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Coldwater species are challenged with increasing water temperatures and fluctuations over their upper thermal limits. This study evaluated the potential of acclimation to higher temperature and dietary antioxidants capacity to mitigate the adverse effects of heat shocks in rainbow trout. To this end, rainbow trout fingerlings were acclimated at optimal (14 °C) and high (20 °C) temperatures and fed on selenium (5 mg/kg) and polyphenol (2 g/kg) supplemented diets for 60 days and then were exposed to heat shocks by increasing water temperature up to 30 °C. Growth performance, survival rate, haemato-immunological parameters, and expression of HSP70α, HSP70β, HSP90β, and IL-1β genes were measured to evaluate the hypothesises. The rainbow trout acclimated to 20 °C and fed on antioxidants supplemented diets showed a significantly higher aftershock survival rate. Moreover, fish acclimated to higher temperature showed higher red blood cell counts as well as serum total protein and albumin during the acclimation trial and heat shocks phase. Acclimation to higher temperature and feeding on antioxidants remarkably enhanced fish immune and antioxidant capacity in comparison to fish adapted to cold water and fed on the basal diet measured by improved respiratory burst and lysozyme activities and upregulation of IL-1β expression during exposure of fish to heat shocks. Furthermore, fish acclimated to higher temperature, especially those fed on antioxidant supplemented diets, showed lower expression levels of HSPs genes during the heat shock phase, indicating that high heat shocks were less stressful for these fish in comparison to cold water acclimated fish. This finding was also supported by lower cortisol levels during heat shocks in fish acclimated to higher temperature. In conclusion, the results of this study indicated that acclimation to higher temperature and/or fed on diets supplemented by selenium and polyphenol, can help to mitigate the adverse effects of the heat shock in rainbow trout. [ABSTRACT FROM AUTHOR]

The long-term effects of three dietary probiotics on rainbow trout during grow-out (mean body weight = 250 ± 50 g) were investigated by feeding for 130 days on eight diet treatments supplemented with Lactobacillus buchneri , L. fermentum and Saccharomyces cerevisiae at 107 CFU/g, singularly or in combination. Fish samples were taken for biochemical and immunological analysis in addition to growth performance indices at days 30 and 130 of the experiment. The expression levels of TNF-α and IL-1β genes were also measured at day 130. A positive effect on food conversion was observed in rainbow trout with dietary inclusion of S. cerevisiae (P < 0.05) over 130 days. Also, the total number of white blood cells and their differential count (blood neutrophils, lymphocytes and monocytes), as well as respiratory burst activity were all significantly affected by different treatments at 130 days (P < 0.05). Moreover, at 130 days there was a significant increase in the expression of TNF-α and IL-1β in yeast present treatment compared to the control group (P < 0.05), but no significant difference in the combined probiotic treatments from control group. Yeast and L. buchneri showed a contrary effect on the immune gene expression regulation. Serum cholesterol was significantly lower in all treatments receiving yeast as a dietary probiotic, either alone or in combination with other probiotics. However, none of the probiotic treatments had a significant effect on trout growth performance, or total protein, albumin, globulin, triglyceride and the red blood cell count after 30 or 130 days. Overall, the results suggest that inclusion of a single dietary probiotic, especially S. cerevisiae, in rainbow trout during grow-out has a greater positive effect than combinations of probiotics on the immune system. • Singular and combined treatments of bacterial and fungal probiotics were evaluated in rainbow trout. • Saccharomyces cerevisiae singularly was more effective in growth and immunological responses in 130 days. • The expression levels of TNF-α and IL-1β genes were significantly increased in fish received singular treatment of S. cerevisiae. [ABSTRACT FROM AUTHOR]