Zool. J. Linn. S o c 57: 249-319. With 17 figures December 1975

Geographical distribution of African freshwater fishes

TYSON R. ROBERTS

Museum o f Comparative Zoology, Cambridge, Massachusetts 02138, U.S.A.

Accepted for publication December 1974

Geographical distribution of African freshwater fishes is discussed with emphasis on the effects of major continental features, hydrographic history, and Pleistocene climatic fluctuations. Differences in the modes of dispersal and biological interactions among various categories of fishes, ecological as well as phyletic, have also had marked effects on 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

I n t r o d u c t i o n ...... 250 Biological background ...... 253 Primary, secondary, and peripheral divisions of freshwater f i s h e s ...... 253 Tolerance of deoxygenated water; air-breathing f i s h e s ...... 256 Mountain-climbing or orobatic f i s h e s ...... 257 Biological interactions among various categories of fishes (complementary distribution patterns) ...... 259 The taxon cycle in African freshwater f i s h e s ...... 264 Geographical background ...... 265 Intercontinental r e l a t i o n s h i p s ...... 266 A r a b i a ...... 267 Changes of sea l e v e l ...... 268 M a l a g a s y ...... 268 Low Africa and High Africa ...... 269 Continental drainage pattern ...... 271 Mountains ...... 271 Great Rift valleys ...... 273 Volcanism ...... 274 Deserts ...... 274 Pleistocene climatic fluctuations ...... 276 African freshwater fishes and the fossil record ...... 279 Ichthyofaunal provinces ...... 281 Maghreb ichthyofaunal province ...... 282 Abyssinian highlands and Nilo-Sudan ichthyofaunal p ro v in ces ...... 288 Upper Guinea, Lower Guinea, and Zaire ichthyofaunal provinces .... 298 East coast, Zambesi, and Quanza ichthyofaunal p ro v in c e s ...... 303 Cape of Good Hope ichthyofaunal p r o v i n c e ...... 307 Relationships of lakes with endemic fishes to the ichthyofaunal provinces . . 309 A d d e n d a ...... 314 References ...... 315 17 249 250 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, Disticho- dontidae, 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 Haplochromis, all derived from one or a few ancestral riverine stocks. Four Haplochromis 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 Haplochromis-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 Haplochromis, 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 & lies, 1972). Other endemic lacustrine fishes are found in at least 22 smaller African lakes. Of particular interest are five species of Haplochromis which apparently evolved in L. Nabugabo after this small 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 to 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 to 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 OF AFRICAN FISHES 253 Togoland, and that part of Ghana occupied by the Volta basin. The Lower Guinean ichthyofaunal province includes ail 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 o f freshwater 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 to 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. It 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 fresh-water but tolerate sea-water well enough to disperse through it. Most of the species in this group are endemic to 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. No 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 to another, are mainly due to 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 to cross drainage divides by Table 1. Families of fishes in the fresh-waters of Africa*

Air- Mountain- Endemic Non-endemic Division breathing climbing genera genera Species ROBERTS R. T. Range beyond Africa 254

ELASMOBRANCHII Carcharhinidae Peripheral No No - 1 1 Widespread marine Pristidae Peripheral No No - 1 1 Widespread tropical Dasyatidae Peripheral No No 1? - 1 Widespread, mostly tropical DIPNOI Lep idosirenidae Primary Yes No 1 - 4 South America BRACHIOPTERYGII Polypteridae (E) Primary Yes No 2-10 TELEOSTEI Elopiformes Elopidae Peripheral No No - 1 3 Widespread, tropical and subtropical Megalopidae Peripheral No No - 2 2 Tropical Atlantic, Indo-Pacific Anguilliformes Anguillidae Peripheral No Yes - 1 5 Widespread, tropical to temperate Clupeiformes Clupeidae Peripheral No No 12 - 20Worldwide, tropical to temperate Denticipitidae (E) Primary? No No 1 - 1 Osteoglossiformes Osteoglossidae Primary? Yes No 1 - 1S.E. Asia, New Guinea, Aust., S. Amer. Pantodontidae (E) Primary Yes No 1 - 1 Notopteridae Primary Yes No 2 - 2 India, S.E. Asia Mormyridae (E) Primary No No 16 - 200 Gymnarchidae (E) Primary Yes No 1 - 1 Salmoniformes Salmonidae Peripheral No Yes 1 N. temperate and Arctic Galaxiidae Peripheral No Yes 1 S. tem perate Gonorynchiformes Chanidae Peripheral No No - 1 1 Indian Ocean, W. Pacific Kneriidae (E) Primary No Yes 4 - 1 8 Phractolaemidae (E) Primary Yes No 1 - 1 Characoidei (Ostariophysi) Hepsetidae (E) Primary No No 1 - 1 Characidae Primary No No 21 - 100 + Central and S. Amer. Distichodontidae (E) Primary No No 10 - 60 Citharinidae (E) Primary No No 2-8 Ichthyboridae (E) Primary No No 10 - 19 Cyprinoidei (Ostariophysi) Cyprinidae “Primary” No Yes 11 6 300+ Europe, Asia (incl. Arabian pen.), N. Amer. Cobitidae Primary Yes Yes — 2 2 Europe, Asia (excl. Arabian pen.) Siluroidei (Ostariophysi) Bagridae “Primary” No Yes 15 1 80 Asia Schilbeidae Primary No 8 - 30 India, S.E. Asia Amphiliidae (E) Primary No Yes 8 - 50 Clariidae Secondary? Yes Yes 9 2 60 Syria, S.E. Asia Malapteruridae (E) Primary No No 1 - 2 Mochokidae (E) Primary No Yes 9 - 140 Ariidae Peripheral No No - 1 Tropical Plotosidae Peripheral No No — 1 1 Indian Ocean, tropical W. Pacific

