Pigmentation on the upper and lower margins of the
midlateral scale rows forms a pair of parallel dark stripes.
Iridescent neon-blue spangles are scattered on the back
and nape. The caudal fin is usually reddish with a central
dark sector. Dorsal fin commonly has a red outer border
with black rays, although margin is sometimes dark with a
blue fin. Anal fin usually has a black margin. Fish from
dark tannin-stained waters such as Coolum Creek and the
upper Noosa River are very dark, almost black [517]. The
blue form is dark brown on top fading ventrally with
shades of blue increasing towards the tail. Scale margins
dark, forming a reticulated pattern. Some males are
reddish on the anterior third of the body. Iridescent blue
spangles of varying densities are present. The blue fins
vary from purple to sky-blue with a strong black margin.
The blue form carries a recessive gene that yields bright
red body colours to varying degrees [517]. The pink form
is similar although less black and the blue is replaced by
pink. Often varying amounts of bright red overlay a background of pink [517]. Details of the distribution of each
colour morph can be found in Hansen [517]. A greenfinned colour form reputedly also occurs on the western
side of Stradbroke Island (T. Page, pers. comm.). Further
details on geographic variation in colour forms and relationships with phylogeographic patterns are given below.
Recent phylogeographic analysis of R. ornatus by Page et
al. [1035] using mtDNA sequence analysis of the ATPase
gene has revealed that this species is divided into four
major clades: 1) central eastern Queensland (Water Park
Creek to Tin Can Bay including populations on Fraser
Island); 2) Searys Creek, some individuals from a single
location near Tin Can Bay; 3) a highly diverse and differentiated group in south-eastern Queensland and northern
New South Wales (Noosa River south to Cudgera Creek in
New South Wales; and 4) a clade containing fish from the
Richmond and Clarence rivers. Clades 3 and 4 were
suggested to have diverged about 2.4 m.y.b.p. whereas
these clades and clades 1 and 2 diverged from one another
between 5.1 and 6.9 m.y.b.p. during the late Miocene at a
time of increasing aridity. Divergence between the population at Water Park Creek and other populations within
clade 1 (which are separated by a distance of 350 km) was
suggested to be relatively recent (0.72 m.y.b.p.).
Interestingly, these authors note that each Rhadinocentrus
lineage is older than many species within Melanotaenia
[1035]. The various colour forms described earlier are not
fully congruent with the phyletic pattern described by Page
et al. [1035]. However, Chris Marshall (pers. comm.)
suggests that a basic split in colour form and morphology
of R. ornatus populations north and south of the Noosa
River is generally consistent with the major phylogeographic patterns described by Page et al. [1035]. Marshall
suggests that northern type fish generally grow larger, do
not have the black lateral lines and reticulations on the
body, and have the iridescent blue scales along the nape
and irregularly on sides of the body. The southern type has
the lateral black lines and reticulations, is smaller and only
has iridescent blue scales along the nape.
Systematics
Melanotaeniidae (commonly known as rainbowfishes) is a
relatively large family confined to northern and eastern
Australia, New Guinea and surrounding islands, and
Madagasgar [38, 39, 52]. At least 68 species from seven
genera are currently recognised, the majority of which
occur in New Guinea; 16 species and four genera occur in
Australia [38, 52, 904]. The Melanotaeniidae are closely
related to the Pseudomugilidae (blue-eyes) and
Atherinidae (hardyheads), and were formerly included in
the family Atherinidae [34, 38, 39].
Rhadinocentrus (meaning soft-spined) is a monotypic
genus, although prior to Allen [32] erecting the new genus
Cairnsichthys, C. rhombosomoides was also originally
placed in this genus. Allen [32] considered both
Rhadinocentrus and Cairnsichthys to be basal members of
the family Melanotaeniidae. The genus is distinguished by
a marked mandibular prognathism (protruding lower
jaw) and shares with Cairnsichthys a series of osteological
characters that separate them both from the remaining
Australasian melanotaeniid genera (Iriatherina,
Melanotaenia, Chilatherina and Glossolepis) including a
reduced parasphenoid process on the vomer, a shelf
(rather than a canal) on the temporal, a more elongated
Distribution and abundance
Rhadinocentrus ornatus has a restricted and patchy distribution in coastal lowland wallum (Banksia heath) and
rainforest ecosystems of central and south-eastern
Queensland, and northern New South Wales. It also occurs
in many streams, lakes and wetlands habitats on the sand
dune islands (Fraser, Moreton, North Stradbroke and
198
Rhadinocentrus ornatus
common at sites in which it occurred (third most abundant species forming 18% of the total abundance at these
sites). This species was also locally common in streams of
the South Coast region where it formed 41% of the total
abundance at sites in which it occurred. Across all streams,
average and maximum numerical densities recorded in 29
hydraulic habitat samples (i.e. riffles, runs or pools) were
0.52 individuals.10m–2 and 3.75 individuals.10m–2, respectively. Average and maximum biomass densities at 94 of
these sites were 0.38 g.10m–2 and 0.95 g.10m–2, respectively.
Highest numerical and biomass densities were recorded
from streams of the South Coast Basin. Rhadinocentrus
ornatus most commonly occurred with the following
species (listed in decreasing order of relative abundance
with rank abundance in parentheses): G. holbrooki, H.
compressa, H. gallii, and G. australis [1093]. Other studies
have reported this species to also commonly co-occur with
M. duboulayi, P. mellis, N. oxleyana and M. adspersa [82,
84, 517]. Around the Evans Head area of northern New
South Wales, R. ornatus often occurs with N. oxleyana, H.
galii, H. compressa, G. australis and G. holbrooki [726].
Bribie islands) off the south-eastern Queensland coast [34,
38, 52, 77, 82, 84, 153, 154, 517, 792, 884, 936, 1042, 1295].
This species occurs in several highly disjunct geographic
locations. Populations are known from small wallum
swamps and streams in the Shoalwater Bay drainage and
Water Park Creek (within Byfield National Park) near
Rockhampton in central Queensland [631, 862, 1328,
1349]. A record of R. ornatus in the Fitzroy River [1349] is
reported to be of dubious authenticity [1338].
Approximately 300 km to the south, it has occasionally
been reported in the Mary River but this species appears to
be extremely rare in this basin [84, 104, 1234, 1349].
Rhadinocentrus ornatus occurs in most drainage basins
from Tin Can Bay (as far north as Big Tuan Creek southeast of Maryborough, C. Marshall, pers. comm.) south to
Currumbin Creek near the border with New South Wales.
It is interesting that R. ornatus has not been recorded from
apparently suitable wallum habitats in the area between
Tin Can Bay and Water Park Creek to the north (e.g. the
Woodgate-Kinkuna National Park and Deepwater Creek
area). This species has not been recorded from the small
coastal streams and wetlands of the Sandgate area and the
Albert River. It is present but patchily distributed in coastal
drainages of northern New South Wales and has been
recorded as far south as the Orara River near Coffs
Harbour [25, 726, 814].
Macro/mesohabitat use
Rhadinocentrus ornatus is found in waterbodies situated in
coastal lowland wallum (Banksia heathland) ecosystems
generally characterised by dystrophic, acidic, stained
waters with siliceous sand substrates and abundant
submerged and emergent vegetation [84, 88]. This species
occurs in a variety of lotic and lentic habitat types including tributaries and backwaters of moderate-sized rivers,
small, short coastal streams, coastal and insular wetlands,
and coastal dune lakes [52, 82, 84, 517, 726, 978]. It has
been collected up to 50 km from the mouth of coastal
rivers in south-eastern Queensland at a maximum elevation of 100 m.a.s.l. (Table 2). Reports of this species from
localities in Obi Obi Creek [104, 1349] and Wide Bay
Rhadinocentrus ornatus is often locally common, although
it has declined in some areas such as the Brisbane River
system [94, 704]. Extensive sampling in rivers and streams
of the south-eastern Queensland mainland yielded relatively few individuals, but it was most common and widespread in the Sunshine Coast area north of Brisbane. In
this region it was the fifth most abundant species collected,
forming 7.7% of the total catch and was present at almost
half of the locations surveyed (Table 1). It was relatively
Table 1. Distribution, abundance and biomass data for Rhadinocentrus ornatus in streams of south-eastern Queensland. Data
summaries for a total of 231 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent summaries
for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species occurred.
Total
% locations
% abundance
(40.98)
Rank abundance
Mary River Sunshine Coast Moreton Bay
rivers and
rivers and
streams
streams
Brisbane
River
Logan-Albert
River
South Coast
rivers and
streams
5.7
–
48.3
5.0
–
1.5
5.0
0.14 (10.86)
–
7.67 (18.03)
0.14 (2.03)
–
0.01 (0.58)
0.70
22 (4)
–
5 (3)
21 (4)
–
27 (5)
12 (1)
0.01 (2.31)
–
0.13
–
–
–
0.18
32 (5)
–
8
–
–
–
11
Mean numerical density
(fish.10m–2)
0.52 ± 0.15
–
0.54 ± 0.19
0.24 ± 0.08
–
0.11 ± 0.07
1.19 ± 0.18
Mean biomass density
(g.10m–2)
0.38 ± 0.16
–
0.17 ± 0.06
–
–
–
0.68 ± 0.27
% biomass
Rank biomass
199
Freshwater Fishes of North-Eastern Australia
debris composed of logs and branches and the fine rootlets
of riparian vegetation [52, 82, 84, 726, 1093]. Most insular
habitats support emergent sedges and rushes (Eleocharis
spp., Lepironia articulata, Ghania spp. and Juncus spp.)
and some aquatic macrophytes (Myriophyllum sp.,
Nymphaea sp., Chara spp. and Utricularia spp.) [84, 88,
517].
Creek [1234] in the Mary River basin are considerably
further upstream from the river mouth. Stream widths at
collection sites vary from 2–7.3 m, with generally high
riparian cover (Table 2). Rhadinocentrus ornatus was most
frequently collected from runs and pools with low water
velocity (weighted mean 0.03 m.sec–1) and moderate
depths (weighted mean 0.44 m). This species was collected
in mesohabitats with predominantly fine-grained
substrates (sand and coarse gravel), but was also associated with cobbles and bedrock outcrops (Table 2). With
the exception of leaf litter beds, in-stream cover was not
overly abundant in the mesohabitats in which this species
was collected in streams of south-eastern Queensland
(Table 2).
Environmental tolerances
Limited quantitative data is available concerning the environmental tolerances of R. ornatus. Table 3 provides data
for Queensland collection sites only; details for collection
sites in New South Wales can be found in Knight [726].
This species is usually associated with dystrophic waterbodies that are acidic to circum-neutral (pH 4.0–8.0) and
slightly to deeply stained with tannins and other organic
acids, thus water transparency is usually very low (Table 3)
[52, 82, 84, 726, 1093]. Conductivity is usually very low in
streams, swamps and lakes supporting this species (usually
<300 µS.cm–1, but up to 658.0 µS.cm–1). Temperatures at
collection sites in Queensland and New South Wales have
ranged from 12 to 32°C, and dissolved oxygen levels from
2.15–16.2 mg.L–1 [25, 52, 82, 84, 726, 1093].
Table 2. Macro/mesohabitat use by Rhadinocentrus ornatus in
rivers of south-eastern Queensland. Data summaries for 231
individuals collected from samples of 29 mesohabitat units at
17 locations between 2000 and 2003 [1093]. W.M. refers to
the mean weighted by abundance to reflect preference for
particular conditions.
Parameter
2
Catchment area (km )
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
Min.
Max.
Mean
W.M.
5.0
3.0
4.0
0
2.0
33.7
125.5
27.0
50.0
100
7.3
93.4
50.0
14.0
22.2
20
4.4
71.7
32.6
10.0
22.7
28
3.6
77.5
Mean depth (m)
0.11
Mean water velocity (m.sec–1) 0
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0.8
0
6.8
0
0
0
0
0.99
0.44
0.48
0.07
Rhadinocentrus ornatus is sensitive to toxins in aquaria
(e.g. ammonia, chlorine and copper) at concentrations
that do not affect other taxa, such as species of
Melanotaenia, Craterocephalus, Ambassis and Hypseleotris
[517]. Aarn et al. [25] suggested that R. ornatus might be
suitable as an indicator of environmental change on the
basis of their relatively narrow environmental tolerances.
Moloney [960] noted that R. ornatus was extremely
susceptible to Mycobacterium (also called fish tuberculosis), reporting a 99% mortality rate of fish in aquaria
infected with this pathogen.
0.44
0.03
8.7
100.0
11.3
51.8
40.3
13.2
47.3
3.2
38.6
3.2
19.0
18.9
3.4
13.8
4.9
19.3
5.1
17.9
20.5
4.4
27.9
3.0
19.0
0.5
2.8
33.5
27.8
13.5
26.8
25.0
46.7
0.6
3.8
0.2
1.9
8.6
19.3
4.0
7.4
5.0
9.3
0.1
0.6
0.1
1.7
5.5
21.5
1.7
3.0
1.4
2.5
Table 3. Physicochemical data for Rhadinocentrus ornatus
from nine sites in Sunshine Coast streams over the period
1990 to 1994 [82, 84] and from 22 samples in South Coast
streams over the period 1994 to 2003 [1093].
Parameter
Min.
Max.
Mean
Sunshine Coast rivers and streams [82, 84] (n = 9)
Water temperature (°C)
16.0
32.0
18.7
Dissolved oxygen (mg.L–1)
3.0
14.6
7.2
pH
4.0
7.3
5.3
Conductivity (µS.cm–1)
68.0
300.0
103.0
Turbidity (NTU)
clear
10
stained
South Coast streams [1093] (n = 22)
Water temperature (°C)
15.8
23.2
Dissolved oxygen (mg.L–1)
2.6
16.2
pH
4.4
8.0
Conductivity (µS.cm–1)
78.0
658.0
Turbidity (NTU)
0.3
331.4
Microhabitat use
Rhadinocentrus ornatus is often found in close association
with dense emergent and submerged marginal vegetation,
leaf-litter beds, undercut banks and submerged woody
200
18.8
5.9
6.8
260.3
41.3
Rhadinocentrus ornatus
Reproduction
The reproductive biology and early development of R.
ornatus is known from field studies in Queensland [82, 84]
and aquarium observations [38, 517, 783, 797] (Table 3).
This species spawns and completes its entire life cycle in
freshwater and is easy to breed in captivity [38, 517, 783,
797, 978]; it was first bred in captivity 70 years ago [978].
Sexual dimorphism is exhibited in the form of more elongate rays in the second dorsal and anal fins of male fish;
males often fight among themselves; males also display a
red nuptial stripe along the nape during courtship (C.
Marshall, pers. comm.) [936].
[84]. From May to September, all fish caught were juvenile
and/or inactive, with a few maturing fish present in
August. Ripe females were captured from early November
to mid-January, as for males. Spent females were present
from early October to May, indicating the cessation of
spawning activity from June/July to October, depending
on water temperatures. Spawning occurs at water temperatures of around 24–28°C in Queensland localities and in
aquaria [38], however, Aarn et al. [25] collected eggs and
larvae of this species in the Upper Orara River near Coffs
Harbour in mid-October at temperatures of 16–17°C. No
increase in precipitation or water level was evident prior to
the collection of eggs and larvae [25]. The relationship of
fecundity to body size in Queensland (Blue Lake) populations could not be determined owing to the low numbers
of ripe female R. ornatus captured and the variability of
numbers of ripe oöcytes in fish of various body sizes [84].
However, Arthington and Marshall [84] recorded egg
counts of 18–76 (mean 40 eggs per female, 23–33 mm SL).
Rhadinocentrus ornatus is believed to mature in 9–12
months [797] and has an extended breeding season [84].
In Blue Lake, North Stradbroke Island, running ripe male
R. ornatus were first observed in early November and ripe
males were captured from then until mid-January; spent
males were present from early November until late April
Table 4. Life history information for Rhadinocentrus ornatus.
Age at sexual maturity (months)
9–12 months [797]
Minimum length of gravid (stage V)
females (mm)
18 mm [1093]
Minimum length of ripe (stage V)
males (mm)
22 mm [1093]
Longevity (years)
3–4 [517, 936]
Sex ratio (female to male)
?
Occurrence of ripe (stage V) fish
November–May [82, 84]
Peak spawning activity
November–January [82, 84]
Critical temperature for spawning
Around 23–28°C [38, 84]
Inducement to spawning
Increase in water temperature and day length [25, 84]
Mean GSI of ripe (stage V) females (%)
5.04 ± 1.08 [1093]
Mean GSI of ripe (stage V) males (%)
0.30 ± 0.20 [1093]
Batch fecundity (number of ova per batch)
18–76, mean = 40 per female (23–33 mm SL) [84]
Fecundity/Length (mm SL) or Weight (g)
relationship (mm SL)
?
Egg size (diameter)
1.20–1.35 mm [25]
Frequency of spawning
Lays a few eggs each day over a number of days [34, 797, 936]
Oviposition and spawning site
Female deposits batches of 3–5 eggs on aquatic plants, Eleocharis sp. is preferred
spawning site; eggs are relatively large and hang from adhesive filaments [25, 783]
Spawning migration
Probably none
Parental care
None
Minimum time to hatching (days)
6 [797], 7 [34, 936], or 8 [783] days at 20°C; 6–10 days at 23–24°C [84], 16 days at
20–22°C [25]
Length at hatching (mm)
4.1–4.6 [25]
Length at free swimming stage
?
Age at loss of yolk sack
?
Age at first feeding
?
Length at first feeding
?
Age at metamorphosis (days)
?
Duration of larval development (days)
?
201
Freshwater Fishes of North-Eastern Australia
aquatic insects (22.5%). This species also consumes
microcrustaceans including copepods, ostracods and
cladocerans (2.4%), macrocrustaceans (mostly atyid
shrimps, 2.0%) and other microinvertebrates such as small
arachnids and hydracarinids (0.9%). A small amount of
algae (e.g. desmids) (1.4%) and fragments of terrestrial
vegetation (0.7%) have been found in the guts of some
individuals (Fig. 1) [82].
The mean GSI values observed for fish collected from Blue
Lake during summer were 0.3% ± 0.2 SE for males and
5.0% ± 1.1 SE for females (<10 individuals of each sex)
[1093]. The eggs are yellow, spherical and relatively large
(diameter 1.20–1.35 mm) with a unipolar tuft of adhesive
filaments [2495; 1453]. The female lays three to five eggs
each day over a number of days, depositing them on
submerged aquatic vegetation from which they hang by
adhesive filaments [34, 783, 797, 936]. The most frequently
used site for spawning of R. ornatus in the Orara River was
the base and roots of the emergent sedge Eleocharis sp.
[25]. The minimum time to hatching varies with temperature, as follows: six days [797], seven days [34, 936] or eight
days [783] at 20°C; 6–10 days at 23–24°C [34, 797, 936]; 16
days at 20–22°C [25]. Moloney [960] reported that eggs in
aquaria appeared to hatch over a period of a few days and
that the first fry were observed approximately two weeks
after courtship had commenced. Length at hatching is
4.1–4.6 mm [25].
Arthington and Marshall [82] observed that in Spitfire
Creek on Moreton Island, R. ornatus had a more diverse
diet than other species present (Nannoperca oxleyana,
Hypseleotris galii, H. compressa) largely as a consequence
of its consumption of terrestrial as well as aquatic taxa.
Spatial variations in diet were also observed in this wetland
system, and related to the tendency to forage at the water’s
surface, where the array of prey of terrestrial origin may
vary considerably due to such factors as source of terrestrial insects (low or high growths of riparian and bank
vegetation), wind direction, and size and weight of prey
[82].
Aarn et al. [25] describe and illustrate characteristics of
larval R. ornatus. Characteristic features are: rounded
cranium, cranial melanophore distribution forming a
narrow ‘V’, lack of melanophores in the cranial parietal
peritoneum, dorsal fin-fold originating at the fourth to
fifth preanal myomere, urogenital funnel present (and
gives rise to the genital rosette), first dorsal fin originates
caudal to origin of anal fin and the anal fin originates next
to the urogenital funnel, notochord flexion takes place
after hatching, larvae maintains flexion during early development, mouth shows mandibular prognathism, there are
34–35 vertebrae, the tip of the notochord is elongate and
the hypurals only partially fuse [25, 631].
In Blue Lake, North Stradbroke Island, R. ornatus had a
more diverse diet than H. galii [92]. In this lake, R. ornatus
consumed a wider variety of aquatic and terrestrial taxa
than H. galii and took a greater proportion of its diet from
food items associated with the water’s surface (overall
>60% including chironomid pupae, adult Diptera,
Hymenoptera, Lepidoptera and Araneae, flower parts and
other plant tissues). Chironomid pupae were the most
important dietary component in 1991 (25%) and adult
Diptera in 1991 (26%). Small quantities of filamentous
algae were consumed in both years but other algae
(desmids and diatoms) were not eaten. Prey diversity and
In captivity, the young of R. ornatus can grow to 20 mm in
three weeks given suitable food [978] and to 41 mm in 10
weeks [783].
Other microinvertebrates (0.9%)
Microcrustaceans (2.4%)
Macrocrustaceans (2.0%)
Other macroinvertebrates (0.9%)
Movement
Rhadinocentrus ornatus is an active swimmer that congregates in small pools [39] but is said not to be as active as
other rainbowfishes [25, 783]. There is no published information on other aspects of the movement biology of this
species.
Unidentified (9.3%)
Terrestrial invertebrates (23.3%)
Aquatic insects (36.6%)
Trophic ecology
Diet data for R. ornatus is available for 508 individuals
from the Blue Lake on North Stradbroke Island and
Spitfire Creek on Moreton Island [82, 84, 92, 105].
