WF Feature
HOW
FISH
MOVE
AND HOW WE CAN HELP THEM
By Steve Ireland
M
ost of us have lain on a
rocky headland on a sunny
day and looked down into
crystal-clear seawater and marvelled at
the way fish move.
The last time I did this was about five
years back, just west of Geordie Bay on
Rottnest Island. My daughter Hannah
– aged five or so was with me and looking
down into the water, there were a few
things that were immediately obvious to
her young eyes.
We were watching a school of tiny herring
four or five metres offshore that had
been following – but not taking – my
bait. Much closer to where we were
laying, hovering near the surface, a few
even smaller, colourful reef fish were
inquisitively poking their heads and bodies
into the nooks and crannies of the rocks
below us.
Hannah looked over at me and said
very quizzically “all fish don’t swim the
same, do they, Dad? They have different
shapes too.”
12 Western Fisheries JULY 2006
Now, I was pleased and plain gobsmacked that she had made this
connection and wanted to explain to her
why this was so, but to my surprise found
that I didn’t know where to start – at least
not until I had got home and found a fish
text book.
The shape of a fish’s body tells a lot about
where it lives and, in particular, how it
feeds. Fish like Australian herring (Arripis
georgianus) with streamlined bodies
– called fusiform by fisheries scientists
–swim at medium to high speeds for most
of the time. They are built for cruising
and endurance when it comes to catching
food or avoiding being someone else’s
source of protein.
Fast swimmers like herring look for their
food in open water and are built for the
job. On the other hand, fish that feed on
reef and around rocks are usually highsided with very little width to their bodies
– this keel-like shape gives them high
manoeuvrability, so they can swim into
crevices and around bits of reef to find the
food they need while avoiding being eaten.
Whilst capable of short bursts of speed,
they are basically highly-agile plodders.
Department of Fisheries research scientist
Dr Martin de Graaf has a long-standing
interest in the science of fish movement –
and how their movement is a combination
of body, shape, fin action and body muscle.
“Tuna species have a torpedo-shaped,
very smooth and very rigid body and a
powerful lunate (crescent moon-shaped)
tail, which has not much surface area.
They move their tail very rapidly, but
keep their body relatively still. Because
tuna don’t have much in the way of
fins, they can’t stop or turn very easily
or swim backwards – they sacrifice
manoeuvrability for sustained speed,” Dr
de Graaf observes.
Dr de Graaf explains that most fishes
bodies are mainly one big piece of muscle
tissue, usually made of two different tissue
types – white-coloured tissue for bursts
of speed and red-coloured for endurance.
In the case of tuna, they are endurance
Figure 1 - Nine
basic fish shapes
Mulloway
Extreme
accelerating
body shape
Flounder
Gurnard Perch
Mangrove Jack
Extreme
cruising body
shape
Salmon
Shark
Tuna
swimmers and so their flesh/tissue is
mainly red in colour.
“Tuna are an open water fish and don’t
need to manoeuvre from left to right. In
contrast, for a fish living on a coral reef to
be successful, it needs to be able to turn at
180 degrees – speed isn’t useful because
all it would do is make the fish hit lots
of coral lumps. High-sided reef fish are
simply built for manoeuvrability - they use
their pectoral fins to move around the reef
and if they need an odd burst of speed, use
their tail fin”, he adds.
Fish body types are sometimes broken
down into three distinct groups by marine
biologists – extreme accelerating body
shapes (say, striped seapike – Sphyraena
obtusata), extreme cruising body shapes
(say, southern bluefin tuna – Thunnus
maccoyii) and extreme manoeuvring
body shapes (say, raccoon butterflyfish
– Chaetodon lunula). Figure 1 shows
these three archetypal body shapes, along
with those of some other fish that are
found in Western Australia that fit in
between these categories.
Footballer Sweep
Extreme
manoeuvering
body shape
Longfin Bannerfish
When most species of fish swim, they
undulate or move their bodies from sideto-side in an S-shape, rather like a snake
does to glide across the earth, starting this
motion at their heads and continuing it
down their muscled bodies, which moves
them forward. Their muscles also move
their fins.
