Effect of high water temperature on mortality, immune response and viral replication of WSSV-infected Marsupenaeus japonicus juveniles and adults

This study evaluated the effect of high water temperature on juvenile mortality and adult immune response and viral replication of white spot syndrome virus (WSSV) infected Kuruma shrimp Marsupenaeus japonicus under standardized conditions. Two methods, oral administration for juveniles and intramuscular injection for adults, were used to infect M. japonicus at two water temperature levels (27 ± 0.5 and 31 ± 0.5 °C). Mortality of WSSV-infected juveniles was largely reduced at 31 °C compared to 27 °C. The total haemocyte count (THC) and phenoloxidase (PO) activity of M. japonicus adults in control treatment (WSSV-free) had no significant difference at 27 and 31 °C (p > 0.05). The THC and PO activity of WSSV high temperature treatment were significantly higher (p < 0.05) than those of WSSV ambient treatment over 24–72 h and 12–72 h post injection, respectively. Real time PCR showed that viral load of WSSV ambient treatment was significantly higher (p < 0.05) than that of WSSV high temperature treatment over 24–72 h post infection. This study confirmed that high water temperature prevented the onset of disease and significantly reduced mortality of WSSV-infected shrimp, and demonstrated that high water temperature inhibited the replication of WSSV instead of increasing the activity of the host immune response. These results provide practical applications to control WSSV in shrimp farming.