This species is a microphagic carnivore (Fig. 1). The total
mean diet is composed primarily of aquatic insects
(36.6%), terrestrial invertebrates especially Diptera,
Hymenoptera and Hemitera (23.3%) and aerial forms of
Algae (1.4%)
Terrestrial vegetation (0.7%)
Aerial aq. Invertebrates (22.5%)
Figure 1. The mean diet of Rhadinocentrus ornatus. Data
derived from stomach content analysis of 508 individuals
from Blue Lake on North Stradbroke Island and Spitfire Creek
on Moreton Island [82, 84, 92, 105].
202
Rhadinocentrus ornatus
long-term variability in precipitation levels, water depth
and velocity [154]. In small streams and swamps, aquatic
macrophytes serving as fish habitat and spawning sites for
R. ornatus can be flooded or swept away at high water
levels and destroyed by exposure at low water levels. Other
melanotaeniids show a preference for habitat with high
levels of macrophyte cover [52], and stream fishes in
general often associate with macrophytes and other forms
of in-stream cover [1095]. Areas with good riparian cover
and aquatic vegetation also provide an abundant source of
terrestrial and aquatic invertebrate food for surface feeding species such as R. ornatus [82, 84, 611].
evenness were higher for R. ornatus than for H. galii in
both years of study and at all times of year [92].
Bayly et al. [149] reported similar variation in the diets of
R. ornatus and H. galii in Fraser Island lakes.
Conservation status, threats and management
Rhadinocentrus ornatus was classified in 1993 as NonThreatened by Wager and Jackson [1353], and since then
has not been given any special conservation designation in
National or State listings [52] either in Queensland or New
South Wales [965]. It is not listed under the
Commonwealth Endangered Species Protection Act, 1992,
the NSW Fisheries Management Act, 1994, the World
Conservation Union (IUCN) ‘Red’ List, the Australian
Society for Fish Biology (ASFB) ‘Conservation Status of
Australian Fishes’ Listing, or the Environment Protection
and Biodiversity Conservation Act 1999 (EPBC Act).
Nevertheless, many ecologists regard R. ornatus as a
vulnerable species owing to its relatively restricted and
patchy distribution along the coastline of central and
south-eastern Queensland and northern New South Wales
[52, 726, 965]
Disturbance of aquatic plant communities in coastal
streams and lakes may have significant implications for the
persistence of R. ornatus [82, 84]. Road and bridge
construction have increased bank erosion and the sediment load in a number of small coastal creeks along the
Sunshine Coast of Queensland [82, 1348]. Real estate
development and housing construction in the vicinity of
small creeks and swampy drainage lines may represent a
serious threat if adequate precautions are not taken to
contain sediment runoff from cleared land [82, 84].
Alien species are also regarded as a threat to R. ornatus [25,
52, 82, 84, 517, 960]. Gambusia holbrooki has established
self-maintaining populations in many waterbodies of the
wallum ecosystem in both Queensland and New South
Wales [84, 726]. Gambusia holbrooki is a particularly
threatening species [77, 78, 416]. Many studies have
demonstrated its trophic flexibility (including the
consumption of fish eggs and larvae) and its innate aggressiveness towards other fishes [78, 960, 983].
The primary threats to R. ornatus are the same factors
threatening populations of Nannoperca oxleyana and
Pseudomugil mellis in coastal wallum ecosystems [52, 82,
84, 726]. They include loss of habitat due to residential
housing development [90, 1358] and road construction
[1348], expansion of exotic pine plantations by forestry,
and water contamination associated with urban and
tourism development, mining operations and agriculture
[82, 84, 90, 726, 790, 965, 1348, 1353]. Aarn et al. [25] note
that R. ornatus was collected from Boambee Creek, south
of Coffs Harbour, by the Australian Museum prior to
urban development and degradation of this stream.
Moloney [960] reported a high level of predation on R.
ornatus eggs and fry by G. holbrooki maintained in experimental aquaria. Rhadinocentrus ornatus was also observed
to switch habitat use from areas of open water to refuge
areas in the presence of G. holbrooki. Moloney [960]
concluded that alien fish such as G. holbrooki have the
capacity to significantly reduce the number of R. ornatus
recruiting to later life stages by interfering with foraging
activities and by direct predation. Dietary studies in Blue
Lake, North Stradbroke Island, have shown that R. ornatus
and G. holbrooki have very similar diet composition at all
times of the year [84, 92]. Both species feed on aquatic and
terrestrial invertebrates and show particularly high
dependence on prey of terrestrial origin [82, 84, 92].
Arthington and Marshall [92] suggested that high similarity of diet composition could lead to interspecific competition if high population densities of G. holbrooki coincide
with circumstances of food shortage. The occurrence of G.
holbrooki in coastal creeks on Fraser and Moreton islands,
in the Noosa River and in many mainland creeks within
Several aspects of the ecology of R. ornatus are particularly
relevant to its protection and recovery in wallum ecosystems. This species is usually found where there is little or
no flow and fish can shelter in beds of emergent and
submerged aquatic macrophytes or near undercut banks
and woody debris [82, 84, 726, 1093]. Cover is an important factor in environments where surface (i.e. avian) and
aquatic predators (piscivores) are present. Cover elements
may also serve to reduce the impact of short periods of
high flow with the power to disrupt spawning activities,
displace eggs and small individuals downstream, or carry
fish into open areas with little protective cover [82].
Rainfall patterns and stream discharge are characteristically highly variable and unpredictable within and
between years in south-eastern Queensland streams and
rivers [1095]. Freshwater habitats within coastal wallum
are particularly vulnerable to local rainfall events and
203
Freshwater Fishes of North-Eastern Australia
the geographic range of R. ornatus represents an ongoing
threat that could well increase. [84]. Dispersal of alien
fishes by natural processes (e.g. widespread flooding) is a
possibility and G. holbrooki is a particularly hardy and
adaptable species [83]. Human distribution of G. holbrooki
still occurs occasionally [83].
purposes is potentially deleterious. Members of the public
who are not familiar with the fauna of particular systems
may inadvertently collect a restricted species such as R.
ornatus, only to discard it later in the day, possibly into a
different waterbody. Public education is the most effective
way to combat this type of impact.
Introduced plants may also substantially modify the freshwater habitats of R. ornatus. Several small, confined waterways along the Queensland coast have been invaded by the
South American ponded pasture species, Brachiaria
mutica (para grass). This alien grass has a severe impact on
aquatic habitat, water quality and invertebrate diversity in
small streams and does not contribute carbon (i.e. energy)
to aquatic food webs [95, 248, 250].
Several approaches to the conservation of rare and endangered fish species have been proposed in draft Recovery
Plans for Pseudomugil mellis and Nannoperca oxleyana [82,
84]. Recovery Plans for these species would also protect R.
ornatus [84]. Arthington et al. [82], Knight [726] and
Morris et al. [965] recommend a range of Specific
Recovery Actions to conserve individual localities and
populations of N. oxleyana and P. mellis which are equally
applicable to R. ornatus. These could include rehabilitation of degraded creeks, reconstruction of channel
morphology and habitat characteristics, planting of riparian vegetation, and elimination of G. holbrooki [82, 84,
726, 965]. Recovery Plans for these rare species have not
been implemented by the agencies responsible for environmental protection in Queensland.
Over-exploitation of R. ornatus is only an issue with
respect to the collection of fish for aquarium stocks. The
intensity and impact of this activity is not known. The
Australia New Guinea Fishes Association (ANGFA) has
issued several warnings to its membership that excessive
collection of rare freshwater species for aquarium
204
Cairnsichthys rhombosomoides (Nichols & Raven, 1928)
Cairns rainbowfish
37 245002
Family: Melanotaeniidae
located on the operculum. The body surface below the
midlateral stripe tends to be white. Many specimens are
distinguished by the presence of an iridescent pink-purple
sheen, the intensity of which varies according to the incidence of light falling upon it. Colour in preservative: all
iridescent structural colours are lost in preservative and
the colour tends towards a uniform dull tan dorsally and
white ventrally. The midlateral stripe remains visible but
the lower stripe is noticeably faded.
Description
First dorsal fin: V-VII; Second dorsal: I, 11–15; Anal: I,
17–21; Pectoral: 11–13; Horizontal scale rows: 10–11;
Vertical scale rows: 36–38; Predorsal scales: 15–16 [23, 43,
52]. Figure: male, 58 mm SL, Polly Creek, North Johnstone
River, September 1997: drawn 1999.
Cairnsichthys rhombosomoides is a moderately sized rainbowfish rarely exceeding 63 mm SL [1108] but occasionally attaining a maximum size of 70 mm SL [38]. The
relationship between body weight (g) and length (SL in
mm) takes the form: W = 2.466 x 10–5 L2.878; r2 =0.873,
n=372, p<0.001 [1108]. Body slender, rhombofusiform
and laterally compressed [23]. Mouth terminal, initially
horizontal becoming oblique caudally; large, reaching
back to beyond anterior margin of eye. Outside margin of
gape with several rows of small conical teeth. Body covered
in faintly crenulate scales. Colour in life: published
descriptions of this species do not do it justice, variously
describing it as drab or dull yellow-green. In truth, it is a
most beautiful bright tan-yellow on the dorsal half of the
body. An intense black midlateral stripe and more diffuse
ventral black stripe extend from the caudal area anteriorly
to pectoral fin base. The fin margins of the dorsal surface
are an iridescent yellow. A large iridescent yellow spot is
The larvae are distinctive and easily distinguished from the
larvae of other melanotaeniids. The head is rounded and
declined about 30° from horizontal and possesses a dense
accumulation of melanophores on the dorsal surface
between the mid-point of the eye and the posterior edge of
the opercula. Melanophores on the operculum, snout and
maxilla densely accumulated. Gut coiled but unstriated in
newly hatched larvae. Eyes, feeding apparatus and gill filaments well developed at hatching [1093].
Systematics
Cairnsichthys rhombosomoides was originally placed in the
genus Rhadinocentrus in 1928, although the authors
admitted that it was unlike the southern member and type
species of the genus, R. ornatus [992]. Munro [975]
205
Freshwater Fishes of North-Eastern Australia
River in 1995 [1096]. The distribution was further
extended to include the North Hull River [1087] in 1996
and the Liverpool and Maria drainages in 1997 [1179].
Although not collected from the Moresby River by Russell
et al. [1183] it is likely to be present (or was present) in
this drainage given its presence in rivers to the immediate
north and south. Similarly, although not yet recorded from
short creeks draining into Trinity Inlet, the historical
connection of these streams with the Mulgrave River; as
indicated by geomorphological evidence [1411] and the
presence of Glossogobius sp. 4 [1349] (a species otherwise
restricted to the Russell/Mulgrave River), suggests it would
be present in this area also. If so, then streams of Trinity
Inlet define the northern limit of its distribution and
streams of the Hull River near Mission Beach form its
southern limit. It has not been collected from the Tully
River, despite extensive sampling [1087, 1093].
concurred, although further comparison was hampered
by insufficient material. The species was, at the time,
considered to be very rare [43]. Allen [32] erected the
monotypic genus Cairnsichthys in 1980 in recognition of
its distinctiveness as part of a generic revision of the
family. Allen [32] was the first to propose a phylogeny for
the Melanotaeniidae, and in his scheme, Pseudomugil and
Popondetta were the most primitive genera, Melanotaenia,
Chilatherina and Glossolepis were considered the
most derived, while Iriatherina, Rhadinocentrus and
Cairnsichthys were intermediate between these two
groups. Of these latter six genera, all but Cairnsichthys are
synapomorphic with regard to the attachment of the
pelvic girdle to the third pleural rib (attached to the
fourth in Cairnsichthys). Subsequently, the family
Pseudomugilidae was recognised as distinct from the
Melanotaeniidae [1190] and composed of the following
genera: Pseudomugil, Kiunga and Scaturiginichthys
(Popondetta having been subsumed within the genus
Pseudomugil). This family (plus the newly erected
Telmatherinidae) were then subsequently placed back
within the Melanotaeniidae along with two genera,
Bedotia and Rheocles from Madagasgar, by Dyer and
Chernoff [395]. The most recent phylogenetic analysis of
the Melanotaeniidae is that of Aarn and Ivantsoff [23]. In
that analysis, the Pseudomugilidae, Telmatherinidae and
the Melanotaeniidae were recognised as valid and different
families. These authors accepted that on the basis of
morphological synapomorphies, Bedotes and Rheocles
remain within the Melanotaeniidae. The family is therefore composed of two subfamilies: the Iriatherininae
(containing Iriatherina werneri) and the Melantaeniinae
(containing Bedotes, Rheocles, Cairnsichthys, Rhadinocentrus,
Chilatherina, Glossolepis and Melanotaenia). The first four
genera are placed within a clade termed the Bedotiini. A
recent phylogenetic assessment [905] of the family using
DNA sequencing techniques unfortunately did not
include any of the genera within the Bedotiinae. The genus
Cairnsichthys is distinguished by a convex rostral margin
of the vomer, caudolaterally directed vomerine condyles,
elongate maxillary external ramus, enclosed mandibular
sensory canal, broad supracleithrum and cranial spinous
process of the pevic fin being attached ligamentously to
the fourth pleural rib.
Cairnsichthys rhombosomoides is a moderately abundant
species in those streams in which it occurs. It was the 14th
most abundant species in the extensive Wet Tropics survey
of Pusey and Kennard [1087]. A study undertaken in 12
sites within the Mulgrave River and 10 sites in the South
Johnstone River found it to be the third and 14th most
abundant species, respectively, contributing 5.8% of the
total number of fish collect from both rivers [1096].
Estimates of relative abundance are highly dependent on
whether appropriate streams are sampled.
Table 1. Distribution, abundance and biomass data for
Cairnsichthys rhombosomoides in two rivers of the Wet Tropics
region. Data summaries for a total of 2761 individuals
collected over the period 1994–1997 [1093]. Data in
parentheses represent summaries for per cent and rank
abundance, and per cent and rank biomass, respectively, at
those sites in which this species occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Distribution and abundance
Cairnsichthys rhombosomoides is limited to the Wet Tropics
region and further restricted within this area also.
Nonetheless, it is not as restricted or rare as some of the
earlier texts suggest. Originally thought to be restricted to a
few streams of the Russell/Mulgrave drainage, the distribution was extended to a single small tributary of the North
Johnstone River in 1989 [34] and to the South Johnstone
25.3
7.9 (34.9)
Mulgrave
River
Johnstone
River
43.2
23.2
11.4 (38.0) 6.8 (32.5)
6 (1)
4 (1)
5 (1)
0.5 (10.0)
0.6 (9.8)
0.5 (10.2)
12 (5)
13 (5)
Rank biomass
15 (5)
Mean density
(fish.10m–2)
3.50 ± 0.54
2.40 ± 0.44 4.36 ± 0.89
Mean biomass
(g.10m–2)
3.67 ± 0.51
2.98 ± 0.53 4.20 ± 0.81
Cairnsichthys rhombosomoides is widespread and abundant in both the Mulgrave/Russell and Johnstone rivers
(Table 1). It is apparently less widely distributed in
the Johnstone River but this more properly is reflects the
greater proportion of study sites located above an
206
Cairnsichthys rhombosomoides
elevation of 100 m.a.s.l. This species is numerically dominant in those sites in which it occurs and contributes about
10% to the total biomass of these sites also. Cairnsichthys
rhombsomoides co-occurs with (in decreasing order of
abundance) M. adspersa, H. compressa, P. signifer and M.
maccullochi (all sites combined). It frequently occurs with
A. reinhardtii (fourth) and O. aruensis (fifth) in the
Mulgrave River, and with M. s. splendida (fifth) in the
Johnstone River [1093]. The number of species with which
it co-ocurrs in the Johnstone and Mulgrave rivers ranges
from three to 15 per site (average = 7.8). The number and
types of species with which it co-occurs is highly dependent on the location of the stream within the catchment
(see below). It is frequently found in sympatry with M.
splendida splendida (47.7% of all site/time combinations
(n = 82) within the Johnstone and Mulgrave rivers
containing C. rhombosomides also contained M. s. splendida) but it is rare that both species are abundant. Density
values of these species are weakly (r2 = 0.203) but significantly (p<0.01) negatively correlated.
related to habitat structure (such as substrate composition, gradient or water velocity). Competition with the
eastern rainbowfish Melanotaenia splendida splendida is
likely to be important given the negative association
between densities of these species reported above.
Additional evidence for this interaction can be found by
examining the distribution of both species within individual streams in which they co-occur. In all circumstances,
Cairnsichthys is restricted to the most upstream reaches
and often a very sharp zone of sympatry is delineated by
rapid changes in gradient posed by cascades or waterfalls.
(A similar pattern of distribution is seen for M. spl. splendida and M. utcheensis in the Johnstone River at higher
elevation [1104]). As Cairnsichthys is the more plesiomorphic of the two species, it is possible that it was the original
rainbowfish in rivers of the Wet tropics region and previous more widely distributed within individual drainages.
Subsequent, and relatively recent, invasion [618] by M. spl.
splendida may have restricted its distribution to that
observed today.
Macro/meso habitat use
Cairnsichthys rhombosomoides occurs in small streams
with good riparian cover at, or below, 100 m.a.s.l. The
average macrohabitat data presented in Table 2 does not
truly reflect the distribution of this species within the
catchments in which it occurs with respect to elevation
and distance from the river mouth, however. Cairnsichthys
rhomsomoides occurs in small adventitious lowland
streams as well as upland tributary streams and many of
the meso-scale habitat parameters listed in Table 2 vary
considerably between these two habitats. Small lowland
streams empty directly into 5th or 6th order rivers, and are
usually (but not always) of low gradient with a mud, sand
and fine gravel substrate and with abundant leaf litter (i.e.
the type of habitat in which Mugilogobius notospilus is
found). Such small streams contain speciose assemblages.
Table 2. Macro/mesohabitat use by Cairnsichthys
rhombosomoides. Data derived from the mean habitat
characteristics of 32 sites within the Johnstone River and
Russell/Mulgrave River drainages sampled over the period
1994–1997. W.M. refers to the mean weighted by abundance
to reflect preference for particular conditions.
Parameter
Min.
2
Catchment area (km )
Distance to source (km)
Distance to river mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
0.13
0.5
8.1
5
2.0
0.0
Gradient (%)
0.02
Mean depth (m)
0.1
Mean water velocity (m.sec–1) 0
The upland tributaries in which Cairnsichthys occurs tend
to be of higher gradient, typified as cascades, with higher
water velocities, a substrate composed of large rocks and
bedrock within a sand/fine gravel matrix. Such streams
tend to contain few species (i.e. Anguilla reinhardtii and
Mogurnda adspersa). Notwithstanding these differences,
the critical macrohabitat components are a relatively intact
riparian canopy and small stream size. As a consequence of
the high riparian cover and resultant shade, vegetative
cover elements such as macrophytes, filamentous algae,
emergent and submerged vegetation are at low abundance.
Given that Cairnsichthys is confined to small streams of
quite divergent habitat structure, it is probable that their
within-drainage distribution is due to biological
constraints rather than constraints imposed by factors
207
Max.
62.6
19.0
64.0
100
14.3
90.0
7.33
0.55
0.36
Mean
W.M.
5.45
3.71
29.2
35.3
5.4
56.5
3.16
3.12
38.2
65.5
7.05
53.8
1.02
0.30
0.11
1.15
0.31
0.08
Mud (%)
Sand (%)
Fine gravel (%)
Gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
4.0
0
0
0
0
40.0
52.0
73.0
73.0
33.9
76.0
67.0
6.5
18.8
24.3
10.9
9.8
17.6
11.9
11.0
17.2
21.3
7.31
11.3
20.7
11.2
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
3.7
3.3
18.0
60.0
9.0
81.2
8.9
11.3
29.0
75.0
0.3
0.3
2.7
5.1
2.9
14.2
2.1
1.9
7.1
19.8
0.3
0.5
4.2
3.2
0.9
16.7
1.2
1.4
6.5
20.6
Freshwater Fishes of North-Eastern Australia
to its use of average water velocities. Although few individuals were collected from the upper water column, it is
evident from the diet depicted in Figure 2, that this species
does make forays to the surface to capture terrestrial invertebrate prey. This species was infrequently collected over a
mud substrate, being most commonly collected from areas
of diverse substrate composition dominated by larger
substrate sizes.
Whatever the reasons for its bimodal pattern of distribution, the extent of present-day gene flow between upland
and lowland populations is of interest. If connectivity is
low, then lowland populations – those most at threat from
habitat disturbance and acute and chronic water quality
degredation – may be at risk in the long term.
Microhabitat use
Cairnsichthys rhombosomoides was most commonly
collected in water between 30 and 50 cm deep (Fig. 1c) and
velocities most commonly less than 0.2 m.sec–1 (Fig. 1a).
As a consequence of being most commonly recorded from
the lower half of the water column (Fig. 1d), the focal
point velocity distribution (Fig. 1b) was almost identical
40
(a)
50
This species was infrequently collected from areas greater
than 0.2 m from cover and most frequently from within
0.2 m of the substrate (as a consequence of its relative
depth use) and from leaf litter. These data suggest that C.
rhombosomoides spends much of its time concealed within
the substrate or litter, however this is not the case. More
frequently, this species occurs in small schools over such
areas of potential cover, using them only when threatened.
(b)
The larvae vary in microhabitat use depending on stage of
development [1109]. Preflexion larvae, characterised by
minor fin development, are confined to areas of zero flow
close to the natal habitat. Larvae were rarely recorded from
depths greater than 50 cm in both upland (Mena Creek)
and lowland (Polly Creek) sites. Larvae always stay close to
some form of cover and avoided areas of bright sunlight.
Very dense cover is avoided, possibly to reduce the potential for predation by cryptic piscivorous gudgeons. As
larvae develop, the range of flows in which they occur also
increases. Nonetheless, the larvae avoid areas of flow
greater than 10 cm.sec–1.
40
30
30
20
20
10
10
0
0
Mean water velocity (m/sec)
(c)
Focal point velocity (m/sec)
20
20
(d)
15
10
10
Environmental tolerances
Information on tolerance to water quality extremes is lacking and data listed below reflects the water quality of the
streams in which C. rhombosomoides has been collected.
