Zoo1. J . Linn. Soc., 57: 249-319. With 17 figures
December 1975
Geographical distribution of African freshwater
fishes
TYSON R . ROBERTS
Museum of Comparative Zoology. Cambridge. Massachusetts 02138. U.S.A.
Accepted for publication December 1974
Geographical distribution of African freshwater fishes is discussed with emphasis o n the effects
of major continental features. hydrographic history. and Pleistocene climatic fluctuations .
Differences in t h e modes of dispersal and biological interactions among various categories of
fishes. ecological as well as phyletic. have also had marked effects o n distribution .
The African continent can be divided into ten ichthyofaunal provinces . The geography of
these provinces and composition of their fish faunas is briefly described . The paper concludes
with a consideration of the faunistic relationships of African lakes with endemic fishes .
CONTENTS
Introduction
. . . . . . . . . . . . . . . . . . . . . .
Biological background
. . . . . . . . . . . . . . . . . . .
. . . . .
Primary. secondary. and peripheral divisions of freshwater fishes
. . . . . . . .
Tolerance of deoxygenated water; air-breathing fishes
Mountain-climbing or orobatic fishes
. . . . . . . . . . . . .
Biological interactions among various categories of fishes (complementary
distribution patterns)
. . . . . . . . . . . . . . .
The taxon cycle in African freshwater fishes . . . . . . . . . . .
Geographical background
. . . . . . . . . . . . . . . . . .
Intercontinental relationships
. . . . . . . . . . . . . . .
Arabia . . . . . . . . . . . . . . . . . . . . . .
Changes of sea level
. . . . . . . . . . . . . . . . . .
Malagasy
. . . . . . . . . . . . . . . . . . . . .
Low Africa and High Africa
. . . . . . . . . . . . . . .
Continental drainage pattern
. . . . . . . . . . . . . . .
Mountains
. . . . . . . . . . . . . . . . . . . .
Great Rift valleys
. . . . . . . . . . . . . . . . . .
Volcanism
. . . . . . . . . . . . . . . . . . . .
Deserts
. . . . . . . . . . . . . . . . . . . . .
Pleistocene climatic fluctuations
. . . . . . . . . . . . . .
African freshwater fishes and the fossil record
. . . . . . . . . .
ichthyofaunal provinces
. . . . . . . . . . . . . . . . . .
Maghreb ichthyofaunal province
. . . . . . . . . . . . . .
Abyssinian highlands and Nilo-Sudan ichthyofaunal provinces . . . . . .
Upper Guinea. Lower Guinea. and Zaire ichthyofaunal provinces
. . . .
East coast. Zambesi. and Quanza ichthyofaunal provinces
. . . . . . .
Cape of Good Hope ichthyofaunal province
. . . . . . . . . . .
Relationships of lakes with endemic fishes to the ichthyofaunal provinces
. .
Addenda
. . . . . . . . . . . . . . . . . . . . . . .
References
. . . . . . . . . . . . . . . . . . . . . .
11
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303
307
309
314
315
250
T. R. ROBERTS
INTRODUCTION
The freshwater fishes of Africa deserve the attention of evolutionists and
biogeographers for various reasons. African rivers and swamps harbor an
extraordinary assortment of archaic and phyletically isolated fish groups, most
of them endemic, and several bizarrely modified. Some of the non-endemic
groups, characoids for example, appear to have a Gondwanic distribution.
Africa has been a major center for spciation and adaptive radiation of
freshwater fishes, including Ostariophysans, the dominant fishes in the
continental freshwaters of the globe, and mormyroids, an endemic electrogenic
group. Africa provides the foremost examples of adaptive radiation of fishes in
ancient lakes.
The great majority of archaic and phyletically isolated fishes occur in
continental fresh-waters, and Africa has more of such species than any other
continent, representing the Polypteridae, Lepidosirenidae, Denticipitidae,
Osteoglossidae, Pantodontidae, Mormyridae, Gymnarchidae, Notopteridae,
Kneriidae, and Phractolaemidae. Of these families, only Lepidosirenidae,
Osteoglossidae, and Notopteridae occur beyond Africa. (South America,
Europe, Asia, and Australia have relatively few archaic fishes; the second
richest continent in this respect is North America, with Petromyzontidae,
Acipenseridae, Polyodontidae, Amiidae, Lepisosteidae, Hiodontidae, Esocidae,
Umbridae, Percopsidae, and Aphredoderidae.) Polypteridae are regarded by
some investigators as close relatives of the paleoniscoids of the Paleozoic era.
Polypterid relationships are discussed by Daget (1950) and by several authors
in the volume on interrelationships of fishes edited by Greenwood, Miles &
Patterson (1973); the consensus is that they are sarcopterygians. Denticipitidae
is known only from the monotypic genus Denticeps, living in forested coastal
streams in Dahomey and W. Nigeria, and Paleodenticeps, an extinct form from
Miocene deposits in Tanzania. Greenwood (1968) considered that
Denticipitidae might be the unspecialized sister-group of all other living
clupeomorphs; he also found some characters indicating possible relationships
with Osteoglossomorpha. Pantodontidae, Mormyridae, and Gymnarchidae are
highly modified osteoglossomorphs. Mormyridae and Gymnarchidae are
provided with electrogenic and electrosensory organs, and mormyrids have
undergone an extensive adaptive radiation paralleling in many ways the
radiation of the Neotropical gymnotoids, the only other freshwater group with
comparable structures. Kneriidae are the most generalized freshwater members
of the Gonorynchiformes, an order regarded by Rosen & Greenwood (1970) as
the unspecialized sister-group of Ostariophysi. Phractolaemidae is represented
by a monotypic genus found only in rain-forest swamps. Anatomical studies by
Thys (1961) indicate it is air-breathing and related to Gonorynchiformes, but
otherwise virtually nothing is known about the biology or past history of this
strange fish.
Lepidosirenidae, Osteoglossidae, Characidae, Cichlidae, Nandidae, and
Cyprinodontidae are shared (not all of them exclusively) with South America,
possibly dating from before the break-up of Gondwanaland. Similarities
between some African and South American catfish families may also be related
to this event. Salmoniform fishes of the family Galaxiidae have also been cited
as having a Gondwanic distribution. The family occurs in southern South
DISTRIBUTION OF AFRICAN FISHES
251
America, the S.W. portion of the Cape of Good Hope, Australia, New Zealand,
and several other isolated islands in the S. temperate zone. Some galaxiids are
known to enter the sea, and members of the family such as Galaxias maculatus
presumably crossed wide expanses of ocean. It seems unlikely that the
distribution of Galaxiidae has anything to do with the break-up of Gondwana
(Myers, 1951; McDowall, 1964, 1970, 1973) (see Addenda, p. 314).
Notopteridae, Bagridae, Clariidae, Schilbeidae, Channidae, Anabantidae, and
Mastacembelidae are shared exclusively with Asia. Ichthyologists have long
been intrigued by this pattern, but the questions raised as to the place of origin
and the route and timing of dispersal of these families from one continent to
the other remain unresolved. Bagridae and Clariidae are known from Miocene
and Pliocene deposits in Africa, but fossils of the other families have not yet
been found there.
Ostariophysi probably originated in Gondwanaland before the separation of
Africa and South America, but there is no agreement as to where and when the
three main branches of Ostariophysi first appeared. Africa is the only major
continental area where characoids, cyprinoids, and siluroids occur together, and
they have been there a relatively long time. The earliest known African fossils
of characoids are Oligocene in age, while those of cyprinoids and freshwater
siluroids are from Miocene deposits. Characoids are the most generalized
Ostariophysi; they are presently restricted to Central and South America and
Africa, and although Eocene fossil teeth from France are remarkably similar to
those of living members of the African characid subfamily Alestiinae (Cappetta
et al., 1972), there is no fossil record of them in either North America or Asia.
Cyprinoids are present in North and Central America, Africa and Asia, but are
entirely absent from South America. Their greatest diversity occurs in Asia, and
it is generally held that they originated there. In Africa, characoids
predominate in large lowland rivers with relatively rich fish faunas, and are
poorly represented or absent in high gradient streams, especially in
impoverished mountainous areas. Cyprinoids, in contrast, are often the
predominant fishes in mountain streams, including the Atlas mountains,
Abyssinian highlands, and S.W. Cape, where characoids are totally lacking. It is
conceivable that cyprinoids originated in Europe or Africa from characoid-like
ancestors, dispersed into Asia via highland routes, subsequently invading and
diversifying in the Asian lowlands in the absence of competition from
characoids. The earliest known cyprinoids have been found in Paleocene and
Eocene deposits in Europe. They are unknown in North America, Asia, and
Africa until Miocene times. Four phyletic lines, represented by Barilius, Barbus,
Labeo, and Garra, are widely distributed in Africa; Barbus and Labeo have been
identified in Pliocene deposits from lower Egypt (Greenwood, 1972a).
There are major differences in the richness and diversity of fishes, and their
generic and species composition, in such large river systems as the Nile, Zaire
(formerly Congo), Zambesi, and Orange. An extraordinarily high level of
endemism occurs in the Zaire basin and in several coastal rivers of Lower
Guinea. In contrast, the generic and species composition throughout the
Nilo-Sudan ichthyofaunal province, including the Middle and Lower Nile, the
entire Niger and Chad basins, and several West African coastal rivers, is
relatively uniform. The endemic African families Mormyridae, Distichodontidae, Ichthyboridae, Mochokidae, and Amphiliidae as well as the
252
T. R. ROBERTS
non-endemic families Clupeidae, Characidae, Cyprinidae, Bagridae, Clariidae,
Cichlidae, and Cyprinodontidae have undergone adaptive radiations or
extensive speciation in riverine habitats. African lakes provide the three
foremost examples of explosive intralacustrine speciation of fishes. Lake
Victoria has 160 species of the cichlid genus Huplochromis, all derived from
one or a few ancestral riverine stocks. Four Huplochromis lineages within the
lake have given rise to forms so distinctive that they have been placed in
monotypic genera (Greenwood, 1956, 1959a). In L. Malawi differentiation of
Huplochromis-like stocks has proceeded even further, producing 200 species
and 21 genera. Malawi also has an endemic species flock of a dozen Clariidae
and three endemic cyprinids of the subfamily Bariliinae. Lake Tanganyika has
the greatest diversity of endemic lacustrine fishes in the world. There are 35
genera and over 120 species of endemic Tanganyikan Cichlidae, plus numerous
endemic forms in eight other families. Unlike the endemic cichlid genera of
Victoria and Malawi, which are thought to be monophyletic at the level of the
genus Huplochromis, the Tanganyikan cichlid genera appear to be derived from
no fewer than four generically distinct riverine stocks. The Tanganyikan fishes
have had a maximum of perhaps six to ten million years in which to evolve,
those in Malawi perhaps a million and a half to two million years, and those in
Victoria about a half million years (Fryer & Iles, 1972). Other endemic
lacustrine fishes are €ound in at least 22 smaller African lakes. Of particular
interest are five species of Huplochromis which apparently evolved in L.
Nabugabo after this smalI lake was cut off from L. Victoria by the completion
of a sand-split only 4000 years ago (Greenwood, 1965).
The main body of this paper is divided into three sections. The first deals
with biological properties of African fishes affecting where they live and their
ability to disperse, adaptations contributing t o their success in particular
habitats, competition among fish groups, and related topics. The section
provides a broad look at African geography, and indicates in general terms how
present and past conditions of river systems, lakes, mountains, forests, deserts,
and other features have affected fish distribution. It includes a brief review of
Pleistocene climatic change in Africa and of zoogeographically significant
Cenozoic fossil remains of African fish groups. In the third and lengthiest
section the present distribution of African freshwater fishes is discussed in
terms of ichthyofaunal provinces. The provinces recognized are the Maghreb,
Abyssinian highlands, Nilo-Sudan, Upper Guinea, Lower Guinea, Zaire, East
coast, Zambesi, Quanza, and Cape of Good Hope. The paper concludes with a
discussion of the faunistic relationships of the endemic lacustrine fishes.
Although some maps have been provided, the problem of reducing them for
publication made it impractical to label the many rivers, lakes, and other
features mentioned in the text. Readers wishing t o follow the discussion closely
may find it useful to have an atlas handy.
The names of the ichthyofaunal provinces are based on terms for
geographical regions with which they correspond closely, although not
perfectly in every instance. Thus “Guinea” is a term formerly applied to the
entire coast of central W. Africa from Senegal to Angola. This meaning is
retained in the modern term, the Gulf of Guinea. Guinea is divided by the
Niger Delta into Upper Guinea and Lower Guinea. The Upper Guinean
ichthyofaunal province includes all of Upper Guinea except Dahomey,
DISTRIBUTION O F AFRICAN FISHES
253
Togoland, and that part of Ghana occupied by the Volta basin. The Lower
Guinean ichthyofaunal province includes all of Lower Guinea east to the Zaire
River, plus the forested part of the Lower Niger basin. The most recent
nomenclature for fishes is followed except in a few instances where this would
cause confusion. Thus no distinction has been made between the familiar
Tilapia and the new generic concepts of Sarotherodon and Coptodon, because
these concepts have not been carefully applied on a continent-wide basis.
Labeobarbus is retained as a “subgeneric” term for a group of large Barbus
widely distributed in Africa, even though Labeobarbus sensu stricto refers to a
group of cyprinids found only in Asia.
BIOLOGICAL BACKGROUND
Primary, secondary, and peripheral divisions of fresh water fishes
The differing abilities of various groups of freshwater fishes to disperse
across the sea must be taken into account when considering their distribution
(Myers, 1938, 1949, 1951; Darlington, 1948, 1957). They may be separated
according t o their tolerance of salt-water into three divisions: Peripheral,
Secondary, and Primary. The Peripheral Division consists of those that live
readily in both fresh-water and salt-water, so that the sea serves as a highway
for their dispersal. I t includes many species that live chiefly in the sea but enter
fresh-water sporadically, as well as those with a diadromous life cycle. Some are
unable to complete their life cycle in fresh-water, but others exist in
fresh-water for generation after generation and may evolve endemic freshwater
forms. The Secondary Division comprises those that live almost exclusively in
f resh-water but tolerate sea-water well enough t o disperse through it. Most of
the species in this group are endemic t o fresh-water. Behavioral patterns and
competition probably play important roles in keeping some of them in
fresh-water . The Primary Division comprises the “obligatory” freshwater fishes.
They have great difficulty crossing sea barriers because they are physiologically
unable to tolerate salt-water. The sea constitutes a formidable barrier for them.
The three divisions are complicated and frequently cut across taxonomic lines.
They should be treated as useful working hypotheses rather than as absolute
facts. The divisions to which the fish families found in African fresh-waters
belong are indicated in Table 1. More than 34 families (many occurring only
sporadically in fresh-water) are referred to the Peripheral Division. Six families
are secondary-division. Twenty-four families are primary-division. N o other
continent has this many primary-division families.
Most primary-division fishes disperse readily within a given hydrographic
basin unless they are inhibited by barriers such as waterfalls or extensive
swamps. The most important extensions in their ranges, those from one basin
t o another, are mainly due t o stream capture and other physiographic changes
that alter the hydrographic network. In some instances a relatively minor
stream capture permits the establishment of an entire fish fauna in an adjacent
basin. Fishes also move from basin to basin, but less readily, by crossing
swampy divides (the poorly-oxygenated waters of which are a formidable
barrier to most fish groups) or by being carried in floodwaters that breach
low-lying watersheds. A very few fishes are able t o cross drainage divides by
Table 1.. Families of fishes in the fresh-waters of Africa*
Division
ELASMOBRANCHII
Carcharhinidae
Priistidae
Dasyatidae
Peripheral
Peripheral
Peripheral
DIPNOI
Lepidosirenidae
BRACHIOPTERY GI I
Polypteridae (E)
Airbreathing
Mountainclimbing
Endemic
genera
-
Non-endemic
genera
Species
Range beyond Africa
I?
1
1
1
Widespread marine
Widespread tropical
Widespread, mostly tropical
No
1
4
South America
Yes
No
2
10
Peripheral
Peripheral
No
No
No
No
-
3
2
Widespread, tropical and subtropical
Tropical Atlantic, Indo-Pacific
Anguilliformes
Anguillidae
Peripheral
No
YeS
-
5
Widespread, tropical to temperate
Clupeiformes
Clupeidae
Denticipitidae (E)
Peripheral
Primary?
No
No
No
No
12
1
20
1
Worldwide, tropical to temperate
1
1
2
16
1
1
1
2
200
1
No
No
No
No
No
No
-
Primary
Yes
Primary
TELEOSTEI
Elopiformes
Elopidae
Megalopidae
h)
VI
P
j
7
P
m
P
Osteoglossiformes
Osteoglossidae.
Pantodontidae (E)
Notopteridae
Mormyridae (E)
Gymnarchidae (E)
Primary?
Primary
Primary
Primary
Primary
Yes
Yes
Yes
No
Yes
No
No
No
No
No
Salmoniformes
Salmonidae
Galaxiidae
Peripheral
Peripheral
No
No
Yes
Yes
-
1
1
N. temperate and Arctic
S. temperate
Gonorynchiformes
Chanidae
Kneriidae (E)
Phractolaemidae (E)
Peripheral
Primary
Primary
No
No
Yes
No
Yes
No
-
1
18
Indian Ocean. W. Pacific
4
1
1
Characoidei (Ostariophysi)
Hepsetidae (E)
Characidae
Distichodontidae (E)
Citharinidae (E)
Ichthyboridae (E)
Primary
Primary
Primary
Primary
Primary
No
No
No
No
No
No
No
No
No
No
1
21
10
2
10
S.E. Asia, New Guinea, Aust., S. Amer.
India, S.E. Asia
1
loo+
60
8
19
Central and S. Amer.
;]
Cyprinoidei (Ostariophysi)
Cy prinidae
Cobitidae
“Primary”
Primary
Siluroidei (Ostariophysi)
Bagridae
Schilbeidae
Amphiliidae (E)
Clariidae
Malapteruridae (E)
Mochokidae (E)
Ariidae
Plotosidae
“Primary”
Primary
Primary
Secondary?
Primary
Primary
Peripheral
Peripheral
Atheriniformes
Cyprinodontidae
Secondary
Gasterosteiformes
Syngnathidae
No
Yes
11
6
300+
Europe,
N. Amer.
Asia (incl. Arabian pen.),
Yes
Yes
-
2
2
Europe, Asia (excl. Arabian pen.)
No
Yes
15
1
80
30
50
60
2
140
No
8
8
-
Asia
India, S.E. Asia
Yes
Yes
No
Yes
No
No
-
1
1
“Yes”
No
22
1
150c
Widespread, tropical to temperate
Y
cn
Perip h era1
No
No
-
4
10
Widespread, tropical to temperate
2
[x1
Channiformes
Channidae
Primary?
Yes
Yes?
-
1
3
India, S.E. Asia, Indonesia
Synbranchiformes
Synbranchidae
Secondary
Yes
No
1
1
2
Widespread tropical
Perciformes
Centropomidae
Monodactylidae
Nandidae
Cichlidae
Peripheral
Peripheral
Secondary?
Secondary
No
No
No
No
No
1
1
1
No
No
Yes
1
6
3
Peripheral
Secondary?
Primary
No
Yes
Yes?
Yes
Widespread tropical
Indian Ocean, Red Sea, W. Pacific
Tropical Asia and S. Amer.
Syria, Madagascar, 5. Asia, Central and
S. Amer.
Widespread, mostly tropical
India, S.E. Asia
Euphrates, India, S.E. Asia
Pleuronectiformes
Cy noglossidae
Peripheral
Tetraodontiformes
Tetraodontidae
Peripheral
Gobiidae
Anabantidae
Mastacembelidae
No
Yes
No
No
No
No
9
2
1
-
9
2
88
~
-
1
1
2
620i
Syria, S.E. Asia
Tropical
Indian Ocean, tropical W.Pacific
?
?
-
20
Yes
3
2
1
1
40
No
No
1
1
2
Tropical Indo-Pacific
No
No
-
1
6
Worldwide, tropical to subtemperate
NO
Excluded from the table are marine families with species which live in t h e sea but occur seasonally or sporadically in t he mouths and lower courses
of rivers. Such families are Ophichthidae, Atherinidae, Belonidae, Gasterosteidae, Serranidae, Kuhliidae, Carangidae, Gerridae, Lutjanidae, Pomadasyidae,
Sciaenidae, Sphyraenidae, Polydactylidae, Blenniidae, and Pleuronectidae. None of them is represented b y species endemic to A f x a n fresh-waters.
4
C
‘11
+P
P
ij
k
2
Vl
z
n
cn
v)
N
UI
256
T. R. ROBERTS
means of terrestrial locomotion, including some African Clariidae. Transport by
waterspouts may occasionally permit fishes to reach isolated interior basins, for
example, elevated crater-lakes in parts of W. and E. Africa. I t has been
suggested that birds occasionally drop live fish into neighboring basins. African
fishes most likely to be dispersed in this fashion are presumably oral-brooding
Cichlidae. Some African cyprinodonts deposit drought-resistant eggs in ponds
that are drying up, and these eggs could be transported in mud on the feet of
migratory birds for long distances and remain viable. Primary-division fishes
have also undoubtedly dispersed coastwise between river mouths, perhaps in
sea-water greatly diluted by floodwaters or in freshwater lenses floating atop
denser sea-water. A very few primary-division fishes have crossed relatively
narrow saltwater channels, notably in the East Indies (Mayr, 1944; Myers,
1951). In those instances in which transport by man can be ruled out, they
may have crossed by means of waterspouts or freshwater lenses.
