The weight and age of the brood fish are important factors in producing high-quality gametes and larvae in any fish. Therefore, two induced spawning experiments were conducted to ascertain the 1) effects of maternal weight, and 2) effects of maternal weight and age interaction on the reproductive performance, egg quality and larval quality of Indian butter catfish, Ompok bimaculatus. In first experiment, four size groups of female O. bimaculatus brood fish, with following size ranges, F50 (51.40 ± 5.22); F80 (81.60 ± 7.13); F120 (120.8 ± 6.37) and F160 (159.80 ± 7.66), were selected in addition to male brood fish in the same weight range. In second experiment, female brood fish of same age-class (<1, 1-1.5, 1.5-2.0 and 2+ year) were divided into two size groups. The brood fish in the large (L) group were, on average, approximately 1.3 to 1.4 times the body weight of the brood fish in the small (S) group. Males of equivalent weight of female were taken without considering their age. Fecundity, egg quality metrics like weight and diameter, fertilization rate, and hatching rate were evaluated. Larvae (5 DPH) were raised for 15 days on optimal diets to examine their growth parameters, survival rate, and deformation rate.
The results revealed that the total fecundity had a substantial positive relation (r= 0.90; p<0.01), and fertilization and hatching rate had a non-significant negative (r= -0.21; p=0.367) and strong significant negative (r= -0.62; p= 0.003) correlation to maternal size in experiment-1. Individually, fish age and fish size had significant relation with fecundity of female (GLM: F= 124.70, p<0.001 for fish age; and F=40.04, p<0.001 for fish weight) and egg hatching rates (GLM: F= 5.42, p= 0.004 for fish age; and F= 13.51, p=0.001 for fish size), however, their interaction effects (fish age x fish size) on fecundity, fertilization and hatching rates were found insignificant (GLM: F=0.299 – 2.269, p= 0.099 – 0.954) in experiment-2. Hatchling deformation rate was found significantly higher in female brood fish of 160 g size and age of 2+ years. The survival rate, total length, and specific growth rate were found considerably (p <0.05) higher in larvae of female brood fish of F80 and F120 and age of 1 – 2 years.
Overall, the findings suggest that maternal weight and age had a substantial effect on Ompok bimaculatus reproductive performance, egg characteristics, and larval fitness during induced captive spawning.