Atheriniformes 255 FISHES AFRICAN OF DISTRIBUTION Cyprinodontidae Secondary “Yes” No 22 1 150+ Widespread, tropical to temperate Gasterosteiformes Syngnathidae Peripheral No No - 4 10 Widespread, tropical to temperate Channiformes Channidae Primary? Yes Yes? - 1 3 India, S.E. Asia, Indonesia Synbranchiformes Synbranchidae Secondary Yes No 1 1 2 Widespread tropical Perciformes Centropomidae Peripheral No No 1 1 6 Widespread tropical Monodactylidae Peripheral No No 1 1 3 Indian Ocean, Red Sea, W. Pacific Nandidae Secondary? No No 2 - 2 Tropical Asia and S. Amer. Cichlidae Secondary No Yes 88 1 620+ Syria, Madagascar, S. Asia, Central and S. Amer. Gobiidae Peripheral No Yes 3 ? ? Widespread, mostly tropical Anabantidae Secondary? Yes No 2 - 20 India, S.E. Asia Mastacembelidae Primary Yes? Yes 1 1 40 Euphrates, India, S.E. Asia Pleuronectiformes Cynoglossidae Peripheral No No 1 1 2 Tropical Indo-Pacific Tetraodontiformes Tetraodontidae Peripheral No No - 1 6 Worldwide, tropical to subtemperate

• Excluded from the table are marine families with species which live in the sea but occur seasonally or sporadically in the 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 by species endemic to African fresh-waters. 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. It 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 o f 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 to 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 primary-division 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

H

Figure 1. Representative African air-breathing fishes: Ay Protopterus (Lepidosirenidae); B, Polyp terns (Polypteridae); C, X enom ystus (Notopteridae); D, Phractolaemus (Phracto­ laemidae); E, Channa (Channidae); F, Mastacembelus (Mastacembelidae); Gt 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 Petrocephalus 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 to 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 (Gobiocichla) 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 to the ability of mountain fishes to 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 to 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 OF 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. It 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 o f 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 260 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 Salmo trutta in the mountainous area of Kabylia in Algeria and an endemic species of the S. Temperate genus Galaxias in the S.W. Cape of S. Africa. The African distribution of eels of the diadromous genus Anguilla is similar. The European eel Anguilla anguilla ascends mountain streams on the Atlantic and Mediterranean coasts of N. Africa, and three species of Anguilla 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 Kribia, 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 Syngnathus 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 Kribia, 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 Lates niloticus, the Nile perch. Lates are large, bass-like predators, living in open, well-oxygenated waters. The genus is usually placed in Centropomidae, but this assignment should be re-examined in the light of DISTRIBUTION OF 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, Kivu, 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/,, niloticus)-, the large-eyed L. mariae occurs offshore and on the bottom at depths to 75 m; and L. microlepis 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 to 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 to 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 to complement primary-division forms in their distribution, but the emphasis is on ecological rather than geographical segregation. Cyprinodonts and cichlids are the two main secondary-division 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 262 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 primary-division 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 to 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 to 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: 130-31). The main exception to 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 OF AFRICAN FISHES 263 Although 13 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, Heterotis, 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 to 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 to their specialized electrogenic and electrosensory adaptations (Lissmann, 1955; 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 to the Ostariophysi or Cypriniformes, and thus possess the Weberian apparatus, a paired chain of four ossicles (modified elements of the first four vertebrae) 264 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 to generalize about the structures involved.

