Long-term protein and lipid growth of Atlantic salmon (Salmo salar) fed diets with partial replacement of fish meal by soy protein products at medium or high lipid level

This study investigated long-term effects on nutrient digestibility and protein and lipid growth of soy protein and lipid levels used in commercial grower diets for Atlantic salmon. Two series of extruded diets were formulated to contain either 45% protein and 32% lipid (medium fat) or 40% protein and 39% lipid (high fat). Each series consisted of six diets in which a soy protein source partially replaced low-temperature (LT) dried fish meal (FM): FM only (control), soy protein concentrate (SPC, 30% of crude protein, CP); SPC added (0.2% DL-methionine (30% of CP, SPC + met); dehulled, defatted soybean meal (HP-SBR I, 20% of CP); full-fat (FF) SBM (10% of CP), and; defatted SBM (10% of CP). Each diet was fed to triplicate groups of 0.56-kg salmon kept in sea pens. The experiment lasted 235 days, during which the salmon reached 2.5 to 2.8 kg. Growth was slower in the FM-control and HP-SBM treatments than in the other treatments. The HP-SBM diet induced enteritis in the distal intestine of the salmon and, at day 215, the apparent digestibilities of nitrogen, lipid and energy were lower in the HP-SBM treatments than in all other treatments. Except a slightly reduced muscle protein concentration in the HP-SBM treatment, no effects of dietary soy were detected on final body composition. Salmon fed the high-fat diets reached on average 122 g higher final weight than those fed the medium-fat diets; however, 91 g of this was in the form of lipid, and corresponded with enlarged deposits of visible fat, (C) 2001 Elsevier Science B.V. All rights reserved.