Study of the spawning season of Hilsa, Tenualosa ilisha in Bangladesh

An experiment was carried out on the reproductive biology of riverine populations of Tenualosa ilisha in Bangladesh to identify peak breeding season using gonadal biology and gonadosomatic index (GSI) information, reproductive and fry production potentiality, which will finally lead to development strategies for conservation of Hilsa fish species. Total 480 Samples were collected from Meghna River, Chandpur, from July 2012 to June 2013 and Tentulia River, Barisal from June 2013 to June 2014. Both Total length (TL) and Gonad length (GL) were measured using a measuring scale, and both Body weight (BW) and Gonad weight (GW) were taken using an electric balance. To detect the peak spawning activity of hilsa of the Meghna River and Tentulia River, the GSI and Dobriyal index (DI) were calculated. The mean GSI value for both female and male hilsa of the Meghna River was found to be varied from 4.84±0.63 to 15.31±1.17 and 0.32±0.04 to 1.04±0.08, respectively, with the highest value in October. In the case of the Tentulia River, the mean GSI value for female and male hilsa was found to be varied from 6.33±0.39 to 15.03±0.37 and 0.32±0.03 to 1.00±0.06, respectively, with the peak in October. Mean DI of female and male hilsa of Meghna River, Chandpur was found to be ranged from 3.31±0.23 to 5.15±0.17 and 1.18±0.04 to 1.71±0.03 respectively, and October was the highest. Mean DI value of female and male hilsa of Tentulia River, Barisal varied from 3.63±0.15 to 5.00±0.12 and 1.18±0.04 to 1.70±0.03 respectively, with the peak in October. Both the GSI and DI results of the present study suggested that hilsa has a prolonged spawning season, but major spawning takes place in October–November, with a distinct peak in October, indicating the peak spawning season for hilsa in Bangladesh.