5
0
0
Total depth (cm)
The data presented in Table 3 indicates that Cairnsichthys
rhombosomoides typically occurs in streams of high water
quality reflecting the well-forested nature of such streams.
The range in water temperatures indicated is typical of
small rainforest streams. Although recorded as present in
streams typified by a substantial range in dissolved oxygen
levels, the mean value listed indicates that the streams in
Relative depth
(e)
(f)
20
40
15
30
10
20
5
10
0
0
Table 3. Physicochemical data for Cairnsichthys
rhombosomoides. Data summaries for sites in which present
over the period 1994–1997.
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by the Cairns rainbowfish
Cairnsichthys rhombosomoides. Data derived from capture
records for 840 fish (except focal point velocity where n =
744) from the Johnstone and Mulgrave rivers over the period
1994–1997.
208
Parameter
Min.
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
15.2
4.91
4.5
5.6
0.21
Max.
28.8
9.96
8.43
63.0
18.1
Mean
21.6
7.58
6.69
28.0
2.01
Cairnsichthys rhombosomoides
this species has low tolerance to elevated salinity, although
this needs to be experimentally determined. In general, the
waters in which C. rhombosomoides occurs are very clear
and leached organic material contributes the bulk of what
little colour is present. The maximum NTU value listed in
Table 3 was recorded after a rainfall event resulted in
substantial downstream transport of sediment originating
from an upstream banana plantation. Allen [38] noted
that, when in captivity, C. rhombosomoides is sensitive to
even small changes in water chemistry
which it occurs are well-oxygenated. The standard error for
the mean was small (± 0.18 mg.L–1) indicating that that the
minimum value recorded (4.91 mg.L–1) was substantially
different from most other readings. The minimum value
was recorded in October when water temperature was
28.8°C: the highest recorded at this site. Air temperature at
the time of measurement was 32°C, the fourth highest for
the sites examined. Such high water temperatures and low
dissolved oxygen levels are apparently not frequently experienced. The mean pH recorded was near neutral although
the range in pH was substantial. Lowland coastal tributaries tended to be quite acidic (pH 4.5–5.5), whereas upland
tributaries, especially those draining basaltic catchments
in the Johnstone River were more basic (7.5–8.5).
Conductivities were uniformly low and it is probable that
Reproduction
The reproductive biology of C. rhombosomoides is similar
to other stream-dwelling rainbowfishes in the Wet Tropics
region. Fish commence breeding in their first year and
Table 4. Life history data for the Cairnsichthys rhombosomoides. Information on reproductive biology derived from a single study
[1108] examining reproduction in one upland population and one lowland population, unless otherwise noted. Information on
larval stages drawn from two studies [1093, 1109] undertaken at the same site.
Age at sexual maturity (years)
<1 (probably 6–7 months)
Minimum length of ripe females (SL in mm) Gender discernible at 34 mm SL, fully mature fish as small as 36 mm SL, mean length of
ripe fish = 47.6 mm SL
Minimum length of ripe males (SL in mm)
Gender discernible at 28 mm SL, fully mature fish as small as 28 mm SL, mean length of
ripe fish = 52.2 mm SL
Longevity (years)
Probably 2 years, Allen and Cross [43] suggest a maximum life span of 3 years in
captivity
Female to male sex ratio during
breeding season
Unity
Occurrence of ripe fish
Ripe females present from April to December, males from April to November
Peak spawning activity
September to October
Critical temperature for spawning
September water temperatures 20°C and 22°C for upland and lowland populations,
respectively
Inducement to spawn
Given that some spawning females are present throughout most of the year, as are
larvae, it does not appear that rising temperature is necessarily a cue for spawning. Peak
spawning occurs at a time of stable low flows (see text)
Mean GSI of ripe female (%)
Peak mean GSI = 4.9% in October
Mean GSI or ripe males (%)
Peak mean GSI = 1.7% in September
Maximum fecundity (number of ova)
131–737 depending on size
Fecundity/length relationship
Log (egg number) = 1.88 ± 0.016 (SL in mm); r = 0.515, p<0.05, n = 17
Egg diameter (mm)
1.139 ± 0.021 mm for ovulated, but not water hardened, eggs, n = 9
Egg diameter significantly larger in upland population (~8%)
Frequency of spawning
Heterochronal-batch sizes varied from 8 to 66 eggs
Oviposition sites
Eggs located in root masses
Mating behaviour
Single pair with elaborate display by male
Parental care
None
Time to hatching
7 days in captivity (presumably at 25.5°C) [43], field data lacking
Length at hatching (mm)
Early preflexion larvae 3.46–5.46 mm
Length at free swimming stage (mm)
Late preflexion 5.38–6.85 mm
Length at first feeding
As above
Length at end of larval development (mm)
14.0–15.5 mm
Duration of larval development
? 30 days
Survivorship
Unseasonal increases in discharge cause high levels of mortality in larvae and
reproduction is complete by the start of the summer wet-season
209
Freshwater Fishes of North-Eastern Australia
Trophic ecology
Information on the diet of this species is derived from a
single study of 107 individuals collected in August 1992,
predominantly from upland tributary sites. The diet is
dominated (54.7%) by small terrestrial invertebrates such
as ants [1097]. A small proportion was comprised of the
adult forms of aquatic Diptera, presumably also taken
from the water’s surface. The remainder of the identifiable
fraction was composed of chironomid and trichopteran
larvae and ephemeropteran nymphs. The relatively large
eyes and mouth of this species are assets for a species relying on terrestrial sources of food and confined to wellshaded streams. A high dependency on terrestrial prey is
consistent with the distribution of this species being
confined to well-vegetated streams. It is probable that the
use of terrestrial prey increases in importance with size.
spawning fish are present from April through to December
(Table 4). Peak spawning activity is from August to
October. Water temperatures at this time are above 20°C
(usually 2°C warmer in lowland tributaries) but it is
unlikely that rising water temperatures stimulate spawning given that low levels of spawning occur from April
onward, at a time when temperatures are dropping. Sexual
maturity and gonad development are commensurate with
increasing body size. Given that fecundity increases with
increasing size, it appears that spawning occurs when
females achieve certain size. That GSI levels peak in
September simply reflects synchronised growth rates in the
maturing female cohort. The eggs are small and numerous.
Egg diameter was slightly greater in the upland population
where fish were also slightly heavier for a given length. The
eggs are deposited in batches within rootmasses. It is probable that the eggs, like those of other melanotaeniids,
possess adhesive filaments. The larvae are small at hatching
but with little yolk, possess well-developed eyes, a welldeveloped feeding apparatus and gut, and commence feeding shortly after hatching. Larval development is complete
at 14–15 mm SL by which time adult meristics (squamation and fin ray counts) are attained.
Conservation status, threats and management
Wager and Jackson [1353] list C. rhombosomoides as Rare
while the ASFB [117] listed this species as Vulnerable.
Although this species has a relatively restricted distribution, many populations are within National Parks within
the Wet Tropics World Heritage Area. Threats to this
species include water resource development within the
Mulgrave River system to supply domestic water for the
Cairns region. Changes in flow regime that increase total
discharge or the extent of variability of flow during the
normally stable low flow period of late winter/spring are
likely to negatively impact on spawning success and larval
recruitment. Channelisation or infilling of lowland tributaries, unregulated abstraction of water for irrigation,
clearing of lowland rainforest for cropping, and urban
development may also pose a threat to this species.
Movement
No data is available to suggest the extent or phenology of
movement in this species. However, a 12-month study
[1093] of the response of fish assemblages to experimental
defaunation found that C. rhombosomoides readily
recolonised such empty habitats in numbers similar to
those present prior to defaunation. Movement into the
experimental sites was from adjacent reaches and therefore only of limited extent in scale (probably in the order
of 100–200 m). Information on the extent of gene flow
between isolated populations is needed.
Aerial aq. Invertebrates (3.5%)
Cairnsichthys rhombosomoides requires an intact riparian
zone and measures are needed to protect the integrity of
such areas. Lowland populations are most at threat as a
result of increased urbanisation and intensive agriculture,
land clearing and expansion of the sugar-cane industry.
Upland populations in the Mulgrave River are reasonably
secure given the presence of populations in streams within
National Parks. However, upland populations in the
Johnstone River catchment are not so protected and may
face threats in the future from degraded water quality
(particularly increased sedimentation and pesticide
contamination from horticultural industries) and unregulated water use. While the distributions of C. rhombosomoides and M. s. splendida are not mutually exclusive,
these species are probably competitors. Thus changes in
flow regime or habitat structure (i.e. loss of riparian
integrity) that favour M. s. splendida will probably be to
the detriment of C. rhombosomoides.
Unidentified (5.5%)
Aquatic insects (36.0%)
Terrestrial invertebrates (55.0%)
Figure 2. The mean diet of Cairnsichthys rhombosomoides.
Summary derived from stomach content analysis of 107 fish
collected from the Mulgrave River in August 1992.
210
Melanotaenia splendida splendida (Peters, 1866)
Eastern rainbowfish
37 245014
Family: Melanotaeniidae
Pectoral fins slightly pointed; caudal fin moderately
forked, lobes mildly pointed. Posterior margin of second
dorsal fin and of anal fin elongated and pointed in males
but not females. Colour variation is marked over the entire
range of this subspecies. In general, the body surface is
light blue/silver grading to white/silver ventrally. Dorsal
surface may be quite dark. Midlateral dark blue/black
stripe running from cheek to caudal extremity, but not
present or well-developed in all populations. Typically,
populations in the Wet Tropics region have a well-developed midlateral stripe whereas populations of eastern
Cape York and of the Burdekin River and further south do
not. A series of narrow black stripes forming a ‘zig-zag’
pattern is a prominent feature on the flank of fish from the
upper Burdekin River. Elsewhere several orange-red
stripes between each horizontal scale row may be present,
predominantly on posterior half of the body. Green and
orange hues also present on body. Fin colour variable
ranging from red to yellow, with dark red, yellow or black
flecking. Colour in preservative: brownish-grey dorsally,
midlateral stripe dark, body pale ventrally; fins pale with
darker margins.
Description
First dorsal fin: V–VII; Second dorsal: I, 9–14; Anal: I,
17–24; Pectoral: 9–16; Horizontal scale rows: 10–13;
Vertical scale rows: 33–38; Predorsal scales: 12–18; Cheek
scales: 7–17 [43, 1093]. (But see below for discussion of
geographic variation). This species is unlikely to be
confused with most other species but it may co-occur with
M. eachamensis, M. trifasciata and M. utcheensis in some
drainages in the northern part of its range. Figure: adult
male, 62 mm SL, South Johnstone River, July 1995; 1996.
Melanotaenia splendida is a small, laterally compressed fish
rarely exceeding 100 mm SL and 16 g. This species is typically between 60–80 mm SL in length although it is capable of reaching 115 mm SL in the wild [697] and 200 mm
SL in captivity [936]. Males grow to a larger size than do
females although the relationship between length and
weight does not vary between the sexes [1108]. The relationship between length (SL in mm) and weight (g) for
Johnstone River population takes the form: W = 1.73 x
10–5 L2.986; r2 = 0.962, n = 1965, p<0.001. Individuals from
the upper Burdekin River population are slightly heavier
for a given length: W = 2.01 x 10–5 L3.020; r2 = 0.956, n
=1880, p<0.001. Mouth terminal and oblique; almost
reaching back to anterior margin of eye, 11.2% of SL.
The larvae are about 4 mm at hatching, moderately welldeveloped, with functional eyes, mouth and gut, and with
211
Freshwater Fishes of North-Eastern Australia
Burdekin River M. s. splendida are deeper in the body than
are populations from elsewhere. The data presented in
Table 1 only partly support this suggestion, with this effect
being confined to smaller fishes only. However, as indicated above, the Burdekin River population is slightly
heavier for a given length than populations from the
Johnstone River.
little yolk deposits. Gut coiled and striated in preflexion
larvae (in contrast to the larvae of M. eachamensis). Anal
fin fold originates behind anal myomere. Melanophores
diffusely distributed along dorsal surface. Metamorphosis
occurs at 14 mm SL [609, 1093].
Body morphology in this species is highly plastic, varying
between the sexes, between individuals from different
drainages, between individuals from different habitats
within drainages, and with size. In the latter case, the relationship between diagnostically important morphological
ratios and body size is rarely linear but varies exponentially with the exponent value varying between 0.666 (for
eye diameter) to 1.055 (for peduncle length). Body depth
at the pelvic fin is the only parameter to vary linearly with
size (exponent = 0.990) [1105]. Table 1 lists the maximum
and minimum values for a range of meristic and morphological characters for 358 M. s. splendida from the Wet
Tropics region (Bloomfield River to the Herbert River)
and 41 individuals from the main channel of the upper
Burdekin River. The Wet Tropics sample did not include
any individuals from streams in which either M.
eachamensis or M. utcheensis were known to occur and
there is therefore a low probability that the sample
contains hybrid forms.
Systematics
Melanotaenia splendida is a member of a widespread and
important family of freshwater fishes in Australia, New
Guinea and Madagascar. Melanotaenia is a widespread and
speciose genus, represented by 13 species in Australia [38,
52, 904]. Allen [32] recognised it as one of the most
derived genera within the family. Recent phylogenetic
analysis of mtDNA cytochrome b and tRNA control
region sequence data is broadly consistent with the current
taxonomy but also indicates that a clade restricted to
northern New Guinea, consisting of M. affinis, M. japensis
and three species of Glossolepis, is polyphyletic [905].
Melanotaenia splendida was previously recognised as being
composed of a number of geographically isolated subspecies: M. splendida splendida (eastern rainbowfish), M. s.
inornata (chequered rainbowfish), M. s. tatei (desert rainbowfish), M. s. rubrostriata (red-striped rainbowfish), M.
s. australis (western rainbowfish) and M. s. fluviatilis
(Murray-Darling rainbowfish). Melanotaenia splendida
fluviatilus was removed from this group and elevated to
full species status (as M. fluviatilus) by Crowley et al. [351]
(in the process reinstating M. duboulayi). The recent investigations of McGuigan et al. [905] further challenge the
view that the species consists of the five remaining subspecies, clearly showing that M. s. australis did not belong
to this species group but was part of a separate clade
consisting of M. s. australis, an undescribed species from
North Queensland (now recognised as M. utcheensis), M.
eachamensis, M. duboulayi and M. fluviatilus. This subspecies (M. s. australis) is now recognised as two valid and
distinct species, M. australis (Castenau, 1873) and M.
solata Taylor, 1964 [52]. The clade in which M. splendida
was placed by McGuigan et al., contained the remaining
subspecies plus M. parkinsoni, M. ogilbyi and M. sexlineata from southern New Guinea and M. maccullochi from
northern Australia and southern New Guinea. This clade
was poorly resolved however, suggesting that the evolution
of species and subspecies within it is relatively recent
[905]. In addition, substantial morphological, meristic
and colour variation between geographically distant
populations of M. s. splendida exists, indicative of substantial genetic diversity within the species and/or a highly
variable and plastic phenotype. Hurwood and Hughes
[618] demonstrated that M. s. splendida has experienced
a recent (in the last 100 000–120 000 years) and rapid
Table 1. Meristic and morphological variation between
geographically isolated populations of the eastern rainbowfish
Melanotaenia splendida splendida [1093]. Proportions given as
percentage of standard length.
Character
Wet Tropics region
Burdekin River
Dorsal spines
Dorsal rays
Anal rays
Pectoral rays
5–7
10–14
17–24
11–16
5–7
10–12
18–21
12–16
Horizontal scale rows
Vertical scale rows
Predorsal scales
Cheek scales
10–13
33–38
12–18
7–17
10–12
34–36
14–16
9–16
25–91
23.3–44.4
22.8–38.0
24.4–35.3
6.6–9.6
7.3–12.2
9.1–15.2
13.4–21.0
43.7–51.1
29–67
29.1–35.8
27.0–32.0
25.9–30.7
7.3–8.9
8.5–11.7
10.5–12.4
14.8–19.5
45.7–50.5
Standard length (mm)
Body depth – male (%)
Body depth – female (%)
Head length (%)
Snout length (%)
Eye diameter (%)
Caudal peduncle depth (%)
Caudal peduncle length (%)
Predorsal distance (%)
These data indicate that body form and meristic characterisics are highly variable, even within a relatively small
an area as the Wet Tropics region. Moreover, the extent of
variation that occurs within a region can be greater than
that between regions. Allen and Cross [43] suggest that
212
Melanotaenia splendida splendida
characteristic of M. s. inornata. The extent to which this
character can be validly used to distinguish between
subspecies is therefore questionable. In the phylogenetic
relationship depicted in McGuigan et al. [905] (their
Figure 3b – boot-strapped maximum parsimony
phylogeny based on combined cytochrome b and tRNAPro
control region sequence), it is noteworthy that one specimen of M. s. splendida from the Burdekin River grouped
with a Northern Territory M. s. tatei specimen whereas
another was included in an unresolved group consisting of
specimens of M. s. splendida from the Atherton
Tablelands, one specimen of M. s. inornata and one of M.
s. rubrostriata. Moreover, in a study of genetic variation in
M. s. splendida on the Atherton Tablelands by Hurwood
and Hughes [618], one specimen from the Walsh River (a
tributary of the Mitchell River and typically considered
within the range of M. s. inornata) was identified as being
a common splendida haplotype. It could be argued that the
Walsh River lies on the border between the distribution of
both subspecies and the presence of an eastern haplotype
in this region is not particularly surprising. However,
Hurwood has identified this same haplotype in the
Leichhardt River, which drains to the Gulf of Carpentaria,
and in the centre of what is traditionally considered the
distribution of M. s. inornata (D. Hurwood, pers. comm.).
expansion of range that may have contributed to the
genetic diversity observed in north-eastern Queensland.
Considerably more research is required to understand the
evolution of forms within the group and may be useful in
understanding the recent evolutionary history of other
groups also.
The Australian subspecific populations of M. splendida
are distinguished by a combination of differences in distribution, colour and slight differences in meristics.
Melanotaenia splendida splendida is said to be restricted to
rivers draining to the east of the Great Dividing Range, M.
s. inornata to streams draining to the Gulf of Carpentaria
and the Arafura Sea, and to the top of Cape York
Peninsula, and M. s. tatei is restricted to central Australia,
primarily to rivers draining into Lake Eyre [43, 52]. It can
be seen from Table 2 that morphological differences
between the subspecies are very slight and really only
serve to define M. s. tatei as being distinctive by virtue of
possessing fewer dorsal fin rays, fewer cheek scales, more
predorsal scales, a longer caudal peduncle and a more
slender body.
Table 2. Meristic and morphological variation in the subspecific forms of Melanotaenia splendida [43]. Proportions given
as percentage of standard length. (Note that ranges for some
characters differ from those listed in the description above.)
Character
M. s.
splendida
M s.
inornata
M s.
tatei
Dorsal spines
Dorsal rays
Anal rays
Pectoral rays
5–8
9–13
17–22
11–16
5–8
9–12
17–21
12–16
5–8
8–11
17–21
13–16
Horizontal scale rows
Vertical scale rows
Predorsal scales
Cheek scales
10–12
33–36
14–18
8–15
10–12
31–35
14–19
9–16
10–12
34–37
17–22
7–12
33.7–48.8
32.7–40.8
25.7–29.9
7.3–9.7
7.1–11.2
9.9–11.8
11.4–15.0
10.9–18.6
46.2–52.9
48.0–55.7
30.5–35.5
26.4–32.1
24.0–26.9
6.9–8.1
7.2–9.2
8.2–9.9
10.8–12.2
15.3–21.0
44.3–48.0
48.2–54.0
Body depth – male (%)
29.0–40.3
Body depth – female (%)
26.9–35.2
Head length (%)
24.4–30.5
Snout length (%)
7.3–10.8
Eye diameter (%)
7.2–10.8
Interorbital width (%)
8.8–10.5
Caudal peduncle depth (%) 10.6–13.2
Caudal peduncle length (%) 14.3–20.8
Predorsal distance (%)
45.2–51.0
Preanal distance (%)
48.0–54.7
Distribution and abundance
Clearly, the pattern of genetic and morphological variation within this species is very complex and, to our minds,
a belief in the existence of subspecific differences in
morphology, distribution and genetics between M. s.
splendida and M. s. inornata is very difficult to sustain at
this stage. Nonetheless, for those more disposed to recognising subspecific forms, the discussion below considers
only that taxon which most authors traditionally view as
the subspecific form M. s. splendida.
This subspecies is very widely distributed along the east
coast of Queensland [43]. Some authors suggest that the
southern limit of M. s. splendida is the Burnett River [1173]
or the Elliott River [825]. Kennard [700] believed such
records were attributable to M. duboulayi. Both Allen [38]
and Wager [1349] list the southern limit of its distribution as
the Boyne River near Gladstone, although Hansen [525]
reported the presence of M. s. splendida slightly further south
in small coastal streams of the Baffle Creek drainage basin.
The location of the northern limit of M. s. splendida is
uncertain. Pusey et al. [1099] recorded M. s. splendida in
the Pascoe River although Herbert et al. [571] believed this
population to be the subspecies M. s. inornata.However,
other authors have recorded M. s. splendida as far north as
the Pascoe and Lockhart rivers [1349]. Populations of M.
s. inornata do occur east of the Great Dividing Range in
According to Allen and Cross [43], M. s. splendida and M.
s. inornata differ only on the basis of colour pattern and
differences in body depth (deeper in the latter). However,
it can be seen from Table 1 that M. s. splendida from the
Wet Tropics region also approach the deep body form
213
Freshwater Fishes of North-Eastern Australia
Cape York Peninsula [571]. For example, this subspecies
is the dominant rainbowfish in aquatic habitats of the
Cape Flattery region [1088].
Melanotaenia s. splendida is abundant wherever it occurs.