Tolerance of deoxygenated water; air-breathing fishes
Tolerance of deoxygenated water varies among freshwater fishes and affects
their ability to disperse. Almost all fishes living in water of shallow to moderate
depths will probably swim to the surface and “gulp air” if they have difficulty
obtaining oxygen from the water. This behaviour is undoubtedly adaptive in
itself, and pre-adaptive for the evolution of physiological and morphological
adaptations for true air-breathing. It occurs in some fishes in which one might
not expect it. Thus, I have observed large individuals of the African mochokid
catfish Hemisynodontis membranaceus swim upside down in open water in
order to gulp air with their inferior mouths (see Addenda). Species that
constantly swim at the surface and gulp at the air when they are in trouble are
not true air-breathers, and will usually die in a relatively short time if they
remain in deoxygenated water. On the other hand, some small cyprinodonts are
apparently able to live indefinitely in otherwise totally deoxygenated habitats
by utilizing oxygen from the top few millimeters of surface water (Lewis,
1972). Regardless of the cause of deoxygenation, in natural habitats the surface
film and the first few millimeters of water beneath it are almost always
saturated with oxygen. Fishes capable of utilizing this layer effectively should
disperse through deoxygenated habitats as readily as the best air-breathers. The
degree to which air-breathing permits certain fishes to pass through
deoxygenated water is of more concern to the zoogeographer than the
particular physiological and morphological adaptations involved. Some
“obligatory” and faculative air-breathers often occur in habitats that are
periodically subjected to deoxygenation, such as swamps and ox-bows that
become cut off from the main rivers during the dry season. They should be able
to disperse through deoxygenated waters as easily as through oxygenated
waters. Other forms in which air-breathing is accessory t o branchial respiration
and does not seem to be so essential to their survival, are nonetheless better
equipped to pass through deoxygenated waters than fishes that cannot breathe
air at all, and their distributions usually show this. Air-breathing fishes are
commoner in tropical fresh-waters than anywhere else. Thus ten or possibly 11
of the 24 primarydivision and two of the six secondary-division freshwater
families inhabiting Africa are air-breathers (Table 1). Seven of these African
DISTRIBUTION OF AFRICAN FISHES
257
air-breathing families are shared exclusively with Asia, suggesting that
air-breathing facilitated dispersal between these two continents. Four of the
families are endemic to Africa. Two are shared with both S. America and Asia
(Osteoglossidae and Synbranchidae), and only one is shared exclusively with S.
America (Lepidosirenidae). Representative African air-breathing fishes are
illustrated in Fig. 1
qg-----
4zc2z*
E
C
Figure 1. Representative African air-breathing fishes: A, Profoptems (Lepidosirenidae);
B, Polypterus (Polypteridae); C , Xenomystus (Notopteridaef; D , Phractolaemus (Phractolaemidae); E, Channa (Channidae); F, Mastacembelus (Mastacembelidae); G , Epiplatys (utilizes
oxygen in surface film) (Cyprinodontidae); H, Ctenopoma (Anabantidae).
Mountain-climbing or orobatic fishes
Another biological property affecting the vagility of fishes, and differing
greatly from group to group, is the ability to climb mountains. This topic,
relevant to discussions of fish distribution between continents as well as within
them, has not received the attention it deserves. Mountains are insurmountable
barriers for many fish groups, but for a few they are veritable highways.
Endemic African orobatic or mountain-climbing fish families are Kneriidae,
Mochokidae, and Amphiliidae; non-endemic orobatic families (all shared with
Asia, and some also with Europe) include Anguillidae, Salmonidae, Cyprinidae,
Cobitidae, Bagridae, Clariidae, Cichlidae, and Anabantidae. The great majority
of African fish families are absent or almost entirely absent from mountain
streams and even highlands, including Lepidosirenidae, Polypteridae,
Denticipitidae, Osteoglossidae, Pantodontidae, Notopteridae, Gymnarchidae,
Phractolaemidae, Hepsetidae, Characidae, Distichodontidae, Ichthyboridae,
Malapteruridae, Centropomidae, and Nandidae (Table 1).Most of these families
are absent from High Africa. As previously indicated, many are air-breathing,
typically inhabiting lowland lakes, sluggish rivers, and swamps. Polypterus
258
T. R . ROBERTS
occurs in High Africa only in L. Tanganyika and in the Lualaba and Malagarasi
drainages. Protopterus has a spotty distribution in East Africa and in the
Zambesi system but is otherwise absent from High Africa. Distichodontidae are
almost all restricted to lowlands, the genera Nannocharax and
Hemigrammocharax providing minor exceptions. Some species of
Perrocephafus live in high gradient streams, and the Mormyridae are faily well
represented in High Africa; yet few if any of the mormyrids are really good
mountain climbers.
Clariid catfishes of the genus Clarias are among those fishes reaching the
highest altitudes in mountain streams and lakes everywhere in Africa except in
the Maghreb and the S.W. portion of the Cape. The Mochokid genera
Chiloglanis and Atopochilus are rheophilic, and Chiloglanis are typical
inhabitants of mountain streams in Upper and Lower Guinea, the Zaire basin,
and S. Africa, even penetrating the Cape ichthyofaunal province. Rheophilic
Synodontis occur in rapids of lowland rivers, but none ascend mountain
streams. Most amphiliid genera are rheophilic, and Amphilius especially has
ascended high altitude streams in the Cameroon highlands, East Africa, and S.
Africa. The African species of Channa are apparently confined to lowland
situations. The Asian Channa orientalis, however, ranges from river mouths and
lowland plains to high.-altitude mountain streams. This is an important food
species, and easily transported alive, so possibly it has been extensively
introduced into mountain areas by man. Three of the four major groups of
Cyprinidae present in Africa, viz. those represented by Barbus, Labeo, and
Garra, occur in high altitude streams in mountainous areas throughout most of
Asia and Africa. The fourth group, represented by Barillus, is commonly
present in large lowland rivers and in high gradient streams, but is absent from
mountain streams at higher altitudes. Cobitidae occur in lowland and highland
streams throughout Asia and Europe. The only two species of loaches in Africa,
one in the Rif Mts. of Morocco and the other in L. Tana in the Abyssinian
highlands, obviously owe their presence t o their ability to climb mountains.
While Cichlidae are typically inhabitants of lakes or low gradient streams,
rheophilic Tilapia and Haplochromis occur in many parts of Africa, and
exclusively rheophilic cichlid genera occur in the Niger basin (Gobiocichfu)and
Zaire basin (Steatocranus, Teleogramma, Orthochromis). Tilapia nilotica occurs
throughout much of the Abyssinian highlands, including L. Tana and other
localities inhabited only by orobatic fishes.
Questions have been raised as t o the ability of mountain fishes t o cross
lowlands. In discussing specialized torrential fishes in India, Hora (1947: 4)
stated that “the highly oxygenated water of torrential streams has induced
structural modifications in their respiratory organs. The gill openings are
restricted and the gills themselves are also reduced, so that such fishes cannot
live for long in sluggish waters generally poor in oxygen . . . for their migration
from one place t o another, a marsh, sluggish stream, or even a deep river can
act as a barrier. . . their dispersal can only be through the continuity of
torrential streams.” Hora has perhaps over-stated the case. Most torrential
fishes probably can live in poorly oxygenated waters for considerable periods.
After a spate followed by a period without rain, torrential fishes may be
stranded in isolated pools of diminishing size, even in quite large mountain
streams. Such pools can become very stagnant and still harbor living fishes
DISTRIBUTION O F AFRICAN FISHES
259
before they dry up entirely or become re-connected by the next rains. The
warmer temperatures of lowland areas might be unfavorable for fishes adapted
to high altitude streams, but no evidence bearing on this aspect for Indian or
tropical African fishes has come to my attention. Whitehead (1963: 198) stated
that L. Victoria acted as a barrier to the westward dispersal of mountain
catfishes such as Leptoglanis, Amphilius, and Chiloglanis inhabiting fast-flowing
upper reaches of eastern affluents of the lake such as the Nzoia and Yala. But
all three of these genera have dispersed widely in Africa and must have crossed
lowland areas to reach some of the isolated mountains where they have been
found. I t is doubtful that L. Victoria is merely a physical barrier to their
passage. There is a zoogeographically important distinction to be made between
the ability to establish permanent populations in an area and being able to
disperse across it. The scarcity or absence of African mountain fishes such as
Varicorhinus, Labeobarbus, Amphilius, and Chiloglanis in lowland areas and in
habitats such as L. Victoria is attributable to biotic pressures which inhibit
their establishment and to their habit of swimming upstream until they reach
headwaters. Families and genera of freshwater fishes that range most widely
within Africa include a disproportionately high number of mountain-climbing
forms. Almost all of the groups shared by Africa and Europe or Asia are
well-represented by orobatic forms. Apart from Cichlidae, there are no orobatic
genera or families shared by either Africa or Asia with South America.
Biological interactions among various categories of fishes (complementary
distribution patterns)
Distribution of the divisions of freshwater fishes is markedly
complementary. Primary-division fishes are richest and most diverse in the main
tropical continental areas (excluding Australia-New Guinea), while
secondary-division forms exhibit endemism mainly in Australia-New Guinea,
Madagascar, non-continental portions of the East Indies, on oceanic islands,
and in portions of the Temperate Zones where primary-division fishes are
almost entirely absent. This pattern is only partially explained by the
differences in the ability of primary- and peripheral-division fishes to disperse.
Of equal importance is the tendency of primary- and secondary-division fishes
to exclude more euryhaline forms from the same habitats. The Amazon basin is
physically accessible to many peripheral-division fish groups inhabiting the
coastal waters of Brazil, and one might expect many of them to have invaded
and speciated in the great variety of freshwater habitats offered by the
Amazon. In fact, however, of the 1300 freshwater Amazonian fishes, only 50
species (belonging to 11 families) belong to the peripheral division (Roberts,
1972: 124-5). Although most of these species are endemic to the Amazon, and
include several distinctive genera, none of the groups is represented by more
than ten species. The peripheral-division catfish family Ariidae has many
endemic forms along the Atlantic coasts of Central and S. America, and a good
number of these extend to the mouth of the Amazon. One might expect
Ariidae in all of the large Amazonian rivers, but they are absent. Presumably
the main factor in their exclusion is the rich primary-division catfish fauna of
the Amazon. Ariidae have evolved endemic riverine forms in Madagascar, New
Guinea, and elsewhere. Ariidae obey the general rule that peripheral-division
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T. R. ROBERTS
fishes have difficulty invading fresh-waters dominated by primary-division
fishes. This rules applies very well to Africa, where the total number of
endemic freshwater species of peripheral-division fishes is around 70, or less
than five per cent of the total freshwater fish-fauna. The most speciose
peripheral-division group is Clupeidae, with 20 endemic species belonging to 12
endemic genera; seven of these genera are endemic to the Zaire basin and
constitute the most extensive radiation of peripheral-division fishes in African
fresh-waters. In continental areas in which primary-division fishes predominate,
peripheral-division forms tend to occupy geographically isolated habitats. Thus
the only salmoniform fishes in Africa are populations of the European trout
Sulmo truttu in the mountainous area of Kabylia in Algeria and an endemic
species of the S. Temperate genus Guluxius in the S.W. Cape of S. Africa. The
African distribution of eels of the diadromous genus Anguilla is similar. The
European eel Anguillu unguilla ascends mountain streams on the Atlantic and
Mediterranean coasts of N. Africa, and three species of Anguillu which spawn in
the Indian Ocean ascend the Zambesi and numerous other rivers in E. and S.
Africa where the ability of the elvers to climb sheer rock surfaces (see Balon,
1971) enables them to grow up in mountain tributaries inaccessible to other
fishes. Yet another peripheral-division group in isolated African mountain
streams is the tropical gobiid genus Sicydium (Myers, 1949) which occurs on
numerous high islands throughout the western Pacific and Indian Ocean
including Madagascar and in the eastern Atlantic on volcanic islands in the Gulf
of Guinea. It occurs on the African mainland only in the elevated coastlands of
Cameroons and Rio Muni. Other peripheral-division fishes live in the same
waters as primary- and secondary-division forms but have unobtrusive habits
and reduced body size. African examples are provided by Gobiidae and
Syngnathidae. Although various gobies inhabit the seas and brackish waters of
the African coastline, only a single genus occurs widely in inland waters. This is
Kribiu, with one or two species or subspecies in the lowland forest streams of
the Guinean region and another species or subspecies in forested portions of
the Zaire basin including the Cuvette Centrale. These forms seldom exceed 30
or 35 mm in length and are usually smaller. Since they reproduce throughout
the year, the average size of individuals in any given population is usually less
than half that of adults, and therefore smaller than the smallest adults of
primary- and secondary-division fishes which inhabit the same streams but tend
to reproduce mainly during the rainy season. Freshwater pipefishes of the
genus Syngnuthus have discontinuous distribution in small forested streams in
Upper and Lower Guinea. The one or two species living permanently in W.
African fresh-waters grow to about 100 mm long, but this is considerably
smaller than the W. African marine and estuarine species of the same genus.
Like Kribiu, they are secretive and reproduce throughout much of the year, so
that populations of these slender fishes usually include many individuals
15-20 mm long, considerably smaller than the primary- and secondary-division
fishes living in the same streams (Clausen, 1956,observations in S.W.Nigeria;
personal observations in S.W. Ghana).
The only large, peripheral-division fish widely distributed in the inland
waters of Africa is Lutes niloticus, the Nile perch. Lutes are large, bass-like
predators, living in open, well-oxygenated waters. The genus is usually placed in
Centropomidae, but this assignment should be reexamined in the light of
DISTRIBUTION O F AFRICAN FISHES
261
modern criteria for determining phyletic relationships (i.e., shared
specializations). A single species of Lates occurs outside of Africa. L. calcarifer
is known from the sea, tidal waters and rivers in the Persian Gulf, and along the
coasts of India, S. China, Indonesia, the Philippines, New Guinea, and N .
Australia. Five species of Lates are endemic to Africa, four of which are
restricted to deep lakes in East Africa. L. niloticus occurs in the Nile, Niger,
Chad, Senegal, Volta, Zaire, Albert, Rudolf, Ganjule, and Abbaya basins. It is
absent from Africa E. of the western rift valley and S. of the Zaire basin
(including the Zambesi) and also absent from lakes Victoria, Edward, Kim,
Tanganyika, and Malawi. There seem to be no records of the species from
salt-water. Throughout most of its range L. niloticus apparently exhibits little
or no morphological differentiation, but in L. Rudolf it forms two subspecies
(Worthington, 1932, 1937). One subspecies lives in shallow, inshore waters of
the lake, the other in deeper, offshore waters. The latter subspecies has
enlarged eyes. A similar situation occurs in L. Albert (Holden, 1967), where L.
niloticus lives inshore, and L. macrophthalmus, a large-eyed form regarded as a
distinct species, lives offshore and in deeper waters. Lake Tanganyika has three
endemic species of Lates and a monotypic endemic genus, Luciolates (Poll,
1953). L. angustifrons occurs inshore and on the bottom to depths of 35 m
(thus occupying the zone where one would expect L. niloticus); the large-eyed
L. mariae occurs offshore and on the bottom at depths t o 75 m; and L.
rnicrolepis seems to be pelagic. Luciolates is also pelagic and apparently
undergoes diurnal vertical migrations in association with the endemic
Tanganyikan clupeids upon which it feeds. The presence of L. niloticus in the
Senegal, Volta, Niger, Chad, Nile, and Rudolf basins is part of the evidence that
these basins freely exchanged aquatic faunal elements in the past. Its
occurrence in lakes Abbaya and Chamo (reported as L. macrophthalmus by
Parenzan, 1939) supports the hypothesis that the S. Ethiopian rift valley lakes
formerly drained into L. Rudolf. If these lakes do have large-eyed populations
of Lates, they are probably either endemic or else more closely related to the
deep-water subspecies of L. niloticus in L. Rudolf than t o the deep-water
species of Lates in L. Albert. The deep-water and offshore forms of Lates
probably evolved independently in each lake from ancestral stocks t o
populations of the living L. niloticus.
Lates has a long fossil record in Africa, the highlights of which can be
quickly reviewed. The earliest remains, from the Fayum of Lower Egypt, are
Middle-Upper Eocene. Miocene deposits with Lates are known from Tunisia,
Libya, Lower Egypt, the vicinity of lakes Edward and Albert, and Rusinga
Island in L. Victoria. Although Lates is absent from L. Edward, Pleistocene
fossils attest to its former presence there (see Addenda). Finally, Quaternary
deposits of large Lates occur at many sub-Saharan and Saharan localities
presently too dry to support any fishes. Except for lakes Victoria, Edward and
Albert, fossil Lates are unknown from High Africa.
African secondary-division fishes also tend t o complement primary-division
forms in their distribution, but the emphasis is on ecological rather than
geographical segregation. Cyprinodonts and cichlids are the two main
secondarydivision groups. The “giants” among cyprinodonts have repeatedly
evolved in habitats that are geographically or ecologically isolated from rich
fish faunas, i.e., Anablepidae, the largest Fundulinae and the largest Poeciliinae
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T. R. ROBERTS
in brackish coastal waters and rivers of Middle and South America; Orestiidae
in Lake Titicaca and neighboring Andean lakes formerly connected with it; and
Adrianichthyidae in lakes on the island of Celebes. In W. Africa, the largest
cyprinodonts are Aplocheilichthys spilauchena, restricted to brackish water and
the lower reaches of rivers, and species of Epiplatys in small streams above
waterfalls or along the margins of swampy areas where they are frequently the
only fishes present. Most African species of Cyprinodontidae occupy habitats
that are marginal to those occupied by the main body of freshwater fishes. The
species in large rivers are of small size and tend to live along the edges of the
rivers rather than out in the mainstream.
Cichlidae are represented by more genera and species in African fresh-waters
than any other fish family, but they are not predominant in the rivers of
Africa. A large majority of the African cichlids are endemic to lakes, where
primarydivision fishes are relatively poorly represented. Primary-division
fishes, with a long evolutionary history in running water, are apparently poorly
adapted to still-water habitats. In particular, their modes of swimming and of
reproduction seem unsuited for successful exploitation of lakes. Most
mormyrids, characoids, cyprinoids, and siluroids, and especially the larger
species, produce large numbers of eggs and often migrate long distances
upstream in order t o spawn. Reproductive activities usually begin with the
oncoming rainy season and end one to three months later. Once the spawning
has been completed, the role of the parents is over. Cichlidae, on the other
hand, produce smaller numbers of eggs but tend to breed throughout much of
the year. Parental involvement does not end with the act of spawning.
Subsequent events depend on whether the parents are substrate spawners or
oral brooders. In substrate spawners, the eggs are attached to a rocky surface or
deposited in sandy or gravelly nests, and then guarded by one or both parents.
After the eggs hatch, the young stay close to the parent for the first two or
three weeks, after which they tend to disperse. In oral brooders, usually the
female parent but sometimes the male, depending upon the species, takes the
eggs into its mouth until they hatch. After the eggs hatch, the young spend part
of their time inside the parent’s mouth and part outside, and only begin to
disperse when they are two or three weeks old. Both forms of parental care
occur in riverine and lacustrine cichlids in Africa. The cichlid flocks of lakes
Victoria and Malawi are composed entirely or almost entirely of oral brooders,
whereas many of the L. Tanganyika forms are substrate spawners. The eggs of
most primary-division fishes probably are more readily dispersed, less subject t o
predation, and find conditions most favorable for development in running
water. Thus some primary-division fishes inhabiting the E. African lakes,
including some mormyrids, characoids, and cyprinoids, apparently do not
reproduce in the lakes but ascend rivers in order to spawn. Most of the parental
care in freshwater fishes in tropical Africa, S . America, and Asia is primarily
involved with enhancing the survival of eggs and young in forms that reproduce
in oxygen-poor waters, with protection from predators as a secondary factor
(Roberts, 1972: 130-3 1). The main exception t o this generalization is provided
by the Cichlidae. The few African primary-division fishes that care for their
eggs and young, including Protopterus, Heterotis Gymnarchus, and
Anabantidae are all air-breathing, often archaic forms which have been largely
unsuccessful in the open waters of the lakes (see Addenda).
DISTRIBUTION O F AFRICAN FISHES
263
Although 1 3 of the 30 African primary- and secondary-division fish families
are air-breathing, the total number of species involved represents less than ten
per cent of the African fish fauna. Air-breathing groups simply have not
speciated as extensively as many other groups. There are four endemic
air-breathing families in Africa. Three of these are represented by monotypic
genera: Pantodontidae, Gymnarchidae, and Phractolaemidae. The fourth,
Polypteridae, is represented by Erpetoichthys, which is monotypic, and
Polypterus, with nine species. Osteoglossidae is represented in Africa by a
monotypic genus, Hetero tis, and Lepidosirenidae by an endemic genus,
Protopterus, with four species. It should be noted that all of the fishes just
enumerated belong to archaic, phyletically isolated groups, and that they live in
the lowland freshwaters of tropical Africa where primary-division fishes are
most numerous. Air-breathing presumably played a significant role in their
survival. The largest air-breathing families in Africa are Clariidae and
Anabantidae, with 50 and 20 African species, respectively. A few deep-water
species of Clariidae in lakes Tanganyika and Malawi have evidently lost the
ability to breathe air. The family Anabantidae has more species in tropical Asia,
where it has radiated extensively. So far as known, there is not a single
air-breather among the 300+ species of Cyprinidae and 600+ species of
Cichlidae living in Africa. Air-breathing occurs in a few neotropical characoids
but has not been reported in any of the African ones. At least some Asian
representatives of the family Mastacembelidae are air-breathers, but there is no
information on whether the 40 African species of this family breathe air.
Apart from Clariidae, Africa entirely lacks air-breathing Ostariophysi, and
this may be significant in explaining why so many archaic or phyletically
isolated air-breathing fishes have been able to survive there. (Note that
air-breathing ostariophysans are entirely lacking in N. America.) In S. America,
there are many air-breathing ostariophysans, including some or all members of
Erythrinidae, Lebiasinidae, Gymnotidae, Electrophoridae, Callichthyidae,
Doradidae, and Loricariidae. The highly predatory Hoplias, Erythrinus,
Callichthys, and Hoplosternum are widely distributed.
Ninety per cent of the 1100 African primary-division fish species belong t o
four groups: Mormyridae (200 species), Characoidei (190), Cyprinidae (300+),
and Siluroidei (300). There are some evident reasons for the success of these
groups. Key adaptations involve non-visual sensory organization and
diversification of feeding habits. The success of Mormyridae is attributable t o
their specialized electrogenic and electrosensory adaptations (Lissmann, 19 5 5 ;
Bennett, 1971). All aspects of mormyrid behavior and biology have been
affected by their electric faculties. The electrical fields generated by their weak
electric organs are only possible in fresh-water, and it is noteworthy that the
only other fishes with electric adaptations comparable to those in Mormyridae
are the Gymnotoidei, primary-division fishes evidently derived from
Characoidei but restricted to Central and S. America. The electric faculties of
gymnotoids and mormyrids evidently enabled them to feed on a rich bottom
fauna of small worms and larval insects which is relatively unavailable to most
other fishes, and numerous examples of evolution of tubular mouths with small
openings occur in both groups. Characoids, cyprinids, and siluroids belong t o
the Ostariophysi or Cypriniformes, and thus possess the Weberian apparatus, a
paired chain of four ossicles (modified elements of the first four vertebrae)
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T. R. ROBERTS
which are functionally analogous to mammalian earbones. The ossicles conduct
amplified vibrations from the air-filled anterior chamber of the swimbladder to
a thin-walled area in the bony chamber surrounding the membranous labyrinth
of the inner ear. Truly comparable structures do not seem to occur in any other
order of fishes. Ostariophysans are able to hear fainter sounds and a greater
range of frequencies than other fish groups studied thus far. Many Ostariophysi
share a group-specific pheromonal “fright reaction’’ (Pfeiffer, 1967), which
seems to be absent in other fishes excepting Gonorynchiformes. Cyprinids and
siluroids also possess barbels with tactile and gustatory functions. Characoids
and cyprinids, most active in daytime, rely upon vision, hearing, and the fright
reaction to warn them of predators, which they avoid by taking flight.
