Quantitative analysis of temperature, salinity and pH on WSSV proliferation in Chinese shrimp Fenneropenaeus chinensis by real-time PCR

White spot syndrome virus (WSSV) is the most serious disease threatening the shrimp farming. Previous studies have elucidated the relationships between WSSV outbreak and environmental factors such as temperature, salinity and pH. But, these studies didn't expatiate the relationships between the copy numbers of WSSV replication and the changes of environmental factors, even educed some contrary conclusions. Here, by the methods of Taguchi and real time PCR, the impact of three factors, temperature, salinity and pH on the proliferation of WSSV was studied together. The five levels selected for three factors were 15 °C, 20 °C, 25 °C, 30 °C and 35 °C for temperature, 15‰, 20‰, 25‰, 30‰ and 35‰ for salinity and 6.5, 7.5, 8.0, 8.5 and 9.0 for pH. ANOVA analysis showed that significant differences existed between 15 °C and 25 °C (P = 0.044), between 20 °C and 25 °C (P = 0.047), and between 35 °C and 25 °C (P = 0.044) for temperature. No significant differences were found among the levels of salinity and pH. This discovered that, of the three factors, the temperature was a crucial factor in determining WSSV proliferation. Hyperthermia (35 °C) and hypothermia (15 °C) could significantly decrease the WSSV proliferation while 25 °C was the optimum temperature of WSSV replication. Moreover, low temperature was a more efficient factor to control WSSV replication and mortality of individuals infected WSSV, because the copy numbers of WSSV were only 0.626 per ng muscle at 15 °C, while there were 5.94 copies at 35 °C. Our study showed that the optimal WSSV proliferation condition was 30 °C for temperature, 35‰ for salinity, and 8.0 for pH, and reversely, the worst WSSV proliferation condition was 15 °C for temperature, 35‰ for salinity, and 9.0 for pH.