Priliminary Study of Sex Ratio, Gonadosomatic Index and Fecundity of Tilapia sp. in The vavuniya Town Tank

Abstract

The Vavuniya District surrounded by the land mass where there is no marine environment justifies the exclusive dependents of inland capture fisheries that is boon for the local fishermen's revenue. As the Vavuniya town tank is located in the strategic location of the Vavuniya urban area subjected to the most vulnerability to the aquatic pollution. Almost 99% of the fish composition is Tilapia sp. The reproductive biology of the particular fish is essential to investigate the abundance, in terms of their sustainability. the sex ratio, gonadosomatic index (GSI) and fecundity of freshly captured Tilapia from Vavuniya town tank was examined during the period of January-June 2011. Although the sex ratio is 1:0.64 (male: female) which shows no significant difference (p>0.05) to the ideal ratio of 1:1 reveals equilibrium state. The correlation between the gonad Weight with standard length (SL) was positive (r= +0.052) in males but negative (r= 0.062) in females. Negative correlation was obtained for GSI with SL for both male r= -0.081) and female (r= -0.260). Compared to male, GSI can be calculated for all females. This indicates the high fertility and the mean fecundity was 788 eggs, with range 425 to 1827. A high positive correlation was obtained between fecundity and SL r = +0.732) and fecundity and total body weight (r = +0.683), which shows a steep relationship between these parameters. As it was the preliminary study, annual survey should be carried out to examine the reproductive biology to meet the strong conclusion about the sustainability of Tilapia sp. in the Vavuniya town tank.