AN ECOLOGICAL AND SYSTEMATIC SURVEY OF FISHES IN THE RAPIDS OF THE LOWER ZA.fRE OR CONGO RIVER TYSON R. ROBERTS1 and DONALD J. STEWART2 CONTENTS the rapids habitats, and the adaptations and mode of reproduction of the fishes discussed. Abstract ______________ ----------------------------------------------- 239 Nineteen new species are described from the Acknowledgments ----------------------------------- 240 Lower Zaire rapids, belonging to the genera Introduction _______________________________________________ 240 Mormyrus, Alestes, Labeo, Bagrus, Chrysichthys, Limnology ---------------------------------------------------------- 242 Notoglanidium, Gymnallabes, Chiloglanis, Lampro­ Collecting Methods and Localities __________________ 244 logus, Nanochromis, Steatocranus, Teleogramma, Tabulation of species ---------------------------------------- 249 and Mastacembelus, most of them with obvious Systematics -------------------------------------------------------- 249 modifications for life in the rapids. Caecomasta­ Campylomormyrus _______________ 255 cembelus is placed in the synonymy of Mastacem­ M ormyrus ____ --------------------------------- _______________ 268 belus, and morphologically intermediate hybrids Alestes __________________ _________________ 270 reported between blind, depigmented Mastacem­ Bryconaethiops -------------------------------------------- 271 belus brichardi and normally eyed, darkly pig­ Labeo ---------------------------------------------------- _______ 274 mented M astacembelus brachyrhinus. The genera Bagrus _________________________ 275 Campylomormyrus (elephant-snouted mormyrids), Chrysichthys ______ 276 Steatocranus and Teleogramma are fully revised. N otoglanidium -------------------------------------------- 27 6 Of 16 nominal species of Campylomormyrus, only Gymnallabes _______________ _____ ____________________ 277 three are regarded as biologically valid. In addition Atopochilus ______________________ __________________________ 278 to one new Steatocranus from the mainstream of Chiloglanis -------------------------------------------- 282 the Lower Zaire River, two new species of this Lamprologus _______ ________________ _______________ 283 rheophilic cichlid genus are described from else­ N anochromis ---------------------------------------- 284 where in the Zaire basin, making a total of 21 new Steatocranus _____________________ 292 fishes described in this paper. Leptotilapia is T eleogramma ---------------------------------------- 300 M astacembelus ________________________ _____________________ 302 placed in the synonymy of Steatocranus, which now comprises eight species. Bryconaethiops Reproduction --------------------------------------- 308 Adaptations ________________ __________________________ 309 yseuxi is shown to be a valid species, and data on the number of mandibular tooth families are Discussion ____ --------------------------------- 314 Literature Cited _____________________________________________ 315 used to distinguish the closely related Atopochilus guentheri and A. royauxi. Two ecological categories of highly specialized ABSTRACT. Rapids habitats at nine localities rapids fishes are recognized: strongly rheophilic along the mainstream of the Zaire River between or current-loving, comprising 58 of the species Kinshasa and Matadi were fished extensively with in our survey, and hyporheic or intrusive, com­ rotenone during low water, yielding over 7000 prising eight species which evidently avoid light specimens belonging to 129 species. A total of 17 as well as strong current by delving deeply into families are represented, the most speciose being the interstices offered by jumbled piles of rocks, Mormyridae ( 19 species), Cyprinidae ( 19), and perhaps, in some cases, burrowing into mud Cichlidae ( 17), and Mochokidae ( 16). Limnologi­ or loose rubble. The most consistent evolutionary cal and ecological observations are reported for modification of the rapids fishes is reduction (but not complete loss) of the eyes. Of 66 highly 1 Museum of Comparative Zoology, Cambridge, specialized rapids fishes, 26 are microphthalmic Mass. 02138. (with small or minute eyes superficial in position), 2 Laboratory of Limnology, University of Wis­ five cryptophthalmic (eyes reduced in size and consin, Madison, Wise. 53706. partially or completely covered over by skin and Bull. Mus. Comp. Zool., 147(6): 239-317, February, 1976 239 240 Bulletin Museum of Comparative Zoology, Vol. 147, No. 6 other tissues), and only one is anophthalmic for us to collect at Inga. We were greatly (totally without eyes) . The most startling dis­ assisted on numerous occasions by the covery of the survey is a cryptophthalmic cichlid of the genus Lamprologus. This is the first re­ citizens of Zaire. A