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