Assessment of the sevenband grouper Epinephelus septemfasciatus with a live nervous necrosis virus (NNV) vaccine at natural seawater temperature

Abstract

We investigated the long-term kinetics of nervous necrosis virus (NNV) infectivity in sevenband grouper, Epinephelus septemfasciatus, injected with a live NNV vaccine at 17.3°C and reared at natural seawater temperature. We also evaluated horizontal infection of NNV from fish vaccinated with live NNV to naïve fish in a cohabitation experiment. Although 10.5% mortality was observed in the vaccinated fish, they were strongly protected from the challenge with homologous NNV. The NNV infectivity titer was detected from day 5 after vaccination, peaked on day 10 at 10(7.43±0.35) TCID50/g, but NNV was under the detection limit (≤10(2.8) TCID50/g) between days 42 and 128. No mortalities or NNV were detected in any of the vaccinated and cohabitated naïve fish, suggesting that NNV spread from fish vaccinated with live NNV should be low if it is limited to fish in the late stage of vaccination (≥42 days from NNV inoculation). The present results demonstrate that a protective immune response to NNV was mounted in sevenband grouper by the live NNV vaccine without controlling fish rearing temperature.