Immunostimulatory and antifertilityeffects of neem (Azadirachta indica) leaf extract on common carp (Cyprinus carpio Linnaeus)

180-day feeding trial was conducted on the growth performance, feeding efficacy, immunological parameters and gonadal reproductive parameters of common carp, Cyprinus carpio fed with neem (Azadirachta indica) leaf extract (NLE) incorporated at different levels (0, 0.25, 0.5, 1.0, 1.5 and 2.0 g kg⁻¹ feed) in rice bran and mustard meal (1: 1 ratio) basal diet. The study revealed highest Net Weight Gain (NWG) in fish fed on NE 1.0 g kg. Results showed that the good growth response was obtained in fish fed with the NLE 1.0 g kg⁻¹ feed and least in fish fed only on basal diet (without NLE). Whereas, higher gonado-somatic index (GSI), relative fecundity and ova diameter values were obtained from fish fed on basal diet while the least were observed from fish fed only on basal diet, while the least value was fish fed with NLE 1.0 g kg⁻¹ feed. Fish fed with NLE 1.0 g kg⁻¹ feed also showed significantly (p<0.05) enhanced phagocytic activity ratio, Phagocytic index, NBT activity, CAT, SOD, GPx and GR responses in comparison with fish fed only on basal diet, where as LPO is significantly decreased on being fed with NLE up to 1g kg-1 feed. The study indicated that incorporation of NLE in feed improved growth, delayed female gonadal maturation and could be used as a potential immunostimulant and to control the prolificbreeding of C. carpio in aquaculture.