The nutritional value of graded inclusion levels of canola protein concentrate (CPC; 75.8% crude protein, 4.4% crude lipid) obtained through aqueous processing was assessed in post-smolt Atlantic salmon over a 168-day growth study and a 34-day digestibility study. In the growth study, eight experimental diets containing 0 (Diets A, E), 10% (Diets B, F), 15% (Diets C, G) and 20% (Diets D, H) CPC were randomly allocated to 24 750-liter tanks at 33 fish (228.0 ± 4.9 g) per tank. Diets A through D were formulated to mimic commercial salmon feeds in geographies where processed animal proteins (PAP) are used (Americas), whereas diets E through H included no PAP (Europe). In the digestibility study, salmon (57.3 ± 6.7g) were randomly assigned to 12 100-liter tanks (21 fish/tank) and were hand-fed for 34 days on four digestibility diets containing 0% CPC (reference diet), 70:30, 80:20 and 90:10 blend of reference diet to test ingredient to determine nutrient digestibility.
Overall, growth performances, measured using the thermal-unit growth coefficient (TGC), varied between 0.143 and 0.160, and were not significantly different among treatments (P>0.05) (Table 1). Feed conversion ratios (FCR) were ≤1.08, and although there was a significant CPC effect (P=0.003), differences were marginal. Over the 168-day study, the best TGC and FCR were obtained with salmon fed 10% CPC, regardless of formula type. However, 20% CPC was optimal for growth and FCR during the first 28 days of this salmon study. Weight gain, TGC and FCR between days 0 and 28 improved in a linear manner (P<0.01) in response to 10-20% CPC. There were no significant differences (P>0.05) in the final whole-body composition or nutrient retention among treatments. Increasing dietary inclusion of CPC from 0-20% demonstrated a positive relationship with intestinal villi length (P=0.0314) and improved histological morphology (e.g., lamina propria). The apparent digestibility coefficients were 91.1% for protein, 88.8% for lipid and 79.6-98.6% or essential amino acids in CPC. Based on these results, CPC stood as a safe and nutritious protein alternative up to 20% inclusion in salmon diet. The effect of higher inclusion level of CPC in nutrient-balanced diets deserve further studies.