Effects of ammonia stress on liver microstructure, antioxidant capability and inflammation‐related genes and post‐exposure recovery in the hybrid sturgeon ( Acipenser baerii ♀ × Acipenser schrencki ♂)

Ammonia is an important water quality factor, which causes several adverse effects in fish. In this study, the 5-month-old hybrid sturgeon (Acipenser baerii ♀ × Acipenser schrencki ♂) with a mean body weight of 50 ± 0.5 g was subjected to ammonia stress (0 mg/L, control group; 10 mg/L, low-concentration group; 50 mg/L, high-concentration group) for 48 h and followed by recovery for 48 h, changes of liver tissue, antioxidant enzyme activity and relative expressions of inflammation-related genes were observed. The results showed that, with an increasing ammonia concentration and exposure duration, hepatocytes showed swelling, congestion and indistinguishable cellular outline. After 48 h of recovery, the degree of swelling decreased, nuclear shifted, and vacuolation reduced; however, the normal levels before stress application were not reached again. Additionally, compared with the control group, the activities of superoxide dismutase, catalase and glutathione peroxidase were significantly upregulated 6 h after stress. Malondialdehyde reached the maximum at 24 h in the low-concentration group and at 12 h in the high-concentration group, indicating the activity of the antioxidant system trying to protect cells from oxidative stress. Furthermore, the relative expression levels of interleukin 1 beta, tumour necrosis factor α genes and heat shock proteins (both HSP70 and HSP90β) in the liver were induced by ammonia stress. These results provide direct evidence for the damage caused by ammonia stress and the self-recovery ability of the hybrid sturgeon.