The taxon cycle in African freshwater fishes I shall conclude this section on the biological background to 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 secondary-division 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 peripheral-division fishes, viz. Anguillidae, Mugilidae, Gobiidae, and numerous others. The earliest secondary-divisitpn 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 OF AFRICAN FISHES 265 Haplochromis. Of tnese genera, only Clarias is a true air-breather. Protopterus, Polypterus, and most other large air-breathing African fishes tend to inhabit periodically deoxygenated habitats but only if they are regularly connected to 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 to its ability to pass through salt-water. But Clarias is also more widely distributed in interior low-sand situations than either Protopterus or Polypterus. 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 to 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 first- and 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. It is also clear that stenotopic species of primary-division groups in the richest forest areas tend to displace eurytopic species of primary-division 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 peripheral-division 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°2l'N) to Cape Agulhas (34° 52'S). At the Equator it is 2300 miles wide. About two-thirds of 18 266 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 ft 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 crossed 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 ft 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 primary-division 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 to 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 primary-division 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 primary-division 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 to 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 Lates 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 to 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 o f 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 35 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 OF AFRICAN FISHES 269 are regarded as indigenous to its fresh waters (Arnoult, 1959, 1963; Kiener & Mauge, 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 Pantanodon 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 1000 ft. 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 facades deeply furrowed by stream erosion. In certain areas rainfall on the coastal areas is sufficient to 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-Bodele, and Sudd. The Chad-Bodele 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

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.

Figure 3. Representative freshwater fishes of Madagascar: A, Ancharius brevibarbis (Ariidae); B, Rheocles alaotrensis (Atherinidae); C, Ptychochromoides betsileana (Cichlidae); D, Typhleotris pauliani (Eleotridae). All Malagasy freshwater fishes belong to secondary- and peripheral-division families. DISTRIBUTION OF AFRICAN FISHES 271

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 ft 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 ft 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 & Bourliere, 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 & Bourliere, 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

Figure 4. Hydrography of Africa at the Miocene-Pliocene transition. Reproduced (with minor modifications) from Howell & Bourliere, 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 effects 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 & Bourliere (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 OF 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, Parakneria, and Oreodaimon. Most African montane fish species are Barbus. Of particular interest is the radiation of trophic morphs of B. intermedins 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 R ift 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 Shire 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 Somalia) 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 ft 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 274 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. Rifts just 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 to 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 poorly-defined transition zone of steppe vegetation (the Sahel) between it and the Sudan. The S. boundary of the desert is generally considered to 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 100° F, with daytime temperatures up to 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 Tenere, 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 Aphanius 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 OF 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. It now appears that about 12,000 to 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 to rise until they overflowed into adjacent basins, and low-lying divides were often flooded or connected by rivers, so that there were fewer barriers to 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 to 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 Mega-Chad 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 278 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 to 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 Ogowe 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 Ogowe 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 Ogowe 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 includeErpetoichthys, Pantodon, 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 Oueme, 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 India 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 280 T. R. ROBERTS