Another way of looking at this is in
mechanical terms, in terms of levers and
fulcrums. The skull of a fish can be said
to act as a fulcrum, staying relatively still,
with its backbone acting like a lever which
moves the fish’s body from side-to-side
and through the water.
The power for swimming is provided by a
fish’s muscle tissue, which makes up about
80 per cent of an entire fish.
The key fin connected with the speed
and strength of a fish’s forward
movement is the tail (caudal) fin – and its
shape plays an all-important part. As you
can see, Figure 2 shows the five different
basic shapes of tails of fish that have a
bone structure.
At one extreme of bone-structured fish,
there is the aforementioned crescent moonshaped (lunate) tail that is well known
from tuna, which makes its possessors the
fastest of fish, able to maintain high speeds
for a long time.
In the middle are fish like Australian
herring and tailor (Pomatomus saltatrix),
which have forked tail fins that enable
them to swim continuously at a very fast
rate. Whilst cruising fish with forked
tails are not as fast as cruising fish with
lunate tails, the extra fin surface of the
forked type of tail provides them with
more manoeuvrability in comparison to
the latter.
At the other extreme are fish with
blade-shaped (truncate or rounded)
tails – these have a even larger relative
surface area than forked tails. As a
result, in comparison to a forked tail, a
blade-shaped tail enables a fish to cruise
at intermediate speeds and increases their
manoeuvrability, but more importantly
enables a fish to accelerate extremely
quickly when needed.
Western Fisheries JULY 2006 13
Fish with ‘continuous’ tail fins – which
are composite tail, dorsal and anal fins
– are also highly manoeuvrable and able
to swim into crevices and piles of flotsam
or wood.
When it comes to the rest of the fins, the
dorsal (top) and the anal (bottom) fins
are mainly concerned with maintaining
a fish’s stability – acting like a keel on
a boat, whilst the pectoral (side fins)
are principally used for up and down
movement.
Pectoral fins on a tuna are like the wings
on a plane – they are bony and very rigid
and give lift, up and down. In contrast,
the pectoral fins on a reef fish are very
flexible, to give high manoeuvrability.
“The area of a fish’s tail and other fins
relative to the size of their body is also
important”, explains the Department of
Fisheries’ senior finfish researcher, Dr Rod
Lenanton. Look at boxfish and ‘blowie’
species – they have a tiny tail and fins
relative to their body size and so meander
all over the place – up-and-down and from
side-to-side. They are in no sense unidirectional, which suits their lifestyle.”
Ultimately, Dr de Graaf says it is evolution
that forces the pattern where fish live.
“Unrelated coral reef fish have the same
flat high-sided body shape as each other.
If you go way back to prehistoric times
and look at the fossils of extinct fish, you
will find that the same body shapes occur
in the same natural habitat as they do in
the present day.”
He points out that fish fossils from the
Palaeozoic age (543 to 248 million years
ago) and the Mesozoic age (248 to 65
million years ago) are found in the same
places where present day species of the
same body and fin shapes live. “500
million years ago, reef fish had a high
body. Reef fish today still have a high
body,” he adds.
Understanding how fish move helps us in
many ways – not only in catching fish but
in building aids such as fishways (see Fig
3) that help fish to adapt better to some of
the human-made obstacles that have been
placed in their environment.
In Western Australia, in common with
other Australian states and many countries
around the world, we have a large number
of dams, weirs and tidal barrages that are
stretched across our inland waterways.
These can have a significant effect on
fish migration, range and spawning and
can also directly cause mortalities, owing
to fish falling, floating or jumping over
and being killed by falling onto rocks or
concrete at the base of the barrier.
Many of Western Australia’s native
freshwater fish need to use different parts
of a river at different stages of their lives.
In some cases, they may have died out in
parts of river systems, owing to a lack of
migratory access to them.
