Abstract
In order to furnish guidelines for better management of Hilsa (Tenualosa ilisha) fishery, the largest single species capture fishery resources of Bangladesh, a research was carried out to study reproductive biology of riverine populations of Hilsa from two rivers of Bangladesh. A total of 480 fish samples (10 male and 10 female per month) were collected from two locations - the upper Meghna River (Chandpur district; sampled from July 2012 to June 2013) and the Tentulia River (Barisal district; sampled from July 2013 to June 2014) of Bangladesh. Length-weight relationship (LWR), relative condition factor (Kn), fecundity, gonadosomatic index (GSI) and Dobriyal index (DI) were calculated and histological studies of monthly gonadal development were performed. Mean (±SE) monthly total length and mean (±SE) monthly body weight of female and male Hilsa varied from 37.21±0.81 to 42.58±0.80 cm and 34.25±0.55 to 37.03±0.75 cm, and 639.50±0.71 to 992.00±61.93 g and 453.60±19.25 to 626.00±18.02 g for the upper Meghna and the Tentulia Rivers, respectively. The exponential 'b' obtained to be 3.069 and 2.933 for Hilsa from the upper Meghna and the Tentulia Rivers, respectively. For both the sampling locations, the highest mean Kn values for female and male were observed during April and the second highest were in October. Hilsa facundity was estimated for the upper Meghna River samples only and the mean fecundity was recorded to be 1484103±97822 eggs for mean total length of 41.10±0.94 cm and mean body weight of 818.40± 41.60 g. For both the locations, high female GSI values were observed during July to November where October values were the highest (15.31±1.17 and 15.03±0.73 for the upper Meghna and the Tentulia Rivers, respectively). Male GSI showed similar pattern, October values being the highest. The DI values for both the locations were in agreement with the GSI values. Histological study of gonads showed that female Hilsa from both the locations were abundant in mature oocytes during July to November where October samples were highest (73% and 75% for the upper Meghna and the Tentulia Rivers, respectively) in occurrence. On the other hand testes were rich in mature germ cells during September to October where October samples showed highest maturity. Moreover, year-round appearance of mature ovarian and testicular germ cells in the histo-sections of gonads is indicative of the fact that Hilsa breeds, at least at limited scale, all the year round. Based on GSI and histological data of female and male Hilsa from both the locations, it can be concluded that the main breeding season of Hilsa in Bangladesh is September to October with peak in October. Since implementation of seasonal ban for Hilsa fishery in Bangladesh is solely dependent upon pin pointing of its breeding season, findings of the present research will provide important guidelines for proper management of the most important fishery of Bangladesh.