Integrating immunity, antioxidative status, and gene regulation against nickel and high-temperature stress in fish:...

Fish face health hazards due to high-temperature (T) stress and the toxicity associated with nickel (Ni), both of which can occur in aquatic ecosystems. The accumulation of nickel in fish may pose risks to human health when contaminated fish are consumed. Consequently, the goal of this study was to clarify how selenium nanoparticles (Se-NPs) help Pangasianodon hypophthalmus by reducing the effects of nickel and high-temperature stress. The fish were reared under different experimental conditions as follows: a control group (no exposure to Ni and T, and fed a control diet); a group concurrently exposed to Ni and T while fed a control diet; and groups concurrently exposed to Ni and T while being fed supplemented diets with Se-NPs at 0.5 mg kg^-1 and 1.0 mg kg^-1 for 38 days. The growth performance of fish exposed to nickel and high-temperature (Ni + T) stress was significantly improved by supplementation with selenium nanoparticles (Se-NPs) at 0.5 mg kg^-1. This supplementation also upregulated the expression of growth hormone (GH) and growth hormone receptor (GHR1) genes, while considerably downregulating the myostatin (MYST) gene. Fish subjected to Ni + T stress exhibited markedly elevated cortisol levels, which were notably reduced by Se-NPs at 0.5 mg kg^-1. Moreover, Se-NPs at 0.5 mg kg^-1 significantly downregulated the expression of stress-related genes, including Caspase 3a (Cas 3a), CYP450, iNOS, and HSP70. Fish fed Se-NPs supplemented diet and exposed to Ni + T stress demonstrated enhanced levels of TNFα and total immunoglobulins, indicating an improved immune response. Dietary Se-NPs also led to a significant reduction in oxidative stress markers, such as glutathione-S-transferase, catalase, and superoxide dismutase, in stressed fish. While Ni + T stress reduced acetylcholine esterase activity, dietary Se-NPs restored these activities. Furthermore, the inclusion of Se-NPs in the diet markedly enhanced the detoxification of nickel in various fish tissues. In conclusion, the study demonstrates that dietary supplementation with Se-NPs at 0.5 mg kg^-1 effectively mitigates the adverse effects of Ni + T stress in fish by modulating gene expression, alleviating cellular metabolic stress, and enhancing physiological functions.