Enhanced resilience of marine fish to extreme environments by nano-ZnO exposure

Abstract

Marine hydrosphere is in grave danger if extreme weather conditions, such as high temperatures and heat waves, become the norm. The functional characteristics of nano Zn oxides (nZnO) might provide a “booster substance” that helps marine species to endure environmental stress. In the present study, physiological indicators and simulated severe environments were used to evaluate the antioxidative ability of nZnO in marine rabbitfish Siganus fuscescens, with an aim to help them resist extreme environmental stress. Rabbitfish were exposed to different diets with ZnSO₄ and nZnO at the optimum requirement level (Zn content of 62.5 μg g⁻¹), and then challenged with a low dissolved oxygen concentration and higher temperature. We demonstrated that dietary nZnO promoted the anti-oxidation defense system of the rabbitfish by improving the activities of the antioxidant enzymes, i.e., catalase (CAT), superoxide dismutase (SOD), and the reduced glutathione/oxidized glutathione (GSH/GSSG) ratio without tissue damage. Compound stressors reduced the median survival duration of the rabbitfish from 4.25 h to 2.5 h (dietary exposure) and 9 h to 5.75 h (dietary nZnO exposure) compared to single environmental stress. nZnO downregulated the HIF gene expression and increased the prolyl hydroxylase (PHD) activity in the liver of the rabbitfish. After 10 h of extreme environmental exposure, the gene expression results indicated that nZnO inhibited the NF-κB/IL-1β/IL-6 pathway and TNF-α/Bcl-2/Bax/caspase 9 pathway and activated the akt/mTOR/elovl5 and elovl8 pathway of the rabbitfish to maintain the resilience of the fish under the extreme environment. These results strongly suggested that nZnO may improve the anti-oxidation ability of fish to resist extreme environments.