Nutritional evaluation of an aqueous-processed canola protein concentrate in diets of Atlantic Salmon Salmo salar at different life stages

Abstract

A novel aqueous processing method was applied on canola defatted meal to produce a protein concentrate (>76 % crude protein, dry matter basis). This aqueous-processed canola protein concentrate (ACPC) was evaluated in three experiments with Atlantic salmon. The objectives were to (1) estimate the nutrient digestibility of ACPC in juvenile fish, (2) appraise its nutrient digestibility in post-smolt salmon, and (3) evaluate the long-term effect of ACPC on growth, survival, nutrient utilization, body composition, fillet pigmentation and gut histology of post-smolt salmon. In the first study, one Reference and one test diet, which was a blend of 70 % Reference and 30 % ACPC (70:30 ratio), were fed to juvenile salmon (57 ± 7 g) and feces were collected using settling columns. In the second study, post-smolt salmon (228 ± 4 g) were fed one Reference and three test diets, which consisted of three Reference to ACPC ratios: 90:10, 80:20 and 70:30. Feces were collected by manual stripping. The long-term study (168 days) was designed as a 2 × 4 full factorial analysis with two types of formula (Americas, with processed animal proteins (PAPs), and Europe, without PAPs) and four inclusion levels of ACPC (0, 10, 15, 20 %) fed to post-smolt Atlantic salmon (228 ± 5 g). Fish were bulk weighed every 28 or 56 days. Distal intestine and fillet were sampled (10 fish/tank) at the end for histological examination and color measurement, respectively. All diets (43–49 % crude protein, 18–25 % crude lipid depending on studies) were extruded and fed to apparent satiation. The apparent digestibility coefficients (ADCs) of ACPC protein in juvenile and post-smolt salmon were 89 % and ≥ 94 %, respectively. The essential amino acids ADCs in juvenile and post-smolt salmon were 83–99 % and 91–99 %, respectively. ACPC protein digestibility was not significantly affected by its inclusion level (P = 0.470). In the third experiment, growth (TGC: 0.143–0.160) and feed intake (668–780 g/fish) were not significantly affected by ACPC inclusion (P ≥ 0.10). Feed conversion ratios varied between 1.04 and 1.08. An unexpected occurrence of disease caused 1.6 % mortality over three weeks during the 24-week long-term study and survival was significantly higher in salmon fed ACPC-containing diets (P < 0.001). ACPC inclusion significantly increased fillet redness (P < 0.001) and increased villus length of distal intestine (P < 0.001). In conclusion, ACPC was a safe and nutritive protein alternative in salmon diets, regardless of inclusion level.