Morphometric and meristic variation between two endangered til apiine fishes o.Esculentus and o. Variabilis and the exotic tilapias o. Niloticus and o. Leucostictus in Lake Kanyaboli, Kenya

Abstract

Lake Kany aboli is unique as a living museum. The most important fishery of this lake is that of an indigenous tilapiine fish, Oreochromis esculentus , which is virtually extinct in Lake Victoria. Oreochromis variabilis has been infrequently reported to occur in thi s lake while two exotic species O. niloticus and O. leucostictus although less dominant, frequently appear in catches. The indigenous tilapiine species have been listed as endangered and it is postulated that hybridization may have taken place with the exo tic tilapias. Morphological and meristic variation was examined in samples of the four tilapia species; Oreochromis esculentus, O. variabilis , O. niloticus and O. leucostictus from Lake Kanyaboli and its environs, to distinguish populations and identify hy brids. All samples of Oreochromis variabilis were collected from the nearby Kalenjuok and Mauna dams as none was found in Lake Kanyaboli. A total of 20 morphological and 8 meristic characters were examined. Discriminant Function and Principal Component ana lyses indicated no correlation in the morphological characters between Oreochromis esculentus and O. niloticus and between Oreochromis esculentus and O. leucostictus . The overall DF was significant (p<0.05). The species were best discriminated by the inte r - orbital width (IOW) the pre - pectoral length (Ppl), the anal fin length (AfL) and the anal spine length (AsL) with a 97% correct classification of specimen. However there were some overlap of individuals between populations of O. niloticus and those of O. leucostictus and O. variabilis . The present analyses do not suffice to state the overlap as due to the presence of hybrids and therefore this necessitates some biochemical analysis