Spatial Changes in Growth and Mortality and Effects on the Fishery of Oreochromis mossambicus (Pisces, Cichlidae) in a Man-made Lake in Sri Lanka

Abstract

Growth and mortality were estimated from the length-frequency data of Oreochromis mossambicus from the gillnet fishery of Parakrama Samudra, a man-made lake in Sri Lanka, separately for its three basins. The asymptotic length (L?) and the growth constant (K) of O. mossambicus in the northern basin of the lake (34.9 cm and 0.3, respectively) are appreciably different from those in other tow basins (middle basin, L? = 38.8 cm and K = 0.24; southern basins are 2.22, 1.64 and 1.07, respectively. The spatial differences in growth are suggested to be due to different fishing pressure and environmental conditions. Yield-per-recruit analysis indicate that in the populations with low L? and high K, exploitation level should be maintained at a low level. Fish yield could be optimized by increasing the size of first capture and exploitation rate in the population with high L? and low K.