It comprised 52%, 38% and 23% of the total catch in a
study of the fauna of the Pascoe, Stewart and Normanby
rivers, respectively [1099] and 18% of the total catch in
floodplain lagoons of the Normanby River [697]. This
species comprised 39% of the catch in the Annan River
[599]. Further south in the Wet Tropics region, it was the
most abundant species in an extensive survey of the
region, comprising 28.4% of the total number of fish
collected and being recorded in 62 of 93 sites and in all but
one of the drainage basins studied [1087]. It was not
recorded from the short streams of Cape Tribulation but is
known to occur in these streams (G. Werren, pers. comm.).
Table 3. Distribution, abundance and biomass data for
Melanotaenia splendida splendida in two rivers of the Wet
Tropics region. Data summaries for a total of 5021 individuals
collected over the period 1994–1997 [1093]. Data in
parentheses represent summaries for per cent and rank
abundance, and per cent and rank biomass, respectively, at
those sites in which this species occurred.
Total
% locations
% abundance
Rank abundance
% biomass
44.9
14.3 (22.8)
Mulgrave
River
Johnstone
River
47.7
62.5
Macro/mesohabitat use
Allen [38] suggests that the preferred habitat of eastern
rainbowfish consists mainly of small streams. However,
over its very wide distribution, this species occurs in a wide
variety of stream sizes from small streams up to large, lowgradient lowland rivers including wetland habitats and
floodplain lagoons [697, 1087, 1098]. Within the Burdekin
River, it is significantly more abundant in reaches with
little stream flow [1098] and this preference for habitats
with sluggish currents seems to be the general requirement
across all studies reviewed.
10.3 (18.9) 15.5 (26.7)
2 (2)
5 (3)
2 (1)
1.9 (6.3)
1.3 (5.8)
2.3 (4.2)
8 (6)
6 (5)
Rank biomass
6 (5)
Mean density
(fish.10m–2)
1.43 ± 0.21
1.01 ± 0.22 1.62 ± 0.02
Mean biomass
(g.10m–2)
3.69 ± 0.58
3.45 ± 0.75 3.80 ± 0.03
is susceptible to bias depending on collecting method
used. For example, in the Burdekin River [1098], this
species comprised 32% of the total in electrofishing
samples but contributed 49% of the seine-netting total.
Even greater disparity between methods was reported by
Burrows and Tait [260]. Their study, in tributary drainages
of the upper Burdekin River, found that rainbowfish
contributed 1.3%, 12.4%, 24%, 37.6% and 82% of bait
trap, gill-net (with 25 mm mesh panels), dip-net, electrofishing and seine-netting catches, respectively. It is our
experience that single pass electrofishing nearly always
underestimates the abundance of M. s. splendida because
of this species’ vagility, swimming speed and preference
for open water. The difficulty in collecting this species by
some methods, particularly those methods favoured by
some agencies (i.e. single pass electrofishing) or consultants (i.e. fish traps), highlights the need for rigorous
sampling especially in studies aimed at determining environmental condition or river health. Melanotaenia splendida splendida is tolerant of environmental degradation,
particularly the loss of riparian vegetation and changes in
habitat due to impoundment, and may have potential as
an indicator species in rapid assessments.
Melanotaenia s. splendida is both widespread and abundant in the Johnstone and Mulgrave rivers (Table 3),
contributing about 14% of the total number of fish
collected from these rivers. This species is dominant in
those sites in which it occurs in the Johnstone River,
contributing over one-quarter of the total number of fish
and 4.2% of the biomass. It is less dominant in the
Mulgrave River however, being only the fifth most abundant species overall and third most abundant species in
those sites in which it occurs. Maximum density estimates
for this species were 3.08 fish.10m–2 and 7.23 fish.10m–2
for the Mulgrave and Johnstone rivers, respectively.
The generalist nature of habitat use is evident from the
data presented for drainages of the Wet Tropics region also
(Table 4). Melanotaenia s. splendida occurred in a large
range of streams sizes (order 1 to 6) and over a wide range
of elevation (5–750 m.a.s.l.). Downstream limits to distribution and abundance are probably related more to predation than aversion to particular environmental conditions.
Pusey and Kennard [1087] suggested that this species was
one of the few able to negotiate large waterfalls and
colonise upland habitats. Recent genetic investigations
question the generality of this suggestion and upland
populations may have arrived in rivers of the Tablelands
by other mechanisms, such as drainage rearrangement,
not involving upstream movement [618].
The relative abundance of M. s. splendida is usually high,
often being the most abundant species in most environments. However, the estimation of rainbowfish abundance
Although occasionally present in high gradient streams (i.e.
maximum gradient of 7.3%), the average gradient of the
streams in which it occurs in the Wet Tropics region
214
Melanotaenia splendida splendida
There is little indication that M. s. splendida is greatly
dependent on any one type of cover element and the
habitats in which it occurs contain a variety of types and
amounts of cover. However, the difference between the
mean and weighted mean coverage of submerged vegetation (composed entirely of the introduced para grass
Brachiaria mutica), shown in Table 4, suggests that this
species achieves greater abundance in habitats relatively
free of this weed.
is much lower (0.5%), with a slight tendency for M. s.
splendida to be more abundant in reaches with a more
gentle gradient. Four other species of rainbowfish
(M. maccullochi, M. eachamensis, M. utcheensis and C.
rhombosomoides) also occur in the Johnstone River
drainage and although syntopy does occur occasionally,
there is a general tendency for distributions to be non-overlapping at the mesohabitat scale, with M. s. splendida being
more abundant in the larger, less steep and more open
streams. Melanotaenia maccullochi in the Johnstone River
is found only in small, lowland low-gradient acidic streams.
It must be emphasised that the data presented in Table 4
concerns habitat use in perennial rainforest streams of the
Wet Tropics region. Given the widespread distribution of
this species and the generalised habitat use indicated by
Table 4, it is probable that a much wider array of habitat
conditions is used. For example, M. s. splendida is one of
the few species that tolerates, and is even advantaged by,
Melanotaenia s. splendida is found in a variety of habitat
types, from cascades to pools, and accordingly, this species
occurs over a wide range of substrate types. The average
substrate composition is very diverse, reflecting the wide
range of habitat types in which it occurs. In larger, more
seasonal rivers of Cape York and central Queensland, the
substrate composition is much more dominated by the
finer particle sizes.
50
Table 4. Macro/mesohabitat use by the eastern rainbowfish
Melanotaenia splendida splendida in the Wet Tropics region.
Summaries drawn from habitat data from 56 sites in the
Johnstone, Mulgrave/Russell and Tully drainages and
weighted means derived from macro/mesohabitat data for
2016 individuals.
Parameter
Min.
0.13
Catchment area (km2)
Stream order
1
Distance to source (km)
0.5
Distance to river mouth (km) 10.1
Elevation (m.a.s.l.)
5
Width (m)
2.8
Riparian cover (%)
0
Gradient (%)
0.001
Mean depth (m)
0.11
Mean water velocity (m.sec–1) 0
Max.
Mean
W.M.
515.5
6
67.0
104.0
750
35.0
99
73.6
3.7
14.4
38.7
103.2
9.7
35.2
74.9
3.8
15.9
47.1
194.0
10.2
31.5
7.33
0.91
0.56
0.50
0.40
0.16
0.40
0.46
0.13
Mud (%)
Sand (%)
Fine gravel (%)
Gravel (%)
Cobbles (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
48
88
72
56
55
81
68
7.5
18.4
22.5
14.5
13.9
17.0
6.6
9.2
17.3
20.9
12.6
11.1
19.3
10.7
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Small woody debris (%)
Large woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
23.7
6.9
33.0
63.1
10.0
81.2
12.3
10.5
35.0
75.0
1.3
0.3
2.3
9.0
0.6
10.4
2.0
2.3
5.6
13.4
1.7
0.5
2.5
6.3
0.5
8.2
1.7
2.3
5.0
12.1
(b)
(a)
50
40
40
30
30
20
20
10
10
0
0
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
20
20
10
10
0
0
20
(e)
Relative depth
Total depth (cm)
(f)
20
15
10
10
5
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Melanotaenia splendida
splendida. Data derived from capture records for 1234 fish
from the Johnstone, Mulgrave/Russell and Tully rivers over the
period 1994–1997.
215
Freshwater Fishes of North-Eastern Australia
Table 5. Physicochemical data for eastern rainbowfish M. s.
splendida. Data summaries derived from: 1) a study undertaken
during the dry season of 1990 in the Pascoe, Stewart and
Normanby rivers of Cape York Peninsula [1099]; 2) a study
undertaken in six floodplain lagoons of the Normanby River
over a six month period in 1993 encompassing the start and
end of the dry season [697]; 3) unpublished data from a study
of fish assemblages in the Johnstone and Mulgrave rivers of
the Wet Tropics region over the period 1994–1997 [1093];
and 4) a study of fish assemblages at 12 sites in the Burdekin
River over the period 1989–1992 [1093].
the change from lotic to lentic habitat conditions caused
by impoundment. In general however, M. s. splendida is
best considered as preferring larger streams with low water
velocities. This species is moderately tolerant of disturbance such as reductions in riparian canopy.
Microhabitat use
Data shown in Figure 1 was derived from records for 1234
fish collected from rivers of the Wet Tropics region and as
such the patterns therein may not apply entirely to other
regions. Most individuals were collected from areas of low
flow (<0.3 m.sec–1) and most commonly, from areas with
no discernible flow. Focal velocities were similar to average
velocities due to the generally low currents speeds overall
and because the most common position in the water
column of M. s. splendida was around that at which average water velocity occurs. Most individuals were found in
the middle two-quarters of the water column.
Parameter
Min.
Max.
Cape York Peninsula (n = 12)
Temperature (°C)
21.0
29.5
Dissolved oxygen (mg.L–1)
6.8
10.0
pH
6.09
8.35
Conductivity (µS.cm–1)
20
420
Turbidity (NTU)
0.1
3.3
Within streams of the Wet Tropics region, most rainbowfish were collected from depths of between 20–70 cm with
few recorded from areas shallower than 20 cm and deeper
than 80 cm. The upper limit may reflect a bias due to the
absence of many sites with depths greater than 1 m in our
study. In floodplain lagoons of the Normanby River, M. s.
splendida frequently occurs in depths greater than 2 m,
although most were collected in water less than 1.5 m
[697]. In this habitat type, it was rare for rainbowfish to be
collected from the bottom 70% of the water column,
perhaps in response to the hypoxic conditions existing at
such depths. Rainbowfish were collected over a variety of
substrate types, reflecting the diversity of habitats in which
it occurs (Table 4), and indicating little preference for any
particular substrate composition.
Mean
25.4
8.0
7.07
127
1.46
Floodplain lagoons Normanby River (n = 11)
Temperature (°C)
22.9
28.3
25.2
Dissolved oxygen (mg.L–1)
1.1
7.1
3.39
pH
6.0
7.5
6.87
Conductivity (µS.cm–1)
80.9
252.5
163.5
Turbidity (NTU)
2.1
7.7
4.9
Wet Tropics Region (n = 79)
Temperature (°C)
17.1
Dissolved oxygen (mg.L–1)
4.91
pH
5.13
Conductivity (µS.cm–1)
6.0
Turbidity (NTU)
0.25
Burdekin River (n = 41)
Temperature (°C)
15
Dissolved oxygen (mg.L–1)
1.1
pH
6.87
Conductivity (µS.cm–1)
49
Turbidity (NTU)
0.6
Melanotaenia s. splendida is predominantly an open-water
species but is frequently found schooling in close proximity
to cover, of which it makes use when threatened (Fig. 1f).
29.7
11.6
8.38
65.6
12.19
23.0
7.08
6.98
36.3
1.79
32.5
10.8
8.47
790
16.0
26.3
6.77
7.73
390
3.5
that determined experimentally and reported above. For
example, 29.7°C was the maximum water temperature
recorded in rainforest streams of the Wet Tropics region
(over the period 1994 to 1997) and moribund fish were
observed on this occasion: although depressed oxygen
levels at this time may have been a contributing factor also.
No data on the lower temperature tolerance limit of this
species is available, although low temperatures have been
suggested to be important in setting the southern distributional limit for M. s. splendida [1105] and southern distributional limits for other rainbowfishes [43]. Occasional
frosts on the Atherton Tablelands may result in water
temperatures approaching 10°C and captive rainbowfishes
die at this temperature. The incidence of fungal infection
in rainbowfish populations in the Wet Tropics region is
greatest during the winter months [1093].
Environmental tolerances
Melanotaenia splendida splendida is one of the few northeastern Australian fish species for which tolerance data of
any kind exist. LD50 temperatures of 34.4°C and 31.4°C
for adult (53–71 mm) and juvenile (24–32 mm) fish,
respectively, have been determined experimentally [174].
Tolerance to elevated temperatures may be slightly higher
in wild populations of some regions. For example,
summer water temperatures frequently exceed 31°C in the
Burdekin River (and elsewhere; i.e. Black-Alice River
[176]) and yet on such occasions, we have seen little indication of heat-related mortality.
Conversely, populations from some regions may exhibit
a reduced tolerance to elevated water temperatures than
216
Melanotaenia splendida splendida
values listed in Table 5 occurred during a runoff event and
it is not known how long such high turbidities might be
tolerated. However, rainbowfish are present in the highly
turbid waters occurring in the south-western portion of
the Burdekin drainage (i.e. Belyando River) and water
bodies in which M. s. splendida occurs in this river range in
turbidity from 172 to 520 NTU [256].
Data presented in Table 5 suggest a preference for welloxygenated waters, however it is evident that low dissolved
oxygen levels are experienced in some habitats. Kennard
[697] was uncertain whether the lagoons of the Normanby
River floodplain remained stratified throughout the day
and whether the observed hypoxia persisted for an
extended period. Nonetheless, this species was abundant
in these habitats. Melanotaenia s. splendida has been
recorded in wetlands of the Tully Murray system in which
dissolved oxygen in the bottom layers had dropped to 0.2
mg.L-1 (i.e. almost complete anoxia) [583]. Fish probably
avoid such anoxic conditions and stay in the upper water
column. A dissolved oxygen level of 4 mg.L–1 would probably be adequate to protect eastern rainbowfish populations in most circumstances. It may not be high enough
for populations in rainforest streams of the Wet Tropics
region however.
It is clear that M. s. splendida tolerates a large range of
water quality conditions and this probably accounts in
part for its widespread distribution and varied habitat use.
It would be extremely useful to know something of its
tolerance to pesticides and herbicides and thus allow better
examination of its potential as an indicator species.
The range in water acidity across the different regions
given in Table 5 is substantial (5.13–8.47) and indicates a
well-developed tolerance to a variety of pH conditions
despite mean values tending to be around neutral. The
range in pH recorded for the Cape York populations
(range = 2.35 units) and for the Burdekin River (1.60
units) is much less than that recorded across the three
regions (range = 3.34 units), suggesting that different
populations may be adapted to localised water conditions
and may not tolerate as wide a range of conditions as is
recorded for the subspecies over its entire range.
However, it is noteworthy that the range encountered
within the streams of the Wet Tropics region (3.25 units) is
almost as great as that over the three regions.
Tolerance to elevated salinity varies between adult and
juvenile fishes and according to acclimation history [174].
Juvenile rainbowfish do not survive abrupt transfer to
salinities of 9‰ and adult rainbowfish are unable to tolerate abrupt transfer to salinities of 15‰, dying within 12
hours of transfer. Gradual acclimation improves survivorship but only marginally so: juvenile fish are able to tolerate 17.8‰ for 14 days, adults are able to tolerate 35.5‰
for five days [174]. Wild populations have been recorded
from salinities as high as 13 500 µS.cm–1 (approx. 13‰)
[1085] and 15.2‰ [176]. Given such a tolerance, M. s.
splendida is likely to be able to withstand short-term exposure to seawater in tidally influence habitats and perhaps
even move through brackish estuarine habitats. However,
it is clear that the eastern rainbowfish is most frequently
collected from freshwater and tolerates very low levels of
dissolved solutes (ie. 6 µS.cm–1) as well as more elevated
levels within the freshwater spectrum.
Reproduction
Information concerning the reproductive biology of M. s.
splendida is available for two river systems of contrasting
hydrology (Table 6). The Black-Alice River near Townsville
is hydrologically variable. Lowland populations in this
river are reproductively active throughout the year
although peak spawning occurs during the wet season
[173]. This pattern is also observed in lowland populations
of M. s. inornata [193]. In contrast, although a proportion
of the populations present in rainforest streams of the Wet
Tropics region are reproductively active year-round also,
the majority of reproduction occurs in the warmer
months leading up to the wet season [308]. Larval mortality is very high at the beginning of the wet season in this
region, particularly in deeply incised streams [1109]. In
both regions, fish mature at small size and breed in their
first year. It is unlikely that many individuals live in excess
of two years.
There is little indication of a critical spawning temperature although little spawning has been observed in
temperatures below 20°C and 21°C in the Johnstone and
Black-Alice river, respectively. Beumer [173] believed
lengthening photoperiod was more important as a spawning stimulus than was increasing temperature. In the
Johnstone River, spawning commences after attainment of
set size limits rather than in response to any environmental cue [308]. Nonetheless, the majority of larvae are
produced during periods of predictably low and stable
flows. Males perform elaborate courtship displays and
compete for females.
Melanotaenia s. splendida is a moderately fecund species,
although peak mean female GSI values (4–5%) are not
especially high. This species is a heterochronal spawner
with the eggs being produced in batches (up to 14% of
total egg number), thus instantaneous GSI values do not
fully reveal the extent of maternal investment. Egg number
and batch size increase with increasing female body size. It
The data presented in Table 5 indicate that eastern rainbowfish are found in waters of a range in clarity. The peak
217
Freshwater Fishes of North-Eastern Australia
Table 6. Life history data for the eastern rainbowfish Mealnotaenia splendida splendida. Data are drawn from studies undertaken
in the Johnstone River (JR) [1093] and the Black-Alice River (BAR) [173], and detailed in the text.
Age at sexual maturity (months)
<1 (probably 6–7 months)
Minimum length of ripe females (mm)
JR – 38 mm (mean = 55.2)
BAR – 38 mm (range = 38–101)
Minimum length of ripe males (mm)
JR – 44 mm (mean = 75)
BAR – 38 mm (range = 38–105)
Longevity (years)
1–2, rarely 3 years, longer in captivity
Sex ratio
BAR – 1:1 with occasional female excess in period leading up to wet season
Occurrence of ripe fish
JR – year round
BAR – year round
Peak spawning activity
JR – strongly focused between August and November
BAR – strongly focused between December and February
Critical temperature for spawning
JR – varies depending on position in catchment, generally 20°C
BAR – temperatures above 21°C
Inducement to spawning
JR – attainment of minimum reproductive size limit, little evidence of environmental
cues although spawning occurs during period of stable low flow
BAR – unknown but increased photoperiod stimulates increased spawning activity
Mean GSI of ripe females (%)
JR – 3.7%
BAR – 3.0%
Mean GSI of ripe males (%)
JR – 0.7%
BAR – 0.4%
Fecundity (number of ova)
JR – maximum fecundity of 1655 eggs for 70 mm SL fish (yolked eggs only)
Fecundity/length relationship
JR – log (egg number) = 1.86 + 0.018 (SL in mm); r = 0.644, p<0.001, n = 185
Egg size (mm)
JR – 1.124 mm for ovulated unfertilised eggs; many size classes of eggs present in ovary
BAR – size of ovulated eggs not given, largest eggs present 0.8–1.0 mm, fertilised and
water-hardened eggs ranged from 0.95–1.73 mm
Frequency of spawning
JR – continuous when temperatures >20°C although majority of spawning complete
before wet season. Eggs produced in batches of 2–177 eggs
BAR – spawning period suggested to be 10–14 days
Oviposition and spawning site
Adhesive eggs deposited amongst aquatic vegetation or root masses
Spawning migration
BAR – upstream migration at onset of wet season
Parental care
Absent – parents will eat young
Time to hatching
BAR – 7–12 days, temperature dependent
Length at hatching (mm)
JR – early preflexion larvae range from 3.92–4.62 mm
BAR – 2.96 mm (range = 2.1–3.47)
Length at free swimming (mm)
As above
Length at feeding
Between 4–5 mm (mid-preflexion)
Duration of larval development
?
Length at metamorphosis
10–14 mm
Survivorship
Very high larval mortality recorded at the onset of the first wet season flood
feeding prior to flexion of the notochord [308]. Larvae are
capable of swimming almost immediately upon hatching
[609] but remain in very low flow environments until
metamorphosis is completed [1109]. Channel morphology, particularly the degree to which the channel is
constrained by deeply incised banks, and the availability of
flow refuges (eddies and backwaters) are important determinants of flow-related mortality. Reproduction in Wet
Tropics streams may continue well into the wet season in
those habitats offering some protection from elevated
flows (i.e. backwaters and anabranch channels) [1109].
Further information on reproduction and early develop-
is probable that batches are fully voided before the next
cohort develops. The eggs possess adhesive filaments,
allowing them to be deposited safely amongst the leaves or
water plants or amongst root masses. Egg size is apparently
geographically variable, being larger in the stable streams
of the Wet Tropics region. Parental care is lacking and
hatching occurs after 7–12 days. Humphrey et al. [609]
report more rapid embryonic development: 3–9 days, with
~60% of each batch hatching after five days at 28 ± 1°C.
Larvae are small and undeveloped at hatching but possess
little yolk reserves. The eyes, mouth and gut develop
rapidly and it is probable that this species commences
218
Melanotaenia splendida splendida
ment of M. s. inornata can be found in Crowley and
Ivantsoff [344].
Movement
Limited information concerning the extent and pattern of
movement in this species is available. An upstream migration at the commencement of the wet season has been
recorded in the Black-Alice River near Townsville [173].
