Effects of Dietary Riboflavin Supplementation on the Growth Performance, Body Composition and Anti-Oxidative Capacity of Coho Salmon (Oncorhynchus kisutch) Post-Smolts

SIMPLE SUMMARY: In China, with the improvement of living standards, consumer demand for coho salmon is growing rapidly. As the only source of flavin nucleotides, exogenous riboflavin is an indispensable nutrient to promote the growth of fish and regulate physiological functions. Therefore, it is particularly relevant to full understanding of the dietary riboflavin requirements of coho salmon. The physiological function of riboflavin is mainly as coenzyme FMN and FAD and covalently bound flavin precursor, involved in the body’s macromolecular metabolism and redox reaction. However, there is incognizance of riboflavin requirements in this fish species. In this study, seven isoenergetic experimental diets containing different riboflavin levels were formulated to study the changes in growth performance, body composition and antioxidant capacity of coho salmon. The results showed that different dietary riboflavin levels affected the growth performance, body composition and antioxidant capacity of coho salmon post-smolts. The optimum riboflavin requirement was determined according to the specific growth rate (SGR). ABSTRACT: The present study investigated the effects of dietary riboflavin on growth performance, body composition and anti-oxidative capacity of coho salmon (Oncorhynchus kisutch) post-smolts. Seven experimental diets were formulated with graded riboflavin levels of 0.00, 3.96, 8.07, 16.11, 31.81, 63.67 and 126.69 mg/kg, respectively. Each diet was fed to triplicate groups of 10 fish with an individually initial mean body weight of 186.22 ± 0.41 g in 21 cages (water volume, 1000-L/cage) and fed three times daily (7:30, 12:30 and 17:30) to apparent satiation for 12 weeks. Fish fed a diet with 31.81 mg/kg riboflavin had the highest specific growth rate (SGR), which was significantly higher than fish-fed diets with 0.00, 3.96, 8.07 and 126.69 mg/kg riboflavin (p < 0.05). Feed conversion ratio showed an inverse trend with SGR. No significant differences were observed in condition factor, hepatosomatic index, viscerosomatic index, muscle moisture, crude protein and ash contents among dietary groups. Muscle lipid had the highest content in the 31.81 mg/kg group and was significantly higher (p < 0.05) than those in the 0.00, 3.96 and 8.07 mg/kg groups. The alanine aminotransferase, aspartate aminotransferase and malondialdehyde contents in the liver and serum of fish were significantly decreased with the increase in dietary riboflavin level up to 31.81 mg/kg, and then increased as dietary riboflavin level further increased. An inverse trend was observed for total superoxide dismutase and catalase activities. Serum total cholesterol and triglyceride levels were significantly decreased with the dietary of riboflavin levels up to 31.81 and 63.67 mg/kg, respectively. The cubic curve regression analysis based on SGR indicated that the optimum dietary riboflavin level was estimated to be 35.26 mg/kg for coho salmon post-smolts.