Ecology and distribution of tilapias

This paper reviews aspects of the ecology of tilapias: i) their geographical distribution, ii) the physical (current velocity, depth, temperature) and chemical (salinity, alkalinity, pH, oxygen and other dissolved gases) factors which influence this and iii) aspects of their behavioral ecology namely feeding behavior, reproductive behavior, selection of microhabitat, schooling behavior and movement. Maps are given showing the natural distribution of the principal substrate-spawning genus Tilapia and the mouth-brooding genus Sarotherodon and the history of their transfers in Africa and introductions to other continents are tabulated. The natural distribution of the tilapia species depends upon : i) historico-geological factors which led to geographical isolation and speciation, ii) ecological factors which demonstrate the requirements and preferences of the species mainly with regard to temperature and salinity and iii) behavioral mechanisms relating to feeding and reproductive strategies. Data on the natural distribution, ecological amplitude and eco-ethological characteristics could help in the selection of species for culture and introductions for fisheries and in the prevention of unfortunate consequences, such as unwanted hybridization, competition for food or spawning grounds, and contamination of pure wild strains or failure of the introduced stocks (e.g. due to unsuitable temperature conditions, overpopulation and nanism, etc.). The dangers of introductions made without sufficient knowledge of the biology of the species and recipient ecosystems and the necessity for better control of fish transfers and future research on the basic and applied ecology of tilapias are all stressed.