Growth, plasma biochemistry and immune-related gene expression of European sea bass (Dicentrarchus labrax) fed bioactive peptides from farmed salmon by-products

The effect of bioactive peptides (BPs) derived from farmed Atlantic salmon (Salmo salar) by-products on growth, blood biochemistry and immune response was tested in European sea bass (Dicentrarchus labrax). Three diets with different levels of BPs (0% BP0, 5% BP5, 10% BP10) in substitution for fish meal (FM) were administered to triplicate fish groups over 58 days. At the end of the trial, fish were subjected to suboptimal environmental conditions (high water temperature, low oxygen) for 7 days. No significant differences (p > 0.05) were observed in final body weight, specific growth rate, feed intake, and feed conversion while lipid efficiency was higher (p < 0.05) in BP10. At the end of the growth trial, plasma profile remarked previous studies on this species; however cholesterol was higher in BP5 while glucose decreased with increasing BP content. In addition, a reduction in plasma total protein, cholesterol, high-density lipoprotein and triglycerides after environmental stressful con- ditions was observed only in BP5 supporting a better lipid utilization for energy purposes as a strategy to counteract high energy demand periods. The immune gene analysis showed in BP5 a reduction of the pro- inflammatory interleukin 1β (IL-1β), IL-8, and a significant increase in the expression of the anti-inflammatory interleukin-10; on the contrary, BP10 led to an increase in the expression of IL-1β, and IL-8. In conclusion, data suggest that BPs from salmon by-products have a promising implication as circular and functional in- gredients for European sea bass diets. In addition to being a valid alternative ingredient to fishmeal in terms of acceptability and growth, it could enhance physiological mechanisms related to lipid metabolism and immune response.