Asian Journal of Fisheries and Aquatic Research

Rainbow trout culture can be constrained by stress and disease, creating interest in plant-based feed additives. This study evaluated the effects of dietary Moringa oleifera leaf powder (MLP) at 0, 20, 30 and 40 g/kg feed on growth performance, survival, hepatosomatic index (HSI) and plasma cortisol in rainbow trout under Nepalese raceway conditions. Three hundred fish with an average initial weight of 55.31±0.46 g/fish were allocated equally to four treatments, each with three replicates, and fed at 3% of body weight twice daily for 90 days. Water quality was monitored, growth and feed-utilisation indices were calculated, HSI was determined and plasma cortisol was analysed using an enzyme-linked immunosorbent assay. MLP40 produced the highest final weight (110.83±1.82 g), specific growth rate (0.76±0.02%/day) and daily weight gain (0.61±0.02 g/fish/day), together with the lowest feed conversion ratio (2.13±0.02). Survival did not differ significantly among treatments. The HSI and water-quality parameters also showed no significant treatment effects. Plasma cortisol declined with increasing MLP supplementation and was lowest in MLP40 (13.89±3.86 ng/mL), compared with 44.01±1.97 ng/mL in the control. Under the conditions of this study, supplementation at 40 g/kg feed was associated with improved growth performance and feed utilisation and a lower plasma cortisol concentration, without significant changes in survival or HSI. Moringa oleifera leaf powder therefore shows potential as a functional feed additive for rainbow trout culture.