FRESH-WATER FISH ZOOGEOGRAPHY IN WEST-AFRICA - FAUNAL SIMILARITIES BETWEEN RIVER BASINS

Similarities between the freshwater fish faunas of 52 west African riv ers have been investigated and three main zoogeographic regions recogn ized. The Sudanian region includes all rivers from Senegal to the Omo, as well as coastal basins from Ivory Coast to the Cross and the Wouri . The Upper Guinean region comprises the coastal basins from Guinea to Liberia and the Lower Guinean one, the coastal rivers of Cameroon and Gaboon. The Sudanian region can be sub-divided into a Sudanian region sensu stricto, including the Sahelo-Sudanese rivers, and the Eburneo- Ghanean region corresponding to coastal basins from the Cess (or Nipou e, Ivory Coast) to the Pra (Ghana). These delimitations give an highly significant within region faunal homogeneity, even if the effect of g eographical proximity between rivers is removed. 21 to 71% of the fish species in each region are endemics. The present patterns of distribu tion are the result of past climatic and geological events affecting w est Africa and, given this framework, the role of alternating wet and dry periods during the early Quarternary is emphasized as well as the importance of mountains as dispersal barriers. Role of recent river co nnections and links via lagoon is emphasized in explaining river fauna l similarities within biogeographical regions.