Dominance of introduced Nile tilapia, Oreochromis niloticus (L.) in Lake Victoria: A case of changing biology and ecosystem
Okeyo Owuor, J.B.
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Nile tilapia, Oreochromis niloticus together with other tilapiines of Oreochromis leucosticus, Tilapia zillii and Sarotherodon melanopleudra (=T. rendalii) were introduced into Lake Victoria (Kenya) between 1951 and 1962 to boost the then declining fishery. Only O. niloticus was able to establish leading further to reduction in endemic tilapiines of Oreochromis variabilis and Oreochromis esculentus. O. niloticus currently forms the third commercially important species after introduced Nile perch, Lates niloticus and a native cyprinid Rastrineobola argentea, whereas other tilapias are extinct or are occasionally caught in the lake. Information was collected from by bottom trawling and from published literature to ascertain possible factors leading to dominance of O. niloticus. Compared to other tilapiines, Nile tilapia is widely distributed, feeds on a variety of food items, grows to larger sizes, is highly fecund and can survive in a wide range of physical chemical parameters in the lake. These attributes could probably be the reason for its dominance over the tilapiine groups in the lake. Studies further show that ecology and biology of the O. niloticus has changed probably in response to changes occurring in the ecosystem. Management measures to sustain the fishery which include reduced fishing pressure, use of legal fishing methods, and control of environmental degradation have been discussed.
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