Background: Probiotics are widely used in aquaculture. They can typically improve the growth, immunity, and antioxidant system of fish. However, they can be used to increase fillet shelf life. Objectives: The present study investigated the effects of dietary supplementation with a commercial probiotic (Bio-Aqua) on growth performance, muscle composition, and shelf life in refrigerated condition. Methods: Four diets were prepared containing ۰ (control=CTR), ۰.۳ (۰.۳B), ۱ (۱B), and ۲ (۲B) g/kg of the probiotics. Three groups of fish were fed the diets over ۱۲ weeks, and their dorsal muscle chemical composition and antioxidant enzymes were determined. Fillet quality was determined after ۰, ۴, ۸, ۱۲ and ۱۶ days of refrigerated condition. Results: At the end of the rearing period, there was no significant difference in the growth performance of the fish among the treatment groups. However, the ۰.۳B group exhibited significantly higher muscle protein content and superoxide dismutase activity. Also, muscle catalase and glutathione peroxidase activities increased dramatically in the ۰.۳B and ۱B treatment groups. Fillet thiobarbituric reactive substances (TBARS), total volatile base nitrogen, total bacterial count, and psychrotrophic bacterial count exhibited elevation over time during refrigerated condition. Dietary probiotics significantly affected the fillet concentration of TBARS, as ۰.۳B and ۱B showed lower TBARS than the CTR and ۲B treatment groups. Total bacterial count in probiotic treatments (particularly ۰.۳B and ۱B) was significantly lower than CRT after ۸ and ۱۶ days in the refrigerator. There were no interaction effects of dietary probiotics and refrigerated condition time on the fillet total volatile base nitrogen and psychrotrophic bacterial count.Conclusion: Based on the results, dietary ۰.۳ or ۱ g/kg of Bio-Aqua can improve antioxidant capacity and decrease lipid peroxidation in rainbow trout fillets.
