Reproductive pattern and histological profiling of maturity stages in Tenualosa ilisha of Chattogram Coast, Bangladesh

Abstract

Hilsa is an anadromous fish belongs to the family Clupeidae known as ‘Indian shad’ in Bengali. Tenualosa ilisha, Hilsa kelee and Hilsa toli are the three species found in the Bay of Bengal, although Tenualosa ilisha is the most common hilsa fish caught in our nearby region. This study is done on the reproductive pattern and histological profile of T. ilisha in the Chattogram coast, Bangladesh. For analyzing the result length-weight relationship, condition factor, relative condition factor, oocyte diameter, fecundity and histological stages were identified by collecting fish sample throughout the year (February, 2019 to January, 2020). The length-weight relationship based on pooled data was W = 0.269874* TL 2.6351 (R2 = 0.682), the logarithmic equation being log W = -1.3098 + 2.6351 logTL. The ‘b’ value of the length-weight relationship indicates the negative allometric growth (b˂3) of T. ilisha. It was found that, the mean of condition factor (K) was minimum (0.9905±0.0859) during May and maximum (1.5343±0.2438) during September, again the mean relative condition factor (Kn) was minimum (0.1404±0.0126) during May and maximum (0.2177±0.0286) during September. Highest GSI value (13.57±1.618) for female was found in January whereas lowest value of GSI (1.698±0.4968) was observed in March. Maximum oocyte diameter was found in January (890.6±122.09 μm) and minimum oocyte diameter was found in March (220.9±35.67 μm). Fecundity was counted by gravimetric methods and was found to vary from 96718 to 117435 with a mean value of 109605±1635 eggs. Throughout the year, six different gonadal developmental stages were found. According to this study, ripe stage was identified in the month of January and in other months it passes different gonadal stages like primary vitellogenic, secondary vitellogenic, maturing, spent and regressing. The findings will provide to a better understanding of the stages of gonadal development of Tenualosa ilisha and the maintenance of the catching period in accordance with these Stages