Effects of total ammonia, temperature and salinity on the mortality and viral replication of WSSV-infected Chinese shrimp (Fenneropenaeus chinensis)

Abstract

In this study, we evaluated the effects of three factors, total ammonia, temperature and salinity, on the mortality of and viral proliferation in white spot syndrome virus (WSSV)-infected Chinese shrimp. Shrimp maintained in 30‰ seawater at 25°C with 0.34 mg L−1 total ammonia (control group) were injected with approximately 20 WSSV particles per shrimp and subsequently subjected to the following conditions: 30‰ seawater at 25°C, with 6 mg L−1 (N1 group) or 14 mg L−1 (N2 group) total ammonia; 30‰ seawater at 18°C (T1 group) or 30°C (T2 group), with 0.34 mg L−1 total ammonia and 20‰ (S1 group) or 40‰ (S2 group) seawater at 25°C, with 0.34 mg L−1 total ammonia. An anova analysis revealed that the cumulative mortality of WSSV-infected Chinese shrimp was significantly lower when reared in the T1 group compared to that of the T2 and control group. Similarly, the mortality of the shrimp in the S1 group was also significantly lower than that of the S2 and control group. No significant differences were detected among the N1, N2 and control groups. Accordingly, the WSSV level in the T1 and S1 groups was significantly lower than those in the control, T2 or S2 groups respectively. No significant differences in viral loads were detected among the control, N1 and N2 groups. The transfer of Chinese shrimp to lower temperature and lower salinity enhanced their resistance to WSSV infection, whereas a change in the concentration of total ammonia had no significant effect on the mortalities and viral loads of WSSV-infected shrimp.