Reproductive Biology and Feeding Habits of Sillago sihama (Forsskal, 1775) and Sillago mengjialensis (Gao, Baki, and Saha, 2022) in Bay of Bengal, Bangladesh

This study investigates the reproductive biology, feeding habits, and growth pattern of Sillago sihama (N = 119) and Sillago mengjialensis (N = 18) collected from Cox’s Bazar, Bay of Bengal, between August 2022 and October 2023. The total length and body weight of S. sihama ranged from 72.19 to 173.50 mm and from 2.49 to 41.32 g, respectively, while they ranged from 78.32 to 159.81 mm and from 3.08 to 27.19 g, in S. mengjialensis, respectively. The sex ratio was male-dominated in both species. Peak gonadosomatic index (GSI) values were recorded in March for S. sihama (females: 0.653 ± 0.121; males: 0.351 ± 0.022) and in November for S. mengjialensis (females: 3.600 ± 0.371; males: 1.068 ± 0.115), indicating distinct and separate spawning seasons. In both species, males matured at smaller size, compared to females, with Lm₅₀ estimated at 93.73 and 98.76 mm for male and female S. sihama, and 86.00 and 128.14 mm for male and female S. mengjialensis, respectively. Histological examination identified immature and mature males and immature and maturing females in S. sihama, whereas mature males and fully ripe females were observed in S. mengjialensis. Fecundity in S. mengjialensis ranged from 8548 to 16,716 eggs per ovary. Feeding analysis revealed omnivory in S. sihama (RLG: 1.12) and carnivory in S. mengjialensis (RLG: 0.75). Length–weight relationships indicated positive allometric growth (b = 3.453) in S. sihama and isometric growth (b = 3.08) in S. mengjialensis. These findings provide important baseline data for future management, conservation, and stock assessment of these species.