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 era/., 1972) (earliest known Characidae). Lower Nile: catfishes (PAriidae) (Stromer, 1904; Peyer, 1928); Lates (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), Lates, 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 osteo- glossoids) (Greenwood & Patterson, 1967); ?Haplochromis (Greenwood, 1960) LATE MIOCENE Tunisia, Bled ed Douarah: Polypterus, ?Barbus (earliest known Cyprinidae in Africa), ? Clarotes, Clarias and/or Heterobranchus (earliest known Clariidae), ?Synodontis, and Lates (Greenwood, 1972). Near Suez: Bagrus, Clarias, ? Heterobranchus, Synodontis, and Lates (Priem, 1914) LOWER PLIOCENE India, Siwalik Hills: Clarias and Heterobranchus (Lyddeker, 1886) (earliest known Asian Clariidae) PLIOCENE Lower Nile: Protopterus, Polypterus, Hyperopisus (earliest known Mormyridae), Alestes, Barbus, Labeo, Bagrus, Clarotes, ^Auchenoglanis, Clarias, ?Heterobranchus, Synodontis, Lates, and Tilapia (Greenwood, 1972) PLIOCENE? L. Rudolf: rDasyatidae, Polypterus, Lates, and Tilapia (Arambourg, in Chappuis, 1939) LOWER PLEISTOCENE L. Albert: Bagrus, Clarotes, Heterobranchus, and Lates (White, 1926). L. Edward; Protopterus, ?Hyperopisus, Hydrocynus, Bagrus, Auchenoglanis, Clarias, Synodontis, Lates, and Tilapia (Greenwood, 1959). L. Rudolf basin: Polypterus, Hydrocynus, Bagrus, Clarotes, Clarias, Synodontis, and Lates (Arambourg, 1947). L. Malawi: Protopterus (Coryndon, 1966) UPPER PLEISTOCENE Sahara (various localities): Bagrus, Chrysichthys, Clarotes, Auchenoglanis, Clarias, Heterobranchus, Synodontis, Arius, Lates, 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. It 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, to 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 to that of today, although the teeth of the “Alestes” 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 Lates 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 (1911, 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 to 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 Maghreb Abyssinian Nilo-Sudan Upper Guinea Lower Lower Guinea Zairean East East coast Zambesi Quanza Cape 1 Lepidosirenidae XX XX XX Polypteridae XX XX Denticipitidae X Osteoglossidae X X Pantodontidae X X Notopteridae XX XX Mormyridae X XX XX XX Gymnarchidae X Kneriidae X X XX XX Phractolaemidae X X Hepsetidae XX XX XX X Characidae X X XXX XX Distichodontidae X XX XX XX Citharinidae X XX XX Ichthyboridae X XX X Cyprinidae X X X XX XX XX X Cobitidae XX Bagridae XXX XX XX X Schilbeidae X XX X X XX Amphiliidae X X XXXX XX Clariidae X X X X XX XX X Malapteruridae X XX X X Mochokidae X XX XX XX Cyprinodontidae X XXX XX XX X Channidae XX XX Synbranchidae X Nandidae XX Cichlidae X X X XXXX X X X Anabantidae X XX XXX X Mastacembelidae X XXX XX X Totals 30 4 5 24 23 27 24 17 17 14 6

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 Gabes, 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 11,000 ft culminate in the Djebel Toubkal, 13,665 ft high. Moraines indicate that the Grand Atlas were extensively glaciated. The DISTRIBUTION OF 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); Paradistichodus (Distichodontidae); Citharidium (Citharinidae); Clarotes, Pardi- glanis (Bagridae); Irvineia, Siluranodon (Sehilbeidae); Andersonia (Amphiliidae); Brachysynodontis, Hemisynodontis, Mochocus (Mochokidae); Gobiocichla (Cichlidae) Upper Guinea: Ladigesia, Lepidarchus (Characidae); Notoglanidium (Bagridae); Roloffla (Cyprino- dontidae); Typhlosynbranchus (Synbranchidae); Afronandus (Nandidae); Thysia (Cichlidae) Lower Guinea: Erpetoichthys (Polypteridae); Denticeps (Denticipitidae); Boulengeromyrus (Mormy­ ridae); Arnoldichthys (Characidae); Raddhabarbus, Sanagia (Cyprinidae); Procatopus (Cyprino- dontidae); Polycentropsis (Nandidae); Chilochromis (Cichlidae) Zaire: Genyomyrus, Myomyrus, Slomatorhinus (Mormyridae); Bathyaethiops, Duboisialestes, Tri- cuspialestes (Characidae); Dundocharax, Thrissocharax (Distichodontidae); Belonophago, Eugnalhichthys, Mesoborus, Microstomatichthyoborus, Paraphago (Ichthyboridae); Leptocypris (Cyprinidae); A margin ops, Gnathobagrus, Rheoglanis, Zaireichthys (Bagridae); Belonoglanis, Para- phractura, Trachyglanis (Amphiliidae); Dolichallabes (Clariidae), Acanthocleithron (Mochokidae); Congopanchax (Cyprinodontidae); Cyclopharynx, Nannochromis, Neopharynx, Lamprologus, Leptotilapia, Orthochromis, Pterochromis, Steatocranus, Teleogramma (Cichlidae); Caecomasta- cembelus (Mastacembelidae) East coast: Petersius (Characidae) Zambesi: Coptostomabarbus (Cyprinidae); Chetia (Cichlidae) Quanza: Dinotopteroides (Clariidae) Cape: Oreodaimon (Cyprinidae); Sandelia (Anabantidae)

Table 5. Number of primary- and secondary-division riverine species in the ichthyofaunal provinces

Total Number Percentage Percentage Number endemic endemic Cyprinidae

Maghreb 15-20 5-8 40 50 Abyssinian highlands c. 18 c. 11 61 61 Nilo-Sudan 272 182 65 26 Upper Guinea 206 117 57 17 Lower Guinea 333 185 55 17 Zaire 650 529 81 14 East coast* 97 54 56 36 Quanza 109 45 41 39 Zambesi 149 73 49 35 Cape 46 28 61 54

