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A review on the status of Tilapiine species in Lakes Victoria and Naivasha, East Africa

This paper discusses the status of tilapiine species both native and those introduced into lakes Victoria and Naivasha. In Lake Victoria, four exotic tilapiine species (Oreochromis niloticus, O. leucosticus, Coptodon zillii and Coptodon rendalii) were reviewed, while in Lake Naivasha, three species were reviewed (O. niloticus, C. zillii and O. esculentus). The O. niloticus in Lake Victoria caused decline of the native O. variabilis and O. esculentus through competition and hybridization. Only O. niloticus has been able to establish in Lake Victoria, currently forming the third commercially important species after the introduced Nile perch, Lates niloticus and a native cyprinid Rastrineobola argentea, whereas other tilapias are extinct or are occasionally caught in the lake. Predation by Nile perch, overfishing, lake pollution and eutrophication are reported to have impacted negatively on the fish stocks in Lake Victoria. The introduced tilapiine species in Lake Naivasha have also declined in catches primarily attributed to the deteriorating lake conditions, competition and feeding behavior of the introduced Common carp, Cyprinus carpio. Only O. leucostictus and O. niloticus are presently recorded in catches in Lake Naivasha, whereas C. zillii is rarely caught in the lake. The biological and population parameters of the tilapiines have shown great variation over time. The O. niloticus and O. leucosticus in the lakes tend to mature early at smaller sizes. These changes are discussed as adaptive characteristics in response to intense fishing and changing ecological conditions. There is therefore need to improve on the measures used to manage the two lakes basing on evidence of the declining fish stocks.