Effects of nano-selenium on the histopathological changes and gene expression of rainbow trout (Oncorhynchus mykiss) spleen under heat stress.

Rainbow trout(Oncorhynchus mykiss) is a typical cold-water fish often threatened by high summer temperatures. Nano-selenium as a feed additive can improve the antioxidant capacity of the body and relieve stress. In this study, different levels of nano-selenium (0, 5 and 10 mg/kg) were added to the feed of rainbow trout to determine the changes in spleen structure and expression of related genes in rainbow trout at the proper temperature (18℃) and heat stress temperature (24℃). The results showed that the addition of 5 mg/kg nano-selenium had a more obvious protective effect on rainbow trout spleen. The addition of nano-selenium improved the antioxidant capacity and immunity of rainbow trout spleen at 18 °C. After heat stress, the addition of 5 mg/kg of nano-selenium significantly increased the expression levels of spleen heat shock protein genes, such as HSP10, HSP47, HSP70, HSP90, antioxidant-related genes, such as glutathione peroxidase (GPx), thioredoxin reductase (Trx), superoxide dismutase (SOD1), catalase (CAT) and immune-related genes, such as tumor necrosis factor-α (TNF-α), Interleukin-1β (IL-1β), Immunoglobulin M (IgM), Complement Component 3 (C3), resulting in the improvement of antioxidant capacity and immunity, and the protection of the spleen to alleviate the damages caused by heat stress. This study provides a theoretical basis for the development of anti-heat stress feeds for rainbow trout.