Reproductive biology of largehead cutlassfish Trichiurus lepturus Linnaeus 1758 along eastern Arabian Sea and western Bay of Bengal

The reproductive biology of Trichiurus lepturus Linnaeus 1758, was studied based on 6167 and 3346 specimens collected weekly along Eastern Arabian Sea (EAS) and Western Bay of Bengal (WBB) respectively during 2014 to 2018. The sex ratio varied significantly (p<0.05) throughout the year with a predominance of females during all months except September and October in EAS while, it did not differ significantly (p<0.05) except during June and July in WBB. The estimated length at first maturity (Lm50) for females was 58.0 cm TL in EAS and 55.5 cm in WBB. Higher Gonadosomatic index (GSI) values were recorded in February and May along EAS and in February and October along WBB. The proportion of ripe and partially spawned fishes were high to moderate during January to May in EAS and during October to March in WBB indicating peak spawning periods for T. lepturus. The presence of ripe, partially spawned, spent and spent-recovering fishes throughout the year in varied proportions implied prolonged spawning throughout the year. Microscopic and histological examination of the ovaries further confirmed T. lepturus to be an asynchronous batch spawner. The estimated absolute fecundity ranged from 21,930 to 1,85,941 [average 28,245±3306 (SE)] and 17,294 to 1,86,667 [average 75,000±10,436 (SE)] per female fish along EAS and WBB respectively. The relative fecundity (per g body weight) varied from 12 to 841 [average 105±12.2 (SE)] and 64 to 241 [average 64±15.1 (SE)] in EAS and WBB respectively. Keywords: Fecundity, Gonadosomatic index, Sex ratio, Sexual maturity, Spawning periodicity