DAO 59:211-216 (2004)  -  doi:10.3354/dao059211

Susceptibility of captive adult winter-run Chinook salmon Oncorhynchus tshawytscha to waterborne exposures with infectious hematopoietic necrosis virus (IHNV)

K. D. Arkush1,2,*, H. L. Mendonca1, A. M. McBride1, R. P. Hedrick2

1Bodega Marine Laboratory, University of California at Davis, PO Box 247, Bodega Bay, California 94923, USA
2Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California at Davis, Davis, California 95616, USA

ABSTRACT: Sexually mature female Chinook salmon Oncorhynchus tshawytscha with no prior history of exposure to infectious hematopoietic necrosis virus (IHNV) were susceptible to experimental infection induced by additions of virus to the water. The resulting infections resembled those observed among naturally infected hatchery and wild populations of Chinook salmon. Virus was detected as early as 4 d post-exposure (p.e.) and subsequently in all virus-exposed fish that died or that were examined at 14 d p.e. when the study was terminated. The greatest concentrations of virus, up to 108 plaque-forming units (pfu) ml-1, were found in the ovarian fluid at 13 to 14 d p.e., but the virus was also found in high concentrations in the gill, kidney/spleen and plasma. In contrast, the virus was not recovered from unexposed control adult salmon that died or were sampled at the end of the study. Despite detecting concentrations of IHNV in excess of 107 pfu g-1 of tissue, no specific microscopic lesions were found in IHNV-exposed compared to unexposed control salmon. The results of this initial study suggest that virus in the spawning environment, either from adult salmon or other sources, may contribute to its rapid spread among adult Chinook salmon, thereby considerably increasing the prevalence of IHNV infection in both wild and hatchery populations of adult Chinook salmon.

KEY WORDS: IHNV · Spawning Chinook salmon

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