Evaluation of the ichthyological diversity of a West African River Basin after the construction of a dam

Fourty-four freshwater fish species, including introduced species, were unt il recently reported from the Bia Basin (Cote d'Ivoire) on which a dam has been constructed in 1959 for hydro-electrical purposes. This study raised t he number to 65 including two introduced species (the osteoglossid Heteroti s niloticus and the cichlid Oreochromis niloticus) and one cichlid hybrid ( Tilapia guineensis x T. zillii). The distichodontids Distichodus rostratus and Citharinus eburneensis, initially supposed to be present, can now be co nsidered either as absent or their original occurrence can be doubted. For Citharinus eburneensis, its disappearance is related to the dam constructio n. In contrast to the Agnebi a nearby basin without a large man-made lake b ut with numerous small water bodies, the ichthyological diversity of the Bi a seems well preserved. Interestingly, Lake Ayame on the Bia is the only ma n-made lake in this country where the production of Oreochromis niloticus i s considerably lower than that of other tilapias, in particular that of Sar otherodon melanotheron.