A SMALL RNA VIRUS ISOLATED FROM SALMONID FISHES IN CALIFORNIA, USA

Beginning in the summer of 1988, examinations of numerous salmonid broodstocks in northern California, USA, revealed widespread infections with a previously undescribed virus. The virus was isolated from ovarian fluids of adult rainbow trout (Oncorhynchus mykiss), cutthroat trout (O. clarki), brown trout (Salmo trutta), and brook trout (Salvelinus fontinalis) and from kidney and spleen samples of juvenile brown and brook trout. The virus was not associated with above-normal losses in adult or juvenile fish. Virions purified from infected CHSE-214 cells were hexagonal with a mean diameter of 37.5 nm (SD = 0.41) and did not possess an envelope. The virus induced a diffuse degnerative cytopathic effect in CHSE-214 cells 14-28 d after inoculation with ovarian fluids or tissue homogenates. The virus replicated in CHSE-214 cells at temperatures from 10 to 20-degrees-C with an optimum at 15-degrees-C. Replication of the virus was not inhibited by addition of 5-bromo-2-deoxyuridine (BUDR) to the growth medium. There was no virus-induced mortality but virus was recovered for periods of up to 3-5 wk following waterborne exposures of rainbow and brown trout and kokanee salmon (O. nerka) but not from chinook (O. tshawytscha) or coho salmon (O. kisutch).