Siluroids, mainly nocturnal, have specialized defenses, including the unique
arrangement of pectoral and dorsal fin spines which is their hallmark
(Alexander, 1966) and cephalic shields and bony plates covering all or part of
the body in several groups, including Amphiliidae. In characoids the formation
of multicuspid jawteeth and morphological differences in successive sets of
replacement teeth evidently provided the main basis for evolution of diverse
feeding habits (Roberts, 1967). In cyprinoids the toothless protrusible jaws
have undergone considerable modification, as have the highly specialized teeth
on the enlarged fifth ceratobranchials. Catfishes also have diverse feeding
habits, but they have not been as well studied in this respect as other
Ostariophysi and so it is difficult t o generalize about the structures involved.
The taxon cycle in African freshwater fishes
I shall conclude this section on the biological background t o African fish
distribution with a brief discussion of the “taxon cycle.” By taxon cycle is
meant the succession of taxa that inhabit a place as it becomes available for
colonization and gradually acquires a richer fauna, and then loses taxa as it
becomes unfavorable. Pleistocene climatic fluctuations must have induced
cycling of taxa over great areas of the African continent. All stages of the cycle
can be observed at the present time. There are large areas in the Sahara, E.
Africa, and S. Africa that are today uninhabited by fishes, where the cycle has
not been re-initiated, and adjacent to these areas are places where it is in the
earliest stages. At the other extreme lie the Lower Guinean and Zairean
ichthyofaunal provinces, where 27 and 24 of the total -30 primary- and
secondarydivision African freshwater fish families are present. In areas
accessible to the sea, such as brackish lagoons and coastal streams, the cycle is
invariably initiated by peripheraldivision fishes, viz. Anguillidae, Mugilidae,
Gobiidae, and numerous others. The earliest secondary-division fishes are
usually Cyprinodontidae. In the interior continental areas, with no direct access
to the sea, the cycle is initiated by primary- and secondary-division fishes.
Certain genera are characterized by species able to perpetuate themselves in
habitats which will support only a single fish species. Such habitats include
highly intermittent streams, thermal springs, oases, caves. They tend to be
ecologically simple, often with a source of food that is highly irregular and
unpredictable. Fish species characteristic of such situations usually have very
wide geographical ranges, but often they are scarce or absent in areas where the
fish fauna is enriched. The best African examples of genera with such species
are Barbus, Clarias, Aplocheilichthys, Nothobranchius, Tilapia, and
DISTRIBUTION O F AFRICAN FISHES
265
Haplochrornis. Of tnese genera, only Clarias is a true air-breather. Protopterus,
Polypterus, and most other large air-breathing African fishes tend t o inhabit
periodically deoxygenated habitats but only if they are regularly connected t o
large rivers or swamps that are relatively stable and ordinarily populated by
numerous fish species. The differences in the abilities of Clarias, Protopterus,
and Polypterus to perpetuate themselves in marginal habitats is reflected in
their distribution. Protopterus and Polypterus, although they have probably
been in Africa throughout the Cenozoic or at least since the Eocene, have
relatively restricted distributions, whereas Clarias, which evidently evolved at a
later date, is far more widely distributed. Part of the explanation, as already
indicated, is attributable to the mountain-climbing ability of Clarias, and
possibly t o its ability to pass through salt-water. But Clurias is also more widely
distributed in interior low-sand situations than either Protopterus or
Polyp terus.
The families of African freshwater fishes can be ranked according to their
occurrence in the taxon cycle as first order, second order, or third order. First
order families are defined as those families characterized by species
encountered where there are no other fishes. In Africa the most important of
these families are Anguillidae, Cyprinidae, Clariidae, Cyprinodontidae, and
Cichlidae. Second order families, those with species which live in places
inhabited by representatives of from one t o five other fish families, include
Lepidosirenidae, Polypteridae, Kneriidae, Characidae, Bagridae, Schilbeidae,
Amphiliidae, Malapteruridae, Mochokidae, Ariidae, Channidae, Synbranchidae,
Anabantidae, and Mastacembelidae. Third order families, or those in which
representatives are only encountered in faunal situations where there are
representatives of more than five other fish families, include Clupeidae,
Denticipitidae, Osteoglossidae, Pantodontidae, Notopteridae, Mormyridae,
Gymnarchidae, Phractolaemidae, Hepsetidae, Distichodontidae, Citharinidae,
Ichthyboridae, Syngnathidae, Centropomidae, Monodactylidae, Nandidae, and
Tetraodontidae. The fish faunas of the Maghreb, Abyssinian highlands, and
Cape ichthyofaunal provinces and of the Sahara desert consist entirely of firstand second-order families. The highest representation of third-order families
occurs in the forested areas of the Lower Guinean, Zairean, and Upper Guinean
ichthyofaunal provinces, and in the large savannah- and semi-desert rivers of the
Nilo-Sudan ichthyofaunal province. As already indicated, primary- and
secondary-division fishes tend to eliminate peripheral-division fishes from the
areas with the richest continental freshwater fish faunas. I t is also clear that
stenotopic species of primary-division groups in the richest forest areas tend t o
displace eurytopic species of primarydivision groups. Almost all of the
first-order families have numerous stenotopic species which occur only where
third-order families are present. The occurrence of similar taxon cycles, and the
mosaic distribution of species, genera, families, and of ecological groupings
such as primary- and peripheraldivision fishes that it produces, is strong
evidence for the role of competition in determining distributional patterns.
GEOGRAPHICAL BACKGROUND
With an area of eleven and a half million square miles, Africa is the second
largest continent. It extends 5000 miles from Cape Blanc (37'21") to Cape
Agulhas (34"52's). At the Equator it is 2300 miles wide. About two-thirds of
18
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T . R . ROBERTS
the continent lies in the N. Hemisphere; its greatest width, 4600 miles, between
the horn of Somalia (E.) and Cape Verde on its W. bulge, is near 12’ N. Because
Africa straddles the Equator and so much of its land area lies in the lower
latitudes, it has been called “the most tropical continent.”
Intercontinental relationships
Except at its N.E. corner, where it is linked to the Arabian peninsula by the
Suez Isthmus and the shallow Gulf of Suez, Africa is entirely surrounded by
deep ocean: the Mediterranean (N.),Atlantic (W.),Indian Ocean (E.), and Red
Sea (N.E.). Except in the north, where the continent stands lower and has
occasionally been flooded by marine transgressions, it has remained stable and
emergent practically since the Precambrian. The existing outline of the
continent (including Arabia, which is geologically a part of Africa) dates from
the earliest Cretaceous, as shown by the presence of seaward-dipping marine
Cretaceous rocks in many maritime provinces. Africa is completely separated
from continental Europe and only narrowly joined to Asia. At the narrowest
point separating Europe from Africa, the Strait of Gibraltar is eight miles wide
and 1200 f t deep. The Mediterranean islands and the rest of Europe are
separated from Africa by even greater depths. Africa is joined to Asia by the
Suez isthmus, an arid corridor 75 miles wide between the Arabian desert and
the Sinai peninsula. The Red Sea varies in width from 130 to 250 miles and has
an average depth of 1600 ft, but at its N. end the Gulf of Suez is nowhere
deeper than 210 ft. The Suez area may be the only place where freshwater
fishes could have ctossed between Africa and Asia via a land connection since
the Pliocene. At the S . end of the Red Sea, Africa is separated from Arabia by
the Bab el Mandeb, the “Gate of Tears,” a strait 17 miles wide and 1020 f t
deep. A little to the north of Bab el Mandeb, however, the Red Sea is separated
from the Indian Ocean by a sill only 100 m deep. Zeuner (1945) believed that
this sill was exposed during the Pleistocene by a fall in sea level of 90 to 200 m.
Other authors hold that the sea level fell no more than 50 to 70 m.
Most of Africa has existed as a rigid block since the Precambrian. Strongly
folded younger rocks are found only at the margins, i.e., the Atlas Mts. in the
N.W. and the Cape Fold Mts. in the extreme S. The Cape ranges, including the
Drakensberg, date from the Triassic. The Atlas were uplifted by the same earth
movements that formed the Alps. In N. Africa the movement commenced at
the end of the Jurassic, was renewed in the Upper Cretaceous and continued
into the Miocene. During the Miocene huge mountains arose between N.W.
corner of Africa and the Iberian peninsula, forming a broad but extremely
rugged continental connection between Africa and Europe. The Mediterranean
was closed off from the Atlantic and gradually dried up, but before the end of
the Miocene the Straits of Gibraltar opened and the Mediterranean refilled.
Thus ended what was probably the last land connection between Europe and
Africa. Presently existing land connections must be given fair consideration
when discussing the dispersal of primarydivision freshwater fishes now
inhabiting widely separated landmasses. On the other hand, freshwater fishes
must have dispersed widely in mega-continents such as Laurasia and Gondwana
before they broke up t o form the present continents, and these events may
DISTRIBUTION OF AFRICAN FISHES
267
explain the distributional patterns of some older fish groups. All of the
primarydivision groups of fishes and all but two families of secondary-division
fishes now inhabiting South America could have been derived from stocks
shared with Africa (Roberts, 1972: 120-21). Distributional evidence and the
fossil record indicate that characoids, presently found only in Central and S.
America and in Africa, have a Gondwanic distribution (Myers, 1966, 1967).
This conclusion is unaltered by the discovery- that characids related to the
African genus Alestes lived in France during the Eocene (Cappetta et al., 1972).
The presence of characoids in Central America is clearly due to an invasion
from S. America after a land connection was established in the Pliocene. There
is no evidence whatever that characoids formerly lived in N. America. It is
unlikely that characoids would have dispersed between S. America and Africa
via N. America without leaving behind a single living species (to say nothing of
a fossil record) in N. America, especially when one considers the number of
archaic primarydivision freshwater fishes that survive in the Mississippi basin
and elsewhere in the United States.
Arabia
Arabia was an integral part of Africa throughout the Mesozoic and most of
the Tertiary. The Red Sea rift developed as a terrestrial trough in the
Oligocene, or possibly earlier. The Mediterranean invaded this trough in the
Miocene and was continuous with the Indian Ocean in the Late Miocene or
Pliocene, thus completely isolating Arabia from Africa for a time. Late in the
Pliocene uplift probably created a temporary land connection across the Bab el
Mandeb. The ancestral stocks of some cyprinoid fishes inhabiting the
Abyssinian highlands and possibly of Barbopsis in the Nogal valley may have
entered Africa from Arabia via this connection. Subsequently the only land
connection with Africa seems to have been the Isthmus of Suez. Four
Nilo-Sudanic fish species occur in the Jordan valley and also in streams flowing
into the Mediterranean: Tilapia galilaea, T. nilotica, T. zillii, and Clarias lazera.
These probably could make their way along the Mediterranean coastline or
across the Isthmus of Suez, even under present conditions. Tilapia are
secondary-division fishes capable of dispersing coastwise in brackish or even
marine waters, while Clarias is capable of aerial respiration and terrestrial
locomotion and may also tolerate salt-water enough t o disperse coastwise. In
addition to the Nilo-Sudanic Tilapia, the Jordan valley has an endemic cichlid
genus, Tristramella (with three species), and an endemic Haplochromis
(Trewavas, 1942). There is no indication that other Nilo-Sudanic fishes were
ever present in Arabia, although the remains of Protopterus, Polypterus, and
Lutes are to be expected there. A number of fish groups shared by Africa and
Asia presumably disappeared from what is now the Arabian peninsula due t o
the advent of arid conditions. The families involved are Notopteridae,
Cyprinidae (Bariliinae), Cobitidae, Bagridae, Schilbeidae, Clariidae, Channidae,
Anabantidae, and Mastacembelidae. Most of these families probably passed
between Africa and Asia prior to the Pliocene. Subsequent to the Pliocene the
aridity of the Arabian peninsula (including the Suez isthmus) and the Red Sea
probably barred most of them from crossing between continents via this route.
268
T. R. ROBERTS
Changes of sea level
Cretaceous epicontinental seas spread widely over N. Africa, reaching to
24" N in Libya and up the Nile valley, and spanning W. Africa from Tunis and
Morocco to the Gulf of Guinea. They shrank after the Cretaceous, leaving a
number of much smaller relict seas upon the rising land in the Eocene. The
main African marine sediments of this period are in the lower Nile, central
Libya, the Niger valley from Timbuktu to the Atlantic, Sokoto in N. Nigeria,
and the interior of Senegal. During the Eocene there were Algerian and
Moroccan bays associated with an early phase of the Atlas Mts. but no
extensive seas in the W. Sahara. Miocene seas covered only Cyrenaica in Libya
and Degardaia in Algeria, and Pliocene seas were even more restricted. Almost
all of N. Africa was land throughout the Miocene, Pliocene, and Pleistocene.
Marine Tertiary formations in E., S., and W. Africa are strictly coastal. Lower
Miocene marine deposits occur along the E. coast at Mombasa, Lindi, Inharrime
and St. Lucia, and on the W. coast in Angola. Pliocene marine deposits are best
known in Zanzibar and Angola. Cretaceous and later deposits in the interior
plateaus of Africa are all of continental origin, formed either in shallow inland
lakes or by wind-blown sand, such as the Kalahari sands (now largely fixed by
vegetation) and the Saharan sands (mobile in many parts of the Sahara, but also
fixed in a belt 2-300 miles wide directly S. of the Sahara and extending almost
the entire width of the continent).
During the Pleistocene, drops in sea level permitted freshwater fishes to cross
shallow straits in various parts of the world. An interesting African example is
provided by the island of Fernando Po (Thys, 1967a), now separated from the
W. African mainland by a strait 3 5 km wide and up to 60 m deep. The native
fauna includes six species of Characidae, Cyprinidae; and Malapteruridae. These
primary-division fishes, along with a Clarias, a cichlid of the genus
Chromidotilapia, and several cyprinodonts, probably reached the island
10-15,000 years ago when lowland conditions existed between it and the
mainland. All of the primary- and secondary-division fishes on Fernando Po
seem to be identical with mainland species, and it is the only one of Africa's
offshore islands inhabited by primary-division fishes.
Malagasy
Malagasy is an enigma to biogeographers. The biota is distinctive and
peculiar, the history of the island largely a mystery. Some investigators believe
it has been separated from continental landmasses since the Permian. Deep-sea
cores indicate the Mosambique channel has been a seaway since at.least the
Eocene (Simpson et al., 1972). On the basis of geological evidence it cannot be
said whether Malagasy has always been above sea level. On the E. it rises steeply
from the sea, with peaks up to 9450 ft, while westwards it slopes gently to the
Mosambique channel, but the uplift and tilting that produced its present aspect
may have occurred as late as the Pliocene or Pleistocene. Although the only
Cenozoic fossils that have been found date from the Pleistocene, the diversity
of lemurs and of many plant groups indicates they have been on the island
much longer (since the Eocene?). One might expect a rich freshwater fish fauna
on such a large, wet tropical island (280,000 square miles), but only 66 species
DISTRIBUTION O F AFRICAN FISHES
269
are regarded as indigenous to its fresh waters (Arnoult, 1959, 1963; Kiener &
Maugt, 1966). Representative species are illustrated in Fig. 3 . The level of
endemism is low: only 11 endemic genera (2 of Ariidae, 3 of Atherinidae, 5 of
Cichlidae, and 1 of Eleotridae), and 23 endemic species (35% of the total
number of indigenous species). Of special interest is Pan tanodon
madagascariensis Arnoult (1963), a peculiar little cyprinodont recently
discovered in forest streams in E. Madagascar. It is closely related to
Pantanodon podoxys from the coast of Kenya and Tanzania. A separate
subfamily, Pantanodontinae, has been proposed for these two species (Rosen,
1965). All of the freshwater fishes of Madagascar belong to widely distributed
secondary- and peripheral-division families. They are faunistically part of the
Indian Ocean-Western Pacific marine province (Briggs, 1974), and will not be
further considered in this paper.
Low Africa and High Africa
Africa is a plateau. All land below 500 ft lies within 500 miles of the coast.
Africa has proportionately less high mountain and less low mountain plain than
any other continent. The distinction between High Africa and Low Africa is a
useful one for biogeographers. Except for its narrow coastlands, the S. part of
the continent lies well above 1000 ft; much of it is at about 4000 ft. This is
High Africa. In Low Africa, to the N., there are broad coastlands (except in the
N.W. and N.E.) and most of the land lies between 500 and 1OOOft. The
dividing line between Low Africa and High Africa (Fig. 2) runs from S. of the
Quanza basin in Angola (W.), passes eastwards and then northwards inside the
S. and E. periphery of the Zaire basin, then continues northwards between the
highlands of Ethiopia and the lowland portions of the Nile basin towards the
Red Sea. The Upper and Lower Guinean fish faunas and the richest portions of
the Zairean and Nilo-Sudanic fish faunas, including almost all of the archaic
and phyletically isolated groups, are restricted to Low Africa. The riverine
faunas of High Africa, including the Zambesian, are relatively poor, and tend to
be dominated by Cyprinidae, especially in the highland portions. On the other
hand, all of the East African lakes, including those richest in Cichlidae, are in
High Africa. The Low African lakes are mostly shallow and without endemic
fishes.
Low Africa and High Africa both consist largely of elevated blocks with a
small number of large saucerlike depressions or basins rimmed by highlands. On
the seaward side the loftier parts of these rims present mountain faqades deeply
furrowed by stream erosion. In certain areas rainfall on the coastal areas is
sufficient t o create numerous short rivers flowing direct to the ocean; such
rivers are most important on the tropical Atlantic coast. The inland slopes, on
the other hand, are generally gradual except for those of the Atlas Mts.,
Abyssinian highlands, and Drakensberg. There are seven major depressions with
perennial water in the interior of the continent. Three of them lie chiefly in the
Sudan and on the S. edge of the Sahara: the Niger, Chad-Bod616, and Sudd. The
Chad-Bod616 is an interior drainage system. The Upper Niger flows through the
Sudan into an area of fluctuating lakes and swamps on the edge of the desert,
the inland Niger delta. This is drained by the Lower Niger, which flows into the
Gulf of Guinea. The Nile drains the loftiest portions of the highlands of
270
T. R . ROBERTS
20'
0'
20
Figure 2. Hydrographic network of Africa. Desert indicated by stippling. Southern limit of
Sahara during interpluvials indicated by broken line. Boundary between Low Africa and High
Africa indicated by solid line.
C
Figure 3. Representative freshwater fishes of Madagascar: A, Ancharius breviburbb (Ariidae);
B, Rheocles alaotrensis (Atherinidae); C , Ptychochromoides beaileana (Cichlidae);
D, Typhleotnk pauliani (Eleotridae). All Malagasy freshwater fishes belong to secondary- and
peripheral-division families.
DISTRIBUTION OF AFRICAN FISHES
27 1
Ethiopia and E. Africa, then flows across the Sudan and then the Sahara desert
to its delta in the E. Mediterranean. All three basins include vast swampy areas
and large shallow lakes, and are separated from each other by low-lying divides
which do not follow any well-marked relief features. The large shallow
depression in the center of Africa is the Cuvette Centrale. It lies at an average
elevation of 2000 ft, is largely covered by rain forest, and is drained by the
extensive hydrographic network of the Zaire R. into the Atlantic. Two large
shallow lakes and vast swampy areas occur at its lowest point, which is centered
near the confluence of the Kasai and the Ubanghi, the two major tributaries of
the Zaire R. South of the Cuvette Centrale lies the Zambesi basin, which drains
E. into the Indian Ocean. Much of it lies on an extensive plateau at about
4000 f t elevation. W. of it is the interior-draining Okavango-Ngami depression;
in some years a small portion of the waters of this drainage overflow into that
of the Zambesi. The southernmost of the great interior drainages is that of the
Orange R. which slopes westward from 6000 f t in the Drakensberg to 2000 ft
and drains into the Atlantic.
Continental drainage pattern
Land surfaces can be classed according to the type of drainage as exorheic,
endorheic, or arheic. Exorheic surfaces drain to the ocean; endorheic surfaces
drain interiorly; and arheic surfaces are without organized drainage. At the
present time Africa is 40% arheic, 48% exorheic, and only 12% endorheic.
About 40% of the arheic surface is in the Sahara; another large portion is
centered in S.W. Africa. The outlets of the exorheic basins, which are narrowly
confined where they break through the basin rims, are the great rivers of
Africa-the Nile, Niger, Zaire, Zambesi, and Orange. .'he predominance of
exorheic surfaces in Africa is a relatively late phenomenon. At the
Miocene-Pliocene transition, Africa was at the end of a long period of tectonic
stability. It was then an entirely peneplain continent, and its surfaces drained
predominantly into the interior (Howell & Bourlikre, 1963 : 648-53). Coastal
drainages, including the Nile, Zambesi, and Benue, were much smaller than
they are today. The largest of the interior drainages were the Djouf-Aouker,
Niger, Chad, and Zaire. Immediately S. of the Zaire basin lay the separate
interior drainages of the Quanza, Katanga-Lufira, and Bangweolu-Mweru, and
still further S. the Okovango-Ngami and Ovambo. The map published by
Howell & Bourlikre, and reproduced here as Fig. 4, shows the location and
extent of the former drainages, although the features indicated on this map
may not have been strictly contemporary.