These problems are made worse by
changes to river flow patterns and water
temperatures caused by the introduction
of these water barriers – fish spawning
migrations are often triggered by river
flow patterns and changes in water
temperature.
During the 1970s fisheries researchers
and managers in Australia and around the
world began to experiment with ‘fishways’
or ‘fish ladders’, to help fish – mainly
trout and salmon in those days – to move
upstream and ‘climb’ over/around dams,
weirs and barrages. These were of rock
ramp-type construction, consisting of steps
“In contrast, big tailor and mulloway
(Argyrosomus hololepidotus) need a strong
body and fins to hold their position in
heavy surf. Milkfish (Chanos chanos)
graze in open shallows and flats with their
small mouths and use their amazing bursts
of speed to evade predators.”
“In mudskippers (Periophthalmus
argentilineatus), their pectoral fins are
modified, so they can walk on sand. In
other species, the tail is the main fin. Tuna
have a very powerful tail, but their strong
pectoral fins also help their speed.”
“Bream and those fish of the Sparid group
of species tend to have long pectoral fins
so they can back up into tight spots.”
In perhaps the strangest use of fins of all,
in goby species the pelvic fins are joined
and act as a kind of suction cup
for climbing.
Dr de Graaf points out that how well fish
can move through the water also depends
on their relative size – small fish have a
much harder job than bigger ones. “It is
easy for big fish to go through the water,
but for very small fish, such as those at the
larval stage, it is like going through maple
syrup, because of the much larger effect
of the viscosity (‘stickiness’) of the water
on them.”
14 Western Fisheries JULY 2006
Freshwater sawfish (top) and trout minnnow. Photos: Murdoch University
made from loosely-piled rocks positioned
to the side of the dam/weir/barrage (see
Figure 3).
Water cascaded down the rocky steps to
the foot of the weir, where the strongswimming trout and salmon were attracted
by the flow of water at the base of the
fishway. Trout and salmon, with their
excellent burst swimming capability,
would zig-zag their way to the top in a
series of bursts, interspersed with a series
of rests using the slower-flowing pockets
of water that could be found in the lee of
large rocks.
These fishways were relatively steep, so as
to save as much building time/money as
possible, but not so steep as to make it too
difficult for salmon and trout to make the
climb. However, this steepness meant that
other fishes which lack the capacity for
burst swimming had no chance of getting
to the top.
Over the last thirty years, the science
of fishway design has come a long way.
During the last decade a new fish design
called a “vertical slot” has emerged, the
first in WA opening on April 2003 on the
Goodga River, in a bid to increase the
habitat available to the relatively rare trout
minnow (Galaxias truttaceus).
In a vertical slot fishway, the water flows
down it from the top, in and out of a series
of large slotted concrete chambers – see
Figure 4. Fish swim into the fishway
quickly at the bottom, resting in the
swirling slowed-down waters in the first
chamber, before burst swimming into the
next chamber up the fishway and resting
again, in this manner making their way to
the top.
Dr David Morgan of Murdoch University’s
Centre for Fish and Fisheries Research
has been involved in the development of
all Western Australia’s three functioning
fishways – on the Hotham, Margaret and
Goodga Rivers. All of these are within
WA’s south west and have been designed
to assist the movement and extend the
range of members of the State’s 10 native
freshwater fish species, in particular five
from the galaxiid (minnow) family, but
also, in the case of the Margaret River
Fishway, lampreys.
The need for these fishways - and the
associated construction process - involved
a number of organisations including the
Department of Environment, Murdoch
University, the Department of Fisheries
and community groups, such as the
Boddington Rivers Action Group and the
Margaret River Environment Centre.
Like Australian herring, galaxiids are
‘fusiform’ in shape with streamlined bodies,
making them relatively fast-swimming.
They have no scales and cruise throughout
the water column.
In April 2003, the Goodga River fishway
was opened – the first vertical slot fishway
in Western Australia. The aim of this was
to increase the habitat available to the
trout minnow by creating a fishway that
enabled fish to move above the Goodga
River Gauging Station weir to breed.
