The Effect of Feeding Varying Levels of Soybean Meal in High-Nutrient-Density Diets on Growth Performance and Body Composition of Juvenile Atlantic Salmon

Six experimental, high-nutrient-density (HND) diets containing practical ingredients (55% protein, 20% lipid) were fed to juvenile (initial weight [mean +/- SE] = 27.6 +/- 1.0 g) Atlantic salmon Salmo salar reared in freshwater for 12 weeks. The control diet was the open-formula Atlantic salmon diet MNR-98HS, which contained 0% soybean meal (SBM) and 30% fish meal (FM). Four experimental diets had 30% FM and soybean levels from 5% to 30%. Two additional diets contained a reduced level of FM (24%) and either 20% or 30% SBM. Weight gain (specific growth rate [SGR]), feed conversion ratio (FCR), protein efficiency ratio (PER), condition factor, trypsin activity, body composition, and hepatosomatic index were determined. No differences in SGR (1.88-1.94), FCR (0.78-0.82), PER (2.20-2.32), or trypsin activity were observed between treatments and the control diet. A negative linear response was observed between SBM content and either body lipid or fecal dry matter. Fish whole-body lipids decreased linearly from 22.0% to 12.9% between control and 30% SBM dietary groups. Results suggest that the use of HND diets may contribute to protein-sparing functions of Atlantic salmon by SBM carbohydrates; however, SBM inclusion may induce changes along metabolic pathways into muscle tissue.