| Summary: | During the period from September 1976 to December 1987, various species of mature salmonid fish, including masu (Oncorhynchus masou), chum (O. keta), pink (O. gorbuscha), kokanee salmon (O. nerka), charr (Salvelinus leucomaenis), and rainbow trout (O. mykiss), were examined to provide information on the distribution of pathogenic viruses in northern Japan. Virus inspections were conducted on ovarian fluids, mixed kidney and spleen specimens, epithelial tumor tissues, and blood samples. Four viruses were isolated during the course of this investigation. Infectious hematopoietic necrosis virus (IHNV) was found in the ovarian fluid of chum and masu salmon. Oncorhynchus masou virus (OMV), discovered in 1978 and specific to masu salmon, has been isolated from ovarian fluids and epithelial tumor tissues at 13 sampling sites. Chum salmon virus (CSV) was isolated from mixed kidney and spleen specimens from healthy chum salmon in 1978 and again in the ovarian fluids of masu salmon in 1987 at two localities on the coast of the Sea of Japan. Infectious pancreatic necrosis virus (IPNV) was isolated from masu salmon at two locations: once from tumor tissue in 1981 and a second time from an ovarian fluid sample in 1987. Viral erythrocytic necrosis (VEN) was found at four locations in the erythrocytes of chum and pink salmon in waters along the Okhotsk coast. Cytoplasmic particles with a hexagonal profile were found in the erythrocytes by electron microscopy. Seventeenth U.S.-Japan Meeting on Aquaculture. 16-18, 20 October 1988. Ise, Japan.
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