• Excluding the 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 to 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 principal 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 OF 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 ft 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 to 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, Alma9a (1970a, b) and Karaman (1972). Alma^a 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

Figure 8. Fishes of the Maghreb: A, Salmo trutta, B, Phoxinellus chaignoni; C, Barbus comiza-, D, Barbus (Labeobarbus) reinii; E, Varicorhinus maroccanus', F, Cobitis taenia; G, Aphanius apoda\ H, Haplochromis desfontainesii. 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 to 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 desfontainesii 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 fluviatilis 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 OF 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 to 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 to 12,000 ft. The Blue Nile does not emerge from the last 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 3000-5000 ft deep, which would require large rivers for them to 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 altianalis 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 ft 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 to lakes George and Edward and arises on the slopes of the Mfumbiro Mts. N. of L. Kivu. George is connected to 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. It 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. No 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 60 yds, is in a gorge 60 miles N. of Khartoum. It 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 12 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 ft 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. It 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. Abbe. S. of the Awash lies a chain of isolated mountain lakes, including Zwai, Hora DISTRIBUTION OF AFRICAN FISHES 291 Abyata, Langana, Shala, Awusa, Abaya, Chamo, and Stefanie. Zwai (150 square miles, alt. 6050 ft) flows S. into Hora Abyata (90 square miles, alt. 5161 ft). When Hora Abyata received floodwaters of Langana as well as those of Zwai, it overflows into Shala. Langana (13 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. It is apparently uninhabited by fishes. Abaya (485 square miles, alt. 4160 ft) 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 (30-40 miles long, 15-20 miles wide, alt. 1700 ft), lies between Chamo and Rudolf. It 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. Abbe 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 to 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

Figure 9. Fishes of the Abyssinian highlands: A-C, Barbus intermedius-, D, Garra dembeensis; E, Noemacheilus abyssinicus; F, Clarias mossambicus; G, Amphilius lampii; H, Tilapia nilotica. 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. Phreatichthys, in addition to being blind and depigmented, is the only DISTRIBUTION OF AFRICAN 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 ft 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). It is pigmented and

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. 5), they occur throughout the headwaters as well as the middle and lower portions of the basin. The date 294 T. R. ROBERTS

A <<> J

Figure 11. Representative Nilo-Sudanic endemics: A, Clupisudis niloticus; B, Cromeria niloticus-, C, Hyperopisus be be-, D, Gymnarchus niloticus; E, Citharinus latus; F, Clarotes laticeps; G, Siluranodon auritus; H, Irvineia voltae; I, Hemisynodontis membranaceus; 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 Tano River of Ghana, covered by rain-forest, are inhabited by a mixture of Nilo-Sudanic and Upper Guinean species (Daget & litis, 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 to 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 Tano 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 Kolente, and Lates niloticus in the Konkoure. 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 to 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 Table 6. Fishes of Lake Rudolf and the Omo River (“E” indicates endemic)

Rudolf Omo References* Rudolf Omo References*

Polypterus bichir X 1 Bagrus docmac X 1 Polypterus senegalus X X 1,4 Auchenoglanis occidentalis X 1 Gymnarchus niloticus X 1 Heterobranchus longifilis X 1 Heterotis niloticus X 1 Clarias lazera X 1 Alestes macrolepidotus XX 1,4 Schilbe uranoscopus X 2 Alestes nurse X 1,2,4 Synodontis schall XX 1,4 Alestes baremose X 1,4 Synodon tis fron tosus XX 1 Alestes dentex X 1 Mochocus niloticus X 1 Micralestes acutidens X 1 Andersonia leptura X 4 Hydrocynus forskalii X 1,4 Malapterurus electricus X 4 Distichodus niloticus X 1 E Aplocheilichthysjeanneli X 4 Citharinus citharus X 2,4 E Aplocheilichthys rudolfianus X 2 Barbus bynni X 2,7 Lates niloticus X 4 Barbus intermedius X X 7 E Lates niloticus longispinus X 2 Barbus wemeri X 4 E Lates niloticus rudolfianus X 2 Labeo cylindricus X 1 Tilapia nilotica X 1,4 Labeo horie X 4 E Tilapia nilotica subsp. X 3,5 Labeo niloticus X 1 E Tilapia nilotica vulcani X 3,5 Barilius niloticus X 1 Tilapia zillii X 1,3 Barilius loati X 1 Tilapia galilaea X 3 E Engraulicypris stellae X 2 Hemichromis bimaculatus X 3,6 Engraulicypris bottegi X 1,8 E Haplochromis rudolfianus X 3,9 Discognathus dembeensis X 1 E Haplochromis turkanae X 9 E Haplochromis macconneli X 9