Lateral migrations in floodplain environments are
reported in the Normanby River [697]. Upstream movement through a fishway on the Fitzroy River was detected
over many months but most commonly occurred during
the period from November to April [1274]. The total
number of individuals using this fishway (88) was low,
however. Upstream migrations to dry season refugia have
been recorded for the closely related subspecies M. s. inornata in the Northern Territory, with migration occurring
during daylight hours and at rates of between 4.8 and 5.4
km.day–1 [190]. No evidence to suggest migration in areas
with perennial flow (i.e. Wet Tropics) but it may occur.
Further research is required to assess the extent of movement of this species in more seasonal Queensland rivers
and on its ability to ascend and descend fishways.
Trophic ecology
Data presented in Figure 2 were derived from gut analysis
of a total of 2567 individuals drawn from four separate
studies: three rivers of Cape York Peninsula (n = 445, dry
season only) [1099]; floodplain lagoons of the Normanby
River (n = 211, combined early and late dry seasons) [697];
Annan River (n = 6) [599], two rivers of the Wet Tropics
region (n = 256, dry season only) [1097]; and the Burdekin
River (n = 1681, over the period 1989–1992) [1093].
Fish (0.1%)
Macrocrustaceans (0.1%)
Molluscs (0.2%)
Microcrustaceans (1.5%)
Other macroinvertebrates (2.1%)
Unidentified (12.9%)
Terrestrial invertebrates (12.3%)
Aquatic insects (19.2%)
Aerial aq. Invertebrates (2.5%)
Terrestrial vegetation (1.7%)
Detritus (2.3%)
Aquatic macrophytes (2.6%)
Algae (42.5%)
Figure 2. The mean diet of the eastern rainbowfish
Melanotaenia splendida splendida. Data derived from stomach
content analysis of 2599 individuals from several northern
Queensland rivers and encompassing riverine and floodplain
habitats (see text for details).
219
Melanotaenia splendida splendida is an omnivorous feeder
taking small aquatic invertebrates (such as chironomid
larvae, ephemeropteran nymphs, trichopteran larvae)
from the stream-bed, as well as aerial forms of aquatic
insects and terrestrial insects (especially ants) from the
water’s surface. Collectively, these two components
account for 34% of the diet.
The single largest component of the diet is algae, comprising almost 43% of the diet. In general, filamentous algae
was the most important source of material within this
category although diatoms were important in the diet of
fish from the South Johnstone River (58% of dry season
diet, n = 94) and in the late dry season diet of rainbowfish
in floodplain lagoons of the Normanby River (19%, n =
87). Aquatic macrophytes (2.3%) were also consumed
occasionally by M. s. splendida. The extent of herbivory
varies with age and size, and probably according to the
availability of other food sources. For example, the diet of
fish between 15–30 mm SL (n = 233) in the Burdekin River
contained 25% filamentous algae, whereas the diet of fish
between 31–50 mm SL (n = 578) contained 41%, and that
of fish >51 mm SL (n = 868) contained 68% filamentous
algae. Temporal variation in the importance of herbivory
was also evident in the Burdekin River. During periods of
low flow, algal consumption rose to an average of 62%
over all age classes but decreased to 45% when flows were
elevated. In part, this effect was due to temporal changes
in the size distribution of the population but also was
related to an increased abundance of small invertebrate
prey during the wet season. Kennard [697] also noted
temporal variation in dietary composition in floodplain
lagoons. At the end of the wet season, herbivory and
planktivory contributed 9.4% and 22.3% of the diet,
respectively. By the late dry season, however almost no
planktonic crustaceans were present in the diet (0.8%)
whereas herbivory had increased in importance to 30.4%.
In addition to the temporal variation in diet discussed
above, substantial differences between diets across the four
studies (and equating primarily to habitat-related differences) were noted. For example, terrestrial invertebrates
were very important to the floodplain fishes (20.5%),
moderately important in the low-gradient seasonal rivers
(12.3% and 10.6%, for rivers of Cape York Peninsula and
the Burdekin River, respectively) but comprised only 2.2%
of the diet in the higher-gradient rainforest rivers.
Microcrustacea (mostly Cladocera) were all but absent
from the diet of riverine populations but comprised 12.3%
of the diet of the floodplain population. These data indicate that the generalism discussed above with respect to
habitat use extends to feeding ecology also. Eastern rainbowfish are omnivorous and possess sufficient flexibility
in feeding modes to allow them to track changes in the
Freshwater Fishes of North-Eastern Australia
fishes such as barramundi, eels, mangrove jack, sooty
grunter, spangled perch, fork-tailed catfish and jungle
perch. Piscivorous birds, especially kingfishers, also eat this
species.
availability or abundance of different prey at different
levels of the water column, in different habitats, and as
food availability changes throughout the year.
Furthermore, in addition to the habitat-based and ontogenetic variability in diet reported above, rainbowfish in the
Burdekin River exhibit substantial phenotypic variation in
prey choice. The stomachs of many individuals contain
only one prey type such as ants or dragonfly eggs whereas
others may contain only chironomid midge larvae for
example. This suggests that this species forages on a particular food type within a patch until satiated. Bunn et al.
[248] noted considerable individual variation in isotopic
signatures among rainbowfishes in a lowland stream of the
Wet Tropics region suggesting substantial variation in diet
among individuals in this region also. Given that variation
in isotopic ratios represents differences in diet integrated
over a medium-term period (i.e. three months), this
observation suggests that individuals remain faithful to a
particular diet within the array of potential diets available
to this species (within the constraints imposed by body
and mouth size, and food availability) for a number of
months. Differences in the content of individual stomachs,
in contrast, represent variation at much shorter time scales
(i.e. hours or days). The substantial phenotypic variation
suggested by these observations may be one reason why
M. s. splendida is such a successful species able to reach
high abundance levels.
Conservation status, threats and management
Melanotaenia splendida splendida is listed as NonThreatened by Wager and Jackson [1353]. This taxon is
probably very secure by virtue of its widespread distribution, abundance and broad environmental tolerance.
Eastern rainbowfish prefer low-flow environments, especially for reproduction and development. Care should be
taken when assessing the environmental flow requirements of this species given that its reproductive biology
(in particular) varies from region to region in relation to
regional variation in hydrology. Changes in the seasonality
of flows (i.e. through supplementation or downstream
releases to satisfy dry season irrigation demands) are likely
to negatively impact on this species, especially on larvae
and juveniles. In those rivers in which spawning occurs
during the period when flooding is most likely, floods may
greatly expand the habitat available to juveniles and thus
increase recruitment success. Flooding may also be necessary to allow fish to move between river channel and
floodplain habitats. This species will persist and thrive in
impounded habitats. This species may have considerable
value as an indicator species but more information
concerning its tolerance to water quality extremes and to
biocide contamination is needed.
Melanotaenia splendida splendida is consumed by other
220
Melanotaenia duboulayi (Castelnau, 1878)
Duboulay’s rainbowfish, Crimson-spotted rainbowfish
37 245004
Family: Melanotaeniidae
becoming deeper-bodied with age. Mouth oblique, upper
jaw protruding, mouth extending back almost to below
anterior margin of eye. Conical to canine-like teeth in
jaws, several rows extending outside mouth; teeth on
vomer and palatines. Head moderate in size, eye relatively
large. Scales large, extending to cheek. Origin of first dorsal
fin between origins of pelvic and anal fins; origin of
second dorsal behind origin of anal fin. First and second
dorsal fins separated by small gap. Caudal fin slightly
forked. Sexually dimorphic. Males with higher first dorsal
fin; tips of anal and dorsal fins pointed in males, rounded
in females. Males with deeper bodies and brighter body
colours, especially when mating. Colour patterns vary
depending on locality. Dorsal surface generally olivebrown, sides silvery to greenish-blue, ventral surface white,
yellow-orange towards tail. Most scales with dusky
margins. Thin, reddish stripe between each row of scales
(faint or missing in females); bright red spot on upper
operculum. Diffuse black midlateral stripe often present.
Fins clear in juveniles and females; males often with red
spots on caudal, dorsal and anal fins. Courting males often
with blackish margins on fins [38, 39, 52, 351].
Description
First dorsal fin: V–VIII; Second dorsal: I, 8–13; Anal: I,
15–21; Pectoral: 12–15; Pelvic: 5; Caudal: 15–17 segmented
rays; Vertical scale rows: 33–36; Horizontal scale rows:
11–13; Predorsal scales: 14–19; Gill rakers on first arch:
11–12; Vertebrae: 27–32 [39, 52, 351, 1093]. Figure: mature
male, 51 mm SL, Mary River, September 1995; drawn
1999.
Melanotaenia duboulayi is a small fish commonly less than
80 mm TL. Males may reach a maximum size of about 130
mm TL in captivity but do not exceed 90 mm TL in the
wild; females usually do not exceed 75 mm TL [39, 509].
Of 12 345 specimens collected in rivers and streams of
south-eastern Queensland, the mean and maximum
length of this species were 36 and 90 mm SL, respectively.
The equation best describing the relationship between
length (SL in mm) and weight (W in g) for 1093 individuals (range 16–82 mm SL) sampled from the Mary River,
south-eastern Queensland is W = 1.0 x 10–5 L3.124, r2 =
0.985, p<0.001 [1093].
The following description is derived largely from Allen
[39] and Crowley et al. [351]. Melanotaenia duboulayi is
a slender species with a laterally compressed body,
221
Freshwater Fishes of North-Eastern Australia
Queensland, south to the Hastings River in northern New
South Wales. This species is also present on Fraser Island
off the south-eastern Queensland coast [38, 39, 553, 1036,
1338]. All records of M. duboulayi north of the Baffle
Creek basin [328, 1173, 1349] are referable to M. s. splendida.
Systematics
Castelnau [284] originally described Melanotaenia
duboulayi in 1878 as Atherinichthys duboulayi and named
this species after its collector, a Mr Duboulay. There has
been considerable confusion surrounding the taxonomy
of this species and numerous synonyms exist (listed in
Crowley et al. [351]). For many years M. duboulayi was
considered synonymous with M. fluviatilis (Castelnau,
1878) [284], with various authors recognising a single
species, two subspecies (M. fluviatilis fluviatilis and M. f.
duboulayi) or a subspecies (M. splendida fluviatilis)
within the splendida group [351]. In 1986, M. fluviatilis
and M. duboulayi were recognised as separate species on
the basis of genetic, morphometric and meristic characteristics; although morphologically differences may be
slight, both species are distinguishable at all life history
stages [39, 351]. Melanotaenia duboulayi and M. fluviatilis
have disjunct distributions, M. fluviatilis occurring in
inland waters of the Murray-Darling Basin and M.
duboulayi occurring only in coastal areas of south-eastern
Queensland and northern New South Wales (see below).
Melanotaenia duboulayi is believed to be the first
Australian fish species to be kept in captivity and there are
records of this species being sent to Germany in 1927 and
maintained in aquaria there [38]. Both M. duboulayi and
M. fluviatilis are extremely popular aquarium species, but
have frequently been erroneously sold as M. nigrans; this
misidentification has been perpetuated throughout much
of the aquarium literature [38, 929].
Melanotaenia duboulayi is reported to have been introduced into North America in the late 1920s and there are
records of this species being caught in the Mississippi
River in 1930 [929]. Meiklejohn [71] suggested that this
may be one of the earliest accounts of the introduction of
an ornamental fish into the waterways of the United States.
Given the popularity of M. duboulayi as an aquarium specimen, it is likely that other introductions have been
attempted within and outside Australia.
Melanotaenia duboulayi is generally a very common
species, widespread within river systems and often locally
abundant, commonly forming schools of hundreds of
individuals [1093]. It was the second most abundant
species collected in a survey of Baffle Creek [826]; and was
reported as generally common in the Kolan River [658]. It
is very widespread and abundant in the Burnett River. In a
review of existing fish sampling studies in this catchment,
Kennard [1103] noted that M. duboulayi has been
collected at 44 of 63 locations surveyed (second most
widespread species in the catchment) and formed 4.9% of
the total number of fishes collected (fifth most abundant).
Small numbers were also collected in the Elliott River
[825] and rivers and streams of the Burrum Basin [157,
736, 1305].
Distribution and abundance
Melanotaenia duboulayi has a relatively narrow distribution in all coastal drainages from Mullet Creek (a small
coastal stream in the Baffle Creek drainage basin situated
just north of Baffle Creek proper) in southern-central
Surveys undertaken by us between 1994 and 2003 in catchments from the Mary River south to the Queensland–New
South Wales border [1093] collected a total of 19 103 individuals from 68% of all locations sampled (Table 1).
Table 1. Distribution, abundance and biomass data for Melanotaenia duboulayi in rivers of south-eastern Queensland. Data
summaries for a total of 19 103 individuals collected over the period 1994–2003 [1093]. Data in parentheses represent
summaries for per cent and rank abundance and per cent and rank biomass, respectively at those sites in which this species
occurred.
Total
% locations
% abundance
Rank abundance
% biomass
Rank biomass
67.8
Mary River Sunshine Coast Moreton Bay
rivers and
rivers and
streams
streams
84.0
11.70 (15.92) 10.40 (12.24)
Brisbane
River
Logan-Albert
River
South Coast
rivers and
streams
24.1
50.0
64.9
80.9
80.0
2.82 (12.53)
3.50 (9.73)
6.73 (13.17)
18.96 (26.68)
7.25 (9.05)
4 (1)
4 (3)
8 (3)
7 (3)
4 (2)
2 (1)
5 (5)
1.72 (2.56)
1.80 (2.84)
0.01 (0.35)
1.75 (3.04)
1.26 (1.74)
1.72 (2.25)
0.48 (0.72)
4 (4)
3 (3)
16 (9)
6 (3)
6 (4)
6 (5)
7 (5)
Mean numerical density
(fish.10m–2)
1.29 ± 0.09
1.15 ± 0.12
0.17 ± 0.04
0.35 ± 0.09
0.76 ± 0.17
2.20 ± 0.25
0.27 ± 0.05
Mean biomass density
(g.10m–2)
1.86 ± 0.12
1.93 ± 0.16
0.02 ± 0.00
3.65 ± 3.34
1.19 ± 0.41
1.96 ± 0.23
0.31 ± 0.12
222
Melanotaenia duboulayi
substrates (sand, fine gravel and coarse gravel) and particularly where submerged aquatic macrophytes, filamentous
algae, leaf litter beds, undercut banks and root masses are
common.
Overall, it was the 4th most abundant species collected
(11.7% of the total number of fishes collected) and was
very common at sites in which it occurred (15.9% of total
abundance). In these sites, M. duboulayi most commonly
occurred with the following species (listed in decreasing
order of relative abundance): P. signifer, R. semoni, C.
marjoriae and G. holbrooki. Melanotaenia duboulayi was
the 4th most important species in terms of biomass, forming 1.7% of the total biomass of fish collected. This species
was most widespread and abundant in the Mary, Brisbane,
Logan-Albert and South Coast basins, where it occurred
in over 65% of locations sampled and comprised more
than 6.7% of the total number of fish collected in each
basin. It was less common or widespread in the short
coastal streams of the Sunshine Coast and Moreton Bay
region. Across all rivers, average and maximum numerical
densities recorded in 656 hydraulic habitat samples (i.e.
riffles, runs or pools) were 1.29 individuals.10m–2 and
27.27 individuals.10m–2, respectively. Average and maximum biomass densities at 464 of these sites were 1.86
g.10m–2 and 19.93 g.10m–2, respectively (Table 1) [1093].
Table 2. Macro/mesohabitat use by Melanotaenia duboulayi in
rivers of south-eastern Queensland. W.M. refers to the mean
weighted by abundance to reflect preference for particular
conditions. Data summaries for 19 103 individuals collected
from samples of 656 mesohabitat units at 199 locations
between 1994 and 2003 [1093].
Parameter
Min.
2
Catchment area (km )
Distance to source (km)
Distance to mouth (km)
Elevation (m.a.s.l.)
Stream width (m)
Riparian cover (%)
5.6
4.0
0.5
0
1.1
0
Gradient (%)
0
Mean depth (m)
0.08
Mean water velocity (m.sec–1) 0
Distributional information and recent survey data indicate that M. duboulayi is widespread and relatively
common in northern New South Wales [82, 282, 553, 814,
1133].
Macro/mesohabitat use
Melanotaenia duboulayi is found in a range of lotic and
lentic habitats including large lowland rivers, upland rivers
and streams, small coastal streams, dune lake and stream
systems on Fraser Island, lakes, ponds and river impoundments (dams and weirs) [38, 39, 1093]. In New South
Wales this species has been classified as a pelagic pooldwelling species [553].
Melanotaenia duboulayi can be widespread within river
systems. In south-eastern Queensland freshwaters we have
collected this species between 0.5–335 km upstream from
the river mouth and at elevations up to 400 m.a.s.l. (Table
2), but it more commonly occurs within 140 km of the
river mouth and at elevations around 100 m.a.s.l. It is present in a wide range of stream sizes (1.1–44.2 m in width)
but is most common in streams around 8 m wide and with
moderate riparian cover (~48%). This species has been
recorded in a range of mesohabitat types but it most
commonly occurs in runs and pools characterised by lowmoderate gradient (weighted mean = 0.18%), moderate
depth (weighted mean = 0.43 m) and low to moderate
mean water velocity (weighted mean = 0.09 m.sec–1)
(Table 2). It also occasionally occurs in shallow riffles with
high gradient (maximum = 3.02%) and high water velocity (maximum = 0.84 m.sec–1). This species is most abundant in mesohabitats with fine to intermediate sized
Max.
Mean
W.M.
9926.8
255.0
335.0
400
44.2
91.0
613.8
43.8
144.5
94
9.3
39.6
322.1
37.6
140.1
103
8.0
47.9
3.02
1.10
0.85
0.35
0.42
0.12
0.18
0.43
0.09
Mud (%)
Sand (%)
Fine gravel (%)
Coarse gravel (%)
Cobble (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
0
0
76.4
100.0
67.2
78.2
66.8
55.0
70.0
5.8
18.9
21.2
26.3
19.6
6.6
1.6
7.2
22.6
24.0
26.7
14.4
3.8
1.3
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Large woody debris (%)
Small woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
86.1
65.9
45.0
65.7
39.1
92.6
31.0
21.4
88.3
100.0
11.9
7.8
1.7
5.5
1.6
13.2
4.4
3.5
14.8
20.2
13.6
7.4
1.8
3.7
1.8
11.9
5.6
4.0
15.8
22.8
Microhabitat use
In rivers of south-eastern Queensland, M. duboulayi was
most frequently collected from areas of low water velocity
(usually less than 0.1 m.sec–1) (Fig. 1a and b). It has been
recorded at maximum mean and focal point water velocity
of 1.28 and 0.82 m.sec–1, respectively. This species was
collected over a wide range of depths, but most often
between 10 and 60 cm (Fig. 1c). A pelagic schooling
species, it most commonly occupies the mid- to upperwater column (Fig. 1d). It is usually found over fine to
intermediate-sized substrates including mud, sand, fine
gravel and coarse gravel (Fig. 1e). It was often collected in
areas less than 1 m from the stream-bank (64% of individuals sampled) and in open water (16.5% of individuals
223
Freshwater Fishes of North-Eastern Australia
weed (Vallisneria spp.) in which other potentially piscivorous fish species (G. aprion, L. unicolor, A. reinhardtii and
T. tandanus) were observed. These authors also suggested
that changes in water temperatures caused by prevailing
sunlight influenced the microhabitat use of M. duboulayi.
In sunny conditions and during the middle of the day,
schools of juveniles were observed foraging in the warm
surface waters. Larger fish were more common in the
lower water column, as were juveniles during cloudy
condition [561]. In experimental aquaria, Brown [240]
examined the behavioural responses to fish predators of
M. duboulayi purported to originate from predatorsympatric and predator-naive populations. He reported
that M. duboulayi from the predator-sympatric population avoided the fish predator (L. unicolor), whereas those
from the predator-naive population did not display typical
predator avoidance activities, but noted that this behaviour could be learned with experience.
sampled) (Fig. 1f). It was collected in close association
with a wide range of submerged cover elements including
aquatic macrophytes, filamentous algae, overhanging and
submerged marginal vegetation, leaf litter beds, woody
debris and root masses (Fig. 1f). Little is known of larval
habitat use, although we frequently observed larval aggregations in the Mary River in similar habitats as adults,
especially in areas of low water velocity among submerged
marginal vegetation [1093].
(a)
(b)
60
60
40
40
20
20
0
0
25
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
30
Environmental tolerances
Harris and Gehrke [553] classified M. duboulayi as intolerant of poor water quality, but we have collected this
species over a relatively wide range of water quality conditions in south-eastern Queensland (Table 3). It was
recorded over a wide range of water temperatures
(8.4–31.7°C), dissolved oxygen concentrations (0.6–19.5
mg.L–1), water acidity (4.4–9.1), conductivity (51–4002
µS.cm–1) and turbidity (0.3–250 NTU) (Table 3).
20
20
15
10
10
5
0
0
Total depth (cm)
30
(e)
Relative depth
20
Table 3. Physicochemical data for Melanotaenia duboulayi.
Data summaries for 18 271 individuals collected from 414
samples in south-eastern Queensland streams between 1994
and 2003 [1093].
(f)
15
20
10
10
0
Substrate composition
5
Parameter
Min.
Max.
0
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
8.4
0.6
4.4
51.0
0.3
31.7
19.5
9.1
4002.0
250.0
Mean
19.6
7.6
7.6
501.5
6.4
Microhabitat structure
Studies of salinity tolerances of the eggs and fry of M.
duboulayi from coastal New South Wales revealed that
experimental chronic (four-day) LD50s were 22 ppt and
21 ppt for eggs and fry, respectively [559, 560, 1405]. These
salinity levels were somewhat higher than those tolerated
by M. fluviatilis. Salinity tolerances of adult fish are not
available. Melanotaenia duboulayi is used by the Sydney
Water Board for real-time continuous monitoring of the
open water-supply canals for contamination by toxicants
[665]. This species was reported to be useful for detecting
ammonia and chlorine contamination events caused by
Figure 1. Microhabitat use by Melanotaenia duboulayi. Data
derived from capture records for 3086 individuals from the
Mary and Albert rivers, south-eastern Queensland, over the
period 1994–1997 [1093].
