α-Ketoglutarate restores redox and energy homeostasis to ameliorate splenic immune dysfunction induced by carbonate-alkaline stress in crucian carp (Carassius auratus)

The global expansion of carbonate-alkaline water bodies poses a major challenge to sustainable aquaculture, but the metabolic basis of splenic immune dysfunction in fish under carbonate-alkaline stress remains unclear. Here, crucian carp ( Carassius auratus ) were exposed to carbonate-alkaline stress (20 and 40 mmol/L NaHCO 3 ) and exogenous α-ketoglutarate (AKG) supplementation for 30 days. Histopathological examination, ultrastructural observation, biochemical assays, and metabolomic analyses were employed to investigate the mechanisms of splenic immune dysfunction and AKG's regulatory effects. The results indicated that carbonate-alkaline stress induced oxidative stress, characterized by increased reactive oxygen species (ROS) concentrations and decreased glutathione (GSH)-dependent antioxidant capacity, accompanied by histopathological damage. Additionally, ATP concentrations significantly decreased, with concurrent mitochondrial structural abnormalities. Metabolomics analysis revealed that carbonate-alkaline stress caused a series of metabolic disorders, including those associated with the glycolysis pathway, GSH metabolism, and purine metabolism. Notably, exogenous AKG supplementation alleviated this damage. AKG regulated redox homeostasis by decreasing ROS concentrations and increasing GSH-dependent antioxidant capacity. Meanwhile, acting as an intermediate of the tricarboxylic acid (TCA) cycle, AKG restored energy supply, characterized by increased ATP concentrations. In conclusion, this study elucidates the underlying metabolic mechanisms of splenic immune dysfunction in crucian carp under carbonate-alkaline stress and demonstrates that AKG alleviates impaired splenic immune function by modulating redox balance and energy metabolic homeostasis. These findings provide novel insights into modulating immune dysfunction in fish exposed to carbonate-alkaline environments through metabolic interventions.