Ovarian Cycle of Freshwater Pearl Mussel, Lamellidens marginalis (Lamarck, 1819) Collected from a Culture Pond in Bangladesh

The current study was undertaken to investigate the ovarian cycle of freshwater pearl mussel, Lamellidens marginalis (Lamarck, 1819) collected monthly from a rearing pond in Bangladesh. Gonadal maturation was determined from 2 to 3 mm thick slices of dorso-ventral section cut from the middle of the mussels for histology. The overall male-female sex ratio, 1:1.08 did not deviate significantly from the 1:1 ratio as expected (j2-test). Lamellidens marginalis females exhibited a prolonged spawning period from February to November when water temperature remains above 22 °C. Oogenesis occurred round the year although the majority of the females were in early and late-developing stages during January and February. Four distinct peaks in maturity indices (MIs) of L. marginalis females were noted during October, February, June and August when most of the females were ripe and ready for spawning. Condition indices (CIs) ranged from 0.42 ± 0.23 (September 2016) to 0.85 ± 0.25 (October 2015) by mean (± SD) exhibiting five peaks over 12-month study period. Further study should be designed to investigate the timing and brooding pattern of this freshwater unionid species.