Mountains
Mountains affect fish distribution by (1) acting as barriers for some groups,
and as dispersal routes for others; (2) influencing local climate; and
( 3 ) providing montane habitats in the form of high altitude lakes and
cold-water, high gradient streams. The effect of mountains on the dispersal of
different African fish groups has been discussed in preceding pages, but not
orographic effects on climate and montane habitats. Mountains play a major
role in regional climatic patterns. Orographic rainfall is the main source of
272
T. R. ROBERTS
(r( Oldmountains
Sedimentary basin
1
7
1
Submarine canyon
Actual coastline
Drainage divide
1000 km
Figure 4. Hydrography of Africa at the Miocene-Pliocene transition. Reproduced (with minor
modifications) from Howell & Bourlihre, 1963, African Ecology and Human Evolution, with
permission from Aldine Publishing Company, Chicago.
water in some drainages, while large areas on the lee side of mountains may be
deprived of water by a “rain-shadow” effect. The outstanding African example
of this pattern is provided by the Abyssinian highlands, with obvious effecp on
fish distribution. Because of orographic rainfall and cooler temperatures leading
to less evaporation, moutains tend to conserve water in areas that would
otherwise be dry, thus serving as floristic and faunistic refuges. This has
important consequences for fish distribution. Most of the present isolated
populations of Nilo-Sudanic fishes in the Sahara are scattered along the bases of
the Saharan massifs. In moister areas, mountains permit the survival of rain
forest where it would otherwise disappear. Howell & Bourlihe (1963: 648-53)
suggested that three more or less isolated permanent massifs could have
provided forest reservoirs in equatorial Africa: The Guinean ridge, the Gabon
ridge, and the ridge separating the Ituri forest from the Sudan. During
DISTRIBUTION O F AFRICAN FISHES
273
interpluvials the rain forest of Upper and Lower Guinea and of the Cuvette
Centrale may have retracted to these areas, with a corresponding retreat of
sylvan fishes. Such fishes are now widely dispersed in the Cuvette Centrale and
in Lower Guinea, but in Upper Guinea they tend to be associated with
mountains, especially the Atlantic coast slopes of the Fouta Djallon and Man.
Montane habitats have added more to the diversity of Asian and South
American fishes than to African fishes. In South America three families are
exclusively montane: Astroblepidae on both slopes of the Andes, Orestiidae in
L. Titicaca and neighboring lakes which were probably once connected with it,
and Parodontidae in mountain streams throughout the continent. There are
also characid genera restricted to Andean slopes. In Asia, Schizothoracinae and
a number of genera in other cyprinid subfamilies are restricted to mountain
streams, as are a number of catfish genera. In Africa the only exclusively
montane genera are Kneria, Para kneria, and Oreodaimon. Most African
montane fish species are Barbus. Of particular interest is the radiation of
trophic morphs of B. intermedius in the Abyssinian highlands (Banister, 1973).
Other African genera with montane species include Clarias, Chiloglanis, and
Amphilius. The relative lack of taxonomic differentiation of African montane
fishes compared to those of Asia and South America can be attributed to the
absence of centrally located, continuous ranges comparable to the Andes or
Himalayas, and the relative youthfulness of most African mountains. The
Cameroons-Bamenda highlands and all of the East African peaks excepting
Ruwenzori were formed during the Pleistocene, and much of the present aspect
of the Abyssinian highlands is also due to Pleistocene activity.
Great Rift valleys
The Great Rift valleys of East Africa have played a major role in the
differentiation of fishes. There are two main branches, the Eastern Rift and the
Western Rift, both with minor side branches or transverse rifts. The E. Rift
extends from near Sofala, on the Mosambique coastline, N. through the Shirk
valley and L. Malawi, across the E. African plateau to L. Rudolf, then cuts
deeply into the Ethiopian highlands (where it separates the plateaus of Ethiopia
and Som.alia) and down the Awash valley before it debouches onto the Red
Sea. The Red Sea and the Jordan Valley are considered by some workers as a
continuation of it. To the W. of the E. Rift, and roughly parallel to it, is the W.
Rift valley, which does not extend beyond Africa. It begins in the S. in the
vicinity of L. Malawi and continues N. to at least L. Albert. Some workers
consider part of the Nile valley below Albert as a continuation of it. It has also
been considered that the S . end of the W. Rift participates with the E. Rift in
forming the graben containing L. Malawi. The physical characteristics of the
rifts are uneven. In many places they have steep faults on either side rising
hundreds or even thousands of feet, but in other places they are indistinct or
even discontinuous. Thus the E. Rift has a gap part of the way between lakes
Malawi and Manyari, and also disappears in the Mosambique coastal lowlands
between Beira and the Zambesi delta. In parts of the E. African plateau, the E.
Rift is 30 to 50 miles wide and 1500 to 3000 f t deep. It deepens and narrows
in S. Ethiopia, where it holds a series of lakes, and in Kenya where it holds L.
Rudolf. The desert plains of the Afar, enclosing salt marshes and saline lakes
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T. R. ROBERTS
well below sea level, are also part of the E. Rift. The W. Rift hold lakes Albert,
Edward, Kivu, and Tanganyika. The bottom of L. Tanganyika is 2200 ft below
sea level. Some impressive features, such as L. Rukwa, lie in lateral branches or
cross-rifts. Some workers consider the gorge of the Abbai (Blue Nile) a lateral
fault, others consider it an erosional feature. The East African Rift system has
been characterized as a perennial intracontinental deep lineament, probably
controlled by mantle mechanisms and repeatedly reactivated (McConnell,
1972). The lineament may have originated as much as 2.7 billion years ago,
although workers are divided on this point; some consider features formed in
the Cretaceous as the earliest ones that properly belong to the system. It has
been suggested that the lack of spreading of the rifts is due to compression of
the African plate between the spreading Mid-Atlantic and Mid-Indian Ocean
Ridges. In any event, there seem to have been several periods of rift activity,
with faulting and subsidence accompanied by volcanics. Many of the present
Rift faults have been scarcely eroded and are relatively modern. The last period
of major faulting began at the end of the Miocene, or beginning of the Pliocene
and may still be going on.
Volcanism
Africa has a long history of volcanism. Most of the rock systems have
associated intrusive or extrusive rocks. The crystalline mountains in the central
Sahara are ancient volcanic mountains. Recent and sub-recent volcanism has
been closely aligned along the Rift valleys. All of the high mountains of E.
Africa excepting Ruwenzori (which is a horst) are Pleistocene volcanoes. Late
volcanicity is also displayed in the Cameroons Mts. and in the Emi Koussi and
Tibesti massifs of the Sahara. Floods of phonolite welled out in Kenya during
the Mid-Tertiary forming plateaus. S. of Afar the Awash R. flows into the lava
fields resulting from recent volcanic activity. A major break or barrier in the W.
Rift valley occurred in the Pleistocene when the Mfumbiro or Virunga group of
volcanoes arose S. of L. Edward, leading to the formation of L. Kivu. Before
this time the area occupied by Kivu apparently was part of the Nile drainage
and had a Nilotic fish fauna. The volcanoes prevented Kivu from draining N.
and effectively isolated it from the Nile drainage; it then overflowed into L.
Tanganyika. The entrance of Nilotic fish stocks into L. Tanganyika and the
Lualaba may date from this event. The junction of the E. and W. Riftsjust N.
of L. Malawi is obscured by the overlying Rungwe volcanics of Pleistocene age.
Many E. African lakes are of volcanic origin. L. Tana in the Ethiopian highlands
resulted from damming by a lava flow, as did a number of smaller lakes in the
Virunga region N. of Kivu. Small crater lakes are numerous and widely
distributed in E. Africa, e.g. Naivasha, Kikorongo, and crater lakes within L.
Rudolf. Volcanic beds underlying E. African lakes often play a role in
determining their chemical characteristics. Hot springs flowing into many of
the lakes dissolve salt from these beds. The sources tend t o be natreous along
the E. Rift and potassic along the W. Rift.
Deserts
Nearly half of Low Africa, or more than a quarter of the land surface of the
entire continent, is occupied by the Sahara, a vast arid land embracing many
DISTRIBUTION OF AFRICAN FISHES
275
kinds of desert (Fig. 2). It stretches 4000 miles all the way across the continent
from W. to E. and has a minimum N.-S. extent of 1200 miles. Its N., W., and
E. limits are defined by the Mediterranean, Atlas Mts., Atlantic, and Red Sea.
There is no outstanding geographical feature to marks its S. limit, but rather a
poorlydefined transition zone of steppe vegetation (the Sahel) between it and
the Sudan. The S. boundary of the desert is generally considered t o coincide
with the limits of moving sand dunes. Physiographically the Sahara consists of a
series of low and moderately elevated plateaus, above which rise three extensive
mountainous masses. The plateaus have an average elevation of around 1000 ft,
although large parts in the N. lie only 600 ft above sea level. The lowest point,
440 ft below sea level, is in the Qattara depression in N.W. Egypt. The
mountains are the Ahaggar (9850 ft) in Algeria, the Air (5900 ft) in
Mauritania, and the Tibesti (11,200 ft) in Chad and Libya. Some of the highest
peaks are snow-capped. Outwards from the massifs radiate numerous dry
watercourses or wadis, the most important of which are the Igharghar and
Tamanrasset, both arising in the Ahaggar. The Igharghar courses N. to the
Chott Melghrir in Tunisia, the Tamanrasset W. and then S. towards the great
bend of the Niger. Saharan rainfall is extremely irregular. Only along the
Mediterranean coast and in isolated highlands is there more than 10 inches
annually. Rain occurs at any time of the year except in the extreme S. part of
the Sahara where it falls only during the northern summer. Run-off is a rare
phenomenon and always of short duration, turning dry wadis into raging
torrents which dissipate in a matter of hours. Evaporation rates are extremely
high. Diurnal temperature ranges are as extreme as lOO”F, with daytime
temperatures up t o 136” F. Absolute desert, with virtually no rainfall and
devoid of plants, occurs in the Tanezrouft, an extensive flat area W. of Ahaggar,
in the Tknkrk, and in the Libyan desert. The only standing water in the
lowlands is in the oases, which are fed from underground. Among the principal
groups of oases are the Kharaga, Dakhla, Bahariya, and Siwa in Egypt; the
Jarabub, Kufra, and Fezzan in Libya; the Biskra, Touggourt, Ouargla, Mzab,
Touat, Gourara, Tidikelt, and Ahaggar in Algeria; and the Tafilelt in Morocco.
Oases are almost entirely lacking in Mauritania and Spanish West Africa.
Erosion, transport, and deposition by wind produces the main surface
conditions in the Saharan plateaus: the “hammada,” rocky desert; the “reg” or
“serir,” stony desert, with a surface of gravel or pebbles; and the “erg,” sandy
desert, in which shifting sand dunes aligned with the prevailing winds rise up to
600 ft. Hammada, with bare rock outcrops often cut by deeply eroded valleys
and gorges, are common around the Ahaggar and Tibesti and on the inland
slopes of the Atlas; they also occur at lower latitudes in the W. Sahara, Ergs are
notable for the absence of oases and of vegetation. The principal ones are the
Great Western Erg in N. central Algeria; the Great Eastern Erg in E. Algeria and
S. Tunisia; the Erg Iguidi in S.W. Algeria and Mauritania; the Erg Chech in S.
Algeria, S.W. of the Touat oases; and the Libyan Erg along the Egypt-Cyrenaica
border. The E. end of the Sahara is flanked by the Red Sea Hills or Etbai
ranges. Gently sloping on their western or inland slopes, these mountains rise as
high as 7400 ft and descend abruptly to the Red Sea. The coastal plain along
the Red Sea is only 10-25 miles wide and has intermittent streams that flow
but briefly. The Nubian desert, between the Nile and the Red Sea, is largely a
limestone plateau trenched by many wadis arising on the inland slopes of the
276
T. R. ROBERTS
Etbai and coursing towards the Nile (but seldom reaching it). The inland slopes
of the Etbai are also drained by the Barka and Gash rivers, which flow
intermittently and lose themselves in the Nubian desert, and by tributaries of
the Atbara.
A total of 19 fish species has been found at Saharan localities. Labeo tibesti
and Tilapia borkuana are endemic to the western slopes of the Borkou-Tibesti
and Ennedi basins. The rest of the species are widely distributed forms of the
Maghreb or Nilo-Sudanic ichthyofaunal provinces. None exhibit any obvious
adaptations to life in caves or subterranean waters; i.e., all have the appearance
of normal, surface-dwelling forms. The species most widely distributed in the
Sahara are Tilapia galilaea and T. zillii. The area with the greatest number of
species, namely Barbus batesi, B. deserti, Labeo niloticus, L. tibesti, Barilius
senegalensis, Hemichromis bimaculatus, Tilapia borkuana, T. zillii, and
Epiplatys senegalensis, lies within the ancient hydrographic network of the
Chad. basin. Tilapia borkuana is apparently related to T. galilaea (Blache, 1964:
236-7). The relationships of Labeo tibesti have yet to be determined. Most of
the Saharan fish populations are in or near mountainous localities with
relatively high rainfall. The only fishes encountered in the more isolated oases
are cichlids (Haplochromis desfontainesii, H. wingati, Pseudocrenilabrus
multicolor, Tilapia zillii, and T. galilaea) and the cyprinodont A phanius
fasciatus. There seem to be no records of fishes from the Nubian desert or Red
Sea slopes of the Etbai ranges.
Africa has a number of smaller deserts geographically isolated from the
Sahara, namely the Namib, Turkana, Danakil, and Somali deserts (Fig. 2).
Fishes are apparently absent in the Namib, and there is no evidence that they
were there earlier in the Pleistocene. The adjacent semi-desertic areas including
the Kalahari and Kaokoveld are devoid of fishes except for a half-dozen species
inhabiting the lower reaches of the Orange River and an endemic Clarias with
reduced eyes in Aigamas Cave, N. of Otavi (near Etosha Pan) (Trewavas, 1936).
L. Rudolf, populated by a moderately rich complement of Nilo-Sudanic fishes
plus several endemic species, lies in the midle of the Turkana. The Danakil
desert has some species of the alkalinophile cyprinodont genus Aphaniops and
an endemic Tilapia (see Addenda) but entirely lacks primary-division
freshwater fishes. The most distinctive of African desert fishes, endemic genera
of Cyprinidae and Clariidae, occur in thermal springs and subterranean waters
in the Somali desert between the Juba and Webi Shebeli rivers. The Juba and
Webi Shebeli are inhabited mainly by a moderate complement of Nilo-Sudanic
fishes where they traverse the Somali.
Pleistocene climatic fluctuations
Pleistocene climatic fluctuations have had pronounced effects on fish
distribution in Africa. Fossil and subfossil mollusc and fish remains, traces of
ancient lakes and river systems, and evidence of human habitation indicate
wetter conditions in wide areas that are now dry and uninhabited. On the other
hand, windblown Kalahari sands extend N. from the Namib and Kalahari to
underlie the S.W. portion of the Cuvette Centrale, and a “fossilized” belt of
sand dunes (now stabilized by vegetation) extends across Africa in a 2-300
mile-wide belt S. of the present southern limit of the Sahara desert, and thus
DISTRIBUTION O F AFRICAN FISHES
277
conditions have also been drier in the past. In the earlier literature on
Pleistocene climates of Africa there is much discussion as to whether changes
were local or continent-wide, and little agreement as to when they occurred. In
the last decade, however, radiocarbon dating has provided accurate ages for
numerous plant, animal, and human remains deposited in the last 3 5-40,000
years. I t now appears that about 12,000 t o 8000 years ago Africa experienced a
continent-wide pluvial in which conditions were generally more humid. At this
time the Sahara underwent a “lacustrine phase,” and lake levels all over Africa
were generally higher. While deserts contracted, forests and savannas became
more widely and continuously distributed. This wet phase was preceded by a
relatively dry interpluvial from about 27,000 to 12,000 years ago, when deserts
expanded, many lakes and river systems dried up, and vegetation contracted.
Wet and dry phases of comparable magnitude probably alternated throughout
the Pleistocene but their chronology and severity is far from being established.
Among recent papers on Pleistocene climatic changes and related topics which
have come to my attention are Mauny, 1956 (distribution of mammals in the
Sahara during the Pleistocene); Faure, 1969 (Quaternary Saharan lakes); Grove
& Goudie, 1971 (lake levels in S. Ethiopia); Grove & Warren, 1968 (past
climates on the S. side of the Sahara); Williams & Adamson, 1973 (effects of
pluvials on the Nile); Williams & Adamson, 1974 (effects of last interpluvial on
the Nile); and Butzer et al., 1972 (Late Pleistocene fluctuations in level of L.
Rudolf).
During pluvials fishes were much more widely distributed than at present.
Lakes were far more numerous, and their levels tended t o rise until they
overflowed into adjacent basins, and low-lying divides were often flooded or
connected by rivers, so that there were fewer barriers t o dispersal of freshwater
organisms. During interpluvials, fishes died out as deserts expanded and lakes
and river systems dried up. The effects of such changes were especially marked
upon the Nilo-Sudanic fish fauna. During the last pluvial, Nilo-Sudanic fishes
were widely distributed in the large lakes and extensive hydrographic network
which occupied much of the S. half of the present Sahara desert (Fig. 5 ) . L.
Chad, or Mega-Chad, extended as a vast lake or series of interconnected lakes t o
the foot of the Tibesti Mts. Other large lakes existed in the W. Sahara, N. of the
great bend of the Niger. Hydrographic connections arose between the Nile and
L. Rudolf, between the Niger and Chad basins, and possibly also between the
Nile and Chad basins. At its maximum extension, the height of MegaChad was
stabilized when it overflowed into the Benue R. (Niger basin). Large rivers
flowed from the Adar Mts. of Mauritania and the Adrar des Iforas, Ahaggar,
Tibesti, and Ennedi Mts. of the central Sahara into the Senegal, Niger, and
Chad basins. The present relict populations of Nilo-Sudanic fishes in these
mountains were probably established during the last wet phase (that is, 12,000
to 8000 years ago). Populations from earlier wet phases probably were killed
off during the last dry phase, which lasted about 15,000 years. At this time
wind-blown sands formed dunes 2-300 miles S. of the present limits of the
Sahara, and most Nilo-Sudanic fishes presumably retreated to S. of the dune
limit (Fig. 1). L. Chad, and possibly L. Rudolf, dried up altogether. Some
Nilo-Sudanic fishes which inhabited lakes Edward and George through most of
the Pleistocene are absent today; they may have died out in this last dry phase
or in an earlier one. Thus it is not surprising that some shallow lakes in the area
2 78
T. R. ROBERTS
occupied by Nilo-Sudanic fishes have no endemic lacustrine fishes in them.
During dry phases rivers flowing from mountainous areas in the southern parts
of the Nilo-Sudanic region, especially the Blue Nile and the Benue, may have
served as important refuges for Nilo-Sudanic fishes.
Dry phases presumably also had pronounced effects on fishes in the
Zambesi, Abyssinian highlands, East coast, and Cape ichthyofaunal provinces.
Retreat of rain forest and encroachment of semi-arid conditions in Upper
Guinea probably account for most of the disjunct fish distributions in that
region.
Many fishes inhabiting rivers and streams in the African rain forest occur
nowhere else. They seem t o require ecological conditions perpetuated only in
large, stable, and relatively undisturbed forests. This is especially true of many
small and brightly colored characins, cyprinids, and cyprinodonts, and secretive
mormyrids and catfishes with cryptic “forest” colorations which are especially
numerous in the Ogow6 basin and in the forested portion of the Cuvette
Centrale in the Zaire basin. I have discussed the ecology of these fishes in a
previous paper (Roberts, 1972). The contractions and expansions of forested
areas during the interpluvials and pluvials must have greatly affected their
distribution and speciation. The main blocks of African rain forest or lowland
evergreen forest, as indicated Fig. 6 , lie almost entirely within the Upper and
Lower Guinea and Zaire ichthyofaunal provinces. An important isolated patch
occurs in Angola, in the area of the divide between the headwaters of the
M’Bridge and Quanza rivers. Until very recently, undisturbed rain forest
occupied roughly half of Upper Guinea and the Zaire basin, and 80%of Lower
Guinea (including the entire Cross, Ntem or Campo, and OgowC basins). The
rain forest of the Zaire basin is broadly continuous with that of Lower Guinea,
straight across the divide between the headwaters of the Zaire, Ntem, and
OgowC and the headwaters of the Sangha, the second-largest S.-flowing
tributary of the Zaire River.
The Dahomey gap, a non-forested area between the forests of Upper and
Lower Guinea, represents a major biogeographical barrier for many animal
groups (Clausen, 1964; Moreau, 1969). Many forest vertebrates range up to this
gap but do not occur on the opposite side of it. Lower Guinean fishes with this
pattern of distribution include Erpetoichthys, Pan todon, Phractolaemus, several
mormyrids and characids, Phago, almost all cyprinodonts, and Polycentropsis.
This is one of the reasons for treating Upper and Lower Guinea as separate
ichthyofaunal provinces. During the longer pluvial periods the rain forest
probably expanded until it covered virtually all of the Upper and Lower Guinea
and most of the Zaire basin. At such times the forest blocks of Upper and
Lower Guinea were probably continuous, and the area of contact between the
Lower Guinea and Zaire blocks of forest much broader than at present, and
probably connected with presently isolated blocks of forest in Angola. Forest
probably also covered most of the plateau area which now drains into L.
Victoria. During interpluvials, on the other hand, the Dahomey gap may have
been considerably wider and much more arid, and the Upper Guinean forest
which is presently continuous was probably fragmented. The rain forests in
Lower Guinea and the Zaire basin were probably contracted, but the effects of
this were probably mitigated, insofar as fishes were concerned, by the
persistence of hundreds of miles of gallery forests along the river banks. In
DISTRIBUTION OF AFRICAN FISHES
279
areas where the hydrographic network is relatively dense, as in the Zaire basin,
re-establishment of rain forest by longitudinal and lateral dispersal of tree
species from gallery forests is probably relatively rapid. In the Dahomey gap,
on the other hand, there are only short coastal rivers with little network
characterized by absence of gallery forest. Dispersal of rain forest across this
gap probably occurred, but slowly. Moreau (1969) considered that the last time
the Dahomey gap was closed by forest was probably about 10,000 years ago. It
is difficult to believe that Erpetoichthys, Pantodon, and Phractolaemus which
presently approach the E. side of the Dahomey gap but do not occur W. of it
reached there only in the last 10,000 years. The fishes presently inhabiting the
Mono and Outmk, the principal rivers in the middle of the Dahomey gap,
represent a reduced complement of the Nilo-Sudanic fauna plus a few Upper
Guinean species.
In the last five centuries, and especially in the last 75 years, much of the
evergreen lowland forest of Africa has been extensively cut or burned, to be
replaced by oil palm plantations, farmland and secondary growth in which the
diversity of animal life, including insects and all classes of vertebrates, is greatly
reduced. Destruction has been most severe in parts of Upper and Lower
Guinea, especially in Nigeria, and in relict forest areas in Bas-Zaire and Angola;
Gabon and parts of the Cuvette Centrale have been least affected.
