Effects of α‐ketoglutarate on growth performance, antioxidant capacity and ammonia metabolization against chronic carbonate alkalinity stress in Songpu mirror carp (Cyprinus carpio Songpu)

A 3 × 2 factorial experiment was conducted to investigate the interaction between carbonate alkalinity and dietary α‐ketoglutarate (AKG) levels on the growth performance, antioxidant capacity and ammonia metabolization of Songpu mirror carp (Cyprinus carpio Songpu). Each diet (0%, 1% AKG) was randomly allotted to 0 mmol/L, 15 mmol/L, 30 mmol/L carbonate alkalinity groups with three replicate aquaria. The weight gain rate (WGR) significantly increased in the 1% AKG group and significantly decreased with increasing carbonate alkalinity (p < .05). Crude ash was significantly affected by the interaction between carbonate alkalinity and dietary AKG levels and significantly increased in the 1% AKG group (p < .05). A significant interaction between carbonate alkalinity and dietary AKG levels on superoxide dismutase (SOD) activities in hepatopancreas was observed (p < .05). The increasing carbonate alkalinities significantly decreased SOD activities in the hepatopancreas and foregut, catalase (CAT) activities in the hepatopancreas, foregut, midgut and hindgut and glutathione (GSH) contents in the hepatopancreas and foregut (p < .05). Despite AKG addition, the blood ammonia content still increased with increasing carbonate alkalinities. The gene expressions of AQP3, Rhag, Rhcg2 and Na⁺/K⁺‐ATPase (NKA) in the gills and glutamine synthase (GS) in the brain were significantly upregulated with increasing carbonate alkalinities (p < .05). In the 1% AKG group, GS gene expression significantly upregulated in the brains, whereas AQP3, Rhag, Rhcg2 and NKA gene expressions significantly downregulated in the gills (p < .05). In summary, the 1% AKG addition can enhance the gene expression of ammonia metabolization and improve the antioxidant capacity of Songpu mirror carp with chronic carbonate alkalinity stress.