Restricted-protein feeding strategy decreased the protein consumption without impairing growth performance, flesh quality and non-specific immune parameters in rainbow trout (Oncorhynchus mykiss)

Protein restriction is a less-studied nutritional strategy in aquaculture species. The present study was designed to investigate the effects of protein restriction for different durations on the growth performance, body composition, the profile of fatty acids and amino acids, and the immune response of rainbow trout for eight weeks. For this purpose, 225 juveniles (27.74 ± 0.43) were distributed in five experimental treatments include P45 (control: feeding a diet with 450 g/kg protein for eight weeks); P35 (feeding a diet with 350 g/kg protein for eight weeks); P35-P45 (every other day feeding a diet with 450 and 350 g/kg protein); WP35-P45 (every other week feeding a diet with 450 and 350 g/kg protein); and 3WP35 (feeding a diet with 350 g/kg protein for three weeks and then, a diet with 450 g/kg protein for five weeks). Rainbow trout fed dietary P35 had a lower value of weight gain (94.73 g) and specific growth rate (2.53) when compared to the other groups (P < 0.05). The lipid and protein contents of fish fed P35 (291.3, 619.2 g/kg) and P35-P45 (288.4, 621.2 g/kg) diets were significantly higher and lower as compared to other treatments (P < 0.05), respectively. There was no significant difference in fatty acids and total nonessential amino acids among these groups. Also, feeding fish with P35 (362.4 g/kg) decreased total essential amino acids as compared to those that were fed with other diets (P < 0.05). Regarding the immune response parameters, the WP35-P45 group had the highest performance. In conclusion, we suggest WP35-P45 to feed fish in rainbow trout aquaculture by considering all the investigated factors.