* References: 1. Boulenger (1909-16); 2. Worthington (1932); 3. Trewavas (1933); 4. Pellegrin (1935); 5. Worthington (1937:312); 6. Trewavas (1973); 7. Banister (1973); 8. Whitehead (1963); 9. Greenwood (1974b). DISTRIBUTION OF AFRICAN FISHES 297 L. Rudolf. This area, sometimes called the Turkana desert, receives enough rain to 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, 33 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 Engraulicypris bottegi. The three endemic species are an Engraulicypris 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 to 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 (1932) described a subspecies of Citharinus citharus from the lake, but observations by Pellegrin (1935) 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 Chiloglanis. 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 to 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 Mormyrops deliciosus, Clarias lazera, Synodontis schall, and S. geledensis. It 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. The 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. It 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 Gunther (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 & litis, 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 Scarries, 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 to almost exclusively by Nilo-Sudanic fishes, and the Casamance, Geba, and Tano 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, Ogowe, 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. 13. 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 Ogowe. 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). Tilapia mvogoi is known only from DISTRIBUTION OF AFRICAN FISHES 299

Figure 12. Fishes of Upper Guinea: A, Mormyrops longiceps; B, Alestes longipinnis; C, Barbus walkeri-, D, Labeo parvus; E, Notoglanidium walkeri-, F, Chrysichthys walkeri-, G, Synodontis ebum eensis; H, Chromidotilapia guentheri. the Nyong, Ja, and Ivindo (Trewavas, 1969); the Ivindo is a tributary of the Ogowe. 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 Ogowe is indicated by the following Zairean species present in the Ogowe but unknown from the rest of Lower Guinea: Polypterus retropinnis, Mormyrops nigricans, M. zanclirostris, Stomatorhinus humilior, Grasseichthys gabonensis, Alestes macrophthalmus, Micralestes uroteania, Alestopetersuis hilgendorfl, Phenacogrammus aurentiacus, Hemi- stichodus vaillanti, Distichodus fasciolatus, Barbus brazzae, Labeo variegatus, Amphilius brevis, and Hylopanchax silvestris. The taxa Pantodon, Phracto- laemus, Xenocharax, Phago, Bryconaethiops microstoma, Barbus jae, Eutropielles, Synodontis batesi, and Atopocheilus are shared by the Zairean province and the Lower Guinean province from the Ogowe 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

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Figure 13. Fishes of Lower Guinea: Af Denticeps clupeoides; B, Marcusenius ntemensis; C, Boulengeromyrus knoepffleri; D, Alestes fdngsleyae-, E, Phenacogrammus major; F, Distichodus kolleri\ G, Raddhabarbus sanagensis; H, Parauchenoglanis boutchangav, I, Procatopus glaucicaudis-, J, Hysopanchax zebra; K, Polycentropsis abbreviata\ L, Chilo- chromis 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, DISTRIBUTION OF AFRICAN FISHES 301

Figure 14. Zairean fishes: A, Odaxothrissa losera; B, M ormyrops lineolatus-, C, Hippopotamyrus wilverthi; D, Campylomorrnyrus mirus-, E, Grasseichthys gabonensis; F, Alestes liebrechtsii; G, Distichodus altus; H, Mesoborus crocodilus; I, Barbus hulstaerti-, J, Leptocypris brevirostris; K, Gnathobagrus depressus; L, Leptoglanis xenognathus-, M, Belonoglanis tenuis-, N, Synodontis congicus; O, Lamprotogus 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 35 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 incorporating 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 camptacanthus, Paramphilius, Doumea, Microsynodontis, and Pelmatochromis 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 henryi 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. DISTRIBUTION OF AFRICAN FISHES 303

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 Ruvu, 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 since the last interpluvial, in other words, in the last 12,000 years or so. The majority of the endemic species belong to Barbus, Labeo, and

D

Figure 15. Fishes of the East coast: A, Anguilla nebulosa; B, Mormyrus kannume, C, Petrocephalus catostoma\ D, Citharinus congicus; E, Labeo cylindricus; F, Schilbe mystus-, G, Chiloglanis neumanni\ H, Tilapia spilurus. 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 longifilis, 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,

