Spawning season and size at first sexual maturity of freshwater mussel Lamellidens marginalis (Lamarck, 1819) in the Brahmaputra River, Bangladesh

Spawning season and size at first sexual maturity of Freshwater mussel Lamellidens marginalis was studied from the specimens collected from Brahmaputra River, Mymensingh district, Bangladesh from July 2015 to June 2016. The present study has investigated sex ratios, gamogenetic cycle, condition index, and size at first sexual maturity by means of standard histological procedures. The results indicated no significant difference in the overall sex ratio (M: F = 1:1.3). The qualitative analysis of gonad developmental stages has provided confirmation of the presence of a yearly reproductive cycle characterized by prolonged gonadal activity. The highest percentages of ripe gonads were observed in July for males (77.78%) and August for females (53.85%). The spawning activity was highest in October for males (50%) and November for females (83.33%). Furthermore, ripening and spawning stages in different shell lengths ranged from 58–63 to 88–93 mm for both sexes. The findings from the qualitative observation of gonad developmental stages, a single annual spawning peak observed between October and November. A statistically significant correlation was detected between the average condition index of male and female. Males reached sexual maturity at smaller standard length (SL50 = 63.25 mm) compared to females (SL50 = 72.10 mm SL). Acquired knowledge regarding the present state and distinctive gonad developmental characteristics of L. marginalis will aid fisheries management professionals and conservation biologist in the effective management of this particular species of mussels in the waters of Bangladesh.