The weir is located 2km upstream of the
river’s entrance into Moates Lake, where
there is a substantial population of trout
minnow and spotted minnows. In WA, the
trout minnow is now found only in the
Goodga and Angove Rivers and is among
the rarest of WAs freshwater fish in WA.
Figure 2 - The five basic
tail shapes of boney fish
Continuous
Lunate
“We monitored fish usage of the fishway
in each season between April 2003 and
February 2005. Before the opening of
the fishway, no fish were found above
the gauging station weir,” David Morgan
remarks.
“The Goodga is a spring-fed system and
the minnows will go as high as the river
continues. In the case of the Goodga
and Moates system, putting in a fishway
tripled the range of the trout minnow.”
Forked
Not only does the fishway allow adult
trout minnow and spotted minnow
(Galaxias maculatus) to migrate upstream
of the weir to spawn, but it also allows
the resulting eggs and juveniles to flow
back downstream into Moates Lake. In
addition, it also enables allowed juvenile
fish to move freely upstream, perhaps in
dress-rehearsals of the spawning activity
they will carry out later in life.
In terms of numbers of fish above the
waterway, by February 2005 there were
densities of 0.61 fish per square metre
for the trout minnow, plus the bonus of
1.69 fish per square metre for the spotted
minnow – a huge improvement on the
previous densities for both species of zero.
By and large, David Morgan is very
pleased with the design of the fishway
used on Goodga River, although he would
like to modify it by placing a plastic pool
slide-like structure at the foot of the 1.5
metre-high weir to minimise the impact of
fish being swept or swimming over it. In
common with many weirs, the Goodga
Gauging Station has a concrete footing,
Truncate
Rounded
Western Fisheries JULY 2006 15
with rocks at the base and 10 to 15 per
cent of fish that fell over it were killed by
the fall, either onto the footing/rocks or
into a specially-designed trap.
“For fishway design to go further, we
need to look at fish speed, in the area of
maximum water velocity for example.
Also, if we could increase our knowledge
about what the maximum gradient is that
we could use, this could bring down the
cost.”
Dr Morgan explains that a major cost of
a fishway is the materials involved and
if fishways could be made as short as
possible, this decreases the capital costs
and makes them more attractive to fund.
The Goodga fishway has a 20-metre length
for each one metre of fall, that is to say a
gradient of 1 to 20.
One problem with making fishways for
native species that do not occur in other
places is that the fishways have to be
purpose designed – designs for widely
occurring fish species such as trout are no
use. This is being done very well, but Dr
Morgan thinks more consideration must
go into helping juveniles of the species for
which fishways are built, as well as adults.
“We need to consider the maximum
velocity that they can move upstream.
Burst speeds are important for different
fish species and sizes.”
Goodga River vertical-slot fishway. Photo: Murdoch University
Interestingly, Dr Morgan says some
populations of fish species have different
swimming abilities, depending on where
they live, in particular the speed of water
in which they live in. “The abilities
of lake and river populations may be
different. Fish living in lakes may have
less fin rays than those living in faster
flowing rivers.”
Dr Morgan explains that fish larvae living
in lakes may metamorphose later than
those living in rivers because the larvae in
rivers need their fins earlier to be able to
cope with the stronger water flows.
“For example, in the Jerdacuttup River,
the dorsal fins of spotted minnow are
completed at 19mm in length, whereas in
Moates Lake they are completed at 24 mm
in length – a 25 per cent difference.”
Dr Morgan says that the WA populations
of some freshwater fish species that also
exist in the eastern states of Australia
actually have a lower number of anal fin
rays than their eastern cousins.
‘In Victoria, New South Wales and
Tasmania, there may be faster water flows.
The rivers where spotted minnows occur
in WA are in the south east of the state,
Figure 3 - Design of rock ramp fishways
Flow pattern.
Transverse ridge rocks forming
a series of pools and falls.
Notch in weir crest to attract
fish to fishway entrance.
