Rainbow trout (Oncorhynchus mykiss) aquaculture in Nepal faces constraints regarding high feed costs and the sustainability of marine-derived proteins. This study validated the on-farm partial replacement of shrimp meal with Black Soldier Fly Larvae Meal (BSFLM). Juvenile trout in Rasuwa, Nepal, were fed four isonitrogenous, isolipidic diets for 90 days: Control (100% shrimp meal), BSF25 (25% replacement), BSF50 (50%), and BSF75 (75%). Results indicated that the BSF25 treatment achieved the highest final weight (23.13 ± 0.13 g) and Specific Growth Rate (SGR: 1.34 ± 0.01 %/day), significantly outperforming the control (14.39 g; 0.81 %/day). Feed efficiency was optimal in BSF25, showing the lowest Feed Conversion Ratio (FCR: 1.49 ± 0.02) and the highest Protein Efficiency Ratio (PER: 1.50 ± 0.02). Water quality monitoring showed stable temperature and pH, and significantly higher dissolved oxygen in BSFLM groups, correlating positively with growth. Survival rates remained high in Control and BSF25 (84%) but dropped significantly at BSF75 (48.27%). In conclusion, replacing shrimp meal with 25% BSFLM optimizes growth, feed utilization, water quality conditions, and survival. Higher inclusion levels negatively affected performance. These findings support BSFLM as a sustainable, cost-effective protein alternative for Nepalese trout aquaculture.