Effects of dietary protein and energy levels on the growth, protein utilization and body composition of juvenile masu salmon (Oncorhynchus masouBrevoort)

Abstract

A feeding trial of three dietary protein levels (30, 40 and 50%) and two dietary energy levels (19 and 21 MJ kg−1 diet) factorial design with three replications was conducted to investigate the proper dietary protein and energy levels for the growth of juvenile masu salmon (Oncorhynchus masou Brevoort). Fish, average weight 21.9 g, were fed the experimental diets for 10 weeks. Weight gain and feed efficiency ratio of fish improved as dietary protein and energy levels increased (P < 0.05), whereas there was no significant difference between those of fish fed the diets containing 40 and 50% protein at the same dietary energy level. Weight gain of fish fed the high-energy diets was significantly higher than those of fish fed the low-energy diets at 40 and 50% dietary protein levels. Protein efficiency ratio and protein retention of fish were not affected by dietary protein levels at the same energy level, whereas these values of fish fed the high-energy diets were significantly or slightly higher than those of fish fed the low-energy diets at each dietary protein level. Moisture content of fish fed the high-energy diets was significantly lower than those of fish fed the low-energy diets at all protein levels (P < 0.05). On the other hand, lipid content of fish fed the high-energy diets was significantly higher than those of fish fed the low-energy diets (P < 0.05). Protein and ash contents of fish were not affected by dietary protein and energy levels. Linoleic acid of fish fed the high-energy diets supplemented with soybean oil and squid liver oil was higher than that of fish fed the low-energy diets supplemented by squid liver oil (P < 0.05), whereas eicosapentaenoic acid and docosapentaenoic acid of fish fed the high-energy diets showed a tendency towards lower values than those of fish fed the low-energy diets at all protein levels. The results of this study indicate that a diet containing 40% protein and 21 MJ kg−1 diet should be optimal for the growth and effective protein utilization of juvenile masu salmon.