Efficacy of a bivalent inactivated vaccine against red seabream iridovirus and Streptococcus iniae in red seabream, Pagrus major

The red seabream (Pagrus major) is an economically important marine fish species that is cultured in Japan. Natural outbreaks of red seabream iridovirus (RSIV) and/or Streptococcus iniae can cause massive mortalities and severe economic losses in red seabream production. No effective single-injection vaccine for protecting red seabream against both diseases has yet become commercially available. Here, we evaluated the efficacy of a bivalent formalin-killed vaccine (PISCIVAC™ Irido Si) against RSIV and S. iniae infections in red seabream. In laboratory trials, intraperitoneally vaccinated fish reared at 25 °C were protected against challenges with RSIV and S. iniae as early as 3 days post vaccination (dpv), with a relative percent survival (RPS) of 69% and 90%, respectively. The protection was also observed in fish reared at 15 °C, with a RPS of 88% and 89% after challenging the fish with RSIV and S. iniae at 10 dpv and 14 dpv, respectively. Furthermore, intramuscular vaccination effectively protected fish against RSIV (RPS of 100% and 65-96% at 10 and 20 dpv, respectively) and S. iniae (RPS of 92-100% at 14 dpv). The vaccine conferred protection against RSIV infection for at least 2 months and against S. iniae infection for at least 6 months in the field trial. These results indicate that PISCIVAC™ Irido Si is effective for protecting red seabream against RSIV and S. iniae infections.