Immune responses and expression of immune-related genes in swimming crab Portunus trituberculatus exposed to elevated ambient ammonia-N stress

The effects of ammonia-N (0, 1, 5 and 20 mg L− 1) on immune responses and immune-related gene expression were determined in swimming crab Portunus trituberculatus. The results showed that the THC and phagocytic activity of P. trituberculatus exposed to 1, 5 and 20 mg L− 1 ammonia-N decreased significantly during the experimental time. The antibacterial and bacteriolytic activities decreased significantly to the minimum at 6 or 12 h respectively, then recovered to the control level except bacteriolytic activity exposed to 5 and 20 mg L− 1 ammonia-N. α2-macroglobulin (α2-M) activity of all ammonia-N exposure groups decreased significantly, then recovered to the control level rapidly and tended to be stable after 12 h. With crabs exposed to 20 mg L− 1 ammonia-N, the gene expression levels of crustin and lysozyme decreased significantly, then recovered to the control level after 12 h. ALF expression also decreased significantly when exposed to 5 and 20 mg L− 1 ammonia-N, then remained stable and significantly lower than the control group after 6 h. In contrast, α2-M gene expression was induced by ammonia-N exposure significantly. The results suggest that high concentration ammonia-N exposure could reduce the crab immunity severely, and induce the short-term response in terms of immune gene regulation.