African freshwater fishes and the fossil record
A summary of zoogeographically important fossil occurrences of living
groups of African freshwater fishes is given in Table 2. A comprehensive review
of freshwater fossil fishes of the African Cenozoic is given by Greenwood
(1974a). The only primary- and secondary-division families with fossils dating
earlier than the Oligocene are Polypteridae, Protopteridae, Cyprinidae, and
possibly Bagridae. The geographical and temporal representation of remains
within Africa is very uneven. The most continuous record is from the Lower
Nile. There are few or no remains from Upper and Lower Guinea, the Zaire
basin, and lakes Victoria, Malawi, and Tanganyika, and very little from High
Africa. The following families are unknown as fossils: Pantodontidae,
Gymnarchidae, Kneriidae, Phractolaemidae, Hepsetidae, Distichodontidae,
Citharinidae, Ichthyboridae, Amphiliidae, Malapteruridae, Nandidae, and
Mastacembelidae. The non-endemic African families Notopteridae, Cobitidae,
Schilbeidae, Anabantidae, and Channidae are unkown in the fossil record of
Africa, but have been found as fossils elsewhere: Notopteridae in the Lower
Tertiary of India, Cobitidae in the Oligocene and Miocene of Europe,
Schilbeidae in the Lower Tertiary of lndia and Teriary of Asia, Anabantidae in
the Pleistocene of the East Indies, and Channidae in the Pliocene of Asia
(Romer, 1966).
One of the most intriguing gaps in the African fossil record is the absence of
any ostariophysans prior to the Eocene. Apart from the characid teeth from
the Oligocene of lower Egypt that have just now come to my attention
(Table 2), the earliest known African characoids are Pliocene in age
(Greenwood, 1972a). The highly distinctive jaw teeth of characoids are
replaced many times throughout life and should be among the commonest
vertebrate remains in suitable freshwater deposits. If characoids truly have a
T. R. ROBERTS
280
Table 2. Zoogeographically important fossil records of groups of African
freshwater fishes
PALEOCENE
Europe: earliest known Cyprinidae
LOWER EOCENE?
Lower Nile: “Polypteridae” (Stromer, 1936)(earliest record of family)
EOCENE
France: Alestiinae (Cappetta et al.. 1972)(earliest known Characidae).
Lower Nile: catfishes (?Ariidae) (Stromer, 1904;Peyer, 1928);Lutes
(Weiler, 1929).Nigeria: Eaglesomia, Macronoides. Nigerium (White,
1935)(Ariidae or Bagridae?)
EOCENE?
Mali (Tamaguilelt, 150 km N. of Gao): Protopterus (Lavocat, 1955)(earliest
known Lepidosirenidae)
OLIGOCENE
Lower Nile: Protopterus (Stromer, 1910);Alestiinae (personal observation
of teeth from Fayum; see Addenda) (earliest known African Characidae)
EARLY MIOCENE
Rusinga Isd., L. Victoria: Protopterus, Polypterus, Synodontis (earliest
known Mochokidae). Lutes, and Tilapia (earliest African record of
Cichlidae) (Greenwood, 1951)
MIOCENE
Libya (Moghara, 150 km S.W. of Alexandria): Synodontis and Lates (Priem,
1920). Cabinda (Malembe): Protopterus (Dartevelle & Casier, 1949)
MIOCENE?
Tanzania, Mahenge: Paleodenticeps (earliest known Denticipitidae)
(Greenwood, 1960);Singida (Singididae, an extinct family of osteoglossoids) (Greenwood & Patterson, 1967);?Haplochromis (Greenwood,
LATE MIOCENE
Tunisia, Bled ed Douarah: Polypterus, ?Barbus (earliest known Cyprinidae in
Africa), PClarotes, Clarias and/or Heterobranchus (earliest known
Clariidae), ?Synodonfis, and Lates (Greenwood, 1972).Near Suez: Bugrus,
Clarias. ?Hererobranchus, Synodontis, and Lates (Priem, 1914)
LOWER PLIOCENE
India, Siwalik Hills: Clanus and Heterobranchus (Lyddeker, 1886)(earliest
known Asian Clariidae)
PLIOCENE
Lower Nile: Protopterus, Polyptenis, Hyperopisus (earliest known
Mormyridae), Alestes, Barbus. Labeo, Bagrus, Clarotes, ?Auchenoglanir,
Clarias, ?Hererobranchus, Synodontis, Lutes, and Tilapia (Greenwood,
1960)
1972)
PLIOCENE?
L. Rudolf: ?Dasyatidae, Polypterus, Lutes, and h’iapia (Arambourg, in
Chappuis, 1939)
LOWER PLEISTOCENE
L. Albert: Bagrus, Clarotes, Heterobranchus, and Lates (White, 1926).
L. Edward; Protopterus, ?Hyperopisus, Hydrocynus, Bagrus, Auchenoglanir.
Clarias, Synodontis, Lutes, and Tilapia (Greenwood, 1959).L. Rudolf
basin: Polypterus, Hydrocynus, Bagrus, Clarotes, Clarias, Synodontis, and
Lutes (Arambourg, 1947). L. Malawi: Protopterus (Coryndon, 1966)
UPPER PLEISTOCENE
Sahara (various localities): Bagrus, Chrysichthys, Clarotes, Auchenoglanis,
Clarias, Heterobranchus, Synodontis, Anus, Lutes, and Tilapia
(Joleaud, 1935;Daget, 1958,1959,1961)
Gondwanic distribution, it should be possible to trace them back to when
Africa and South America formed a single continent. I t is noteworthy that the
characid teeth from the Eocene of France are definitely referable to the
African subfamily Alestiinae, indicating that the basic dichotomy between the
present African and South American subfamilies of Characidae (Roberts, 1969:
441-2) is an ancient one. The earliest African catfishes which can definitely be
assigned to a primary-division family (Synodontis, Mochokidae) date from the
Early Miocene. Here again, if African catfishes have a Gondwanic relationship,
it should be possible to trace them back much further. Most of the early catfish
remains found thus far, however, are fragments of serrated fin spines and of
DISTRIBUTION OF AFRICAN FISHES
281
crania which are difficult, perhaps impossible, t o assign to family. Cyprinidae
are known from the Paleocene and Eocene of Europe but unknown in Africa
until Miocene times.
Miocene remains from Bled ed Dourah in Tunisia and from Mahenge in
Tanzania indicate the fish fauna in these areas was then totally different from
what it is today. The Tunisian remains represent, at the generic level, a modern
assemblage. The species may have been similar or even identical to those
inhabiting the present Nilo-Sudan province. A comparable assemblage of genera
is present in Pliocene deposits from the Lower Nile. The Tanzanian remains, on
the other hand, include a family of osteoglossoids that is now extinct, and a
representative of an archaic family of clupeomorphs otherwise known from a
living species in coastal streams of Dahomey and W. Nigeria. African fish fossils
of Pliocene age are known only from the Nilo-Sudan province. The generic
composition of the Pliocene Nilotic fish fauna was evidently comparable t o
that of today, although the teeth of the “Alestex” described by Greenwood
(1972a) are unlike those in any living species and may represent an extinct
genus. Pleistocene remains from lakes Edward and Malawi and from the Sahara
desert indicate that many genera were formerly more widely distributed than
they are today. Hydrocynus and Lutes are absent from the present L. Edward,
and Protopterus is absent from the present L. Malawi. Many genera retreated
from vast areas of what is now Saharan desert since the Upper Pleistocene.
ICHTHYOFAUNAL PROVINCES
The first attempts to divide Africa or the “Ethiopian region” into
ichthyofaunal provinces by Boulenger (1905), Pellegrin (191 1, 1921, 1933),
and Nichols (1928) revealed some large-scale patterns but were based on
inadequate information. The later versions published by Blanc (1954), Poll
(1957, 1974), and Matthes (1964) provide much more insight into
zoogeographic relationships. I recognize the following provinces:
1. Maghreb
2. Abyssinian highlands
3. Nilo-Sudan (including lakes Albert, Edward, George, and Rudolf)
4. Upper Guinea
5. Lower Guinea
6. Zaire (including lakes Kivu and Tanganyika)
7. East coast (including lakes Kioga and Victoria, and all lakes in the
Eastern Rift valley excepting Malawi and Rudolf)
8. Zambesi (including L. Malawi)
9. Quanza
10. Cape of Good Hope
Some basic information about the familial, generic, and species composition of
the provincial fish faunas is presented in Tables 3 t o 5. While the general
faunistic conceptions have been recognized by previous workers in the
publications cited above and elsewhere, I have made substantial modifications
in the provincial boundaries (Figs 4 to 7).
19
282
T. R. ROBERTS
Table 3. Distribution of primary- and secondary-division families in the
ichthyofaunal provinces
Lepidosirenidae
Pol ypteridae
Denticipitidae
Osteoglossidae
Pantodontidae
Notoptendae
Morrnyridae
Gyrnnarchidae
Kneriidae
Phractolaemidae
Hepsetidae
Characidae
Distichodontidae
Citharinidae
Ichthyboridae
Cyprinidae
Cobitidae
Bagridae
Schilbeidae
Arnphiliidae
Clariidae
Malapteruridae
Mochokidae
Cyprinodontidae
Channidae
Synbranchidae
Nandidae
Cichlidae
Anabantidae
Mastacembelidae
Totals 3 0
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
X
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
X
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
24
23
27
24
17
17
14
6
X
X
X
x
x
x
x
X
X
x
x
x
x
x
x
X
x
4
x
5
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
X
Maghreb ichthyofaunal province
“Maghreb,” from an Arabic word meaning “the West,” designates the
inhabited portion of Africa which extends along the Mediterranean coast from
Egypt to the Atlantic Ocean and includes Libya, Tunisia, Algeria, and Morocco.
During the Moslem domination Spain was part of the Maghreb. The term is
thus especially appropriate in biogeography. The outstanding physiographic
feature of this region is the Atlas Mts. extending 1500 miles W.S.W.-E.N.E.
from Cape Noun (W.) to the Gulf of Gab& traversing Morocco, Algeria, and
Tunisia. The Atlas constitute a massive, corrugated system with lofty ranges,
high plateaus, with Mediterranean climatic conditions in the coastal areas. The
highest and most continuous ranges are in the Grand Atlas of Morocco, where
elevations averaging 11,000f t culminate in the Djebel Toubkal, 13,665f t high.
Moraines indicate that the Grand Atlas were extensively glaciated. The
DlSTRlBUTlON O F AFRICAN FISHES
283
Table 4. Endemic primary- and secondary-division riverine genera in the
ichthyofaunal provinces
Maghreb:
none
Abyssinian highlands:
none
Nilo-Sudan: Heterotis (Osteoglossidae); Hyperopisus (Mormyridae); Gymnarchus (Gymnarchidae);
Cromeria (Kneriidae); Paradisrichodus (Distichodontidae); Cifharidium (Citharinidae); Clarotes, Pardiglanis (Bagridae); Irvineia. Siluranodon (Sehilbeidae); Andersonia (Amphiliidae); Brachysynodontis,
Hemisynodontis, Mochocus (Mochokidae); Gobiocichla (Cichlidae)
Upper Guinea: Ladigesia, Lepidarchus (Characidae); Notoglanidiurn (Bagridae);Roloffia (Cyprinodontidae); Typhlosynbranchus (Synbranchidae); Afronandus (Nandidae); Thysia (Cichlidae)
Lower Guinea: Erpetoichthys (Polypteridae); Denriceps (Denticipitidae); Boulengeromyrus (Mormyridaef ;Arnoldichthys (Characidae); Raddhabarbus, Sanagia (Cyprinidae); Procatopus (Cyprinodontidae); Polycenrropsis (Nandidae); Chilochromis (Cichlidae)
Zaire: Genyomyrus, Myomyrus, Stomatorhinus (Mormyridae); Bathyaethiops, Duboisialestes, Tricuspialestes (Characidae); Dundocharax, Thrissocharax (Distichodontidae); Belonophago,
Eugnathichth ys, Meso borus, Microstomatich thy o borus, Paraphago (Ichthyboridae) ; Lep tocypris
(Cyprinidae); Amarginops, Gnathobagrus, Rheoglanis, Zaireichthys (Bagridae); Belonoglanis: Paraphractura, Trachyglanis (Amphiliidae); Dolichallabes (Clariidae), Acanfhocleithron (Mochokidae);
Congopanchax (Cyprinodontidae); Cyclopharynx, Nannochromis, Neopharynx, Lamprologus,
Leptotilapia, Orthochromis, Pterochromis, Steatocranus, Teleogramma (Cichlidae) ; Caecomastacembelus (Mastacembelidae)
East coast:
Petersius (Characidae)
Zambesi: Coptostomabarbus (Cyprinidae); Chetia (Cichlidae)
Quanza:
Cape:
Dinotopteroides (Clariidae)
Oreodaimon (Cyprinidae); Sandelia (Anabantidae)
Table 5 . Number of primary- and secondary-division riverine
species in the ichthyofaunal provinces
Maghreb
Abyssinian highlands
Nilo-Sudan
Upper Guinea
Lower Guinea
Zaire
East coast’
Quanza
Zambesi
Cape
Total
Number
Number
endemic
Percentage
endemic
Percentage
Cyprinidae
15-20
c. 18
272
206
333
650
97
109
149
46
5-8
c. 1 1
182
117
185
5 29
54
45
73
28
40
61
65
57
55
81
56
41
49
61
50
61
26
17
17
14
36
39
35
54
Excluding th e Victoria Nile
well-watered coastal ranges are forested by oak, Aleppo pine, cedar, and thuya.
S. of the Algerian Tell or Mediterranean portion of the Atlas, are extensive
semi-arid plateaus (average elevation 3000 ft) in which lie “chotts,” immense,
brackish or saline shallow lakes. The chotts are subject t o diurnal temperature
fluctuations up to 100’ F, and their water quality fluctuates greatly depending
on rainfall. The only fishes which permanently live in them are probably the
alkaline-adapted cyprinodonts of the peri-Mediterranean genus Aphanius. Still
284
T. R. ROBERTS
Figure 5. Nilo-Sudan, Zambesi, and Quanza ichthyofaunal provinces. Broken line indicates
approximate limit of northward extension of Nilo-Sudan fish fauna during pluvials. Arrows
indicate location where tributaries of the Niger were captured by the Volta.
further S. lies the Saharan Atlas in which the only permanent standing water is
in oases.
The larger rivers in the Atlas are perennial and subject to terrific spates. The
phncipal rivers of the coastal Atlas are the Sebou, Oumer Rbia, Tensift, and
Sous draining into the Atlantic, and Moulouya, Cheliff, and Medjerda draining
into the Mediterranean. All of the rivers originating on the inland slopes drain
interiorly onto the highland plateaus or into the desert, excepting the Dra,
which arises on the S. slope of the Grand Atlas and drains westward into the
Atlantic. In their lower courses the rivers of the Atlas are all intermittent or
completely dry throughout the year. The lower courses of the Atlantic
DISTRIBUTION O F AFRICAN FISHES
285
Figure 6. Upper Guinea, Lower Guinea, and Zaire ichthyofaunal provinces. Rain forest
indicated by stippling. Major rapids and falls in Zaire basin indicated by bars. Stanley Falls and
Portes d’Enfer indicated by arrows.
drainages descend abruptly to the sea, with the exception of the Sebou. The
lower course of the Sebou flows through the fertile Rharb valley, which lies in
the intermontane plain between the Rif Mts. and Grand Atlas. The Moulouya
arises in the Grand Atlas and flows 320 miles N.N.E., passing through a
semi-arid valley before it flows into the Mediterranean. Like all other rivers in
the Atlas, its volume is very irregular. The 450-mile long Cheliff is the largest
river in Algeria and the only river originating in the Saharan portion of the
Atlas which reaches the Mediterranean. The most important of the rivers
flowing into the Sahara is the Wadi Saoura, which waters a string of oases in the
Saharan Atlas of Algeria and then continues as a dry stream bed deep into the
286
T. R. ROBERTS
MAGHREB
Figure 7. Maghreb, Abyssinian highlands, East coast, and Cape of Good Hope ichthyofaunal
provinces.
Sahara. During one exceptional flood the waters of the Saoura reportedly
flowed 500 miles into the desert. In E. Algeria and Tunisia there is a series of
lowland chotts, the chief of which is the Chott Melghir, which lies 60 f t below
sea level. This chott is watered by the intermittent Oued Djedi and other
streams arising in the Saharan Atlas, and also receives a contribution of
underground water from the Wadi Igharghar. The Igharghar arises on the N.
slopes of the Ahaggar Mts. in the middle of the Sahara desert and flows 800
miles northward, entirely underground, to supply the Oued Rhir oases near
Touggourt in S. Algeria. The lowland chotts, like those in the plateaus, are
subject to extreme environmental vicissitudes and seldom contain fishes other
than Aphanius.
DISTRIBUTION OF AFRICAN FISHES
287
The freshwater fish fauna of the Maghreb is extremely poor. Representative
species are illustrated in Fig. 8. Primary-division fishes are represented
exclusively by members of the suborder Cyprinoidei: from six t o ten species of
Cyprinidae and a single species of Cobitidae. The Cyprinidae have been badly
over-named. Thus there are eight nominal species in Barbus (Labeobarbus), but
they were described before it was learned that members of the subgenus
Labeobarbus are exceptionally variable in the characteristics of mouth, lip, and
barbel form and body proportion traditionally used in distinguishing species of
Cyprinidae (Worthington, 1932; Banister, 1973). They have yet to be revised.
There is an endemic species of Varicorhinus, V. maroccanus. Varicorhinus has a
special relationship with Labeobarbus, but the nature of this relationship has
yet to be carefully studied on a broad basis. In some instances a single species
includes Varicorhinus- as well as Labeobarbus-type morphological varieties
(Jubb, 1967; pers. obs.). The relationships of the Maghreb Varicorhinus and
Labeobarbus have not been studied. There are 17 nominal forms of Barbus
(Barbus) in the Maghreb, and they have been recently revised by two
independent workers, Almaqa (1970a, b) and Karaman (1972). Almaqa
recognized eight endemic African species in the subgenus Barbus and
tentatively regarded a ninth species as a valid endemic species of Varicorhinus.
In what is probably a better classification, Karaman recognized only two
species, B. comiza and B. capito. Finally, there are two endemic species of
Phoxinellus, one of which Karaman (1972) referred to Acanthobrama.
The Phoxinellus, the only African representatives of this genus, are restricted
to Algeria and Tunisia. Elsewhere, Phoxinellus occurs in the Balkan peninsula
A
A
Figure 8. Fishes of the Maghreb: A, Salmo trutfa; B, Phoxinellus chaignoni; C , Barbus comiza;
D, Barbus (Labeobarbus) reinii; E, Varicorhinus maroccanus; F, Cobiiis taenia; G,Aphanius
apoda; H, Haplochromis desfonrainesii.
288
T. R. ROBERTS
and in the Near East (early records of Phoxinellus from the Iberian peninsula
are invalid). Acanthobrama is otherwise restricted to Anatolia and Palestine. Of
the two species in the subgenus Barbus recognized by Karaman, the highly
variable B. capito is widely distributed in temperate Asia and Europe.
According to Karaman it occurs in coastal drainages from S. Morocco to
Tunisia, and as scattered populations in the Saharan desert in areas watered by
the Saoura and Igharghar wadis (including several central Saharan localities
slightly N. of the Ahaggar Mts.). B. comiza occurs only on the Atlantic slopes
of the Grand Atlas in Morocco and in the Iberian peninsula. The subgenus is
widely distributed in Eurasia but does not occur elsewhere in Africa. The
subgenus Barbus and probably the genus Phoxinellus presumably entered
Africa directly from Europe. The distribution of B. comiza indicates that it
crossed the Strait of Gibraltar. A Gibralter crossing also accounts for the only
cobitid species in the Maghreb. Cobitis taenia is the only member of its genus in
Africa. C. taenia, perhaps the most widely distributed fish species in Eurasia,
ranges all of the way across Siberia, Russia, and Europe to the S . end of the
Iberian peninsula. It is also present in Italy and is one of the few native
freshwater fishes on the island of Sicily. In Africa, its populations are restricted
to the Rif Mts. of the Tangier peninsula and the Sebou drainage (Pellegrin,
1929), in other words, a relatively small area adjacent to the Strait of Gibraltar.
The Varicorhinus and Barbus (Labeobarbus) are restricted to the Atlantic
slopes of the Atlas. Although they are widely distributed in Asia, neither the
subgenus Labeobarbus nor Varicorhinus occurs in Europe. As pointed out long
ago by Boulenger (1919), they presumably arrived in the Atlas from
somewhere in Africa. The populations geographically closest t o those in the
Atlas live on the coastal and inland slopes of the Fouta Djallon in Upper
Guinea.
The secondary- and peripheral-division freshwater fishes of the Maghreb are
few in number and may be rapidly reviewed. Secondary-division fishes are
represented by three species in the alkalinophile cyprinodont genus Aphanius,
Tilapia zillii, and Haplochromis desfontainesii. Aphanius iberus occurs in
Morocco and on the Iberian peninsula, A. apoda is endemic to Morocco, and A .
fasciatus occurs in Tunisia and many other Mediterranean localities excepting
the Iberian peninsula. Haplochromis desfon tainesii is evidently endemic to
N.W. Africa (Greenwood, 1971). It occurs at widely scattered localities in
Libya, Tunisia, and Algeria. It is evidently able to disperse in underground
rivers: it occurs in wells and at oases at Saharan localities where this seems to
be the most likely explanation for its presence (Girard, 1889).
Peripheral-division fishes include isolated mountain populations of.Salmo trutta
in the Rif and in the Kabylia. Freshwater populations of Blennius ji’uviatilis and
of the stickleback Gasterosteus aculeatus occur along the Mediterranean coast.
Elvers of Anguilla anguilla ascend the rivers and climb high into the mountains,
while species belonging to many marine families enter the lower reaches of the
rivers when they flow to the ocean.
Abyssinian highlands and Nilo-Sudan ichthyofaunal provinces
The hydrography of N.E. Africa is dominated by the drainage of the Nile,
which covers 1,100,000 square miles or roughly a tenth of the African surface.
DISTRIBUTION O F AFRICAN FISHES
289
The only river longer than it is the Amazon. From the source of its most
distant headwaters to the delta the distance by river is 4160 miles. The
headwaters arise in the mountainous area E. of the northern end of L.
Tanganyika. The Nile has three major tributaries, the most important being the
Blue Nile, arising in the central highlands of Ethiopia. Next is the While Nile,
draining lakes Albert and Victoria. The Atbara, arising in the N.W. highlands of
Ethiopia and the last t o join the Nile, is of much less importance than the other
two. The lower 1670 miles of its course the Nile flows through arid country
where the only tributaries it receives are wadis which are usually dry and
supply water only during brief periods due to run-off caused by storms.
