The effects of acute ammonia stress on liver antioxidant, immune and metabolic responses of juvenile yellowfin tuna (Thunnus albacares)

The impact of acute ammonia nitrogen (NH₃−N) stress on the antioxidant, immune, and metabolic capabilities of the liver in juvenile yellowfin tuna (Thunnus albacares) is not yet fully understood. This study set NH₃-N concentrations at 0 (natural seawater, control group), 5, and 10 mg/L, and sampled the liver at 6, 24, and 36 h for analysis. As time progresses, NH₃-N exposure leads to an increase in malondialdehyde (MDA) concentrations. The activity of superoxide dismutase (SOD) and the relative expression levels of related genes, as well as the activity of immune enzymes and ATPase, decrease. The levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and interleukin-10 (IL-10) exhibit different fluctuation patterns. Low concentrations of NH₃-N increase the activity of catalase (CAT) and glutathione peroxidase (GHS-PX) and the relative expression levels of the Na⁺K⁺-ATPase gene. The relative expression levels of the interleukin-6 receptor (IL-6r) gene show a decreasing trend. High concentrations of NH₃-N decrease the activity of CAT, GSH-PX, and the relative expression levels of related genes. When the NH₃-N concentration is below 5 mg/L, the stress duration should not exceed 36 h. When the NH₃-N concentration is between 5 and 10 mg/L, the stress duration should not exceed 24 h, otherwise, it will have a negative impact on the liver of the juvenile yellowfin tuna. This study provides scientific data for the artificial breeding and recirculating aquaculture of juvenile yellowfin tuna.