Partial Replacement of Fish Meal With Soy Protein Concentrates and Poultry Byproduct Meal for Atlantic Salmon (Salmo Salar) Post-Smolts Reared in a Recirculating Aquaculture System

초록

This study evaluated the effects of partially replacing fish meal (FM) with a balanced mixture of poultry byproduct meal (PBM) and soy protein concentrate (SPC) on the growth, physiological responses, and economic performance of Atlantic salmon (Salmo salar) post-smolts reared in a recirculating aquaculture system (RAS). In total, four extruded diets were tested for 12 weeks: two experimental formulations-high-FM control, experimental diet (ED)1; 25% FM replaced with PBM + SPC, ED2-and two commercial reference feeds. Growth performance, feed efficiency (FE), and survival were statistically comparable across treatments, indicating that PBM-SPC inclusion did not compromise nutrient utilization. The proximate composition, amino acid (AA) profile, and lipid deposition in fish stabilized. The PBM-SPC diet maintained a favorable n-3/n-6 fatty acid (FA) ratio and a high retention of eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) comparable to FM-based feeds. Plasma biochemical indices and digestive enzyme activities were unaffected, demonstrating normal hepatic and metabolic function. Among diets, plasma antioxidant enzyme activities and serum lysozyme levels were similar, suggesting a maintenance of oxidative stress and immune balance. Expression of hepatic genes interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), IL-10, FA synthetase (FAS), and peroxisome proliferator-activated receptor alpha (PPAR alpha) confirmed that the PBM-SPC diet did not trigger any inflammatory or metabolic stress. However, histology revealed normal liver and intestinal morphology without signs of steatosis or enteritis. The PBM-SPC diet reduced feed costs and achieved a lower economic conversion ratio (ECR) while maintaining profitability equivalent to or greater than commercial feeds. Overall, the results demonstrate that partial substitution (25%) of FM with PBM and SPC sustains optimal growth, physiological stability, and economic efficiency of post-smolt S. salar under RAS conditions.

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