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Diseases of Aquatic Organisms

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DAO 32:15-40 (1998)  -  doi:10.3354/dao032015

Viral hemorrhagic septicemia virus, Ichthyophonus hoferi, and other causes of morbidity in Pacific herring Clupea pallasi spawning in Prince William Sound, Alaska, USA

Gary D. Marty1,*, Ellen F. Freiberg1, Theodore R. Meyers2, John Wilcock3, Thomas B. Farver4, David E. Hinton1

1Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California, One Shields Avenue, Davis, California 95616, USA
2Alaska Department of Fish and Game, Juneau Fish Pathology Laboratory, PO Box 25526, Juneau, Alaska 99802, USA
3Alaska Department of Fish and Game, PO Box 669, Cordova, Alaska 99574, USA
4Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, California 95616, USA

Pacific herring Clupea pallasi populations in Prince William Sound, Alaska, USA, declined from an estimated 9.8 × 107 kg in 1992 to 1.5 × 107 kg in 1994. To determine the role of disease in population decline, 233 Pacific herring from Prince William Sound were subjected to complete necropsy during April 1994. The North American strain of viral hemorrhagic septicemia virus (VHSV) was isolated from 11 of 233 fish (4.7%). VHSV was significantly related to myocardial mineralization, hepatocellular necrosis, submucosal gastritis, and meningoencephalitis. Ichthyophonus hoferi infected 62 of 212 (29%) fish. I. hoferi infections were associated with severe, disseminated, granulomatous inflammation and with increased levels of plasma creatine phosphokinase (CPK) and aspartate aminotransferase (AST). I. hoferi prevalence in 1994 was more than double that of most previous years (1989 to 1993). Plasma chemistry values significantly greater (p < 0.01) in males than females included albumin, total protein, cholesterol, chloride, glucose, and potassium; only alkaline phosphatase was significantly greater in females. Hypoalbuminemia was relatively common in postspawning females; other risk factors included VHSV and moderate or severe focal skin reddening. Pacific herring had more than 10 species of parasites, but they were not associated with significant lesions. Two of the parasites have not previously been described: a renal intraductal myxosporean (11% prevalence) and an intestinal coccidian (91% prevalence). Transmission electron microscopy of a solitary mesenteric lesion revealed viral particles consistent with lymphocystis virus. No fish had viral erythrocytic necrosis (VEN). Prevalence of external gross lesions and major parasites was not related to fish age, and fish that were yearlings at the time of the 1989 'Exxon Valdez' oil spill (1988 year class) had no evidence of increased disease prevalence.

Clupea pallasi · 'Exxon Valdez' · Histopathology · Hypoalbuminemia · Ichthyophonus hoferi · Pacific herring · Plasma chemistries · Viral hemorrhagic septicemia virus (VHSV)

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