Gillnet selectivity of Ompok bimaculatus (siluridae) and Puntius dorsalis (cyprinidae) in a small-scale riverine fishery

Abstract

Gillnet selectivity of two indigenous fish species, Ompok bimaculatus and Puntius dorsalis was determined in a small-scale fishery at Uruwal Oya, in the Gampaha district. The optimal lengths (Lopt) of the two species for different mesh sizes were determined by the Baranov-Holt method. The relationships between Lopt and mesh size (M) of gillnet for the two species are described by the following equations: O. bimaculatus: Lopt = 4.076 + 3.694 M (r = 0.992; p < 0.01) P. dorsalis: Lopt = 2.445 + 3.410 M (r = 0.994; p < 0.001) The mean sizes of maturity of O. bimaculatus (21.6 cm for males and 26.1 cm for females) and P. dorsalis (13.4 cm for males and 14.8 cm for females) approximately correspond to Lopt in stretched gillnet mesh sizes of 5.8 cm and 3.8 cm respectively according to the above relationships. Therefore there seems to be a need for regulating mesh size of gillnets in this fishery in order to prevent immature O. bimaculatus and P. dorsalis being caught.