number of missions ported blind species of percoid fishes. provided accommodations and other forms Some relationships between the rapids fishes of assistance at various times, especially the and the ichthyofauna of the Zaire basin and of Catholic mission at Tumba and the Prot­ Africa as a whole are pointed out in the discussion. estant missions in Luozi and Kibunzi. In The opportunities for speciation and adaptation provided by rapids habitats have contributed Kinshasa we received much help from our significantly to the diversity of the highly en­ friends M. and Mde. R. LeFer. demic ichthyofauna of the Zaire basin, a process For consulting with us on the rapids much less noticeable elsewhere in Africa, where fishes and for helping with the identifi­ highly specialized rapids fishes are relatively few. cation of a number of species we found A few rheophilic genera, namely Campylomormy­ rus, Atopochilus, and Steatocranus, presumably particularly troublesome, we are indebted evolved in the Zaire basin, subsequently spreading to our friend and colleague, Prof. :Max Poll, to one or more river systems in the adjacent Lower who has been studying and publishing on Guinean and Nilo-Sudanic ichthyofaunal provinces. the fishes of Zaire steadily since 1932. Mr. The great majority of species of rapids fishes in Gordon Howes responded with his char­ the Zaire basin are endemic, many of them ap­ parently restricted to the 300-km stretch of the acteristic promptness and thoroughness to Lower Zaire River between Kinshasa and Matadi. our requests for information about types Most of the rapids genera, however, are widely and other specimens housed in the British (if discontinuously) distributed in the Zaire basin, Museum. Drs. Ruth Turner and John wherever suitable habitat occurs. Perhaps the Lawrence, of the Museum of Comparative most striking aspect of the taxonomic composition of the Zairean rapids fishes is the preponderance Zoology, kindly identified mollusks and of Cichlidae, which cor.tributed more than a insects recovered from the guts of our fish third of the endemic rapids species and also more specimens. The photographs of fishes were than a third of the total number of individual prepared by Mr. Alphonse Coleman and specimens taken during our rapids survey. Such Miss Paula Chandoha in the photographic predominance of Cichlidae is a noteworthy con­ trast to the situation in rich riverine faunas every­ lab of the Museum of Comparative Zoology, where else in Africa, including low gradient rivers and were paid for by a grant from the in the Zaire basin, where cichlid species, en­ Milton Fund of Harvard University. Pub­ demic or not, are always few in number and lication was assisted by a grant from the seldom contribute substantially to the numbers Wetmore Colles Fund. of individuals present. Evolution in rocky rapids habitats may well have contributed to preadapt For the loan of specimens in their care, Zairean cichlids, including Lamprologus, to ex­ we express our thanks to Dr. Donn E. plosive lacustrine evolution along the rocky shores Rosen, American Museum of Natural of Lake Tanganyika. History; Drs. William N. Eschmeyer and Warren C. Freihofer, California Academy ACKNOWLEDGMENTS of Sciences; Dr. Thys van den Audenaerde, The fieldwork for this survey was con­ Musee Royale de l'Afrique Centrale; and ducted with a grant from the National Dr. Reeve M. Bailey, Museum of Zoology Geographic Society; we are grateful to the of the University of Michigan. We are Society's Committee for Research and Ex­ indebted to Dr. Ethelwvnn Trewavas, ploration for their support. Permission to British Museum (Natura( History), for collect and export specimens for study was reviewing the manuscript and providing granted by the Office National de la constructive criticism. Recherche et du Developpement of the Republic of Zaire, under the direction of INTRODUCTION Dr. Nguete Kikhela. The Societe Nationale The Zaire or Congo basin, with an area d'Electricite ( SNEL) granted permission of 3,822,000 km, lies at the heart of Africa. RAPIDS FisHEs OF ZAIRE • Roberts and Stewart 241 About 37o/o of its catchment is in the north­ the next 300 km, as the river flows over ern hemisphere and 63o/o in the southern. the sill and on through a gorge in the The Upper Zaire River or Lualaba arises in Crystal Mountains, it is broken by numer­ Zambia and flows northward to Kisangani; ous cataracts, with intermittent stretches its catchment lies south of the Equator and of calm water. The last of the rapids, just includes lakes Bangweulu, Moero, Kivu, upstream from Matadi, are about 130 km and Tanganyika. The Middle Zaire River from the sea. Between Kinshasa and flows westward in a great arc from Kisan­ Matadi the river drops 270 m; the average gani to Kinshasa. Its