The headwaters of the Blue Nile (or Abbai, as it is known in Ethiopia) flow
into L. Tana. The outlet of L. Tana is the Blue Nile. The only falls of any
height on the Blue Nile are at Tisisat, 20 miles below L. Tana, where it drops
150 ft over a precipice. It then enters a ravine which increases in depth and
width until it becomes a rugged valley six to ten miles wide with mountains on
either side towering 6000 ft above it. In its upper course the Blue Nile makes a
great bend (nearly full circle) around the Chokai Mts., the volcanic peaks of
which rise t o 12,000 ft. The Blue Nile does not emerge from the Iast mountain
range until it has flowed some 350 miles; its last important rapids are located
just above Roseires. Only a small part of the water volume in the Blue Nile is
contributed by L. Tana. Most of its flow comes from intermittent affluents,
chiefly the Rahad and Dinder on its right bank and the Didessa and Dabus on
its left. During the dry season these quit flowing and form many disconnected
pools. The only perennial affluents are relatively small streams arising in the
Chokai. These Chokai streams are misfits, in the sense that the sides of their
valleys are 3000-5000ft deep, which would require large rivers for them t o
have been formed by erosion. The rocky stream beds, variable water levels, and
extreme muddiness of the Upper Blue Nile and its tributaries evidently make
them a harsh habitat for fishes.
L. Victoria overflows into the White Nile by the Ripon Falls (now
submerged). According to Worthington & Worthington (1933 : 183-4), Barbus
altiunalis formerly swam up the Ripon Falls into L. Victoria (the falls are now
submerged because of the dam constructed downstream at Owen Falls). The
White Nile seeps its way through the whole of L. Kioga, a shallow, dendritic
lake with many swampy arms filled by papyrus and other floating vegetation.
Below Kioga the river is broken by a series of rapids and then passes through a
narrow rock cleft, dropping 140 f t over Murchison Falls, an important barrier
to upstream fish movements. A little further down, the White Nile barely enters
the N. end of L. Albert and then flows on. (The portion of the White Nile
between lakes Victoria and Albert is also known as the Murchison Nile or
Victoria Nile.) L. Albert is fed by a river system which has links t o lakes George
and Edward and arises on the slopes of the Mfumbiro Mts. N. of L. Kim.
George is connected t o Edward by the Kazinga Channel, and the outlet of
Edward, the Semliki R., flow directly into Albert. Between Albert and the
plains the White Nile is broken by the Foa rapids below Nimule and receives
some important tributaries from the S.E., including the Aswa. When it reaches
the plains it flows into the Sudd, a swampy area of some 35,000 square miles
dominated by papyrus and elephant grass. Except for man-made channels, the
waterways are usually totally closed by masses of floating vegetation, beneath
290
T. R. ROBERTS
which the water is deoxygenated. I t is estimated that half the water of the
White Nile is lost by evapotranspiration in the Sudd. Underlying the Sudd is a
shallow saucer-like basin with extensive deposits of allivium; in former times
the area may have held a lake comparable to L. Chad. At present a small body
of open water of variable size (up to 40 square miles) called L. N o is formed on
the White Nile where it flows out of the N. end of the Sudd. At this point the
While Nile receives the Bahr el Ghazal, which drains a large area to the W. and
S.W. The Bahr el Ghazal drainage is separated from the N. part of the Zaire
basin by a rather dry, hilly divide. Soon after receiving the Bahr el Ghazal, the
White Nile is joined by the waters of the Sobat, which drains a large area to the
E. The principal S. tributary of the Sobat, the Pibor, is separated from the
interior drainage of L. Rudolf by a low divide in extremely dry country. The E.
tributaries of the Sobat drain part of the W. slopes of the Ethiopian highlands.
The portion of the White Nile from L. Albert to Nimule is also known as the
Albert Nile, and that from Nimule to the junction with the Bahr el Ghazal as
the Bahr el Jebel. From the mouth of the Sobat to Khartoum the White Nile is
a large placid stream of low gradient, often with a narrow fringe of swamp. In
the 1100 mile stretch between Khartoum and Aswan the Nile flows through a
narrow valley, making a giant S-shaped loop, and drops from 1217 to 282 ft. In
this part of its course lie the Six Cataracts, famous for their role in the history
of Nilotic civilizations. At each cataract the Nile is broken by rapids flowing in
rockstrewn channels and around numerous islands. The Sixth Cataract, where
the Nile narrows to 60yds, is in a gorge 60 miles N. of Khartoum. I t is here
that the river enters the desert. The Fifth Cateract, six miles long, is N. of
Berber. Before reaching the Fifth Cataract the Nile receives the Atbara. At
flood, the Atbara and its principal tributaries the Takazza and Dar es Salaam
contribute a substantial volume of muddy water to the Nile; in the dry season
flow is intermittent and they are reduced to a series of pools, the Atbara failing
to reach the Nile in some years. Most of the tributaries dry up completely.
Below the Fifth Cataract the Nile begins its great loop, a major deviation in its
northerly course to the Mediterranean. The Fourth Cataract, regarded as the
wildest, is about 30 miles upriver from Merowe. The Third Cataract is at
Dongola. The First Cataract, at Aswam, and the Second Cataract, near the
Egyptian border, have been submerged by the waters of L. Nasser. From Aswan
to Cairo the Nile, placid again, is bordered by a flood plain of alluvium which
widens to a maximum of about 1 2 miles. Beyond this narrow floodplain lies
the desert.
The mountainous Ethiopian plateau rises steeply from the Nile lowland. Its
highlands are divided into two sections by the E. Rift valley. The N.W. section,
culminating in Ras Dashan (15,158 f t high) is the larger and higher of the two;
most of it, including L. Tana, drains W. or N. into the Nile. In the S., however,
it is drained by the Omo R. into L. Rudolf. The narrow S.W. section descends
gradually to the semi-arid Ogaden plateau which slopes towards the Indian
Ocean. I t is drained mainly to the E., by the Webi Shebeli (1200 miles long)
and the Juba, into the Indian Ocean. Other important hydrographic features of
the highlands lie in the Rift valley. The main river is the Awash, which arises
near Addis Ababa and flows N.E. in a deep gorge for most of its length, finally
losing itself in the Danakil depression near the heavily mineralized L. Abbk. S.
of the Awash lies a chain of isolated mountain lakes, including Zwai, Hora
DISTRIBUTION O F AFRICAN FISHES
291
Abyata, Langana, Shala, Awusa, Abaya, Chamo, and Stefanie. Zwai (150
square miles, alt. 6050ft) flows S. into Hora Abyata (90 square miles, ah.
5161 ft). When Hora Abyata received floodwaters of Langana as well as those
of Zwai, it overflows into Shala. Langana (1 3 miles long and 9 miles wide) lies
just two miles W. of Hora Abyata. Shala (175 square miles, alt. 5141 ft) has no
outlet. Hora Abyata and Shala are saline and uninhabited by fishes. Awusa (60
square miles, alt. 5604 ft), between Shala and Abaya, is fed by mineral springs
and drains internally but it is only slightly brackish. I t is apparently
uninhabited by fishes. Abaya (485 square miles, alt. 4160 f t ) lies between
Awusa and Chamo; it is fresh-water and drains into Chamo during periods of
exceptional flood. Chamo (210 square miles, alt. 4045 ft) is a freshwater lake
of internal drainage; at one time it probably drained into Stefanie through a
headstream of the Galaria Sagan, which now arises in a swamp E. of the lake
and has an intermittent flow. Stefanie (30-40miles long, 15-20 miles wide, alt.
1700 ft), lies between Chamo and Rudolf. I t is swampy and strongly saline, and
appears to be in the process of drying up. There is much evidence that the
Awash had a greatly augmented volume of water during the pluvials. Zwai,
Hora Abyata, Langana, Shala, and numerous lakes now represented by dry
basins had high water levels which were presumably stabilized when they
overflowed into the Awash. Probably L. Abb6 was the largest in a series of
lowland freshwater lakes which the Awash drained to the sea. It has shrunk
greatly in relatively recent times. Abaya, Chamo, and Stefanie probably were
connected and drained into L. Ruldof. This dichotomy in the history of the
highland lakes is supported by evidence from fish distribution. Nilotic fish
species are almost entirely absent from the Awash and the lakes which were
formerly drained by it, while the lakes which drained into Rudolf are
populated largely by Nilotic species.
The impoverished fish fauna of the Ethiopian highlands, representatives of
which are illustrated in Fig. 9, is dominated by Cyprinidae. Fishes recorded
from L. Tana are Clarias mossambicus (from a tributary), Clarias tsanensis
(supposedly endemic), numerous varieties of Barbus (Labeobarbus) intermedius
(Boulenger, 1909-16; Banister, 1973), a few small Barbus in need of systematic
revision, Varicorhinus beso, two species of Garra, a cobitid, Noemacheilus
abyssinicus, and Tilapia nilotica. Of these fishes only T. nilotica occurs in the
Nile lowlands. N. abyssinicus, known only from the type specimen collected at
Bahardar on L. Tana in 1902, is the only member of the Asian genus
Noemacheilus that has been found in Africa. The geographically closest
populations of the genus occur in Syria. The Awash is populated by Clarias
mossambicus, some small Barbus (including B. paludinosus), B. intermedius, V.
beso, Garra, and T. nilotica. L. Zwai has B. intermedius and two other large
Barbus which are supposedly endemic species perhaps related t o it, B.
paludinosus (and other small species of Barbus?), and Garra. Clarias
mossambicus and B. paludinosus are widespread in E. and S.E. Africa. B.
intermedius is widely distributed in Ethiopia and N. Kenya. In addition to Tana
and Zwai, it has been recorded from lakes Langana, Abaya, Chamo, Stefanie,
and Baringo. It is also known from the Blue Nile, Awash, Webi Shebeli-Juba,
Uaso Nyiro, and Omo drainages. Excepting the orobatic Tilapia nilotica, there
is a complete absence of Nilotic species in the Awash R. and in several
highlands lakes populated by Barbus intermedius that were formerly drained by
292
T. R . ROBERTS
A
Figure 9. Fishes of the Abyssinian highlands: A-C, Barbus inrermedius; D, Garra dembeensir;
E, Noemacheilus abyssinicus; F, Clarias mossambicus; G , Amphilius lampii; H, Tilapia niIotica.
the Awash. The fishes of L. Abaya were described by Parenzan (1939).
Although the validity of his new species and some of his other identifications is
questionable, the lake has at least eight lowland Nilotic species, in addition to
highland forms found elsewhere in Ethiopia. Most of these Nilotic species, with
the exception of Hyperopisus bebe, are present in the Webi Shebeli-Juba
drainage and in the Omo-Rudolf drainage. Several of them have also been
recorded from lakes Chamo and Stefanie (Parenzan, 1939). The headwaters of
the Juba arise just E. of Abaya and Chamo but are separated from the lake
drainages by a high mountainous divide. It seems likely that the Nilotic species
in question gained access to Abaya, Chamo, and Stefanie via a former
connection of these lakes with the Rudolf basin.
Somalia is all desert or semi-desert. The only large perennial rivers are the
Webi Shebeli and Juba which arise on the E. slopes of the Ethiopian highlands
and flow across the S. part of the country. Primary-division fishes living away
from these rivers are subterranean. Midway between the lower courses of the
Webi Shebeli and the Juba, where they are widest apart, there is a low-lying
limestone plateau with extensive underground waterways radiating out from it.
These are inhabited by the endemic genera Uegitglanis and Phreatichthys.
Uegitglanis is blind and depigmented but otherwise similar to surface-dwelling
Clarias. Phreatichfhys, in addition to being blind and depigmented, is the only
DISTRIBUTION O F A F R I C A N FISHES
293
scaleless cyprinid in Africa; it is related to Barbus. N. of the Somali lowlands, in
the Horn of E. Africa, are the Migiurtinia Mts., a hot, arid region of moderate
elevation (1500 to 3000 f t in the W., 600 ft in the E.). On the gentle S.E. slope
of these mountains, draining into the Indian Ocean, is the Nogal valley. The
highland tributaries of the Nogal tend to go underground within 50 km of their
sources, so that its lower reaches are always dry. The extensive underground
waters are widely populated by the endemic Barbopsis, a medium-size
Barbus-like fish with minute eyes (Fig. 10) (Poll, 1961). I t is pigmented and
v
Figure 10. Barbopsis devecchii.
very different in appearance from Phreatichthys. The geographically nearest
surface-dwelling populations of Barbus are in the Webi Shebeli, over 250 miles
distant. There is no evidence as to when the ancestors of Barbopsis reached the
Nogal valley or from where they came. They could have come from the
Abyssinian highlands, the Nilo-Sudan, the East African coastal region, or
possibly Arabia. Because of the geographical isolation and distinctness of
Barbopsis, and the uncertainty of its faunistic relationships, I have not placed
the Nogal valley in an ichthyofaunal region. In N. Somalia, the Danakil
depression, and the Eritrean lowlands the only surface-dwelling fishes belong to
secondary- and peripheral-division families. These include several species of the
alkalinophile cyprinodontid genus Aphaniops, generally encountered in shallow
bodies of standing water subject to extreme fluctuations in temperature and
usually highly mineralized, and Gobius, reported by Poll (1961) from wadis on
the sharply descending N. slopes of the Migiurtinia Mts.
The Nilo-Sudanic fish fauna, endemic representatives of which are illustrated
in Fig. 11, ranges more or less continuously throughout the Nilo-Sudanic
province. The N. limit of distribution of Nilo-Sudanic fishes is obviously
controlled by climate. The majority of Nilo-Sudanic fishes in the Senegal,
Niger, and Chad basins probably extend N. as far as there are flowing rivers.
Relict populations of a few species occur in the Western and Central Sahara and
probably descended from stocks isolated since the end of the last pluvial
(around 8000 years ago). The S. limit of distribution, on the other hand,
determined largely by the Atlantic Ocean and the watershed of the Zaire basin,
has been relatively stable and almost independent of climatic influence. On the
Atlantic coast, the Volta basin is populated almost exclusively by Nilo-Sudanic
species, of which it has a rather full complement, presumably gained when two
of its headwaters captured N.E.-flowing tributaries of the Niger R. As might be
expected from the locations of these captures (Fig. S), they occur throughout
the headwaters as well as the middle and lower portions of the basin. The date
294
T. R. ROBERTS
/
I
-
B
A
e
e
A
Figure 11. Representative Nilo-Sudanic endemics: A, Clupisudis niloticus; B, Cromeria
niloticus; C , Hyperopisus bebe; D, Gymnarchus niloticus; E, Citharinus latus; F, Clarotes
laticeps; G , Silumnodon auritus; H, Irvineia voltae; I, Hemisynodontis membmnaceus;
J , Tetraodon fahaka.
of the captures is unknown. If the relict population of fishes described by
Daget (1961b) from the E. flank of the Bandiagara escarpment was stranded
when the Black Volta captured its present N.E.-flowing headwaters, then the
capture probably occurred since the end of the last interpluvial, that is, no
more than 12,000 years ago. More probably, however, the Bandiagara
population was isolated directly from the present Niger system. In Ivory Coast,
the entire Comoe system and the upper courses of the Bandama and Sassandra
rivers are inhabited almost exclusively by Nilo-Sudanic fishes, while the lower
courses of the Sassandra and Bandama and the entire Tan0 River of Ghana,
covered by rain-forest, are inhabited by a mixture of Nilo-Sudanic and Upper
Guinean species (Daget & Iltis, 1965; personal observations on the Tano). The
Comoe may have gained its Nilo-Sudanic fishes by stream capture from the
Volta system. Freshwater lagoons link the lower courses of the Comoe and the
Tano, and extensions of presently existing lagoons would serve t o link up the
lower courses of the Comoe, Sassandra, and Bandama. Very few Nilo-Sudanic
DISTRIBUTION OF AFRICAN FISHES
295
fishes are present in the Prah R., between the Tan0 and the Volta, or in the
coastal rivers between the Sassandra and the Gambia. Of these few, some of the
most notable are Hydrocynus lineatus in the Prah, Protopterus annectens in the
Kolentk, and Lutes niloticus in the Konkourk. In the Senegal system, the lower,
middle, and probably some of the upper courses are largely populated by
Nilo-Sudanic fishes. The Bafing, however, which flows down the interior slopes
of the Fouta Djallon, is almost exclusively inhabited by Upper Guinean forms
(Daget, 1962). The primary- and secondary-division freshwater fishes in the
lower and middle courses of the Gambia are predominantly Nilo-Sudanic,
whereas those in the upper Gambia are almost exclusively Guinean (Daget,
1960). Nilo-Sudanic fishes presumably reached the Gambia from the Senegal
by crossing the low-lying country in between their lower courses. During the
last interpluvial, the Senegal and Gambia rivers may have been greatly reduced
or even ceased t o flow, and the present relatively full complement of
Nilo-Sudanic fishes may be largely or entirely the result of colonization during
the last pluvial.
The watershed to the S. of the Niger and Chad systems is shared with only
two Lower Guinean river systems, the Cross and the Sanaga. Heterotis niloticus
and a number of other Nilo-Sudanic forms are present in the Cross, probably as
a result of dispersal across the low-lying swampy area between the lower Niger
and lower Cross. The Chad and Nile basins share an extensive watershed with
the Zaire basin. Six Zairean species have invaded the middle and lower courses
of the Logone and Chari and are not found elsewhere in the Nilo-Sudanic
region (Blache, 1964); it is not known whether there has been a corresponding
invasion of the Ubanghi (Zaire system) from Chad. A few small Nilo-Sudanic
species occur in small streams in the Ituri forest in the N.E. corner of the Zaire
basin (Lambert, 1961).
The Nilo-Sudanic fish fauna is remarkably uniformly distributed throughout
the main part of its range. There are of course localized endemics within the
province, especially among the numerous small species of Barbus inhabiting
high gradient streams. Other localized endemics include Citharidium and several
species of Synodontis in the Niger; several Mormyrus and Synodontis in the
Nile; a species of Clarotes and Pardiglanis, a genus related to Clarotes, in the
Juba; and the rheophilic cichlids Gobiocichla in the Niger and “Leptotilapia ”
irvinei in the Volta. The genus Leptotilapia is otherwise known only from two
species in the Zaire basin, from where it was originally described. Leptotilapia
is listed as an endemic Zairean genus in Table 4; and I am confident that future
studies will vindicate this action. The Voltaic species probably represents an as
yet unnamed genus. Relict distributions of Nilo-Sudanic genera are rare: a
notable example is that of the schilbeid genus Irvineia, with one species in the
Volta basin and one in the Juba (Trewavas, 1964).
A major break in the main range of the Nilo-Sudanic fishes occurs in the
hilly and in part mountainous divide separating the Chad and Middle Nile
basins. This semi-arid region is largely devoid of fishes. During the pluvials
numerous river systems presently dried up were probably perennial and
populated by fishes, but there is no direct evidence as to when the last
exchange of fishes occurred across the intervening watershed. Another break in
the main range of the Nilo-Sudanic fishes occurs in the gently sloping semi-arid
or arid country between the present headwaters of the Pibor and the N. end of
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
E
E
E
E
E
E
E
E
E
X
References.
X
X
X
X
X
X
X
X
X
Omo
Bagrus docmac
Auchenoglanis occiden talis
Heterobranchus longiyilis
Clarias larera
Schilbe uranoscopus
Synodontis schall
Synodontis frontosus
Mochocus niloticus
Andersonia leptura
Malapterurus electricus
Aplocheilichthys jeanneli
A plocheilich thy s rudolfianus
Lates niloticus
Lates niloticus longispinus
Lates niloticus rudolfianus
Tilapia nilotica
Tilapia nilotica subsp.
Tilapia nilotica vulcani
Tilapia zillii
Tilapia galilaeo
Hemichromis bimaculatus
Haplochromis rudolfianus
Haplochromis turkanae
Haplochromis macconneli
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Rudolf
X
X
X
X
X
X
X
X
X
X
Omo
4
1.3
3
3,6
3.9
9
9
35
2
2
174
3.5
1
1
1
1
2
1.4
1
1
4
4
4
2
References*
* References: 1. Boulenger (1909-16); 2. Worthington (1932); 3 . Trewavas ( 1 9 3 3 ) ; 4. Pellegrin (1935); 5 . Worthington (1937:312); 6. Trewavas
(1973); 7 . Banister (1973); 8. Whitehead (1963); 9. Greenwood (1974b).
Polypterus bichir
Polyp terus senegalus
Gymnarchus niloticus
Heterotis niloticus
Alestes macrolepidotus
Alestes nurse
Alestes baremose
Alestes dentex
Micralestes acutidens
Hydrocynus forskalii
Distichodus niloticus
Citharinus citharus
Barbus bynni
Barbus intermedius
Barbus wemeri
Labeo cylindricus
Labeo hone
Labeo niloticus
Barilius niloticus
Barilius loati
E Engraulicypris stellae
Engraulicypris bottegi
Discognathus dem beensis
Rudolf
Table 6. Fishes of Lake Rudolf and the Orno River (“E” indicates endemic)
N
h
CA
nJ
m
W
5
0
n
j
Y)
DISTRIBUTION O F AFRICAN FISHES
297
L. Rudolf. This area, sometimes called the Turkana desert, receives enough rain
t o flood the Lotagipi flats in some years. During the pluvials these flats
probably held a shallow lake with a fair complement of Nilo-Sudanic fishes;
during the last pluvial, L. Rudolf overflowed into them, and was part of the
time directly connected with the Nile system via the Pibor. A total of 43
species have been recorded from the Rudolf basin (Table 6), of which six are
endemic, 3 3 are shared with the Lower Nile, and four with the Ethiopian
highlands and Webi Shebeli-Juba basin but not the Lower Nile. The species
shared with the Ethiopian highlands and Webi Shebeli-Juba are Barbus
intermedius, Labeo cylindricus, Discognathus dembeensis, and Engruulicypris
bottegi. The three endemic species are an Engruulicypris and two
Aplocheilichthys. The absence of endemic cichlid species apart from
Haplochromis is noteworthy. A reputed Pelmatochromis known only from L.
Rudolf has subsequently been identified as Hemichromis bimaculatus
(Trewavas, 1973). Two endemic subspecies of Tilapia nilotica have been
recognized from L. Rudolf: one widespread in the lake, the other restricted t o
Crater Lake A of Central Island. The only other taxonomically distinct fishes in
the lake are two subspecies of Lates niloticus: one inshore, the other offshore
and in deeper water. Worthington ( 1 932) described a subspecies of Citharinus
citharus from the lake, but observations by Pellegrin (193 5) on additional
specimens indicated that they were not taxonomically distinct from Nile
specimens of the same species.
There seem to be no major barriers between L. Albert and the While Nile.
The Semliki rapids on the Semliki R. evidently prevent the upstream movement
of crocodiles and fishes from L. Albert into lakes Edward and George
(Worthington & Worthington, 1933: 213-17). The Murchison Falls on the
Victoria Nile are an insurmountable barrier to upstream movement of all fishes
with the possible exception of forms with remarkable climbing abilities such as
Chiloglunis.
