Tilapias and Indigenous Fish Biodiversity in Sri Lanka
C. H. FERNANDO, R.R.A.R. SHIRANTHA, M.J.S. WL1EYARATNE and P.R.T. CUMARANATUNGA
Some species of tilapias are now found worldwide in natural and artificial habitats in the tropics and sub tropics. Claims have been made from time to time that tilapias have displaced indigenous fishes and damaged fish culture. In this paper an attempt is made to examine some of these statements and evaluate whether there is a basis for such claims. In Sri Lanka, introduced tilapias are found mainly in manmade reservoirs and still there are no records of established populations of exotic tilapias in-the river systems in the country where indigenous and endemic freshwater fish species are found. The major threats to freshwater fish biodiversity include habitat degradation and overexploitation for the ornamental fish trade. In Sri Lanka, introduction of tilapias to lacustrine waters has been beneficial in terms of contributing to fish production. Tilapias have been in natural and artificial habitats throughout the tropics and the sub-tropics for over 50 years. Considering the immense number of introductions of tilapias into individual habitats in many parts of the tropics and subtropics, surprisingly few substantiated cases of their damaging indigenous fish communities have so far been recorded. Some of these claims of cases of presumed or real damage to local fish stocks are ambiguous or ware unsubstantiated speculations. To expect absolutely no negative effects at all on the indigenous fishes by tilapias is unrealistic. On the other hand substantial quantities of tilapias are now harvested from reservoirs or raised in culture where no such enterprises existed earlier.