| Summary: | Apparent digestibility coefficients (ADCs) of macronutrients and energy, and apparent absorption coefficients (AACs) of amino acids and elements were assessed in an experiment with 0.9 kg Atlantic salmon reared in saltwater tanks. Duplicate groups of fish were fed five diets, where 0, 6.25, 12.5, 25 and 50% of crude protein (CP) from fish meal (FM) was replaced with CP from wheat gluten (WG). In Experiment 2, triplicate groups of 0.9 kg salmon were fed a FM diet, a diet with 15% of CP from FM replaced with extracted, toasted soybean meal (SBM), and a diet with 35% of CP from WG, for 18 weeks. Experiment 2 was designed to determine whether WG caused pathological changes in the intestinal epithelium, and if a diet with 35% of CP from WG could support rapid growth. There was a trend toward increased ADC of fat and energy in the diets with WG, and the diet with 25% WG was ranked significantly higher than the FM control. The ADC of CP and AACs of all amino acids except alanine and lysine increased significantly with increasing proportion of dietary protein from WG, and the results indicate that absorption of individual amino acids from WG was between 94% and 100%, WG is low in lysine, but the results indicate that the requirement for lysine was nearly met and the requirement for other essential amino acids was met even with the highest WG inclusion level, due to high dietary protein concentration and the supplementary amino acid profile of FM. There was no reduced absorption of Ca, P or Mg in the salmon fed diets with WG. The absorption of Zn was higher in all the diets with WG than in the FM diet. The fish doubled their weight during Experiment 2, and there were no significant differences in growth among dietary treatments in salmon fed the WG, FM or SBM diets. No indication of intestinal pathology was seen in the salmon fed the FM or WG diets, while 60% of the examined fish fed SBM had SBM-induced changes in the mucosa of the posterior intestine.
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