Effects of antioxidant supplementation (nano‑selenium, vitamin C and E) on growth performance, blood biochemistry, immune status and body composition of rainbow trout (Oncorhynchus mykiss) under sub-lethal ammonia exposure

Abstract This study aimed to investigate the protective effect of diets supplemented with different combinations of three antioxidants (nano‑selenium (NanoSe), vitamin C and E) on rainbow trout (Oncorhynchus mykiss) under sub-lethal concentration of ammonia exposure. For this goal, triplicate groups of 25 fish/tank (11.89 ± 0.34 g) were subjected to ammonia stress (0.024 mg/L) and fed with three experimental diets as T1 (0.1 mg/kg NanoSe, 100 mg/kg vitamin C and 30 mg/kg vitamin E), T2 (0.2 mg/kg NanoSe, 200 mg vitamin C and 60 mg/kg vitamin E), T3 (0.3 mg/kg NanoSe, 300 mg/kg vitamin C and 90 mg/kg vitamin E) and a basal diet as control, for 40 days. The obtained results showed that the fish fed with T2 and T3 diets had significantly higher final weight, weight gain, specific growth rate, protein efficiency ratio and lipid efficiency ratio, when compared to T1 and the control group. Also, all the supplemented diet treatments showed lower food conversion ratio, compared to the control group. Furthermore, while serum catalase showed meaningful decrease in T3 treatment only, all T1, T2 and T3 groups had decreased superoxide dismutase activity. Similarly, a significant decrease was observed in serum malondialdehyde in fish fed the supplemented diets. In addition, while serum total protein increased in T1 and then decreased in T2 and T3, triglyceride levels increased in T2 and T3 treatments. Furthermore, total immunoglobulin levels, serum lysozyme and albumin significantly increased in T2 and T3.. In terms of body crude protein, crude lipid, crude fiber, dry matter, ash and carbohydrates, we observed no significant changes. Totally, our results suggest that diets supplemented with NanoSe, vitamin C and vitamin E in T2 could increase growth performance, antioxidant capacity and immune responses in juvenile rainbow trout exposed to ammonia stress.