Hattori and Warburton [561] examined the microhabitat
use of M. duboulayi by underwater observation in a tributary stream of the Mary River, south-eastern Queensland.
Fish were reported to be more abundant in areas with
aquatic macrophytes, but avoided dense beds of ribbon
224
Melanotaenia duboulayi
and aquarium studies [84, 351, 509, 770, 797, 950, 1093,
1133]. Details are summarised in Table 4. This species
spawns and completes its entire life cycle in freshwater and
is easily bred in captivity [38, 770, 794, 797]. Maturation
commences at a relatively small size. Minimum and mean
lengths of early developing (reproductive stage II) fish
from the Mary River, south-eastern Queensland, were 21.9
mm SL and 42.3 mm ± 0.7 SE, respectively for males and
26.1 and 38.4 mm ± 0.8 SE, respectively for females (Fig.
2). Gonad maturation in both sexes was commensurate
with somatic growth, the mean length at each reproductive stage being generally different from all other stages
(Fig. 2). Gravid (stage V) females were slightly smaller than
males of equivalent maturity (minimum 26.8 mm SL,
mean 49.0 mm ± 0.5 SE for females; minimum 36.4 mm
SL, mean 54.0 mm ± 2.0 SE for males).
malfunctions of water treatment equipment, however it
appears to be less suitable for detecting cyanobacterial
toxins. Laboratory experiments revealed that the respiratory system of M. duboulayi is unaffected by short-term
exposure to potentially toxic microcystin (up to 2.6
µg.mL–1) or other cyanobacterial compounds [665].
Melanotaenia duboulayi is also reported to be comparatively tolerant to endosulfan exposure (96-hour LC50:
0.5–11.4 µg.L–1, depending on test method) [1280].
Arthington el al. [95] conducted laboratory experiments to
establish the chronic lower thermal tolerances of adult M.
duboulayi using fish from south-eastern Queensland. Fish
acclimated for four days at 15°C, lost orientation at 5.7°C
and moved only spasmodically at 4.2°C [95]. Ham [502]
reported little difference in the lower temperature tolerance of juvenile and adult M. duboulayi from south-eastern
Queensland. Fish acclimated for seven days at 15°C were
observed to lose orientation at temperatures of about
3.5°C, move spasmodically at 2.2°C and cease movement
completely at about 1.8°C [502]. Fish acclimated for seven
days at 10°C were reported to have a significantly greater
tolerance of low water temperatures, losing orientation at
temperatures of about 2.8°C, moving spasmodically at
1.8°C and ceasing movement completely at about 1.5°C
[502]. Upper thermal tolerances for M. duboulayi are not
available.
Reproductive stage
I
II
III
IV
V
Males
100
(93) (34) (21) (25) (100) (7)
(56) (59) (48) (13) (37)
80
60
Reproduction
Quantitative information on the reproductive biology and
early development of M. duboulayi is available from field
40
20
0
55
Males
50
Females
Females
100
45
80
40
60
(82) (55) (29) (30) (137) (30)
( 51) (91) (36) (14) (16)
40
35
20
30
0
25
I
II
III
IV
V
Month
Reproductive stage
Figure 2. Mean standard length (mm SL ± SE) for male and
female Melanotaenia duboulayi within each reproductive
stage. Fish were collected from the Mary River, south-eastern
Queensland, between 1994 and 1998 [1093]. Samples sizes
can be calculated from the data presented in Figure 3.
Figure 3. Temporal changes in reproductive stages of
Melanotaenia duboulayi in the Mary River, south-eastern
Queensland, during 1998 [1093]. Samples sizes for each
month are given in parentheses.
225
Freshwater Fishes of North-Eastern Australia
South Wales [1133, 1135], was generally very similar to
that observed for fish from the Mary River [1093], except
that spawning appeared to be concentrated within a
slightly shorter period (October to February) in each river.
No consistent pattern in overall sex ratios was observed
for populations from the Brisbane River [950].
Arthington and Marshall [84] reported that females in the
Noosa River commenced spawning at 23 mm SL. Milton
and Arthington [950] recorded minimum and mean
lengths of ripe females (equivalent to stage V) from tributaries of the Brisbane River as 30.8 and 41.1 mm SL,
respectively. Length at first maturity (equivalent to reproductive stage III) for fish from the Tweed River, northern
New South Wales, was reported as 30 and 25 mm LCF for
males and females, respectively [1133].
The spawning stimulus for M. duboulayi is unknown but
corresponds with increasing water temperatures and
photoperiod in late winter and early spring. In aquaria,
spawning is reported to occur at water temperatures
between 22 and 27°C [770, 797]. Milton and Arthington
[950] observed that the peak spawning period for fish in
the Brisbane River (October–December) coincided with
minimum surface water temperatures of 20°C. The peak
spawning period generally coincides with pre-flood periods of low and relatively stable discharge in rivers of
south-eastern Queensland. However, breeding may also
continue through the months of elevated discharge at the
commencement of the wet season in December–January.
Melanotaenia duboulayi is thought to spawn repeatedly
over an extended period, perhaps as an adaptation to the
relatively unpredictable timing of the onset of wet season
flooding [950]. Maximum spawning activity of adults and
the presence of larvae tend to occur when the likelihood of
flooding is low, coinciding with predictably high water
temperatures and relatively stable low flows. These conditions are likely to increase the potential of larvae to
encounter high densities of small prey, avoid physical
Melanotaenia duboulayi has an extended breeding season
from late winter through to summer but spawning appears
to be concentrated in spring and summer. In the Mary
River, immature and early developing fish (stages I and II)
were most common between January and June (Fig. 3).
Developing fish (stages III and IV) of both sexes were present year-round. Gravid males (stage V) were present
between August and January. Gravid females were present
for longer (August to March) and were relatively abundant
throughout this period (Fig. 3). The temporal pattern in
reproductive stages mirrored that observed for variation
in GSI values. Peak monthly mean GSI values (3.0% ± 0.7
SE) occurred in August for males and remained elevated
until November (Fig. 4). Peak monthly mean GSI values
(7.1% ± 0.5 SE) occurred slightly later in females
(October) but remained elevated for eight months of the
year (Fig. 4). The phenology of reproductive activity and
GSIs for fish from the Noosa River [84], tributaries of the
Brisbane River [950] and the Tweed River, northern New
20
8
Spring
(n = 1999)
Males
6
Females
Summer
(n = 3238)
15
4
10
2
5
0
0
Month
Figure 4. Temporal changes in mean Gonosomatic Index
(GSI% ± SE) of Melanotaenia duboulayi males (open circles)
and females (closed circles) in the Mary River, south-eastern
Queensland, during 1998 [1093]. Samples sizes for each
month are given in Figure 3.
AutumnWinter
(n = 7016)
Standard length (mm)
Figure 5. Seasonal variation in length-frequency distributions
of Melanotaenia duboulayi, from sites in the Mary, Brisbane,
Logan and Albert rivers, south-eastern Queensland, sampled
between 1994 and 2000 [1093]. The number of fish from
each season is given in parentheses.
226
Melanotaenia duboulayi
River ranges from 35–333 eggs (mean 132 ± 9 SE, n = 81
fish) [949]. Relationships between body length, body
weight and total fecundity are given in Table 4. Fish of 40
mm SL produced about 120 eggs, whereas fish of 70 mm
SL produced about 650 eggs [1093]. In aquaria, M.
duboulayi is reported to deposit 10–40 eggs per day [794]
and up to 200 eggs are laid over a period of several days
[797].
flushing downstream due to high flows and thereby
maximise the potential for recruitment into juvenile
stocks, as has been hypothesised for other small-bodied
fish species in the Murray-Darling Basin [614, 615].
Sampling in rivers of south-eastern Queensland [1093]
revealed that juvenile fish less than 20 mm SL were present
year-round supporting the suggestion made earlier that
this species has an extended spawning period. These data
further suggest that suitable conditions for recruitment of
larvae through to the juvenile stage and beyond may
persist year-round.
In the wild, spawning probably occurs in beds of aquatic
macrophytes and submerged marginal vegetation [950,
1093] and eggs are reported to be deposited within 10 cm of
the water surface [950]. No parental care of eggs has been
reported. Eggs are relatively large. The mean diameter of
1793 intraovarian eggs from stage V fish from the Mary
Total fecundity for fish from the Mary River is estimated
to range from 27–1125 eggs (mean 280 ± 12 SE, n = 217
fish) [1093]. Batch fecundity for fish from the Brisbane
Table 4. Life history information for Melanotaenia duboulayi.
Age at sexual maturity
10–12 months [950]
Minimum length of gravid (stage V)
females (mm)
23 mm TL [84]; 26.8 mm SL [1093]; 30.8 mm SL [950]
Minimum length of ripe (stage V) males (mm) 36.4 mm SL [1093]
Longevity (years)
In the wild, 3–4 years [950]; in aquaria, possibly up to 8 years [39]
Sex ratio (female to male)
? Variable year-to-year [950]
Occurrence of ripe (stage V) fish
Late winter, spring and summer (August–March) [1093]; spring and summer
(October–February) [950]
Peak spawning activity
Spring and early summer [950, 1093]
Critical temperature for spawning
? >20°C in the wild [950], 22–27°C in aquaria [38, 351, 770]
Inducement to spawning
? Possibly increasing temperature [950]
Mean GSI of ripe (stage V) females (%)
7.0 % ± 0.8 SE
Mean GSI of ripe (stage V) males (%)
5.6 % ± 0.2 SE
Fecundity (number of ova)
Total fecundity = 27–1125, mean = 280 ± 12 SE [1093]; batch fecundity 35–333,
mean = 132 ± 9 SE [949], In aquaria 10–40 eggs deposited per day [794] and up to
200 eggs are laid over several days [797]
Total Fecundity (TF) and Batch Fecundity (BF)/ Log10 TF = 2.666 log10 L – 2.088, r2 = 0.457, n = 217 [1093];
Length (mm SL) or Weight (g) relationship
Log10 TF = 1.354 log10 W + 1.703, r2 = 0.477, n = 217 [1093];
BF = 7.763 L – 154.24, r2 = 0.79, n = 22 (Noosa River) [84]
Egg size (diameter)
Intraovarian eggs from stage V fish = 0.93 mm ± 0.01 SE [1093]; water-hardened eggs
0.88–0.93 mm [351], 1.0–1.5 mm [794], 1.41 mm ± 0.32 SE [950]
Frequency of spawning
Probably repeat spawner over extended spawning period [950]
Oviposition and spawning site
In the wild, spawning probably occurs in beds of aquatic and submerged marginal
vegetation near the water surface [950, 1093]
Spawning migration
None known
Parental care
None known
Time to hatching
Varies with temperature. In aquaria eggs hatch after 4.5 days at 27°C [351], 6–7 days
at 22–26°C, 7 days at 25–28°C [38], and 7–10 days at 25–27oC [770]
Length at hatching (mm)
Newly hatched prolarvae 3.7–4.2 mm SL [351]
Length at free swimming stage
? Capable of swimming soon after hatching [351]
Age at loss of yolk sack
?
Age at first feeding
12–24 hours [1295]
Length at first feeding
?
Age at metamorphosis (days)
? Squamation commences at 11.5–12.0 mm TL and is complete at 20 mm TL [351]
Duration of larval development
? Growth is rapid and a length of 20 mm TL may be achieved after eight weeks [38]
227
Freshwater Fishes of North-Eastern Australia
[158, 159]. Although M. duboulayi appears tolerant to
elevated salinities (see above), the presence of tidal barriers may impact on this species by preventing or hindering
recolonisation of freshwaters if displaced by floods to
brackish estuarine areas downstream of tidal barrages.
River was 0.93 mm ± 0.01 SE [1093]. Crowley et al. [351]
reported that the diameter of water-hardened eggs from fish
collected from the Mary River and an unnamed lagoon on
the Sunshine Coast, ranged between 0.88–0.93 mm. Leggett
[794] reported that water-hardened eggs were 1.0–1.5 mm
diameter. Milton and Arthington [950] reported that the
mean diameter of eggs (possibly water-hardened) from
Brisbane River fish was 1.41 mm ± 0.32 SE.
Melanotaenia duboulayi appears to undertake movement
wholly within freshwaters, however the purpose, scale or
timing of these movements is unknown. Many more individuals were collected at the base of a fish lock located in
the lower Burnett River than were collected at the top (252
versus five individuals) [11], perhaps indicating that these
fish were attempting to move upstream. Johnson [658]
collected a small number of individuals from a fish ladder
located further upstream in this river. We have also
observed large aggregations of adult fish below a weir on
Barambah Creek, a tributary of the Burnett River. These
fish were observed immediately after an increase in
discharge, suggesting that upstream dispersal movements
may occur when flow conditions allow [1093].
The demersal eggs are spherical with an adhesive tuft of
filaments arising from a small area of the chorion above
the animal pole [351, 770, 950]. The perivitelline space is
relatively small and 30–35 small, dark gold oil droplets are
present in the yolk [351]. Further details of egg characteristics are available in Crowley et al. [351]. Eggs are reported
to hatch after 4.5 days at 27°C [351], 6–7 days at 22–26°C,
7 days at 25–28°C [38], and 7–10 days at 25–27°C [770].
Details of larval morphology are available in Crowley et al.
[351]. Newly hatched larvae are small (3.7–4.2 mm TL)
[351] and are capable of swimming soon after hatching
[794]. Squamation commences at 11.5–12.0 mm TL and is
complete at 20 mm TL [351].
Trophic ecology
Diet data for M. duboulayi is available for 1237 individuals
from four separate studies in south-eastern Queensland
and northern New South Wales (Fig. 6). This is an omnivorous species that consumes animal and vegetable material within the water column and at the water surface.
Terrestrial invertebrates (mostly ants) comprised 20.8% of
the total mean diet and aerial forms of aquatic insects
(mostly dipteran adults) a further 17.2%. Aquatic insects
(mostly drifting immature stages of Trichoptera,
Ephemeroptera and Diptera) were also important, forming 26.4% of the total diet. Aquatic vegetation in the form
Growth is reported to be rapid and a length of 20 mm TL
may be achieved after eight weeks [38]. Milton and
Arthington [950] reported that M. duboulayi reached
sexual maturity within one year of age (estimated at 10–12
months). Length at age data using evidence from scale
annuli from fish in the Brisbane River [950] indicate that
1+ fish (males and females) were around 35–38 mm SL,
2+ were 47–49 mm SL, 3+ fish were 65 mm SL and 4+ fish
were greater than 73 mm SL, with males generally slightly
larger than females in each age group. The dominant age
class in this population was 1+ fish [950]. Fish in aquaria
may live up to eight years [39].
Movement
There is very little quantitative information concerning
the movement biology of M. duboulayi. Small numbers of
individuals have occasionally been reported to use fishways on weirs and tidal barrages in south-eastern
Queensland rivers. Broadfoot et al. [232] collected 39 individuals in a tidal barrage fishway on the Kolan River and
Stuart and Berghuis [1276, 1277] collected 12 individuals
in a tidal barrage fishway on the Burnett River during
November and December. It is possible that these fish were
attempting to return to freshwaters after being displaced
downstream into estuarine areas below the barrage by
elevated flows. Berghuis et al. [162] suggested that this
might also explain the presence of M. duboulayi downstream of a tidal barrage in the Mary River catchment
between February and April. Further sampling within and
downstream of tidal barrages in this catchment has yielded
additional fish in these areas between November and April
Fish (0.1%)
Other microinvertebrates (0.1%)
Microcrustaceans (1.3%)
Macrocrustaceans (0.5%)
Molluscs (0.1%)
Other macroinvertebrates (0.3%)
Unidentified (19.3%)
Aquatic insects (26.4%)
Terrestrial invertebrates (20.8%)
Algae (10.5%)
Aquatic macrophytes (2.6%)
Detritus (0.2%)
Terrestrial vegetation (0.6%)
Aerial aq. Invertebrates (17.2%)
Figure 6. The mean diet of Melanotaenia duboulayi. Data
derived from stomach content analysis of 1237 individuals
from the Burnett [205], Noosa [84] and Brisbane rivers [80] in
south-eastern Queensland, and the Tweed River in northern
New South Wales [1133].
228
Melanotaenia duboulayi
power to disrupt spawning substrates (i.e. native
submerged macrophytes) and displace eggs, larvae and
small individuals downstream [94, 950]. Patterns of rainfall and stream discharge are characteristically highly variable and unpredictable within and between years in
south-eastern Queensland streams and rivers [1095,
1100]. Some brief spates cause rapid rises and falls in water
level and may strand in-stream vegetation and leaf litter
on stream-banks and in clumps suspended in riparian
shrubs [94]. We have suggested that the seasonal timing of
spawning in M. duboulayi (concentrated in spring and
summer) represents an adaptation to the probability of
low flow conditions and the availability of suitable spawning sites, as well as shelter and food supplies for larvae and
juveniles. Flow modifications (particularly rapid fluctuations in water level or flow releases during naturally low
flow periods of spawning and larval development) may
have severe impacts on recruitment by damaging or exposing fish eggs attached to submerged and aquatic vegetation in shallow marginal habitats, or by flushing eggs and
larvae downstream. Microscopic invertebrate prey is also
likely to be reduced in abundance by flow-related habitat
disturbances, or flushed downstream during spates and
aseasonal flow releases [614, 615, 718].
of algae (filamentous algae, diatoms and desmids), charaphytes and macrophytes comprised a further 10.5% of the
diet. Small amounts of microcrustaceans, macrocrustaceans, fish eggs, terrestrial vegetation and molluscs are
also consumed (Fig. 3). Little spatial variation in diet was
apparent, although individuals from the Tweed River, New
South Wales, consumed a higher proportion of aquatic
insects and aquatic vegetation and a lower proportion of
allochthonous material. Diel variation in feeding activity
and dietary composition is evident in M. duboulayi from
streams in the Brisbane region [1093]. This species undertakes distinct crepuscular foraging on aquatic insects
during their peak drifting period at dawn and dusk, with
supplementary foraging on allochthonous material at or
near the water surface occurring during daylight hours
[1093]. This species is believed to be an effective mosquito
control agent [39, 80].
Conservation status, threats and management
The conservation status of M. duboulayi was listed as NonThreatened by Wager and Jackson [1353] in 1993 and this
species remains generally common throughout most of its
range in eastern Australia. Potential threats to M.
duboulayi in south-eastern Queensland are similar to
those identified for many other small-bodied fish species
in this region, for example Atherinidae, Pseudomugilidae,
Retropinnidae and Eleotridinae.
The implications of modified flows combined with instream barriers are not well understood for M. duboulayi.
This species appears to undertake movement wholly
within fresh water systems but they are probably not associated with reproduction [1093]. Milton and Arthington
[950] suggested that juvenile melanotaeniids disperse
throughout the stream network when elevated flows occur
during summer months. We observed large aggregations
of adult fish below a weir on Barambah Creek, a tributary
of the Burnett River, immediately after an increase in
discharge, suggesting that upstream dispersal movements
of adults may occur when flow conditions allow [1093].
Such movements could be disrupted by dams, weirs, and
culverts.
Melanotaenia duboulayi is highly dependent on energy
supplies from the terrestrial environment. Inputs of
allochthonous organic matter may be severely disrupted
by land and riparian clearing [1092]. In addition, infestations of introduced para grass, Brachiaria mutica, may
disrupt the foraging behaviour of this surface-feeding
species in degraded urban streams. Long stolons and mats
of this ponded pasture grass often extend into slow-flowing areas of stream channels, obliterating patches of native
submerged macrophytes and invading open water areas
where rainbowfish usually forage [80, 94, 1093]. Para
grass, a C4 plant, does not contribute to energy flow
through the aquatic food web of tropical streams [95, 248,
250] and this may also apply in subtropical streams. Food
resources of aquatic origin (e.g. insects, crustaceans,
molluscs and algae) are likely to be further limited in
degraded systems by bank erosion and sedimentation of
the stream-bed [1092].
Harris and Gehrke [553] classified M. duboulayi as intolerant of poor water quality, yet this species tolerates relatively wide-ranging water quality conditions in streams
and dune lakes of south-eastern Queensland, and in
aquaria. Melanotaenia duboulayi is sensitive to ammonia
and chlorine contamination events caused by malfunctions of water treatment equipment, however it appears to
be less suitable for detecting cyanobacterial toxins [665]. It
is unaffected by short-term exposure to potentially toxic
microcystin derived from cyanobacteria [665] and
comparatively tolerant of endosulfan exposure [1280].
Thus the impacts of degraded water quality conditions in
streams draining urban and agricultural catchments may
be relatively slight when short-term exposure is the norm.
Melanotaenia duboulayi is most abundant in mesohabitats
with fine to intermediate-sized substrates (sand, fine
gravel and coarse gravel), submerged aquatic macrophytes, filamentous algae, leaf-litter beds, undercut banks
and root masses. These structures may provide protection
from surface (e.g. avian) and aquatic predators. Cover may
also serve to reduce the impact of high flows with the
229
Freshwater Fishes of North-Eastern Australia
Alien species are also regarded as a threat to M. duboulayi
[83, 94, 950] especially the poeciliid Gambusia holbrooki, a
widespread species common in many waterbodies within
the geographic range of this rainbowfish in Queensland
and New South Wales [84, 726, 1093]. Gambusia holbrooki
is a particularly threatening species known to consume
fish eggs and larvae and to interact aggressively with native
fishes [77, 78, 416, 983]. Moloney [960] reported a high
level of predation by G. holbrooki on the eggs of the ornate
rainbowfish, R. ornatus, when the two species were maintained in experimental aquaria. He concluded that alien
fish such as G. holbrooki have the capacity to significantly
reduce the number of rainbowfish recruiting to later life
stages by direct predation and interfering with foraging
activities [960]. Dietary studies in the Brisbane and Noosa
rivers have shown that M. duboulayi and G. holbrooki have
very similar diet composition at most times of year [84,
92, 94], particularly in relation to their high dependence
on prey of terrestrial origin. Arthington et al. [95]
observed that M. duboulayi was rarely present or abundant
where Gambusia was present in streams of the Brisbane
region. These authors speculated that similarities in foraging behaviour and diet increased the potential for competition among these species. In contrast, our recent more
extensive sampling of rivers and streams in south-eastern
Queensland [1093] indicates that M. duboulayi and G.
holbrooki frequently occur together, often in large
numbers. Co-occurrence data such as these provide no
evidence for the impact of alien fish species such as G.
holbrooki on M. duboulayi.
