Abstract

Before the introduction of non-indigenous species like Oreochromis niloticus and Tilapia zillii (Gervais) in Lake Victoria, the great majority of the ichthyofauna of the lake was made up of two groups of indigenous cichlids, the haplochromines and the tilapiines. The latter, although much less diversified, represented an important part of the total fisheries catch, and were a highly-valued food resource for the local community. Two species constituted this tilapia stock: Oreochromis variabilis (Boulenger) and O. esculentus (Graham). In less than 20 years, several hundreds of species have disappeared from Lake Victoria among which are these two native tilapias. Today, these two species are no longer present except in a few satellite lakes of Lake Victoria. Most of these populations are considered either as endangered or as having suffered genetic modification by hybridization with closely related introduced species. Tilapias are well known for their hybridizing abilities in the natural environment when native species are in contact with introduced species. The hybrids between O. niloticus and O. variabilis were observed before the latter species had disappeared from the lake. It also seems likely that O. esculentus hybridized with O. niloticus. In order to protect the remaining populations of native tilapias in this region, it is important to be able to characterize the endemic species genetically to determine their degree of genetic. This will make the conservationists know how to handle these species and if at all we have pure breeds for protection of biological diversity.

Keywords: Hybridization; Oreochromis esculentus; Endangered; Oreochromis variabilis; Oreochromis niloticus; Lake Victoria