Fish Biology and Life History Indicators. In: Mgaya, Y.D. and Mahongo, S.B. (Editors), Lake Victoria Fisheries Resources: Research and Management in Tanzania.
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Date
2017-11-29
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Publisher
Springer
Abstract
Life history traits like growth, reproduction, food and mortality are principal factors in the survival of the fish. This chapter examines the life history indicators of three commercial fish species in Lake Victoria, namely Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus) and the cyprinid known as ‘Dagaa’ (Rastrineobola argentea). The size at first maturity for Nile perch has been declining due to stress in the population caused by heavy exploitation, changes in food availability and deteriorating water quality parameters, particularly dissolved oxygen concentration. The fish exhibits ontogenic shifts in food. R. argentea has an offshore surface dwelling behaviour with about 68% found distributed in waters of more than 40 m depth. Its size at first maturity varies from place to place. R. argentea breeds throughout the year but with distinct peaks during the rainy season. An increase in fecundity has been observed in Nile tilapia and it is considered a mechanism to compensate for the intensive fishing pressure in the lake. Studies indicate an increase in size and growth parameters for Nile tilapia despite the heavy fishing pressure as a result of increased demand in local and foreign markets. The success of the species could be due to the ability of the species to expand their niche. It has diversified its food to include Caridina nilotica, chironomids, chaoborids, molluscs and bottom detrital matter. An ecosystem approach guided by a precautionary principle is required in order to manage the fishery resources in Lake Victoria and to ensure their sustainability.
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Keywords
Lake Victoria, Fish biology, Life history, Indicators, Commercial species