Life-History Strategies of Nile Tilapia, Oreochromis niloticus(Linnaeus, 1758) (Teleostei, Cichlidae), in Irrigation Reservoirs of Sri Lanka

Abstract

As in many tropical countries, reservoir fishery of Sri Lanka is dominated by the exotic cichlid, Oreochromis niloticus(Linnaeus, 1758). Oreochromis niloticuspopulations in irrigation reservoirs are expected to be under the influence of various disturbances such as changes in hydrological regimes, trophic conditions and fishing pressure. In the present study, an attempt was made to investigate the effect of biological productivity and fishing pressure on life history patterns of O. niloticuspopulations in 10 irrigation reservoirs of Sri Lanka. Oreochromis niloticuspopulations in environmentally stressed reservoirs, exhibited low age at maturity than those inhabiting reservoirs with relatively low biological productivity. Hydraulic retention time (HRT) in reservoirs also had negative influence on size and age at maturity of O. niloticus. As length at first capture of O. niloticusis positively related to mean length at maturity, these attributes have significant implications on the optimal fishing. Fishing intensity (FI) in O. niloticuspopulations also had negative influences on mean length and age at maturity. Hence, the present study supports the opinion that altricial or opportunistic traits having faster growth and achieving maturity early in the life dominate disturbed environments and that precocial or equilibrium traits exhibiting delayed maturity occur in more stable environments. Possible shifting of life history strategies of O. niloticusto opportunistic traits due to disturbance events could be manipulated by increasing FI for smaller individuals in the population.