Asian Journal of Fisheries and Aquatic Research

Zinc (Zn) is an essential trace element involved in physiological regulation and immune function in aquatic animals. This study evaluated the effect of ambient Zn exposure on selected haemolymph immune parameters of Penaeus monodon and its subsequent susceptibility to white spot syndrome virus (WSSV). Adult shrimp were acclimatised and then exposed for 14 days to nominal Zn concentrations of 0.5, 1.0, 1.5 and 2.5 mg/L, while unexposed groups served as controls. After the exposure period, shrimp from the relevant groups were orally challenged with WSSV-infected tissue, and immune responses were assessed on day 14 of Zn exposure and on days 2 and 5 after viral challenge. Total haemocyte count, phenoloxidase activity, nitroblue tetrazolium reduction, acid phosphatase activity and alkaline phosphatase activity were analysed, together with survival. Zinc exposure produced concentration-dependent responses. The 1.0 mg/L treatment showed the most consistent immunostimulatory effect, including elevated haemocyte count and phenoloxidase activity, and was associated with improved survival after WSSV challenge. In contrast, higher Zn concentrations, particularly 1.5 and 2.5 mg/L, were associated with reduced post-challenge immune responses and lower survival. These findings indicate that ambient Zn can modulate haemolymph immune responses in P. monodon, but the response is dose dependent and excessive exposure may impair immunocompetence under viral stress.