Effects of Water Temperature on the White Spot Syndrome Virus Infection in Postlarvae Litopenaeus vannamei

This study evaluated the effects of high water temperature (32 ± 1 °C) on the white spot syndrome virus (WSSV) infection in Litopenaeus vannamei postlarvae (PL 15 ). WSSV challenge was done by immersion. One group of PL 15 was continuously maintained at 32 ± 1 °C until the end of the experiment after challenge and a control group of PL 15 was constantly maintained at 28 ± 1 °C until the end of the experiment after challenge. Other groups were kept at 32 ± 1 °C until temperature was altered from 32 ± 1 °C to 28 ± 1 °C at 0, 1, 3, 5 and 7 days after infection. Gross signs and mortality were monitored every 12 h until the end of the experiment. WSSV infections were confirmed by nested-PCR, histopathology, immunohistochemistry and bioassay methods. Challenged shrimp were kept at 32 ± 1 °C for 0, 1, 3 and 5 days before the temperature was reduced to 28 ± 1 °C revealing that maintaining the temperature at 32 ± 1 °C for a longer period could delay clinical signs and onset of mortalities. Nevertheless, 100 % mortalities occurred in all groups and the control group within 7 days. All moribund PL 15 were WSSV-positive by nested-PCR assay as well as histopathology, immunohistochemistry and bioassay methods. In contrast, PL 15 constantly maintained at 32 ± 1 °C until the end of the experiment, and for 7 days after challenge before switching to 28 ± 1 °C did not show clinical signs and mortality. Surviving PL 15 from both groups were WSSV-negative by nested-PCR assay as well as histopathology, immunohistochemistry and bioassay methods. This study clearly indicated that postlarvae maintained constantly at 32 ± 1 °C for 7 days were able to eliminate/clear WSSV infection.