Immune responses of L itopenaeus vannamei to non‐ionic ammonia stress: a comparative study on shrimps in freshwater and seawater conditions

To investigate the effect of non‐ionic ammonia ( NH 3 ‐N) stress (0.1 and 0.5 mg L −1 ) on the immunity of L itopenaeus vannamei cultured in long‐term freshwater, the total haemocyte count ( THC ), the activity of phenoloxidase ( PO ), nitric oxide synthase ( NOS ), superoxidase dismutase ( SOD ) and the content of malondialdehyde ( MDA ) were determined and further compared with those of seawater shrimps. The results showed that NH 3 ‐N stress significantly reduced THC and the activity of PO and SOD ( P  < 0.05). Under 0.1 mg L −1 NH 3 ‐N stress, NOS activity increased first and then decreased significantly, while it dropped dramatically under 0.5 mg L −1 NH 3 ‐N stress ( P  < 0.05). During NH 3 ‐N stress, MDA content increased continuously, and the MDA content in hepatopancreas of freshwater shrimps was higher than that of seawater shrimps. It was concluded that NH 3 ‐N stress significantly influenced the non‐specific immunity and could also upset the balance of antioxidant system of L . vannamei in both freshwater and seawater shrimps. Compared with in seawater, the shrimps in freshwater were more vulnerable to NH 3 ‐N stress because of higher lipid peroxidation and lower immunity.