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

Rock bream Oplegnathus fasciatus were immersed in cultured RSIV suspension at 17°C for 30 min, and reared for 80 days without controlling temperature. Fish rearing temperature naturally increased at approximately 0.1°C/day from 17°C. Mortalities of fish without and with RSIV at 105.8, 103.8 and 101.8 TCID50/mL were 5.8%, 30.8%, 22.5% and 6.7%, respectively. Surviving fish were reared at 26°C, and intramuscularly injected with RSIV at 101.8 or 100.8 TCID50/fish. Survivors from RSIV-immersion at ≥ 103.8 TCID50/mL were strongly protected against RSIV challenge whereas those at ≤ 101.8 TCID50/mL died, suggesting that fish immunization with live RSIV at low temperature could be conducted by immersion route.