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Diseases of Aquatic Organisms

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DAO 70:201-208 (2006)  -  doi:10.3354/dao070201

Dynamics of viral hemorrhagic septicemia, viral erythrocytic necrosis and ichthyophoniasis in confined juvenile Pacific herring Clupea pallasii

Paul Hershberger1,*, Alexandra Hart2,3, Jake Gregg1, Nancy Elder1, James Winton3

1Western Fisheries Research Center, Marrowstone Marine Field Station United States Geological Survey, Biological Resources Discipline, 616 Marrowstone Point Road, Nordland, Washington 98358, USA
2Department of Biology, University of Washington, Box 351800, Seattle, Washington 98195, USA
3Western Fisheries Research Center, United States Geological Survey, Biological Resources Discipline, 6505 NE 65th Street, Seattle, Washington 98115, USA

ABSTRACT: Capture of wild, juvenile herring Clupea pallasii from Puget Sound (Washington, USA) and confinement in laboratory tanks resulted in outbreaks of viral hemorrhagic septicemia (VHS), viral erythrocytic necrosis (VEN) and ichthyophoniasis; however, the timing and progression of the 3 diseases differed. The VHS epidemic occurred first, characterized by an initially low infection prevalence that increased quickly with confinement time, peaking at 93 to 98% after confinement for 6 d, then decreasing to negligible levels after 20 d. The VHS outbreak was followed by a VEN epidemic that, within 12 d of confinement, progressed from undetectable levels to 100% infection prevalence with >90% of erythrocytes demonstrating inclusions. The VEN epidemic persisted for 54 d, after which the study was terminated, and was characterized by severe blood dyscrasias including reduction of mean hematocrit from 42 to 6% and replacement of mature erythrocytes with circulating erythroblasts and ghost cells. All fish with ichthyophoniasis at capture died within the first 3 wk of confinement, probably as a result of the multiple stressors associated with capture, transport, confinement, and progression of concomitant viral diseases. The results illustrate the differences in disease ecology and possible synergistic effects of pathogens affecting marine fish and highlight the difficulty in ascribing a single causation to outbreaks of disease among populations of wild fishes.

KEY WORDS: Disease · Fish · Viral hemorrhagic septicemia · Viral erythrocytic necrosis · Ichthyophonus · Pacific herring · Wild fish

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