The one truly remarkable instance of disjunct distribution of fishes
otherwise restricted to the Nilo-Sudan ichthyofaunal province is the presence
of Polypterus bichir, Polypterus senegalus, Ichthyborus besse, and Ctenopoma
muriei in the middle Lualaba River in the S.E. corner of the Zaire basin. In
order to account for these fishes in the Lualaba, Poll (1957) suggested that the
Lualaba formerly flowed into the Nile. An alternative explanation is that they
entered the Lualaba via L. Tanganyika, as a result of the same transfer of fishes
that resulted in the presence of Nilotic fishes in lakes Kivu and Tanganyika
when the headwaters of the Nile were cut off by the elevation of the Mjumbiro
or Virunga mountains.
There is no evidence, either from distribution of living fishes or the fossil
record, that the Nilo-Sudanic fish fauna formerly extended into the Eastern
Rift valley S. of L. Rudolf. The Juba and Webi Shebeli are the only rivers on
the E. coast of Africa having Nilo-Sudanic fishes in any numbers. A relict
population of Nilo-Sudanic fishes occurs in the Uaso Nyiru. This is an
eastward-flowing river which arises in a mountainous area S.E. of L. Rudolf and
loses itself in the Lorian swamps (not t o be confused with a river of the same
name which flows into L. Natron in the Eastern Rift valley). Boulenger (1912)
recorded 20 species from the Uaso Nyiru and noted that its fish fauna has
much in common with that of the Juba and Webi Shebeli. During the pluvials
20
298
T. R. ROBERTS
its lower course was almost certainly connected with the Juba-Webi Shebeli. It
is the southernmost river E. of the Eastern Rift valley inhabited by Mormyi-ops
deliciosus, Clarias lazera, Synodontis schall, and S. geledensis. I t also has
Mormyrus kannume and Clarotes laticeps, two Nilo-Sudanic fishes present in
the Tana and Athi, the northernmost rivers in the East coast ichthyofaunal
province. Tlie remaining Uaso Nyiru fishes are either endemic or are shared
with the Abyssinian highlands and/or the East coast ichthyofaunal province.
The record of the endemic Nilo-Sudanic species Citharinus latus from the
Kingani or Ruvu River in Tanzania cited by Bailey (1969) has never been
substantiated and is probably due to a misidentification. I t originated with
Pfeffer (1896), when the only species of Citharinus known were the
Nilo-Sudanic species C. latus and C. citharus. Pfeffer published fin-formulae
and scale counts which agree perfectly with those of C. latus because they are
not based on his Ruvu material but rather represent a synopsis of the fin- and
scale-counts for that species published by Giinther (1864: 302) and
Steindachner (1870: 539). C. congicus, a Zairean species, has been found in the
Ruaha (Matthes, 1967), and might be expected in the Ruvu. No other
Citharinus have been found in the East coast ichthyofaunal province.
For further discussion of the distribution of Nilo-Sudanic fishes see
Boulenger, 1907 (Nile); Blache, 1964 (Chad basin); Daget, 1954 (Niger);
Johnels, 1954 (Gambia); Daget, 1960a (Gambia); Daget, 1962 (Upper Guinea);
Daget & Iltis, 1965 (Ivory Coast); Daget, 1960b (Black Volta and Comoe); and
Roman, 1972 (exchanges between Volta and Niger basins).
Upper Guinea, Lower Guinea, and Zaire ichthyofaunal provinces
The main coastal rivers of Upper Guinea are, from Senegal to Ghana: the
Senegal, Gambia, Casamance, Geba, Corubal, Konkoure, Great Scarcies, Little
Scarcies, Rokel, Sewa, Moa, Lofa, St. Paul, St. John, Cess, Cavally, Sassandra,
Bandama, Comoe, Bia, Tano, Prah, and Volta. The Senegal, Bandama, Comoe,
and Volta are inhabited largely t o almost exclusively by Nilo-Sudanic fishes,
and the Casamance, Geba, and Tan0 by a mixture of Nilo-Sudanic and Upper
Guinean forms. The rivers in Sierra Leone and Liberia apparently are populated
almost exclusively by Upper Guinean fishes. They arise in mountainous areas
and their basins lie entirely within the rain forest (Fig. 6). They are all
relatively small, the largest being the Cavally, 400 miles long and draining an
area of only 8600 square miles. Representative Upper Guinean species are
shown in Fig. 12.
The main river systems in Lower Guinea are, from Nigeria to Zaire: the
Cross, Vouri or Wouri, Sanaga, Nyong, Ntem or Campo, Benito, Utamboni,
Ogowk, Nyanga, Kwilu-Niari, and Chiloango. The fishes of these rivers are
poorly known, and the literature on them very scattered. Representatives are
illustrated in Fig. 1 3 . Apart from the Cross R., Nilo-Sudanic elements have
been almost entirely excluded (see Addenda). Many species are shared with the
Zaire province, especially in the Ntem and OgowC. Judging from changes in
direction of river flow indicated on maps, a headwater of the Nyong may have
been captured by the Ja, a major tributary of the Sangha R. (Zaire basin).
Alestes opisthotaenia has a limited distribution in the Ja and a few coastal
rivers of Cameroon (excluding the Sanaga). TiZapia mvagoi is known only from
DISTRIBUTION OF AFRICAN FISHES
299
v
Figure 12. Fishes of Upper Guinea: A , Mormyrops longiceps; B, Alestes Iongipinnh; C, Barbus
walkeri; D, Labeo parvus; E, Notoglanidium walkeri; F, Chrysichthys w l k e r i ; G , Synodontis
ebumeensis; H, Chromidotilapia guen then.
the Nyong, Ja, and Ivindo (Trewavas, 1969); the Ivindo is a tributary of the
Ogowt. Evidence for stream capture among headwaters of the Nyong, Ntem,
Ja, and Ivindo is discussed by Thys (1966: 90-1). A recent influx of species
from the Zaire system into the Ogowt is indicated by the following Zairean
species present in the OgowC but unknown from the rest of Lower Guinea:
Polypterus retropinnis, Mormyrops nigricans, M . zanclirostris, Stomatorhinus
humilior, Grasseichthys gabonensis, Alestes macrophthalmus, Micralestes
uroteania, Alestopetersuis hilgendorfi, Phenacogrammus aurentiacus, Hemistichodus vaillanti, Distichodus fasciolatus, Barbus brazzae, Labeo variegatus,
Amphilius brevis, and Hylopanchax silvestris. The taxa Pantodon, Phractolaemus, Xenocharax, Phago, Bryconaethiops microstoma, Barbus jae,
Eutropielles, Synodontis batesi, and A topocheilus are shared by the Zairean
province and the Lower Guinean province from the Ogowt basin northwards
In marked contrast, almost no genera or species are shared exclusively by the
Chiloango and Kwilu-Niari (and Nyanga?) and Zaire province.
The Zaire drainage, including L. Tanganyika, is by far the largest in Africa
and has the densest hydrographic network (Fig. 1). It extends from 8"N to
13"s.More than one-third of it, or an area almost as great as Upper and Lower
Guinea combined, is rain forest. All African primary- and secondary-division
families are represented in the Zaire drainage except Denticipitidae,
300
T. R. ROBERTS
n
A
-"
"-
K
E
Figure 13. Fishes of Lower Guinea: A, Denticeps clupeoides; B, Marcusenius ntemensis;
C, Boulengeromyrus
knoepfflen; D, Alestes
kingsleyae; E, Phenacogrammus major;
F, Distichodus kolleri; G, Raddhabarbus sanagensis; H, Pamuchenoglanis bqutchangai;
I, Procatopus glaucicaudis; J , Hysopanchax zebra; K,Polycentropsis abbreviata; L,Chilochromis duponti; M,Sicydium bustamantei.
Osteoglossidae, Gymnarchidae, Cobitidae, Nandidae, and Synbranchidae. In
addition to the endemic genera of primary- and secondary-division fishes
indicated in Table 2, there are five endemic Zairean riverine genera of
pellonulin Clupeidae. A high percentage of the species in the following families
are found nowhere else: Polypteridae, Clupeidae, Kneriidae, Characidae,
Distichodontidae, Citharinidae, Ichthyboridae, Cyprinidae, Bagridae,
301
DISTRIBUTION OF AFRICAN FISHES
A
I
A
I
B
J
C
K
1
D
e L- ___ -
M
h
--
E
F
N
0
G
P
H
Q
Figure 14. Zairean fishes: A, Odaxothrissa losera; B, Mormyrops lineolatus; C,Hippopotamyrus
w2verthi; D, Campylomormyrus mirus; E, Grasseichthys gabonensis; F, Alestes liebrechtsii;
G , Distichodus altus; H, Mesoboms crocodilus; I, Barbus hulstaerti; J , Leptocypris brevirostris;
K, Gnathobagrus depressus; L,Leptoglanis xenognathus; M,Belonoglanis tenuis; N,Synodontis
congicus; 0 ,Lamprologus congolensis; P, Teleogramma brichardi; Q, Tetraodon mbu.
302
T. R. ROBERTS
Schilbeidae, Amphiliidae, Clariidae, Mochokidae, Cyprinodontidae, Cichlidae,
Anabantidae, Mastacembelidae, and Tetraodontidae. Representatives are
illustrated in Fig. 14. Of the nine species in Polypterus, seven occur in the Zaire
basin and four are Zairean endemics. All but two of the 15 species in the
“elephant snouted” mormyrid genus Campylomormyrus are Zairean endemics.
There are seven species in the characid genus Hydrocynus, three of which are
Zairean endemics. Twelve Distichodus occur in the Zaire basin, all but two
endemic, and 3 5 Synodontis, all but three endemic. All four species of
Tetraodon in the Zaire basin are endemic. The Zairean ichthyofaunal province
has nearly twice the total number of riverine species as the next richest African
ichthyofaunal province, and nearly three times the number of endemic riverine
species (Table 5). Geographical or ecological factors that presumably favored
this richness include (1) the sheer size of the Zaire basin; (2) the density of its
hydrographic network (related in large part to the high rainfall); ( 3 ) climatic
stability of the Zaire basin due to its equatorial position and forest cover;
(4) extent of both rain forest and savannah or steplands areas within the Zaire
basin, and the large number of low and high gradient, blackwater, whitewater,
and clearwater streams; (5) hydrographic barriers of varying effectiveness on
virtually all major tributaries in the Zaire basin, as well as on the mainstream of
the Zaire River, often marking the transition from low gradient to high gradient
stream conditions or from forest to savanna areas and tending to prevent
species from dispersing throughout the basin; ( 6 ) expansion of the catchment
area of the Zaire at the expense of adjacent basins by river capture, often
lncorporating large parts of their fish fauna with its own, for example, in the
“Zambesian” portion of the Zaire basin, which includes L. Bangweulu and L.
Mweru.
The distribution of the taxa Polypterus, Phagoborus, and Parailia, Barbus
camp tacan thus, Paramphilius, Dou mea, Microsynodon tis, and Pelma to chromis
indicates an early faunistic relationship between the Upper Guinean, Lower
Guinean, and Zairean provinces, Two species of Polypterus are shared
exclusively by Upper Guinea and the Zaire basin. The genus Parailia is
represented by four species, two endemic to the N. part of Upper Guinea and
two endemic to the Zaire basin. Phagoborus and Microsynodontis are shared
exclusively by the N. part of Upper Guinea, Lower Guinea, and the Zaire basin.
There are endemic species in each area. (The Lower Guinean Phagoborus, from
Cameroon, was originally described as a monotypic genus. Gavialocharax, but
after comparing specimens of it with ones from Upper Guinea and the Zaire
basin, I find there are no grounds to separate them at the generic level.)
Pelmatochromis occur in Upper and Lower Guinea and most of the Zaire basin.
The genus apparently does not occur elsewhere. Faunistic relationship between
the Upper and Lower Guinean regions is also indicated by the following
identical or closely related taxa shared exclusively by them: Afronandus in
Upper Guinea and Polycentropsis in Lower Guinea (the only genera of
Nandidae in Africa); Isichthys hentyi in the N . part of Upper Guinea and
throughout Lower Guinea; Mormyrus goheeni from Liberia and from
Cameroon; Mormyrops breviceps and the closely related (possibly identical) M.
caballus from Cameroon; Alestes longipinnis throughout both Upper and
Lower Guinea; and Alestes brevis, Labeo brachypoma, and Tilapia mariae in
Ghana and Nigeria but absent from the intervening Dahomey gap.
303
DISTRIBUTION OF AFRICAN FISHES
East coast, Zambesi, and Quanza ichthyofaunal provinces
The most important coastal rivers in East Africa between the Juba in the N.
and the Zambesi in the S. are the Tana, Athi, Pangani or Rum, Wami,
Rufiji-Ruaha, Rovuma, Msalu, Lurio, Ligonha or Longonha, and Lugela. There
is no comprehensive report on the fishes of this region, and the literature on
them is very scattered. Important recent references are Bailey, 1969
(non-cichlid fishes of Tanzanian coastal rivers); Whitehead, 1963 (fishes of Athi
and Tana rivers); Trewavas, 1966 (Cichlidae of coastal rivers); Matthes, 1967
(fishes of the Ruaha); and Greenwood, 1962 (Barbus). The fishes in the
southern part, in Mosambique, are virtually unknown.
The East coast fish fauna is very poor. Representatives are illustrated in
Fig. 15. There are less than 100 primary- and secondary-division species, and
although more than half of them are endemic, there is only one endemic genus.
Much of the N. part of the area is semi-arid or arid, and the entire area was
probably dried during the interpluvials to such an extent that the earlier fish
fauna was largely eliminated. Most fishes presently inhabiting this area may
have arrived shce the last interpluvial, in other words, in the last 12,000 years
or so. The majority of the endemic species belong t o Barbus, Labeo, and
A
B
C
G
Figure 15. Fishes of the East coast: A.Anguilla nebulosa; B,Mormyms Icannume,
C , Petrocephalus catosroma; D, Citharinus congicus; E, Labeo cylindricus; F, Sch17be mystus;
G, Chiloglanb neumanni; H, Tilapia spilums.
304
T. R. ROBERTS
Tilapia, eurytopic genera in two of the first-order families in the taxon cycle
for African riverine fishes. The faunistic relationship with the Zambesi
ichthyofaunal province is very strong. Pareutropius longijllis, an Atopochilus,
and several other Ruaha endemics seem to be most closely related to Zairean
species, a faunistic relationship supported by the presence of Citharinus
congicus in the Ruaha (Matthes, 1967). The most likely source of the original
stocks of these species is the Malagarasi.
The Zambesi ichthyofaunal province includes the entire hydrographic basins
of the Cunene, Ovambo, Okavango-Ngami, Zambesi, and Limpopo, plus the
coastal rivers in between the lower Zambesi and the Limpopo, and south of the
Limpopo up to and including the Pongola or Malputo. Representatives of the
moderately rich Zambesi fish fauna are illustrated in Fig. 16. Basic information
on fish distribution has been assembled and discussed by Bell-Cross (1965;
1972), Jubb (1967), and Poll (1967). The Zambesi, 1600 miles long, and with a
drainage area of 500,000 square miles, arises in the N.W. of Zambia and flows
southeastward in a great S-shaped curve across Zambia and Mosambique to the
Indian Ocean. The most important affluents on its right are the Lungwebungu
and Luanginga from Angola, the Chobe from the marshes of N. Bechuanaland,
Figure 16. Zambesian fishes: A, Kneria polli; B, Morrnyrus lacerda; C , Hydrocynus vittatus;
D, Distichodus rnmsarnbicus; E, Barilius zambezensis; F, Coptostomabarbus bellcrosri;
G , Malaptemrus electicus; H, Serranochromis angusticeps.
DISTRIBUTION O F AFRICAN FISHES
305
and the Shangani and Sanyati from the High Veld of S, Rhodesia. On its left
side lie the Kafue and Luangwa from N.E. Zambia and the Shire R. from L.
Malawi. The Limpopo, 1050 miles long, and with a drainage of 138,000 square
miles, arises on the Witwatersrand N. of Johannesburg and flows northeastward
through S. Africa and Mosambique to the Indian Ocean. Its upper course is
known as the Crocodile R. Principal tributaries are the Shashi, Magalakwin,
Bubye, and Olifants (not to be confused with the Olifants of the S.W. Cape).
Its mouth lies about 400 miles S. of that of the Zambesi.
The Sabi or Save, 400 miles long, and the Pungwe, 200 miles long, are the
two principal rivers between the Zambesi and the Limpopo. They arise in the
high plateau area of S. Rhodesia. South of the Limpopo, the Incomati (500
miles long) and the Pongola (350 miles long) arise in the Drakensberg of S.
Africa and wind their way to the Indian Ocean near Lourenp Marques. The
lower courses of the Zambesi, Save, Pungwe, Limpopo, Incomati, and Pongola
traverse a low-lying, poorly-drained coastal plain less than 300 f t above sea
level. Exchange of fishes across this area probably occurs under present
conditions, and was presumably extensive during the pluvials. The fishes of the
Pungwe and the Lower Sabi are very similar to those of the Lower Zambesi.
The Sabi and the Lundi, its principal tributary, are interrupted by waterfalls
near their confluence, and many of the Zambesian species present in the Lower
Sabi are absent above the falls (Jubb, 1967).
In its Upper course the Zambesi drains a huge shallow alluvial basin more
than 4000 f t above sea level. Due to the highly seasonal rainfall and high
evaporation, many of its upper tributaries are intermittent. The main stream is
characterized by long stretches of low gradient alternating with short sections
of rapids. The Middle Zambesi extends from Victoria Falls to the Cabora Bassa
rapids. The Middle Zambesi has a relatively poor fish fauna compared to the
Upper and Lower Zambesi (Jackson, 1961 ; Bell-Cross, 1972). Victoria Falls
constitute a major barrier to upstream fish movements and presumably to
downstream movements as well. The general level of the country is the same
below the falls as it is above them while the river drops into a great fissure. The
falls, over a mile wide, drop 200-350f t into the chasm below. For 45 miles the
extremely turbulent river zigzags sharply as it follows a series of fault lines,
becoming incised nearly 1500 f t below the plateau. For the next 600 miles its
flow was generally deep and turbulent until the construction of Kariba Dam.
The Middle Zambesi receives the Kafue and Luangwa. The Lower Zambesi,
about 350 miles long, is shifting and shallow, with numerous sandbanks, and
ends in a complex delta. The fish fauna of the Lower Zambesi is poorly known,
but richer than that of the Middle Zambesi.
The Okavango or Cubango R., 1000 miles long, arises on the Bik plateau in
central Angola and loses itself in the Okavango swamps N.W. of Maun. During
heavy rains, the floodwaters escaping from the upper end of the Okavango
swamps reach the Zambesi via the Chobe R., and overflow from the S. end of
the swamps occasionally reaches the salt pans of L. Ngami and the Makarikari
depression. When L. Ngami was discovered by Livingstone in 1849 it was an
imposing sheet of water, but was probably even then in process of drying up.
By 1910 it was largely, if not entirely dry except during the rainy season;
Woosnam (in Boulenger, 191 1) attributed the immediate cause of its drying up
to the obstruction of the Teoughe, a major channel of the Okavango which fed
306
T. R. ROBERTS
into it, by reed beds and siltation. The fishes of the L. Ngami area are known
from a collection of 25 species made by Woosnam and reported upon by
Boulenger (1911). All of these species are widely distributed in the Okavango
R. and in the Upper Zambesi (see Addenda).
The Cunene R., 6-700 miles long, arises in W. central Angola. Its flow is
disrupted by a series of rapids and by the Rua Cana Falls where it flows over
the rim of the continental plateau onto the Atlantic coastal slope. The falls are
4 0 0 f t high. The Cunene has a strong faunistic relationship with the Upper
Zambesi and the Kafue. Bell-Cross (1965) recorded 40 species from the
Cunene. Several are Zambesian endemics otherwise known only from the
Upper Zambesi/Okavango and Kafue, namely Mormyrus lacerda, Hippopotamyrus castelnaui, Barbus poechii, Synodontis macrostigma, and Haplochromis giardi. The fishes of the Kafue are isolated from the main course of the
Middle Zambesi by waterfalls in the Kafue gorge. The connection of the
“plateau Kafue” with the Upper Zambesi apparently was severed when it was
captured by the “valley Kafue” and became part of the Middle Zambesi
system.
Bell-Cross (1965) suggested that the Cunene, Upper Zambesi, Okavango,
plateau Kafue, and Chambeshi once formed a unified western drainage, while
the Middle and Lower Zambesi and the Shirk, minus the plateau Kafue, was a
separate eastern drainage. He considered that the fishes of the western drainage
were derived from the Zaire basin (Kasai and Lualaba), and that those of the
eastern drainage had Nilotic sources. This hypothesis discounts the possibility
that the western and eastern drainages were centers of speciation in their own
right. The presence of Zambesian species in the Lualaba is largely atmbutable
to the capture of the Chambeshi by the Luapula. Resemblance of the fish
faunas of the eastern drainage with the Nile is because the species involved are
extremely widespread. Not a single fish species is shared exclusively by the Nile
(or the Nilo-Sudanic province) and the Zambesian province. While many species
in the two provinces belong to the same genera, the genera involved are all
widely distributed beyond them. On the basis of what is now known about the
present and past distribution of fishes, there is hardly a route by which Nilotic
species could gain access to the Zambesi province. The presence of Nilotic
species in the Middle Lualaba of the Zaire basin seems to be due to a late event
which had no effect on composition of fishes in the Upper Lualaba or Zambesi
systems. There is no evidence that Nilo-Sudanic fishes extended further S.
along the East African coast than the Tana and Athi rivers or that they ever
penetrated into the eastern rift valley further S. than L. Rudolf. Some of the
species previously thought to be Zambesian endemics occur in the S. plateau
tributaries of the Zaire R., including Barilius zambesensis and Auchenoghnis
ngumensis (Poll, 1967), possibly due to stream capture by the Zaire.
The Zambesian fish fauna is absent or poorly represented in the Angolan
coastal drainages N. of the Cunene. These evidently constitute a separate
ichthyofaunal province. The principal drainages are, from N. to S . , the
’M’bridge, Loje, Dande, Bengo, Quanza or Cuanza, and Caturnbela. The Quanza
R., over 600 miles long, with its important tributaries the Lucala and the
Luando, drains the largest area. The main courses of the more important rivers
are interrupted by rapids or falls. Although the Quanzan province is inhabited
by n o fewer than 14 primary- and secondarydivision families (Table 3), over
DISTRIBUTION O F AFRICAN FISHES
307
60% of the species belong t o Cyprinidae and Cichlidae. Ot outstanding interest
are several forms of Varicorhinus and Barbus known only from specimens
collected by W. J. Ansorge in the Lucala R . just above the Lucala railway
station and reported upon by Boulenger (1911, 1916). The faunistic
relationships of the Quanzan fishes have been documented and discussed by
Trewavas (1936, 1973), Ladiges (1964), and Poll (1966, 1967). According to
Trewavas (1973), the cichlid fauna of the Bengo and Lower Quanza R. is
related t o that of the Chiloango and Ogowk, while the cichlid fauna of the
Upper Quanza is related t o that of the Cunene and Zambesi. It is unclear t o
what extent these relationships extend t o other fish groups. An obstacle to
understanding the faunistic relationships of the Quanzan fishes is the total lack
of information regarding the fishes of the high gradient, southern tributaries of
the Lower Zaire R. such as the Inkisi and Mpozo.