A

B

C

D

Figure 16. Zambesian fishes: A, Kneria polli; B, Mormyrus lacerda; C, Hydrocynus vittatus; D, Distichodus mossambicus\ E, Barilius zambezensis\ F, Coptostomabarbus bellcrossi; Gf Malapterurus electricus; H, Serranochromis angusticeps. DISTRIBUTION OF 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 Louren^o Marques. The lower courses of the Zambesi, Save, Pungwe, Limpopo, Incomati, and Pongola traverse a low-lying, poorly-drained coastal plain less than 300 ft 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 ft 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 200-350 ft into the chasm below. For 45 miles the extremely turbulent river zig-zags sharply as it follows a series of fault lines, becoming incised nearly 1500 ft 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 Bie 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, 1911) 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 400 ft 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, Hippo- potamyrus castelnaui, Barbus poechii, Synodontis macrostigma, and Haplo­ chromis 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 Shire, 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 attributable 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 Auchenoglanis ngamensis (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 Catumbela. 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 no fewer than 14 primary- and secondary-division families (Table 3), over DISTRIBUTION OF AFRICAN FISHES 307 60% of the species belong to Cyprinidae and Cichlidae. Of 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 to that of the Chiloango and Ogowe, while the cichlid fauna of the Upper Quanza is related to that of the Cunene and Zambesi. It is unclear to what extent these relationships extend to 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 to 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 350 miles inland from its mouth. The Aughrabies drops 480 ft 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 ft 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 C j Q D

B

Figure 17. Fishes of the Cape: A, Galaxias zebratus; B, Oreodaimon quathlambae\ C, Labeo seeberi; D, “Gephyroglanis” slateri-, 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 uGephyroglanis,'‘ is restricted to the Orange drainage, the other to the Olifants. Gephyroglanis is otherwise known only from Lower Guinea and the Zaire 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 to 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 OF 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 to a small group of “red-finned minnows” confined to rivers in the S.W. Cape. B. capensis is most closely related to 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. to 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. Area Altitude No. of (ft) (square miles) (ft) species Endemics Faunistic relationships

Abyssinian highlands Tana 46 1350 5960 c. 10 Cyprinidae: Barbus ethiopicus and B. microterolepis (derived from Abyssinian highlands; B. interm edius?) (Banister, 1973); Cobitidae: Noemacheilus Awash R. abyssinicus; Clariidae: Clarias tsanensis Nilo-Sudan Albert 190 1640 2190 46 Cyprinidae: Engraulicypris bredoi (Poll, 1945a: 308-10); Nile Cyprinodontidae: Aplocheilichthys kassenjiensis and Apl. mahagiensis (David 8c Poll, 1937); Centropomidae: Lates macro phthaim us (Holden, 1967); Cichlidae: 4 Haplochromis (Trewavas, 1938) Edward 383 700 3000 40-50 Cyprinodontidae: Aplocheilichthyspelagicus (Worthington, 1932; L. George (strong); Nile; 129-30); Cichlidae: Tilapia eduardiana, several Haplochromis, Victoria Nile (Trewavas, 1933; Greenwood, 1973) George 20 104 3000 40-50 Cichlidae: several Haplochromis (Greenwood, 1973) L. Edward (strong); White Nile; Victoria Nile Luhondo 223 10 5800 4 or 5? Cyprinidae: 1 to 4 Barbus (Banister, 1973: 87-8) and 1 Vari­ Nile? corhinus Ndalaga 69 1.2 5627 5 Cyprinidae: Labeo mokotoensis (Poll, 1939a) Nile? Rudolf 238 2780 1335 31 Cyprinodontidae: Aplocheilichthys rudolfianus (Worthington, 1932); Centropomidae: 2 subspecies of Lates niloticus (Worthington, 1932); Cichlidae: several Haplochromis (Greenwood, 1974b) Abaya 43 450 4200 15 Mormyridae: Marcusenius annamariae; Cyprinidae: Labeo Nile; L. Rudolf brunelli (Parenzan, 1939) Upper Guinea (Ghana) Bosumtwi 265 19 350 4 Cichlidae: Tilapia discolor Prah basin Lower Guinea (Cameroon) Barombi Mbo 364 1.7 1000 15

Barombi Kotto 20 1.3 360 6 Ejagham 79 0.5 400 1 Zaire Kivu 1590 1040 4770 12

Tanganyika 4700 12,700 2534 c. 200

Bangweulu 33 3800 3765 49

Moero 50 173 3035 68

Tumba 16 296 1140 88

Mai Ddombe 20 886 655 17 (Inongo) Clariidae: Clarias maclareni; Cichlidae: 4 Sarotherodon, 3 m ono­ Mungo basin typic genera perhaps derived from Sarotherodon, and 1 mono­ typic genus perhaps derived from Tilapia (Trewavas et al., 1972; Trewavas, 1973a; 23) Cichlidae: Pelmatochromis loennebergi (Trewavas, 1962) Meme basin Cichlidae: Tilapia deckerti (Thys, 1967) Lower Guinea; Cross R.

