Potentiality to natural immunization inducement against VHS in olive flounder by live VHSV immersion vaccination at temperature controlled culture condition.

Viral hemorrhagic septicemia virus (VHSV) is the etiological agent of viral hemorrhagic septicemia (VHS), one of the most severe viral diseases affecting cultured olive flounder (Paralichthys olivaceus) in Far East Asia. VHS occurs during the winter or spring season when the water temperature is low (9-15 °C). In our previous study found that VHSV infection had controlled by using water temperature (above 17 °C). By using water temperature, we demonstrated optimal live VHSV immersion vaccine treatment concentration, also live VHSV immersion vaccine treatment method. We confirmed that the effective VHSV immersion treatment was 10 TCID/mL at 17 °C. It was no need pretreatment before live VHSV immersion vaccination. The VHSV titer of vaccinated fish organs was under the estimated limit (<1.8 log TCID/mL) within 3 days in 10 TCID/mL live VHSV immersion at 17 °C. High survival rates were observed in live VHSV immersion with 10 and 10 TCID/mL at 17 °C and then infected VHSV at 10 °C. VHSV specific antibody was not detected from in the surviving flounder under VHSV infection after immersion treatment with live VHSV. In addition, the potentiality of natural immunization against VHS in olive flounder was suggested by live VHSV immersion vaccine at temperature controlled fish culture condition.