Dove [1432] provided a list of parasite taxa recorded from
M. duboulayi in south-eastern Queensland.
230
Melanotaenia eachamensis Allen and Cross 1982
Lake Eacham rainbowfish
37 245005
Family: Melanotaeniidae
Description
First dorsal fin: V–VI; Second dorsal: I, 9–13; Anal: I,
15–21; Pectoral: 11–14; Horizontal scale rows: 10–12;
Vertical scale rows: 33–38; Predorsal scales: 14–18; Cheek
scales: 9–15 [38, 1105]. Meristic characters overlap with
those of Melanotaenia splendida splendida, although average values are significantly different [1105]. Figure: mature
male, 52 mm SL, Dirran Creek, North Johnstone River,
October 1996; drawn 1998.
10.8% of SL, respectively). Morphological comparisons
are based on M. eachamensis from Dirran Creek and
M.splendida from a variety of locations in the Johnstone
River [1105]. Colour varies slightly from locality to locality but overall body tends to be silvery or bluish with dark
midlateral stripe, 2–3 thinner dark bands present ventrally
of midlateral stripe and extending almost to pectoral fins.
Fins tend to be uniform bright red with little to no yellow
pigmented blotches. Fin margins of dorsal and anal fins
tend almost to black in breeding males. Sexually dimorphic: fins longer, more pointed and more brightly
pigmented in males. Specimens derived from type locality
(i.e. Lake Eacham) tend to be less brightly coloured.
Colour in preservative: colours faded, body dull
yellow/white to brown, faint to dark stripe and little fin
colour [38]. Larvae distinguished from those of M. s.
splendida by origin of the first dorsal fin-fold above first
preanal myomere (as opposed to postanal origin), gut
simple, uncoiled and never striated in all preflexion larvae,
slightly denser pigmentation on dorsal and ventral
midlines in most preflexion larvae [308].
Melanotaenia eachamensis is a small, laterally compressed
fish rarely exceeding 65 mm SL in length and 5 g in weight,
commonly about 40 mm in length. The relationship
between length (SL in mm) and weight (g) is W = 1.05 x
10–5 L3.06; r2 = 0.933, n = 214, p<0.001 [1093]. No sexual
dimorphism with respect to length–weight relationship
[1108]. Greatest body depth (at origin of first dorsal fin)
26.5% of SL, slightly less than M. s. splendida (28.2%).
First dorsal fin inserted more anteriorly than in M. s. splendida (44.5% versus 47.7% of SL). This difference observed
in larval fishes also [308, 1377]. Head depth 23.1% of SL,
eye diameter 9.7 % of SL, eye positioned more anteriorly
than in M. s. splendida (i.e. snout length of 7.6% versus
8.2% of SL, respectively). Peduncle longer and deeper than
in M. s. splendida (18.2% and 11.0% versus 17.5% and
Systematics
The systematics of M. eachamensis have been studied very
thoroughly in recent years. This species was originally
231
Freshwater Fishes of North-Eastern Australia
total number of fishes collected but only 0.2% of the total
biomass (16th most abundant). This species is the most
abundant species with respect to density (63.2% of total)
and the second most abundant with respect to biomass
(9.1% of total) at those sites in which it occurs, with mean
and maximum densities of 2.01 ± 0.62 fish.10m2 and 9.90
fish.10m2 respectively, and mean and maximum biomass
of 2.11 ± 0.70 g.10m2 and 11.2 g.10m2 respectively, being
estimated from a total of five sites and 16 samples. Other
species with which it occurs include Mogurnda adspersa,
Poecilia reticulata (alien), Anguilla reinhardtii and
Craterocephalus stercusmuscarum (2nd, 3rd, 4th and 5th
with respect to density, and 3rd, 4th, 1st and 5th with
respect to biomass) [1093]. McGuigan [904] reports that
M. eachamensis may frequently occur in sympatry with M.
s. splendida but only very occasionally with M. utcheenis,
but note that this conclusion is based on the presence of
mixed or hybrid haplotypes and it is not known whether
this admixture represents old or contemporary hybridisation. Translocated Hephaestus fuliginosus (a native species)
were recorded by us in Dirran Creek toward the end of
1997 [1093]; the impact of this species on M. eachamensis
is unknown.
described in 1982 from specimens collected from Lake
Eacham, on the Atherton Tablelands [38]. The population
present in the type locality became extinct shortly thereafter due to predation pressure from translocated native
fishes, principally Glossamia aprion [132]. Captive populations were maintained however [293, 608]. The lacustrine
population was subsequently shown to be ‘predator naïve’
and consequently susceptible to exploitation by translocated piscivorous fishes [241, 1377]. Initial electrophoretic
examination of captive populations of M. eachamensis and
wild populations of M. s. splendida from the Atherton
Tablelands suggested full specific status for the former
species may have been unwarranted [349, 634]. However,
subsequent research utilising DNA sequencing methods
demonstrated that M. eachamensis was a valid species and
that extant populations were still present in the wild
[1427]. Moreover, this study suggested that hybridisation
between these two species may occur in the wild.
Morphological evidence also indicated the presence of
extant populations in the wild and seemed to indicate the
presence of morphological forms intermediate between
that of M. eachamensis and M. s. splendida [35, 1105,
1426]. Morphological intermediates were assumed to be
hybrids [1105] but subsequent genetic examination has
revealed the presence of another distinct lineage in the
Johnstone River (the ‘Utchee Creek’ form, now known as
M. utcheensis McGuigan) [904]. Melanotaenia eachamensis
is an old lineage and evolutionarily more closely related to
M. s. australis and M. duboulayi than to taxa within the
‘splendida’ subspecies complex [904, 1427].
Macro/mesohabitat use
The data listed in Table 1 includes study sites on Dirran
Creek only, for at the time in which the study commenced,
this creek was the only system in which pure strains of M.
eachamensis were known to exist. This stream is a high altitude tributary of the North Johnstone River (Table 1). It is
worth noting that McGuigan [904] identified a population
of M. eachamensis in the upper reaches of the South
Johnstone River also. Dirran Creek is of moderately high
gradient and with a relatively open riparian canopy,
running predominantly through land used for dairy and
cattle grazing. The riparian canopy would previously have
been more extensive.
Distribution and abundance
Melanotaenia eachamensis is restricted to the Wet Tropics
region, and within this region is restricted to the headwaters of the Johnstone and Barron rivers [904]. Pusey et al.
[1105] suggested that it may be present in the headwaters
of other rivers draining the Atherton Tablelands, such as
the Tully River. All known localities supporting M.
eachamensis are located above 500 m.a.s.l. Populations
previously identified as M. eachamensis occurring at elevations between 100 and 500 m.a.s.l. in the Johnstone River
[1105], have subsequently been identified as the new
distinct species M. utcheensis [904]. Efforts to reintroduce
M. eachamensis back into the type locality using stock
reared in captivity have proved unsuccessful.
Over the range of sites examined, Dirran Creek varies
from 7.1 to 17.5 m in width. Average water depth and flow
velocity varied from 0.3 to 0.67 m and 0.11 to 0.26 m.sec-1,
respectively. The close similarity between arithmetic and
weighted means suggests little spatial variation in abundance due to spatial variation in width, depth or water
velocity, at least not over the ranges measured by us. The
composition of the substratum in sites containing M.
eachamensis was dominated by rocks and bedrock (Table
1). In-stream cover was generally limited in extent with
the exception of bank-associated submerged vegetation
(almost exclusively para grass) and root masses. The
disparity between arithmetic and weighted means for
these cover elements suggests that M. eachamensis is more
abundant in streams with prolific South American para
Loose schooling occurs in M. eachmansis especially for fish
less than 40 mm SL; larger fish tend to occur singly or in
small groups. This species is moderately abundant where
it occurs and the original lake population was reportedly
large [132]. Melanotaenia eachamensis was the ninth most
abundant species collected in the Johnstone River catchment over the period 1994–1997 contributing 3.4% of the
232
Melanotaenia eachamensis
Microhabitat use
Melanotaenia eachamensis may occur across a moderate
range of water velocities from still water to about 0.5
m.sec–1, although the majority of fish collected were from
areas with no flow. The focal point velocity experienced by
most fish was accordingly 0 m.sec–1 although it is apparent
that those fish not collected from areas of still water experienced focal point velocities similar to the average velocity (Fig. 1b). This species occurred over a wide range of
depths reflecting the distribution of depths across the
range of sites sampled. In general, most fish were collected
from the bottom half of the water column although M.
eachamensis appears to make use of the entire water
column on occasion.
grass (Brachiaria mutica) infestations and abundant root
masses. However, it should be noted that the relationship
is probably not a linear one as the maximum density
recorded occurred was in a site with only 50% coverage by
para grass. Both para grass and root masses may provide
refuge against high water velocity or abundant spawning
sites.
Table 1. Macro/mesohabitat use by Melanotaenia
eachamensis. Data summaries based on site data for five sites
collected over the period 1994–1997.
Parameter
Min.
27.8
Catchment area (km2)
Stream order
4
Distance to source (km)
10.5
Distance to river mouth (km) 95
Elevation (m.a.s.l.)
720
Width (m)
7.1
Riparian cover (%)
5
Gradient (%)
0.1
Mean depth (m)
0.3
Mean water velocity (m.sec–1) 0.11
Mud (%)
Sand (%)
Fine gravel (%)
Gravel (%)
Cobbles (%)
Rocks (%)
Bedrock (%)
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Small woody debris (%)
Large woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
2
3
3
26
5
0
0
0
0
0
0
0
0
0
0
Max.
Mean
W.M.
57.5
4
21.5
104.5
790
17.5
40
45.6
4
17.1
98.8
748
12.0
21
45.1
4
16.9
99.0
749
12.3
24
2.6
0.67
0.26
1.1
0.5
0.19
50
1.0
0.46
0.19
8
17
11
6
23
65
63
3.0
5.2
4.4
4.4
7.8
50.2
25.4
4.6
3.8
5.7
5.0
10.8
51.6
19.6
5
0
12
91
3
3.5
0.7
1.2
5
24
1.0
0
2.6
37.2
0.8
1.3
0.2
0.3
1.0
7.0
0.9
0
4.1
55.9
1.4
1.6
0.3
0.5
0.4
10.2
The habitat described above is in distinct contrast to that
of the type locality, Lake Eacham, a deep crater lake. This
species has also been recorded from other crater lakes on
the Atherton Tablelands, Lake Euramoo [1426] and
Bromfield Swamp [904]. These waterbodies and Lake
Eacham have abundant sedge habitats at their margins, or
in the case of Bromfield Swamp, distributed in a patchy
mosaic across its surface. Despite occurring, or having
once occurred in these lakes, M. eachamensis is best
considered a stream-dwelling rainbowfish [1105].
(a)
50
40
40
30
30
20
20
10
10
0
0
Focal point velocity (m/sec)
Mean water velocity (m/sec)
(c)
30
20
15
(b)
(d)
20
10
10
5
0
0
Total depth (cm)
Relative depth
(e)
(f)
30
60
20
40
10
20
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Melanotaenia eachamensis in
Dirran Creek, North Johnstone River. Summaries are derived
from capture records for 62 individuals collected over the
period 1994–1997.
233
Freshwater Fishes of North-Eastern Australia
unknown, as are tolerances to pesticides and herbicides.
Most streams of the Atherton Tablelands in which M.
eachamensis is likely to occur, are in forested areas, or areas
devoted to cattle grazing. Such streams are unlikely to
receive contaminants other than sediment, however given
the expansion of the sugar-cane industry on the
Tablelands, this situation may not persist.
This species was recorded most frequently over coarse
substrate types (Fig. 1e) reflecting the average substrate
composition of the sites in which it is found (see above).
However, M. eachamensis frequently occurs over areas of
fine gravel and gravel also, reflecting its preference for
areas of lower flow than the average water velocity occurring within the stream. The great majority of M.
eachamensis were collected in association with submerged
para grass (Fig. 1f), however, this species was rarely found
deep within the para grass stands but was most frequently
outside of, but within 20 cm of the outer margin of the
stand. The majority of the remaining fish were either
distant from cover or were within 20 cm of the stream-bed
and thus associated with the stream-bed. Larval M.
eachamensis prefer marginal habitats with low water velocities (<0.1 m/sec) but of variable depth (but <100 cm).
Larvae are always associated with access to cover and may
be more abundant in areas of deep shade [1109].
Reproduction
Details of the life history of M. eachamensis are
summarised in Table 3. Spawning occurs over an extended
period from August to April but peak gonadosomatic
values occur during August to November. Spawning does
not appear to occur when water temperatures are below
17°C. Spawning may continue during periods of high flow
but is concentrated during periods of stable low flows.
Larval survival decreases during periods of high flow
[1109]. The eggs are demersal and adhesive; field investigations have found eggs most commonly attached to fine
root masses downstream in well oxygenated areas. Females
produce batches of 40–50 eggs in captivity [277] but much
higher batch sizes have been observed in wild populations.
Eggs are small (1.28 mm diameter) and fecundity is significantly positively related to fish size. Maturity is reached at
an early age and size, and females mature at a smaller size
than do males. This species is unlikely to live for more than
two years in the wild. The time to hatching is reported to
be 10 days at 26°C, however such a high temperature rarely
occurs in the natural habitat. Larvae are small at hatching
and lack a well-developed yolk sac, exogenous feeding
commences shortly after hatching. Larval development is
complete at between 11 and 14 mm in length.
Environmental tolerances
No quantitative information is available on environmental
tolerances of M. eachamensis. Data presented in Table 2
were derived from routine sampling at five sites at which
M. eachamensis was present. A minimum temperature of
13.2°C was recorded over the period 1994–1997 although
winter frosts are not uncommon on the Atherton
Tablelands and minimum values may be less than that
recorded here. The incidence of fungal infection is highest
during periods of low temperature. The maximum water
temperature (25.7°C) listed in Table 2 was recorded in
January during a period of low flow but it is notably lower
than that seen for other small streams located at lower altitude. This species has only been recorded from moderate
to well-oxygenated conditions and occurs in near neutral
waters.
Movement
No information available on the extent or pattern of
movement.
Table 2. Physicochemical data for M. eachamensis. Data
summaries for fish collected from five sites and 16 sampling
occasions within Dirran Creek over the period 1994–1997.
Parameter
Min.
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
13.2
5.1
6.7
18.9
0.5
Max.
25.7
8.1
7.8
52.6
8.5
Trophic ecology
Melanotaenia eachamensis is omnivorous, but more than
50% of the diet is composed of aquatic invertebrates
(principally comprised of ephemeropteran nymphs and
trichopteran and pyralid larvae) (Fig. 2). Terrestrial invertebrates and adult forms of aquatic insect larvae collectively comprise 12.7% of the diet, indicating that feeding
at the water’s surface is important. Plant matter in the
form of filamentous algae, diatoms and desmids are
important also (10.4%). Elsewhere plant material may
form a larger part of the diet. Many rainbowfish specimens
from the upper South Johnstone River included in a previous description of the diet M. s. splendida [1097] were in
all likelihood M. eachamensis; plant material, especially
diatoms and desmids, were an important component of
the diet (>50%) of fish from this area. The diet of M.
Mean
19.8
6.9
7.3
33.7
4.1
Dirran Creek has extremely low conductivity levels (Table
2). Melanotaenia eachamensis appears to be able to tolerate
moderately elevated turbidity for short periods: the maximum value in Table 2 was recorded during a storm-associated runoff event. Average turbidity values indicate
conditions of good water clarity. Larval tolerances are
234
Melanotaenia eachamensis
eachamensis is not greatly dissimilar to that of M. s. splendida from Wet Tropics streams [1097].
Conservation status, threats and management
Melanotaenia eachamensis was initially thought to be the
first Australian freshwater fish to have become extinct in
the wild [1353]; this species is now listed as Vulnerable
[117]. Its distribution on the Atherton Tablelands is
limited [904]. Potential threats include the destruction of
habitat, flow regulation, hybridisation with other rainbowfishes and interactions with introduced species. The
removal of riparian vegetation and subsequent changes to
in-stream channel morphology and the presence of invasive grasses is likely to result in reductions in abundance.
Although para grass is used as a microhabitat by M.
eachamensis, it is unlikely, for a number of reasons, that
reaches with very prolific infestations will continue to
support large populations of M. eachamensis. First, M.
eachamensis uses only the margins of para grass stands,
thus para grass proliferation to the point where it dominates the in-stream habitat is likely to reduce the overall
habitat availability and suitability. Second, macroinvertebrate and microalgal production are likely to be depressed
Other (6.4)
Unidentified (17.4%)
Algae (10.4%)
Detritus (2.4%)
Terrestrial invertebrates (7.7%)
Aerial aq. invertebrates (5.0%)
Macrocrustaceans (2.0)
Aquatic insects (59.1%)
Figure 2. Mean diet of Melantaenia eachamensis. Data for 148
individuals collected from Dirran Creek, Johnstone River
drainage, over the period 1994–1997.
Table 3. Life history data for Melanotaenia eachamensis. Data are summarised from three studies conducted within the
Johnstone River catchment over the period 1994–1997 [308, 1108, 1109].
Age at sexual maturity (years)
<1 (probably 6 to 7 months)
Minimum length of ripe females (mm)
37 mm
Minimum length of ripe males (mm)
49 mm
Age at death (years)
Probably not greater than 2 years in wild populations
Female to male sex ratio during breeding season ?
Occurrence of ripe fish
August through to April
Peak spawning activity
August through to November
Critical temperature for spawning (°C)
Reproductive activity absent in Dirran Creek when water temperatures less than
17°C, larvae absent until temperatures greater than 20°C
Inducement to spawning
? Spawning period corresponds to period of stable low flows
Mean GSI of ripe females % (± SE)
8.47 ± 0.49
Mean GSI of ripe males % (± SE)
1.99 ± 0.20
Maximum fecundity (number of ova)
2126, fecundity related to size
Fecundity/length relationship
egg number = 51.6(SL) – 1273; n = 39, r = 0.65, p<0.001
Egg diameter – mm (± SE)
1.238 ± 0.022 (from ripe fish)
Frequency of spawning
Continuous while temperatures above 17°C, eggs produced in batches of between
4 and 452. Batch size varies with female size and varies between 7 and 23% of the
total number of eggs
Oviposition
Adhesive eggs found in root masses in well oxygenated areas such as below riffles
and rapids
Parental care
Absent – adults will eat larvae
Time to hatching (days)
?
Length at hatching (mm)
4.00–4.15 mm
Length at free swimming stage (mm)
As above
Length at first feeding (mm)
4.65–5.92 mm, little indication of large yolk deposit visible in much smaller fish
End of larval development (mm)
11–14 mm
Duration of larval development
?
Survivorship
Larvae experience high mortality with onset of wet season flooding
235
Freshwater Fishes of North-Eastern Australia
Fluctuating flows during the spawning period may result
in desiccation of eggs, stranding of larvae in marginal
habitats or physical removal of larvae during peak flows.
Given its short life-span, interference to the flow regime
may impact on population levels over a relatively short
time period. Reintroduction of M. eachamensis into Lake
Eacham is unlikely to succeed whilst introduced predators
are still present in this system. Translocation of native
fishes into Tablelands streams in which they were previously absent, for the purposes of enhancing recreational
fisheries, is likely to impact on populations in streams. For
example, H. fuliginosus has been stocked in the upper
Johnstone River and its sudden appearance in Dirran
Creek suggests that this species is expanding its range on
the Tablelands. It would be tragic if stream populations
suffered the same fate as the lacustrine population of Lake
Eacham. Impacts associated with the presence of the introduced guppy (Poecilia reticulata) are unknown in type and
severity but are probably minor, providing habitat degradation does not occur in the future.
in sites dominated by para grass. A more extensive inventory of the distribution of M. eachamensis on the Atherton
Tablelands, accompanied by thorough habitat mapping is
needed to discern the relationship between abundance and
para grass. In addition, such a program could be used to
determine the conditions under which M. s. splendida is
favoured and whether this is to the detriment of M.
eachamensis. Hybridisation between these species was seen
by McGuigan [904] as a serious threat to the continued
existence of the genetic distinctiveness of M. eachamensis.
Stream regulation and reductions in flow are likely to
reduce habitat availability and suitability. This species
prefers habitats with moderate flow and accessible
marginal areas. A pronounced reliance on the larvae of
aquatic invertebrates may necessitate adequate flows that
allow production of this faunal component and to ensure
the removal of fine sediments. Periods of stable flow are
apparently necessary for spawning and successful larval
recruitment, but flows must be sufficiently high to result
in access to bank-side structures such as root masses for
oviposition and marginal areas for larval habitat.
236
Melanotaenia utcheensis McGuigan, 2001
Utchee Creek rainbowfish
37 245025
Family: Melanotaeniidae
SL (6.6–8.9%)); caudal peduncle length 17.8% of SL
(14.6–22.9%); caudal peduncle depth 11.5% of SL
(14.6–22.9%). Males and females do not differ significantly with respect to these parameters, the only major
differences being in colour (see below) and in fin length.
The pelvic, second dorsal and anal fins are longer in males:
a common sexual dimorphism observed in rainbowfishes.
