Alpha‐Lipoic Acid Restored Antioxidant Capacity of Megalobrama amblycephala Inhibited by Ammonia

ABSTRACT This study assessed recovery of alpha‐lipoic acid (α‐LA) on antioxidant capacity of blunt snout bream ( Megalobrama amblycephala ) juveniles after ammonia stress. Around 270 healthy juveniles (13.7 ± 1.6 g) were separated into three groups and exposed to ammonium chloride solutions at 0 (G1), 5.45 (G2), and 10.89 mg/L (G3). Ammonia stress lasted for 72 h, then all fish were transferred to aerated tap water for the recovery experiment. Each group was further divided into three subgroups, which were fed with three diets with 0, 0.6, and 1.2 g/kg α‐LA, respectively. The recovery experiment also lasted for 72 h. Gill and liver were collected after ammonia stress and recovery for the enzyme activities, histology, gene expression and correlation analysis. The results showed that total antioxidant capacity (T‐AOC), superoxide dismutase (SOD), and catalase (CAT) activities of liver and gill in G2 and G3 were significantly lower than G1 ( p < 0.05) after 72 h of ammonia exposure; MDA contents in G2 and G3 were significantly higher than G1 ( p < 0.05). Ammonium stress led to deterioration of cell nucleus and endoplasmic reticulum degradation. However, T‐AOC, SOD and CAT activities of liver and gill were significantly higher than the control group at the 72nd hour after recovery with α‐LA. MDA content was significantly lower than the control group ( p < 0.05). Furthermore, SOD, CAT, T‐AOC and glutathione peroxidase (GPX) activities in liver and gill were positively correlated with dietary α‐LA levels. Overall, dietary α‐LA supplement restored antioxidant ability of fish after ammonia stress.