Deciphering the Dynamics of Reproduction and Diet for Bigeye Ilisha (Ilisha megaloptera) from the Saurashtra Coast, Northeastern Arabian Sea

With no exhaustive information available for Ilisha megaloptera, the present study aimed at elucidating the reproductive and feeding dynamics from 764 individuals landed by gillnetters at Veraval, India, in the northeastern Arabian Sea. Standard length ranged from 18.4 cm to 35.2 cm. Growth was isometric in males and negatively allometric in females. Sex ratio (F:M) was 1.22, with significant dominance of females at most size classes. Maturity sizes for females and males were 24.21 cm and 24.92 cm. Observation showed that Ilisha megaloptera spawned throughout the year with major and minor peaks occurring from February to May and November to December, respectively. The monthly percentage contribution of spawning females and males ranged from 16.0 to 72.22 and 22.22 to 73.68, and the gonadosomatic index for females varied between 3.59 and 7.68. Absolute fecundity ranged from 22,875 eggs to 121,013 eggs. Asynchronous ovarian development with three distinct modes in egg distribution indicated multiple spawning events. Feeding intensity was low, with 26.05% exhibiting part-full stomachs and 7.20% full stomachs. Feeding activity was lowest during spawning peaks and highest in fishes measuring 26.0–29.9 cm. Below 22.0 cm, feeding was solely on zooplankton, dominated by copepods. Feeding henceforth was mostly on nekton: crustaceans (39.35%) and teleost juveniles (38.72%). Ontogenetic shifts and seasonal variations in prey signified optimal foraging. Precipitation and salinity significantly impacted the monthly gonadosomatic index and predator– prey weight ratio. The present study provides a detailed report on bionomics for Ilisha megaloptera and could contribute to the management of Ilisha spp. stocks in the Indian Ocean, considering the paucity of information available for other species in this genus