A survey on the distribution of viruses in wild Japanese flounder Paralichtys olivaceous and other marine fishes

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For a survey on the distribution of fish pathogenic viruses among wild Japanese flounder Paralichthys olivaceus, 434 fish were collected in 14 coastal areas of Japan in 1999 and 2001. Using established fish cell lines, aquabirnaviruses were isolated from 135 out of 358 fish (38%) caught in almost all the coastal areas and the representative isolate was identified as YTAV (yellowtail ascites virus) by cross-neutralization tests. In addition to the aquabirnavirus, VHSV (viral hemorrhagic septicemia virus) was isolated from 34 out of 434 fish (8%) collected in Wakasa Bay, Minami Izu and the Seto Inland Sea mainly in winter and spring. In a pathogenicity test, 4 isolates of aquabirnaviruses did not cause any mortality or morbidity in young Japanese flounder by intramascular injection at 10^<3.0> - 10^<7.6> TCID_<50>/fish. On the other hand, mortalities of 60% and 100% were produced by the inoculation of an isolate of VHSV at 10^<2.0> and 10^<6.0> TCID_<50>/fish, respectively, in flounder. Virus isolation trials were also performed from wild Japanese horse mackeral Trachurus japonicus (141 fish), darkbanded rockfish Sebastes inermis (101 fish) and other marine fishes (134 fish with 7 fish species) in 2000 and 2001, but only aquabirnaviruses were isolated from some of them.