Cape of Good Hope ichthyofaunal province
The Cape of Good Hope, as defined by geographers, coincides with an
ichthyofaunal province. It includes the entire hydrographic basin of the
Orange-Vaal River and all of the drainage systems S. of the Orange-Vaal and W.
of the Pongolo R. The principal relief feature is the Drakensberg ranges,
extending some 700 miles from E. Transvaal t o Capetown (W.). To the S. lies a
narrow coastal plain, backed by folded mountain ranges, notably the
Drakensberg, Outeniqua, and Langeberg. The principal rivers of the coastal
plain are the Oliphants (S.W. Cape), Gouritz, Gamtoos, Sundays, Great Fish,
Great Kei, and Umzimvubu, all deeply entrenched in rugged terrain except for
their short lower courses. The Orange R., 1300 miles long, arises on the inner
slopes of the Drakensberg and flows westward after leaving the mountains,
receiving the Caledon, Vaal, Molopo, and lesser streams before reaching the
Atlantic at Alexander Bay. On its lower course are several high falls, chief of
them the Aughrabies, which lies in arid country about 3 50 miles inland from its
mouth. The Aughrabies drops 480 f t after a cataract fall of 140 ft. Although
the Orange system drains 336,000 square miles, its flow is so reduced during
the spring months that it sometimes fails to reach the Atlantic. Between the
lower course of the Orange and the perennial Cunene R. (a distance of 1200
miles) are many dry watercourses to the Atlantic, which discharge only at rare
intervals and then briefly. Lying between the Orange basin and the Zambesi is
the Kalahari, semi-desert plateau 3500-4000 f t high. In the S. part of the
Kalahari are extensive areas of fixed sand dunes; in the N. numerous dry
watercourses and lake beds.
The freshwater fish fauna of the Cape, consisting of 54 species including
peripheral-division forms (Jubb, 1967), is notable for the high proportion of
localized endemics, the predominance of Cyprinidae, and the very small
number of Zambesian species. Representative Cape fishes are illustrated in
Fig. 17. There are 22 endemic Cyprinidae: 17 Barbus, four Labeo, and
Oreodaimon quathlambae, a monotypic genus and species known only from a
tributary of the Umkomaas R. in Natal (see Addenda). Greenwood & Jubb
(1967) provisionally regarded Oreodaimon as a derivative of Barbinae. The six
non-cyprinid Cape endemics are Galaxias zebratus; Amphilius natalensis ; two
bagrid catfishes currently assigned to the genus Gephyroglanis; and two species
308
T. R. ROBERTS
A
Figure 17, Fishes of the Cape: A, Galaxias zebmtus; B, Oreodaimon quathlambae; C, Labeo
seeben; D, “Gephyroglanis” slaten; E, Pseudocrenilabrus philander; F, Sandelia capensis.
of Sandelia, an endemic genus of Anabantidae closely related to Ctenopoma. G.
zebratus, the only African representative of the S. Temperate Zone
peripheral-division family Galaxiidae, is restricted to the lower reaches of the
Olifants R. and a few other rivers in the S.W. part of the Cape. One of the Cape
“Gephyroglanis” is restricted to the Orange drainage, the other to the Olifants.
Gephyroglanis is otherwise known only from Lower Guinea and the Zaxe
basin; as the genus is defined only by the absence of palatal teeth (a loss trait),
it may well be polyphyletic. Sandelia are restricted to small areas in the S.W.
and S.E. Cape. The geographically nearest relatives, members of the genus
Ctenopoma, occur in the Zambesi and in the Cunene.
Remarkably few Zambesian species extend into the coastal portion of the
Cape region beyond the Pongolo R., and none extend beyond the Umtavuma.
Marcusenius macrolepidotus, the only mormyrid, reaches the Umhlatuzi.
Barbus paludinosus and B. viviparus reach the Uvongo and Umtavuma. No
Zambesian Labeo extends beyond the Tugela, the last low-gradient stream after
the Pongolo. Engraulicypris extends only to the Umfolozi, Clarias gariepinus
and C. theodorae to the Umtavuma and Umfolozi. Cyprinodontidae do not
extend beyond the Mkuzi R. in Natal. Characidae, Barilius, Eutropius,
Chiloglanis, Synodontis, Chetia, and Serranochromis stop at the Pongolo or a
short distance N. of it. This rapid petering out of Zambesian elements is
probably related to another observation, namely that the Umtavuma and the
next few rivers immediately W. of it are inhabited by very few species, none of
which is endemic to them. Thus the only native fish in the Umzimvubu is
Barbus anoplus, which ranges from the Incomati t o the Gouritz and throughout
the Orange-Vaal basin. The paucity of fishes in these rivers indicates that they
have only recently become suitable habitats accessible to freshwater fishes.
DISTRIBUTION O F AFRICAN FISHES
309
The most localized of the Cape endemics occur in the S.W. Cape. Of
particular interest is the 170 mile long Olifants R. The native fish fauna consists
of Galaxias zebratus, the “Gephyroglanis’. already mentioned, and five endemic
species of Cyprinidae. There are four species of Barbus, representing three
distinct stocks, and one Labeo. Barbus phlegethon and B. calidus belong t o a
small group of “red-finned minnows” confined to rivers in the S.W. Cape. B.
capensis is most closely related t o an endemic species in the Orange-Vaal
system (B. holubi). B. serra belongs to a group otherwise absent from the Cape:
the geographically nearest representative of this group is B. mattozi, present in
coastal rivers of Angola S. to the Cunene, the Gwaai R. of the Middle Zambesi
system, and the Limpopo (Jubb, 1967). The Labeo, L. seeberi, is very
distinctive.
The fishes of the Orange-Vaal system are also of special interest. Despite the
large drainage area and numerous mountain tributaries, there are only 14 native
species, including five Orange-Vaal endemics. The endemics are three Barbus,
one Labeo, and one “Gephyroglanis. ’’ Three more Barbus and another Labeo
are widely distributed Cape endemics. There are four Zambesian species:
Engraulicypris brevianalis, Clarias gariepinus, Tilapia sparrmannii and
Pseudocrenilabrus philander. The distribution of these species indicate that
they probably gained access to the Orange-Vaal system by indirect routes
rather than directly from either the Limpopo or the Zambesi basin. All four
range W. of Ponogolo R. t o or beyond the Uvongo R. in Natal, and at least two
of them are also present in the Cunene. Engraulicypris brevianalis may be of
particular significance, since it occurs in the Orange-Vaal system only below
Aughrabies Falls, and is also found in the Cunene (Jubb, 1967: 127-9). This
suggests an invasion route through S.W. Africa. Barbus hospes, an Orange-Vaal
endemic, is also known only from below the Aughrabies.
Relationships of lakes with endemic fishes to the
ichthyofaunal provinces
There are some two hundred or more natural lakes in Africa inhabited by
fishes, the number of species present ranging from one to around 250. In the
great majority of the lakes the species are identical with those in the river
systems with which they are presently connected or have been recently
connected. Endemic lacustrine species occur in at least 25 African lakes
(Table 7). The absence of endemic fishes in the majority of African lakes is
attributable to the fact that most lakes are very transitory features and there
simply has not been enough time for them to evolve. The explanation for the
absence of endemics in L. Chad and their paucity in Rudolf and Albert lies
primarily in Pleistocene climatic history. L. Chad probably was completely dry
much of the time, perhaps even within historic times, and Rudolf dry or
uninhabitable for fishes during the last interpluvial. The Lower Pleistocene of
Albert and Edward is characterized by a highly distinctive mollusk fauna of 14
bivalves and 17 prosobranch gasteropods (pulmonate gasteropods absent). More
than half of these forms are extinct and unknown in deposits from any other
region (Adam, 1959: 125). By the middle Pleistocene most of them had
probably died out due to arid conditions (Adam, 1959: 130). The mollusks
Table 7. African lakes with endemic fishes (References in Boulenger, 1909-16 not cited)
Max. depth.
(ft)
Area
(square miles)
Altitude
(ft)
No. of
species
46
1350
5960
c. 10
Nilo-Sudan
Albert
190
1640
2190
46
Edward
383
700
3000
40-50
Cyprinodontidae: Aplocheilichthys pelagicus (Worthington, 19 32; L. George (strong); Nile;
Victoria Nile
129-30); Cichlidae: Tilapia eduardiana. several Haplochrornis,
(Trewavas. 1933; Greenwood, 1973)
George
20
104
3000
40-50
Cichlidae: several Haplochromis (Greenwood, 1973)
L. Edward (strong); White
Nile; Victoria Nile
223
10
5800
4 or 5 ?
Nile?
5627
5
Cyprinidae: 1 to 4 Barbus (Banister, 1973: 87-8) and 1 Vancorhinus
Cyprinidae: Labeo mokofoensis (Poll, 1939a)
Abyssinian highlands
Tana
Luhondo
Ndalaga
69
1.2
Endemics
Faunistic relationships
Cyprinidae: Barbus efhiopicus and B. microferolepis (derived from Abyssinian highlands;
B. intermedius?) (Banister, 1973); Cobitidae: Noernacheilus
Awash R.
abyssinicus; Clariidae: CIarias tsanensis
Cyprinidae: Engraulicypris bredoi (Poll, 1945a: 308-10) ;
Nile
Cyprinodontidae: Aplocheilichthys kassenjiensis and Apl.
rnahagiensis (David 8; Poll, 1937); Centropomidae: Lutes macrophrhdrnus (Holden, 1967); Cichlidae: 4 Haplochromis
(Trewavas, 1938)
Nile?
238
2780
1335
31
Cyprinodontidae: Aplocheilichthys rudolfianus (Worthington,
1932); Centropomidae: 2 subspecies of Lazes niloticus
(Worthington, 1932); Cichlidae: several Haplochrornis
(Greenwood, 1974b)
Abaya
43
450
4200
15
Nile; L. Rudolf
Upper Guinea
(Ghana)
Bosumtwi
Mormyridae: Marcusenius annarnariae; Cyprinidae: Labeo
brunelli (Parenzan, 1939)
265
19
3 50
4
Cichlidae: Tilapia discolor
Prah basin
Rudolf
Lower Guinea
(Cameroon)
Barombi Mbo
Barombi Kotto
Ejagham
364
1.7
1000
15
20
79
1.3
0.5
36 0
400
6
1
Clariidae: Clarias maclareni; Cichlidae: 4 Sarotherodon. 3 monotypic genera perhaps derived from Sarotherodon, and 1 monotypic genus perhaps derived from Tilapia (Trewavas er al.,
1972; Trewavas, 1973a: 2 3 )
Mungo basin
Cichlidae: Pelmatochromis loennebergi (Trewavas, 1962)
Cichlidae: Tilapia deckerti (Thys, 1967)
Meme basin
Lower Guinea; Cross R.
Cichlidae: 5 Haplochromis (Poll, 1932, 1939b)
Nile (weak); L. Tanganyika
(weak)
Zaire
Kivu
1590
1040
4770
12
Tanganyika
4700
12.700
2534
c. 200
Bangweulu
33
3 800
3765
49
Moero
50
173
3035
68
Tumba
16
296
1140
88
Mai Ddombe
(Inongo)
20
886
655
17
Zaire basin (strong); late
Clupeidae: Limnothrissa (monotypic) and Stolothrissa (monoinfusion of nilotic forms
typic); Characidae: Alestes rhodopleura; Cyprinidae: 7 Earbus.
via L. Kivu with little
2 Varicorhinus, 1 Labeo. and 1 Engraulicypris; Bagtidae: 6
impact; possible infusion
Chrysichthys. Lophiobagrus (monotypic), and Phyllonemus
of Zambesian elements via
(two species); Clariidae: 1 Clarias, Dinotopterus (monotypic),
Lualaba and Lukuga;
and Tanganikallabes (monotypic); Mochokidae: 5 Synodonris;
little if any influence from
Cyprinodontidae: 1 Aplocheilichthys. Lamprichthys (monoEast coast province
typic); Centropomidae: 3 Lutes. and Luciolates (1 or 2 species);
Cichlidae: 1 Tylochromis, 2 Tilapia, 5 Haplochromis, 34
Lamprologus, and 3 5 genera (87 species); Mastacembelidae: 12
Mastacembelus (Poll, 1953, 1956, 1 9 7 4 ; Poll & Matthes, 1962;
Matthes, 1962)
Lualaba and L. Moero (strong);
Distichodontidae: Nannocharax minutus; Mastacembelidae: 2
Mastacembelus
Middle Zambesi (moderately
strong)
Clupeidae: Poecilothrissa moeruensis and Potamothrissa srappersii; Lualaba and L. Bangweulu
(strong)
Mormyridae: Campylomormyrus bredoi (Poll, 1954b);
Cyprinidae: several Earbus, Engraulicypris moeruensis; Cichlidae:
3 Haplochromis; Mastacembelidae : Mastacembelus moeruensis
Cuverte Centrale of Zaire
Characidae: Clupeopetersius (monotypic) (Matthes, 1964)
basin; L. Mai Ndombe?
Characidae: Alestopetersius leopoldianus; Cichlidae: “Paratilapia”
(= Hemichromis?) cerasogaster
Cuvette Centrale of Zaire
basin
W
L
L
Table 7 .-cont.
Max. depth.
Area
(ft)
(square miles)
East coast
KYW
Victoria
Nabugabo
Chala
Altitude
(ft)
No. of
species
26
1040
3600
?
279
26,600
3720
c. 200
15
12
3750
24
“deep”
1.5-2
32002
Endemics
Cichlidae: 1 or 2 Haplochromis (Greenwood, 1967)
Faunistic relationships
Victoria Nile; L. Victoria
Clariidae: Xenoclarias (2 species) (Greenwood, 1958);Cyprinidae: Tana and Athi rivers;
2 Barbus; Cyprinodontidae: Cynopanchax (monotypic);
Victoria Nile and L.
Cichlidae: c. 160 species of Haplochromis and four monotypic
Kyoga (strong)
genera derived from Haplochromis (Greenwood, 1974)
Cichlidae: 5 Haplochromis (Greenwood, 1965)
L. Victoria
1
Cichlidae: Tilapia hunreri ( e w e , 1955: 364)
Pangani R.
5
Cichlidae: 2 Tilapia (Lowe, 1955; Trewavas, 1966)
Pangani R.
“shallow”
15
2 700
2-3?
182
3420
Magadi
1-2?
42
1980
1’
Cichlidae: nlapia grahami
L. Natron; Uaso-Nyiro R.
Natron
1-2?
348
2001
l?
Cichlidae: Tilapia alcalica (closely related to T. grahami) (Coe,
1969)
L. Magadi; Uaso-Nyiro R.
11.900
1540
Jipe
Manyara
Zambesi
Malawi
2470
1 or 23
c. 250
Cichlidae: 1 or 2 Tilapia
Mormyridae: Marcusenius nyasensis; Cyprinidae: 6 to 8 Barbus,
Zambesi R.
1 Varicorhinus, 2 Labeo, 2 Barilius, and “Engraulicypris”
sardella; Bagridae: B a g m meridionalis; Clariidae: Bathyclanas
(12 species) (Jackson, 1959; Greenwood, 1961); Cichlidae:
Tikapia squamipimis; c. 100Haplochromis and 21 genera (c. 100
species), perhaps all derived from Haplochromis- or Pseudocrenilabrus-like ancestors (Trewavas, 1935, 1949); Mastacembelidae: Mastacembelus shiranus
DISTRIBUTION O F AFRICAN FISHES
313
presently inhabiting Albert and Edward all range more or less widely beyond
them. Mollusks in Pleistocene deposits of the Omo-Rudolf basin, with the
exception of Pseudobovaria fuchsi from the Lower Pleistocene, belong to
wide-ranging living species (Adam, 1959: 137).
The faunistic relationships of African lakes with endemic fishes are indicated
in Table 7. Of major interest are the differences in the sources of the rich and
highly diversified faunas of lakes Victoria, Malawi, and Tanganyika. The
Victoria fish fauna may have been largely derived from a depauperate riverine
fauna rather similar to that of the Tana and Athi rivers of the East coast
ichthyofaunal province (Greenwood, 195 1; Whitehead, 1962). Greenwood
suggested that Haplochromis bloyeti, an East coast form, may be close to the
ancestry of the Victoria Haplochromis. I have included Victoria in the East
coast province. Almost the entire Malawi fish fauna could conceivably have
been derived from the Lower Zambesi with which it is presently connected
(although the present Murchison rapids on the Shirk River are said to be largely
effective as a barrier to the upstream movement of Lower Zambesi fishes into
the lake). Haplochromis callipterus, a Zambesi endemic, and Pseudocrenilabrus
philander, widespread in the Zambesi system, have been suggested as possible
ancestors of the endemic Malawi forms allied t o Haplochromis. Serranochromis
may also have been among the ancestral forms. A major obstacle to an
understanding of the faunistic relationships of fishes in the Lower Zambesi and
L. Malawi is the total lack of information concerning the fishes in the coastal
rivers of Mosambique N. of the Zambesi. The Tanganyikan fishes have very
diverse faunistic relationships. The most important and perhaps the oldest
faunal relationship is that with the Zaire hydrographic basin. The ancestral
riverine cichlid stocks were probably more diverse in L. Tanganyika than in
Malawi and Victoria, although it should be noted that most riverine cichlids in
the Zaire basin are presently restricted to below Stanley Falls. The non-cichlid
Tanganyikan fishes are also extremely diverse. In addition to the strong Zairean
faunistic relationship, there apparently have been contributions from the Upper
Nile and from the East coast and Zambesian provinces.
There does not seem to be any evidence of faunal exchange between lakes
Malawi and Tanganyika. Greenwood (1961) considered that Bathyclarias of
Malawi belong in the same genus as the monotypic Dinotopterus of
Tanganyika. He pointed out that these endemic lake clariids agreed in having
less exposed cranial bones, more laterally placed eyes, and, in most instances,
less arborescence of the suprabranchial air-breathing organs than riverine
clariids. In addition, he found that while the Tanganyikan form has a relatively
well-developed adipose fin, the Malawi forms at least have a rudimentary one.
Regarding the adipose fin, it should be noted that it is a primitive characteristic
of all catfishes. In Clariidae, it has repeatedly been modified, reduced or lost
(and perhaps, in some instances, regained). Thus its condition is a poor
indicator of phyletic relationship. A well-developed adipose occurs in
Dinotop terus, Heterobranchus, and Encheloclarias, and poorly-developed to
rudimentary adipose fins in Dinotoperoides, Bathyclarias, and the subgenus
Heterobranchoides of Clarias. Relative lack of arborescence of the
suprabranchial organ and less exposed cranial bones are reduction characters
and therefore also of little utility in assessing relationship. Less exposed cranial
bones occur in many riverine clariids. Reduction of the suprabranchial organ
21
314
T. R. ROBERTS
has also been reported in Xenoclarias, an endemic genus in L. Victoria
(Greenwood, 1958), and in Clarias rnaclareni, an endemic species in L. Barombi
Mbo (Trewavas et al., 1972). The similarities between Bathyclarias and
Dinotopterus are attributable to convergence in lacustrine environments and to
their having evolved from generalized riverine clariids. In both instances the
riverine ancestors were presumably either Clarias or Heterobranchus.
ADDENDA
Page 3 51. The'hypothesis of Gondwanic distribution of Galaxiidae has been
resurrected by Croizat, Nelson & Rosen (1974) and Rosen (1974).
Page 256. The observation of Hemisynodontis membranaceus gulping for air
was made in a large pool isolated from the mainstream of the Black Volta River
near Lawra, northern Ghana, at the end of the dry season in 1964. Several
hundred Africans methodically stamped back and forth across the pool,
nowhere deeper than about 1 m, until the fish asphyxiated and could be
speared or taken with baskets. Hemisynodontis swam upside down at the
surface for several meters as they gulped for air. I have not observed them at
the surface at any other time, and doubt that they would swim at the surface in
order to feed. Specimens kept in tanks at the University of Ghana frequently
swam upside down in midwater.
Page 261. A distinctive Lates from Miocene deposits in the lakes Edward and
Albert area will be reported on by Greenwood (personal communication).
Page 262. Large population of Protoptents aethiopicus live in open waters in
Lake Victoria (personal communication from P. H. Greenwood).
Page 276. The Danakil Tilapia, T. frunchettii Vinciguerra (1932), may be
closely related to T. gulilaea (personal communication from E. Trewavas).
Page 298. Thys (1966: 89) reported Lates niloticus and Bagrus docmac from
the Sanaga, and suggested that they entered from the Chari or the Benue.
Page 306. L. Ngami was filled with water in 1954-55 (personal
communication from R. H. McConnell).
Page 307. Recent searches for Oreodaimon in the Umkomaas drainage have
been unsuccessful (personal communication from P. H. Skelton). In 1970 a
population was found in the Tsoelikana River, a mountain tributary of the
Orange R. (Pike & Tedder, 1973). The Tsoelikana arises in the Drakensberg, on
the N. slope of the divide between the Orange and Umkomaas drainages.
Oreodaimon evidently owes its persistence (and perhaps its existence) to an
ability to live in mountain streams.
Table 2. A small number of multicuspid characid jaw-teeth, including a
premaxillary tooth referable to Alestiinae, were collected from Yale Quarry G,
Jebel el Qatrani, Fayum, by the Yale Paleontological Expedition to Egypt,
1962-63 season. Radiometric dates for Quarry I , on the level above Quarry G,
indicate a minimum age of about 25 million years (Simons & Wood, 1968: 4).
These fossils have been deposited in the vertebrate paleontology collection of
the Museum of Comparative Zoology, Harvard (cat. no. MCZ 13373).
DISTRIBUTION O F AFRICAN FISHES
315
ACKNOWLEDGEMENTS
I particularly wish to thank P. H. Greenwood, R. H. McConnell, G. S. Myers,
and E. Trewavas for their extensive comments on the manuscript of this paper.
Helpful comments were also received from K. Banister, J . Haller, P. H. Skelton,
and D. J. Stewart.
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