Evaluation of the acute toxic effects of ammonia on juvenile ussuri cisco (Coregonus ussuriensis) based on histopathology, antioxidant enzyme activity, immune response and the integrated biomarker response.

Aquaculture intensification system is challenged by high ammonia concentrations, which can affect fish physiology. In the present study, we assessed the effects of ammonia on ussuri cisco based on histopathology, antioxidant enzyme activity, immune response, and integrated biomarker responses. After exposure to 60.0 mg/L ammonia, liver vacuolization, bruising, nucleolysis, cell swelling, cell rupture, and structural irregularities were observed. It was found that the degree of liver damage increased with the duration of stress and was most severe at 72 h. During ammonia stress, the serum levels of SOD, CAT, MDA and T-AOC in the treatment groups showed a tendency to increase and then decrease. In addition, the serum activities of GOT, GPT and AKP were significantly higher in the treatment group than in the control group after ammonia exposure. We also evaluated the immune regulatory mechanisms of the NF-κB pathway and showed that immune-related genes (TNF-α, TAK1, NFKBIA, IKBKB, P50, P65, IL-8, IL-1β and A20) were differentially elevated during the exposure period, especially TNF-α, IL-8, IL-1β and A20 which were all highly expressed. CAT, GPT, AKP and SOD were identified as representative markers of biotoxic effects. This will help to more accurately estimate the ecological risk of environmental ammonia to fish populations.