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 sublethal 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 T-1 (0.1 mg/kg NanoSe, 100 mg/kg vitamin C and 30 mg/kg vitamin E), T-2 (0.2 mg/kg NanoSe, 200 mg vitamin C and 60 mg/kg vitamin E), T-3 (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 T-2 and T-3 diets had significantly higher final weight, weight gain, specific growth rate, protein efficiency ratio and lipid efficiency ratio, when compared to T-1 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 T-3 treatment only, all T-1, T-2 and T-3 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 T-1 and then decreased in T-2 and T-3, triglyceride levels increased in T-2 and T 3 treatments. Furthermore, total immunoglobulin levels, serum lysozyme and albumin significantly increased in T-2 and T-3. 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 T-2 could increase growth performance, antioxidant capacity and immune responses in juvenile rainbow trout exposed to ammonia stress.
