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Diseases of Aquatic Organisms

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    Assessing the risk of wild fish around aquaculture environment as a source of red sea bream iridovirus (RSIV) outbreak

    Yasuhiko Kawato*, Kaori Mizuno, Shogo Harakawa, Yuzo Takada, Yusaku Yoshihara, Hidemasa Kawakami, Takafumi Ito

    *Corresponding author:

    ABSTRACT: Red sea bream iridovirus (RSIV) causes substantial economic damage to aquaculture. In the present study, RSIV in wild fish in an aquaculture environment was surveyed to evaluate the risk of wild fish being an infection source for RSIV outbreaks in cultured fish. In total, 1102 wild fish, consisting of 44 species, were captured from two aquaculture areas in western Japan using fishing, gill nets, and fishing baskets between 2019 and 2022. Eleven fish from seven species were confirmed to harbor the RSIV genome using a probe-based real-time PCR assay. The mean viral load of the RSIV-positive wild fish was 101.1 ± 0.4 copies/mg DNA, which was significantly lower than that of seemingly healthy red sea bream (Pagrus major) in a net pen during an RSIV outbreak (103.3 ± 1.5 copies/mg DNA) that occurred in 2021. Sequencing analysis of a partial region of the major capsid protein gene demonstrated that the RSIV genome detected in the wild fish was identical to that of the diseased fish in a fish farm located in the same area where the wild fish was captured. Based on the diagnostic records of RSIV in the sampled area, the RSIV-infected wild fish appeared during RSIV outbreak or after the ceasing of the disease in cultured fish, suggesting that RSIV detected in wild fish was derived from the RSIV outbreak in cultured fish. Therefore, wild fish populations around aquaculture environments may not be a significant risk factor for RSIV outbreaks in cultured fish.