Effects of dietary vitamin E and selenium nanoparticles supplementation on acute stress responses in rainbow trout (Oncorhynchus mykiss) previously subjected to chronic stress

The aim of the present study was to evaluate the effects of dietary vitamin E, nanoselenium (nanoSe), and their combination on growth and acute stress responses in rainbow trout previously subjected to chronic stress. The fish were divided into five groups according to stocking density and diet: Normal (20 kg m− 3; basal diet), Dense (80 kg m− 3; basal diet), Vit E (80 kg m− 3; 500 mg kg− 1 vitamin E-supplemented diet), NanoSe (80 kg m− 3; 1 mg kg− 1 nanoSe-supplemented diet), and Combination (80 kg m− 3; 500 mg kg− 1 vitamin E and 1 mg kg− 1 nanoSe-supplemented diet). The fish in each group were weighed after 60 days. The best growth under high density condition was observed in fish fed on vitamin E-supplemented diets (Vit E and Combination groups). Following high stocking rearing, fish were subjected to an acute confinement stress by decreasing water volume in the tanks (200 kg fish m− 3) for 45 min and sampled at 0, 2, 4, 8 and 24 h post-stress to evaluate the fish performance to additional stressors. The levels of serum cortisol, glucose, lactate, alanine aminotransferase, aspartate transaminase, and alkaline phosphatase were significantly higher in the Dense group at most of time points after initiation of acute stress. The results showed that rainbow trout can reach adaptation to chronic stress conditions, resulting in intensified stress responses to an acute stressor. The data also showed that vitamin E-supplemented diets can exert positive effects on the welfare of chronically stressed rainbow trout subjected to an additional acute stressor.