Immunization of Rock Bream Oplegnathus fasciatus at Low Temperature by Immersion with Live Red Sea Bream Iridovirus (RSIV)

Rock bream Oplegnathus fasciatus were immersed in cultured RSIV suspension at 17 degrees C for 30 min, and reared for 80 days without controlling temperature. Fish rearing temperature naturally increased at approximately 0.1 degrees C/day from 17 degrees C. Mortalities of fish without and with RSIV at 10(5.8), 10(3.8) and 10(1.8) TCID50/mL were 5.8%, 30.8%, 22.5% and 6.7%, respectively. Surviving fish were reared at 26 degrees C, and intramuscularly injected with RSIV at 10(1.8) or 10(08) TCID50/fish. Survivors from RSIV-immersion at >= 10(3.8) TCID50/mL were strongly protected against RSIV challenge whereas those at <= 10(1.8) TCID50/mL died, suggesting that fish immunization with live RSIV at low temperature could be conducted by immersion route.