Cichlidae: 5 Haplochromis (Poll, 1932, 1939b) Nile (weak); L. Tanganyika (weak) Clupeidae: Limnothrissa (monotypic) and Stolothrissa (mono­ Zaire basin (strong); late typic); Characidae: Alestes rhodopleura; Cyprinidae: 7 Barbus, infusion of nilotic forms 2 Varicorhinus, 1 Labeo, and 1 Engraulicypris-, Bagridae: 6 via L. Kivu with little Chrysichthys, Lophiobagrus (monotypic), and Phyllonemus impact; possible infusion (two species); Clariidae: 1 Clarias, Dinotopterus (monotypic), of Zambesian elements via and Tanganikallabes (monotypic); Mochokidae: 5 Synodontis; Lualaba and Lukuga; Cyprinodontidae: 1 Aplocheilichthys, Lamprichthys (m ono­ little if any influence from typic); Centropomidae: 3 Lates, and Luciolates (1 or 2 species); East coast province Cichlidae: 1 Tylochromis, 2 Tilapia, 5 Haplochromis, 34 Lamprologus, and 35 genera (87 species); Mastacembelidae: 12 Mastacembelus (Poll, 1953, 1956, 1974; Poll & Matthes, 1962; Matthes, 1962) Distichodontidae: Nannocharax minutus-, Mastacembelidae: 2 Lualaba and L. Moero (strong); Mastacembelus Middle Zambesi (moderately strong) Clupeidae: Poecilothrissa moeruensis and Potamothrissa stappersii; Lualaba and L. Bangweulu Mormyridae: Campylomormyrus bredoi (Poll, 1954b); (strong) Cyprinidae: several Barbus, Engraulicypris moeruensis; Cichlidae 3 Haplochromis; Mastacembelidae: Mastacembelus moeruensis Characidae: Clupeopetersius (monotypic) (Matthes, 1964) Cuvette Centrale of Zaire basin; L. Mai Ndombe? Characidae: Alestopetersius leopoldianus; Cichlidae: “Paratilapia" Cuvette Centrale of Zaire (= Hemichromis'?) cerasogaster basin Table 7 —cont.

Max. depth, Area A ltitude No. of (ft) (square miles) (ft) species Endemics Faunistic relationships

East coast Kyoga 26 1040 3600 ? Cichlidae: 1 or 2 Haplochromis (Greenwood, 1967) Victoria Nile; L. Victoria Victoria 279 26,600 3720 c. 200 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) Nabugabo 15 12 3750 24 Cichlidae: 5 Haplochromis (Greenwood, 1965) L. Victoria Chala “deep” 1.5-2 3200? 1 Cichlidae: Tilapia hunteri (Lowe, 1955: 364) Pangani R. Jipe “shallow” 15 2700 5 Cichlidae: 2 Tilapia (Lowe, 1955; Trewavas, 1966) Pangani R. Manyara 2-3? 182 3420 1 or 2? Cichlidae: 1 or 2 Tilapia Magadi 1-2? 42 1980 1? Cichlidae: Tilapia grahami L. Natron; Uaso-Nyiro R. Natron 1-2? 348 2001 1? Cichlidae: Tilapia alcalica (closely related to T. grahami) (Coe, L. Magadi; Uaso-Nyiro R. 1969) Zambesi Malawi 2470 11,900 1540 c. 250 Mormyridae: Marcusenius nyasensis-, Cyprinidae: 6 to 8 Barbus, Zambesi R. 1 Varicorhinus, 2 Labeo, 2 Barilius, and “Engraulicypris'’ sardella-, Bagridae: Bagrus meridionalis-, Clariidae: Bathyclarias (12 species) (Jackson, 1959; Greenwood, 1961); Cichlidae: Tilapia squamipimis-, c. 100 Haplochromis and 21 genera (c. 100 species), perhaps all derived from Haplochromis- or Pseudo- crenilabrus-like ancestors (Trewavas, 1935, 1949); Mastacem- belidae: Mastacembelus shiranus DISTRIBUTION OF 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, 1951; 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 Shire 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 to 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 Dinotopterus, Heterobranchus, and Encheloclarias, and poorly-developed to rudimentary adipose fins in Dinotoperoid.es, 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 maclareni, 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 351. 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 Protopterus aethiopicus live in open waters in Lake Victoria (personal communication from P. H. Greenwood). Page 276. The Danakil Tilapia, T. franchettii Vinciguerra (1932), may be closely related to T. galilaea (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 OF 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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