Resting pool.
Fishway exit.
Flow.
Fishway entrance
close to weir.
Fishway channel on 1:20 slope.
Not to scale.
16 Western Fisheries JULY 2006
Figure 4 - Design of vertical slot fishways
Water Flow
Fishway Exit
Resting Pool
Fishway Entrance
Baffel
Fishway channel slope 1:20
where water flows are seasonal and water
tends to pool up. Fewer anal fin rays
suggest the WA fish don’t need so much
stability as those “over east” because we
have lesser water flows.”
After considering the problems faced by
50mm-long minnow species in getting
around the barriers placed in their way in
WA’s south east by humankind, Dr Morgan
has more recently turned his mind to the
two metre-plus form of the freshwater
sawfish (Pristis microdon), an endangered
species which lives in the Kimberley’s
Fitzroy River, and the problems posed to
fish migration by the Camballin Barrage.
The Camballin Barrage is an
approximately three to four metre-high
barrier erected across the Fitzroy during
the 1960s to redirect water to the 17-mile
Dam on Uralla Creek, in order to irrigate
Camballin Station. Unfortunately, a
side-effect of the barrage is to totally stop
fish migration past it for ten months a year
– even though the river is still flowing.
The Fitzroy River contains an amazing
24 freshwater species – more than in all
the rivers in Western Australia south of
the Fitzroy combined. This includes six
species listed as threatened by the IUCN
World Conservation Union (which include
the freshwater sawfish). In addition
the Fitzroy contains barramundi (Lates
calcarifer), the species most sought after
by recreational fishers and indigenous
communities in the Kimberley.
“The most important part of fishway design
is to design for target species and their
migration. If we had designed the Goodga
fishway just for winter, it wouldn’t have
worked – we found little evidence of
minnows moving in winter, they breed in
the autumn and the juveniles migrate back
up the river in late spring.”
“You need to know the cues for breeding,
spawning periods and the timing of
migration – which is hard to do for all
species in a tropical area. You need to
decide on one or two key species for your
fishway – such as sawfish and ‘barra’.”
Department of the Environment.
At present there is a significant difference
in the number of fish species that are
captured above and below the Camballin
Barrage – and at the foot of the barrage
a number of migratory marine species,
including the dangerous bull shark
(Carcharhinus leucas), have taken to
congregating. When juvenile barramundi
migrate up the Fitzroy in the late wet, they
can be trapped below the barrier by the
falling water levels and be predated on
by the bull sharks – as are the freshwater
sawfish, for which the Fitzroy is one of the
last strongholds.
Upstream of the barrage are large
numbers of Aboriginal communities for
which the fish in the river – in particular,
barramundi – is a very important food
source. It is very important to find a
way both to increase the range of the
freshwater sawfish to assist in its survival
and to ensure these communities – and
recreational fishers - have the best possible
chance to catch ‘barra.’
“Although some studies about fishway
usage suggest that many of the species
found in the Fitzroy River have been
shown to use vertical slot fishways, a
fishway of this kind wouldn’t work for
freshwater sawfish – they only work for
a fish that can turn corners,” Dr Morgan
remarks.
“A conventional rock ramp would work
– it may be only two metres wide, but any
fishway would be better than no fishway.”
Over the years, humans and their ways of
making a living have had a major impact
on the movements of freshwater fish by
building weirs and irrigation dams in the
waterways they live in. Fishways are a
good way for us to balance up the scales,
at least to some degree. g
In a report to Land Water Australia in
October 2005, after comprehensive
surveys above and below the Camballin
Barrage in November 2004 and July
2005, Dr Morgan and four other authors
recommended that a feasibility study be
conducted into constructing a fishway at
the barrage, and to determine the impacts
of this to the water that collects in the
large pool above the barrage and flows
into Snake Creek.
The report is the result of a collaboration
between Murdoch University, the
Kimberley Land Council’s Land and
Sea Unit, the Yirriman Project and the
Western Fisheries JULY 2006 17