Melanotaenia utcheensis is deeper in the body than M.
splendida (28.2%) and M. eachamensis (26.5%). Note that,
in contrast, McGuigan [904] reported that M. eachamensis
is deeper in the body than M. s. splendida. The first dorsal
fin is inserted slightly more anteriorly in M. utcheensis
than in M. splendida (47.7%) but slightly more posteriorly
than M. eachamensis (44.5%). Differences in fin ray and
vertical and horizontal scale row counts may also be used
to distinguish between these three species (see accompanying chapters) but as is evidenced in the ranges in
morphometric and meristic features given here, there is
often substantial overlap between species. We have noted
that the first spine of the second dorsal fin is somewhat
thickened and pungent but its value as a diagnostic character remains to be demonstrated.
Description
First dorsal fin: V–VII; Second dorsal: I, 10–12; Anal fin: I,
16–20; Pectoral: 11–15; Horizontal scale rows: 9–11;
Vertical scale rows: 32–35; Predorsal scales: 13–16 [904,
1093]. Figure: large mature male specimen, 60 mm SL,
Utchee Creek, March 1995; drawn 2003.
Melanotaeia utcheensis is a moderate-sized rainbowfish
rarely exceeding 60 mm SL, more commonly between 45
to 50 mm SL [1093]. The mean (± SE) and maximum
length observed by us over the period 1994–1997 was 39.7
± 0.25 mm SL and 85 mm SL, respectively [1093]. The
relationship between weight (g) and length (SL in mm) is:
W = 1.223 x 10–5 L3.09; r2 = 0.975, n = 56. Information
concerning morphometric variation given in the original
description of M. utcheensis [904] contains some apparent
errors and is difficult to interpret. For this reason, we have
reanalysed data in Pusey et al. [1104], using only material
from sites located in the upper reaches of Utchee Creek
(the exact type locality) (n = 56), to describe the morphometrics of this species. Greatest body depth, at first dorsal
fin, 30.3% of SL (27.2–34.2%); head length 28.3% of SL
(25.9–30.9%); predorsal length 46.5% of SL (44.1–49.3%);
eye large 9.8% of SL (8.8–11.5%), particularly in smaller
specimens and set forward on head (snout length 8% of
Melanotaenia utcheensis has a distinctive colour pattern.
The body is silver/blue in colour with a dark blue midlateral
237
Freshwater Fishes of North-Eastern Australia
utcheensis there are two mtDNA lineages, one occurring
primarily on the Atherton Tablelands and the other in
streams in the coastal uplands [905]. McGuigan [904]
states that the two lineages are morphologically distinct
but conservatively retained them within the single species.
stripe extending from the caudal fin across the operculum
to the snout. Two, sometimes three, thin, bright orange
stripes extend on the dorsolateral surface from the caudal
fin to about the base of the first dorsal fin. A similar orange
stripe extends from the caudal fin forward to about the
base of the pectoral fin, below the midlateral stripe.
Ventrally of this stripe, there is diffuse thick black stripe
extending forward from the insertion of the last anal ray.
This stripe may be discontinuous and is most intensely
pigmented in reproductively active males. The two scale
rows immediately below the midlateral stripe are
frequently more silver than scales above the stripe. The
scales have a light purple iridescence, the intensity of
which depends on the incidence of light falling upon
them. A large orange spot is present on the operculum.
The dorsal and anal fins have a thin black margin, as does
the pelvic fin, but are otherwise a dusky brown with
reddish blotches, except when males are in breeding condition these fins may be an intense red. Female colouration
is similar but never as intense. Colour in preservative: most
colours fade greatly, less so in alcohol than formalin, and
the body tends towards a dull tan. The midlateral stripe
remains prominent but the orange stripes fade to a dark
brown [904, 1177].
Distribution and abundance
Melanotaenia utcheensis is endemic to the Wet Tropics
region and further restricted within this region to the
Johnstone River Basin [904]. This lineage occurs in a small
number of tributary streams of the North Johnstone River
on the Atherton Tablelands (Short Creek, Ithaca River,
Gillies Creek and an unnamed tributary) and in Bromfield
Swamp at the head of the North Johnstone River. We have
used the term lineage here rather than species because,
with the exception of the population in Short Creek and
the unnamed tributary, these populations are admixed to
varying degrees with M. eachamensis or M. s. splendida
mtDNA lineages. Pure populations of M. utcheensis are
present in Utchee Creek in the South Johnstone River
drainage, and Fisher and Rankin creeks of the lower North
Johnstone River. An admixed lineage (with M. s. splendida)
was also detected in Tregothanana Creek in the lower
Johnstone River [904].
We recorded M. utcheensis in 11 locations (from a total of
52) over the period 1994–1997 [1093], all located in creeks
listed by McGuigan [904] but not including any located on
the Atherton Tablelands. This species was the 13th most
widely distributed species, the most abundant (contributing 18.8% of the total of 27 164 fish) and the ninth most
abundant with respect to total biomass (1.3% of a total of
525.1 kg). This species was the most abundant species at
those sites in which it occurred and contributed 54.9% of
the total number of fish from such sites. A mean density of
1.06 ± 0.13 fish.10m–2 was estimated. A mean biomass
density of 1.26 ± 0.13 g.10m–2 was estimated, accounting
for 9.5% of the total biomass: the fourth most significant
species. Melanotaenia utcheensis commonly occurred with
(in decreasing order of abundance) Pseudomugil signifer,
Mogurnda adspersa, Hephaestus tulliensis and Anguilla
reinhardtii [1093].
Systematics
Melanotaenia utcheensis has been long recognised as a
distinct colour variety of either M. s. splendida or M. trifasciata [43, 797], and has been sold in the aquarium trade as
a distinct form, the Utchee Creek type [904]. Allen and
Cross [43] include this type within M. s. splendida but
suggest that it may be an undescribed species. In an analysis of the morphometry and distribution of M. eachamensis, Pusey et al. [1104] identified populations of the Utchee
Creek type as intermediate in morphology between M.
eachamensis and M. s. splendida but were forced to assign
them to M. eachamensis. Schmida [1202] in an analysis
based largely on colour variation, and McGuigan et al.
[905] in a genetic analysis, placed the Utchee Creek type in
a group containing M. eachamensis, M. duboulayi, M.
fluviatilus and M. s. australis (now M. solata Taylor). This
taxon was formally described in 2001 [904].
Further genetic analysis (based on mtDNA sequence data)
demonstrated that M. utcheensis is more closely related to
M. duboulayi than it is to M. eachamensis [904]. These
species belong to an old lineage, whereas M. s. splendida is
a much younger species that has colonised the Wet Tropics
region only recently (see M. splendida chapter). There is
some evidence of admixture of mtDNA lineages of M.
utcheensis and M. s. splendida when the two species occur
in sympatry, but it is unknown whether this is due to
historical or contemporary hybridisation [904]. Within M.
Macro/mesohabitat use
Melanotaenia utcheensis occurs in small, third or fourth
order streams located above about 50 m.a.s.l. (note
however that a distinct lineage of M. utcheensis occurs on
the Atherton Tablelands at elevations above 500 m.a.s.l.).
Such streams have a moderate gradient of about 1%, are
about 12 m in width and have an intact riparian canopy
covering about 40% of the stream surface (Table 1).
Although M. utcheensis occurs in reaches with a gradients
ranging from 0.05% (pools) to 4.1% (rapids), this species
238
Melanotaenia utcheensis
is most abundant in shallow riffles or runs (<0.4 m) with a
gradient of about 0.4% and water velocities less than 20
cm.sec–1.
(a)
Table 1. Macro/mesohabitat use by Melanotaenia utcheensis.
Data summaries based on site data for 11 sites collected over
the period 1994–1997.
Parameter
Min.
2
Max.
Mean
50
30
40
20
30
(b)
20
10
10
0
0
W.M.
1.9
Catchment area (km )
Stream order
3
Distance to source (km)
3
Distance to river mouth (km) 33
Elevation (m.a.s.l.)
55
Width (m)
0.52
Riparian cover (%)
5
34.4
4
15
41.5
80
4.07
70
16.9
3.9
10.4
35.1
62.5
1.17
37.5
14.9
3.9
11.3
34.6
64.3
0.45
42.1
Gradient (%)
6.9
Mean depth (m)
0.2
Mean water velocity (m.sec–1) 0.04
23.5
0.56
0.23
11.9
0.35
0.16
12.0
0.39
0.15
Mud (%)
Sand (%)
Fine gravel (%)
Gravel (%)
Cobbles (%)
Rocks (%)
Bedrock (%)
0
0
0
0
0
2
0
9
5
15
42
39
51
98
1.6
1.9
8.5
16.5
19.9
18.6
22.75
1.5
2.3
9.3
20.7
19.5
31.9
13.7
Aquatic macrophytes (%)
Filamentous algae (%)
Overhanging vegetation (%)
Submerged vegetation (%)
Emergent vegetation (%)
Leaf litter (%)
Small woody debris (%)
Large woody debris (%)
Undercut banks (% bank)
Root masses (% bank)
0
0
0
0
0
0
0
0
0
0
0.8
0
2.0
4.0
0
31.3
1.8
3.0
26.0
44.0
0.1
0
0.6
1.4
0
5.7
0.5
0.6
4.0
7.9
0.3
0
0.5
1.7
0
5.2
0.6
0.3
2.3
8.7
Mean water velocity (m/sec)
Focal point velocity (m/sec)
(c)
(d)
30
25
20
20
15
10
10
5
0
0
(e)
Total depth (cm)
(f)
25
80
20
60
Relative depth
15
40
10
20
5
0
0
Substrate composition
Microhabitat structure
Figure 1. Microhabitat use by Melanotaenia utcheensis in the
Johnstone River. Summaries are derived from capture records
for 66 fish collected from Utchee, Fishers and Rankin creeks
over the period 1994–1997.
Although M. utcheensis may occur in reaches dominated
by bedrock, this species most frequently occurs, and is
most abundant, in reaches with a diverse substratum
dominated by cobbles and rocks (Table 1). Cover is very
limited in the streams in which M. utcheensis occurs, with
the exception of root masses and beds of leaf litter. It is
noteworthy that macrophytes, filamentous algae and
submerged vegetation (para grass Brachiaria mutica) are
very limited in abundance due to the presence of an intact
canopy.
most fish occur in localised areas of no or low flow(<0.1
m.sec–1). This species occurs over a range of depths but is
most common in depths of 20–40 cm (Fig. 1c) and is similarly widely distributed in the water column (Fig. 1d). It
tends to occur infrequently in the upper one third of the
water column.
There appears to be little direct substrate preference as the
distribution of particle sizes evident in Figure 1e closely
approximates that seen in reaches in which this species
occurs (Table 1). About 20% of the 66 fish upon which
Figure 1 is based were collected more than 20 cm from
cover (i.e. in open water), the remainder were most
frequently in association with the substrate, although not
necessarily in contact with the stream-bed. In deeper water
(>30 cm), M. utcheensis often congregates in small groups
Microhabitat use
Melanotaenia utcheensis occurs in a range of water velocities up to about 0.7 m.sec–1 but most commonly occurs in
low to moderate flows up to 0.2 m.sec–1 (Fig. 1a). Focal
point velocities are much reduced however (Fig. 1b) and
239
Freshwater Fishes of North-Eastern Australia
eachamensis), some larval production occurs throughout
the year as evidenced by the presence of fish in the 10–15
mm size interval on all occasions. However, the only indication of a distinct larval/juvenile cohort is in October (the
smallest individual (8 mm SL) was also collected at this
time) and the large numbers of fish between 20 and 35
mm SL in the wet season sample suggests greatest larval
production prior to the onset of the wet season.
of two to three individuals downstream of large rocks
where the current is much reduced. In shallower waters,
this species tends to occur lower in the water column
amongst the cobbles and rocks. These factors are the principal reasons for the reduction in focal point velocity, relative to average water velocity, experienced by M. utcheensis
(Figure 1b).
Environmental tolerances
Melanotaenia utcheensis occurs in streams of good water
quality. The range in water temperature given in Table 2 is
indicative of conditions experienced in well-shaded rainforest streams. The maximum temperature recorded over
the period 1994–1997 was 32.7°C and occurred at a very
open site with a dominant substrate of basaltic bedrock:
M. utcheensis numbers at this time were depressed relative
to previous occasions suggesting either some mortality or
a retreat downstream to cooler waters.
200
Feb., March; n = 1066
160
May, July; n = 667
October; n = 418
120
80
40
Table 2. Physicochemical data for Melanotaenia utcheensis.
Data summarties for 5098 individuals collected from 53
samples in the Wet Tropics region over the period 1994–1997
[1093].
Parameter
Min.
Water temperature (°C)
Dissolved oxygen (mg.L–1)
pH
Conductivity (µS.cm–1)
Turbidity (NTU)
18.2
5.7
6.4
8.3
1.7
Max.
32.7
9.2
8.1
67.6
29.7
Mean
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Standard Length (mm)
Figure 2. Temporal variation in population size distribution of
Melanotaenia utcheensis in the Johnstone River.
24.5
7.1
7.2
35.7
8.6
These data also indicate a gradual increase in mean size
through the year and the unimodal size distribution of fish
greater than 30 mm SL suggests that few fish live longer
than one or two years. It is probable, given the close relatedness of M. utcheensis and M. eachamensis, that many
aspects of their life history, such as fecundity, egg size and
reproductive investment, are similar. In all likelihood, M.
utcheensis spawns in the late dry season prior to the onset
of summer rains, is short-lived and is a moderately fecund
batch spawner, producing small, adhesive eggs that are
deposited amongst root masses and bank-side vegetation.
Streams in which M. utcheensis occurred tended to be of
neutral pH and of very low conductivity. In general, water
clarity was moderately high but high levels of suspended
solids during runoff events can contribute to transient
high turbidity. That part of the Johnstone River catchment
in which M. utcheensis occur tends to be dominated by
sugar-cane farming, and banana and tea plantations and
these activities may at times contribute high levels of sediment. Generally however, the relatively high discharge in
these streams removes sediment quickly and it does not
settle out to any great extent (i.e. see low proportion of
mud in the sediment given in Table 1).
Movement
There is little information on the movement biology of
this species except that provided by a defaunation experiment in which mesoscale habitats were recolonised by M.
utcheensis in numbers approximately equal to that
observed prior the commencement of the experiment
[1093]. McQuigan [904] interpreted the presence of
distinct lineages (i.e. one present on the Tablelands and
the other in lowland creeks) as indicative of restricted gene
flow and long-term isolation. However, the lack of any
distinction between M. utcheensis lowland populations in
the North and South Johnstone rivers may indicate
contempory gene flow.
Reproduction
The reproductive biology of M. utcheensis has not been
studied in detail. Examination of the length–frequency
distribution (Fig. 2) of samples collected in Utchee and
Fishers creeks during the wet season (February and
March), early dry season (May and July) and the late dry
season (October) suggests that, in common with other
rainbowfishes in the Johnstone River (see accompanying
chapters for M. splendida, C. rhombosomoides and M.
240
Melanotaenia utcheensis
least, this species should be listed as Restricted, given that
it endemic to the Johnstone River basin.
Trophic ecology
The diet of M. utcheensis has not been studied in detail. It
is probable that its diet is similar to M. eachamensis, given
their close relatedness and the general similarity in habitats used, and as such would be dominated by aquatic
insect larvae with significant contributions by terrestrial
invertebrates and microalgae. This species co-occurs with
Anguilla reinhardtii and Hephaestus tulliensis, both of
which may be piscivorous, and predation may be an
important influence on the behaviour and ecology of this
species.
Populations of M. utcheensis appear secure: we saw no
evidence of population declines over the period
1994–1997. However, streams in which M. utcheensis
occurs are located in areas of intense agriculture and are
occasionally subjected to high levels of suspended sediment. No information is available on the types and
amounts of biocides that this species may be exposed to
during periods of heavy runoff nor on their tolerance to
such toxicants. We have observed low frequencies of developmental abnormalities (lordosis and asymmetric jaw
development) in populations receiving runoff from
banana plantations [1093]. In addition, riparian extraction of water during the dry season in order to irrigate tea
and banana plantations, may impact on this species if
water levels are greatly reduced.
Conservation status, threats and management
Melanotaenia utcheensis does not have an official conservation status but McGuigan [904] believed it should be
ranked as Vulnerable. This high listing was due to the
potential for genetic introgression by M. s. splendida to
dilute the genetic distinctiveness of this species. At the
241
Melanotaenia maccullochi Ogilby, 1915
MacCulloch’s rainbowfish
37 245009
Family: Melanotaeniidae
Description
First dorsal fin: IV–VII; Second dorsal: I, 7–12; Anal: III,
13–19; Pectoral: 11–14; Horizontal scale rows: 9–10;
Vertical scale rows: 31–35; Predorsal scales: 14–18; Cheek
scales: 9–14. Meristics highly variable across range. Figure:
mature male, 48 mm SL, unnamed lowland tributary of
the North Johnstone River, September 1995; drawn 2000.
Colour in life varies across the entire range. The basic
colour pattern is one in which the body is a silver base
colour, overlain with a series of fine horizontal black lines
(one per scale row), head and nape dark brown/black,
dorsal and anal fins pale to bright red and variously
marked with black lines and diffuse dark submarginal
band. Allen and Cross [43] suggest that populations in the
southern most portion of its range lack strongly defined
horizontal lines on the body and often lack lines and bands
on the fins. They are however, distinguished by very bright
red fins [38]. This colour form was suggested to occur
from the McIvor River, north of Cooktown, south to its
southern range limit. However, well-defined horizontal
lines and bands on the fins are both present in the populations within the dune fields of Cape Flattery only 30 km
north of the McIvor River, and in populations in the
Johnstone River basin [1093]. Populations further to the
north (Papua New Guinea and the Jardine River) frequently
show yellow hues on the fins and body as well as bold black
stripes on the dorsal and anal fins. An additional difference
described by Allen and Cross [43], but not described in
Allen [38], is that northern populations lack the bright neon
nuptial stripe on the forehead present in southern populations. Further study is needed to determine whether colour
Melanotaenia maccullochi is one of the smallest of the
rainbowfishes. Allen [43] states that the maximum size
attained (for both sexes) is 60 mm SL but that specimens
in excess of 45–50 mm SL are rare. Of 445 specimens
collected from the floodplain of the Johnstone River, 82%
were less than 35 mm SL and the maximum length was 53
mm SL [1093]. No specimens greater than 40 mm SL were
collected from aquatic habitats of the dune fields of Cape
Flattery [1093, 1101], and most specimens were less than
25 mm SL. Body slender, greatest body depth (at first
dorsal) 30.3–37.8% of SL (males) and 28.1–32.3%
(females); head length 25.3–31.0%; snout length 7.0–9.3;
eye diameter 9.0–12.5%; interorbital width 8.5–11.4%;
caudal peduncle depth 10.0–13.1%; caudal peduncle
length 16.7–19.5%; predorsal distance 43.0–56.3%;
preanal distance 49.9–58.4% [43].
242
Melanotaenia maccullochi
differences indicate genetically different populations,
whether observed differences are clinal across the species’
range or whether observed differences are in some way
related to the optical properties of the water in which this
species occurs (i.e. extent of tannin staining). Colour in
preservative: very little red colouration retained, horizontal lines prominent.
distinct group of M. maccullochi although the distance to
the next population is only approximately 100 km to the
south. However the barrier between these two populations
is significant, consisting of steep mountains abutting the
coastline with very little floodplain development (the Cape
Tribulation area typifies this barrier well). This next population, the Wet Tropics subgroup, extends from the floodplain on the northern bank of the Daintree River [38,
1185, 1349] south to the Cardwell area [38]. Within this
area M. maccullochi has been recorded from the following
drainage basins (in addition to the Daintree River catchment): the Barron (the type locality), Mulgrave (specifically Behana Creek) [1093, 1349], Johnstone [1093, 1349]
and Moresby rivers [1183], Maria Creek [1179], the Hull
River [1179] and the Murray/Tully River wetland systems
[1085, 1349]. This species is not common in the Wet
Tropics region despite its presence in the drainages listed
above. For example, it was recorded by us from only three
sites in each of the Johnstone and Mulgrave/Russell
drainages (from a total of 56 and 47 sites, respectively). It
should also be emphasised that, within each drainage,
these sites were adjacent to one another (i.e. within 200 m)
and it is therefore even more uncommon than these data
initially suggest. It is unlikely, and disappointing, that M.
maccullochi still persists in the Barron River system given
the extent of floodplain reclamation that has occurred in
this drainage. However, a number of small wetlands still
persist on the Barron delta [229] and it would be prudent
to survey and protect these valuable habitat remnants. It is
our experience that M. maccullochi is very frequently
syntopic with Pseudomugil gertrudae. The latter species
was collected in Eubanangee Swamp by Pusey and
Kennard [1085] and it seems likely that M. maccullochi
occurs there also. Similarly, we predict that populations of
both should exist in the extensive swamp systems located
to the east of the Malbon Thompson Range to the north of
the mouth of the Mulgrave/Russell systems, and the
Graham Range to the south. These habitats have not been
surveyed.
Systematics
Melanotaenia maccullochi was originally described by
Ogilby in 1915 from material collected in the Barron River
drainage [1021]. This population no longer exists. No
synonyms exist [1042]. McGuigan et al. [905] placed it in a
clade consisting of several of the subspecific forms of M.
s. splendida plus three New Guinean species: M. sexlineata,
M. parkinsoni and M. ogilbyi. The distribution of the
species is highly fragmented and some populations are
phenotypically unique, but unfortunately the extent of
genetic variation among Queensland populations is
unknown.
Distribution and abundance
Melanotaenia maccullochi occurs as a number of isolated
populations in south-western Papua New Guinea and
northern Australia. The Papua New Guinean distribution
extends from the lower and middle sections of the Fly
River west to at least the Bensbach River near the Irian
Jayan border [38]. This species is apparently absent from
the main channel of the Fly River itself but occurs in small
tributary creeks and floodplain swamps. In Australia,
several isolated populations are known to exist in
Queensland and recent surveys have detected this species
in the Northern Territory [38, 1349].