Effects of hypoxic stress on liver metabolism, oxidative stress, and immunity in yellow catfish (Pelteobagrus fulvidraco) at different water temperatures
Fish are susceptible to small changes in the aquatic environment, particularly fluctuations in water temperature and dissolved oxygen levels. The culturing process frequently exposes yellow catfish to extreme temperature fluctuations and an insufficient oxygen supply, representing significant challenges to their survival and growth. Therefore, the present study was conducted to investigate the effects of low oxygen stress on liver metabolism, oxidative stress, and immunity of yellow catfish at various water temperatures by simulating actual aquaculture conditions. The results revealed that yellow catfish, under prolonged exposure to low oxygen levels, had increased anaerobic metabolism in the liver tissues compared to the normoxic group. The activities of hexokinase and pyruvate kinase were significantly increased , suggesting that yellow catfish adapted to the low oxygen environment by producing metabolites such as lactate for energy. Glycolytic enzyme activities, hexokinase and phosphofructokinase were altered in the Low and high temperature groups under low oxygen conditions. Enrichment analysis showed that differential genes in the liver of yellow catfish were significantly enriched in the nucleotide metabolism, lipid metabolism, and carbohydrate metabolism pathways, implying that the interactions between temperature and the level of DO may have a significant effect on these pathways. The present study found that the combined stress of water temperature and dissolved oxygen significantly increased the activity of catalase, an antioxidant enzyme, in the liver. Gene ontology enrichment analysis revealed that the differentially expressed genes in the livers of all treatment groups were significantly enriched in redox reaction pathways, suggesting that the oxidative-antioxidative balance of yellow catfish may have been disturbed. Histological results revealed variable degrees of structural damage in both temperature and low oxygen exposed liver tissues. In low oxygen conditions, fluctuations in water temperature significantly increased alkaline phosphatase activity in the liver of yellow catfish. Additionally, differential genes in the ECM receptor interaction and PPAR signaling or immune related pathway were significantly enriched in the liver, suggesting that the combined temperature and dissolved oxygen effect may weaken or alter the immune system. We hope that this study will provide new insights and data support for research on the culture management and environmental adaptation of yellow catfish, thereby promoting the sustainable development of aquaculture.