VIRAL HEMORRHAGIC SEPTICEMIA VIRUS, ICHTHYOPHONUS-HOFERI, AND OTHER CAUSES OF MORBIDITY IN PACIFIC HERRING CLUPEA-PALLASI SPAWNING IN PRINCE-WILLIAM-SOUND, ALASKA, USA

Pacific berring Clupea pallasi populations in Prince William Sound, Al aska, USA, declined from an estimated 9.8 x 10(7) kg in 1992 to 1.5 x 10(7) kg in 1994. To determine the role of disease in population decli ne, 233 Pacific herring from Prince William Sound were subjected to co mplete 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, he patocellular necrosis, submucosal gastritis, and meningoencephalitis. Ichthyophonus hoferi infected 62 of 212 (29%) fish. I. hoferi infectio ns were associated with severe, disseminated, granulomatous inflammati on and with increased levels of plasma creatine phosphokinase (CPK) an d aspartate aminotransferase (AST). I. hoferi prevalence in 1994 was m ore than double that of most previous years (1989 to 1993). Plasma che mistry values significantly greater (p < 0.01) in males than females i ncluded albumin, total protein, cholesterol, chloride, glucose, and po tassium; only alkaline phosphatase was significantly greater in female s. Hypoalbuminemia was relatively common in postspawning females; othe r risk factors included VHSV and moderate or severe focal skin reddeni ng. Pacific herring had more than 10 species of parasites, but they we re not associated with significant lesions. Two of the parasites have not previously been described: a renal intraductal myxosporean (11% pr evalence) and an intestinal coccidian (91% prevalence). Transmission e lectron microscopy of a solitary mesenteric lesion revealed viral part icles consistent with lymphocystis virus. No fish had viral erythrocyt ic necrosis (VEN). Prevalence of external gross lesions and major para sites 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 ev idence of increased disease prevalence.