DAO 44:7-16 (2001)  -  doi:10.3354/dao044007

Pathology associated with an aquareovirus in captive juvenile Atlantic halibut Hippoglossus hippoglossus and an experimental treatment strategy for a concurrent bacterial infection

R. Roland Cusack1,*, David B. Groman2, Anne-Margaret MacKinnon3, Frederick S. B. Kibenge2, Dorota Wadowska2, Nick Brown4

1Veterinary Pathology, Nova Scotia Department of Fisheries and Aquaculture, PO Box 550, Truro, Nova Scotia B2N 5E3, Canada
2Aquatic Diagnostic Services, Dept. of Pathology and Microbiology, Atlantic Veterinary College, Charlottetown, Prince Edward Island C1A 4P3, Canada
3Fish Health Unit, Dept. of Fisheries and Oceans, PO Box 5030, Moncton, New Brunswick E1C 9B6, Canada
4R & R Finfish Development Ltd., RR#1 Sandy Cove, Digby, Nova Scotia B0V 1E0, Canada

ABSTRACT: A large-scale mortality of larval and juvenile halibut Hippoglossus hippoglossus occurred at a semi-commercial halibut farm in Atlantic Canada. Investigation of the cause revealed aquareovirus particles in necrotic liver tissue of affected fish. Cytopathic effect on CHSE-214 cell lines occurred from all fish cultured for viruses, and the viral morphology of the particles in culture was consistent with that observed in necrotic host tissue. The virus was placed in the family of Reoviridae, genus Aquareovirus based on morphology and RT-PCR results. Multifocal hepatocellular necrosis was a consistent finding in all fish as well as acute necrosis of proximal renal tubules. Concurrent bacterial infections were present in some specimens. Fish experimentally treated with oxytetracycline or a combination of oxytetracycline and chloramine-T had a significantly lower mortality rate than untreated fish. Fish treated with chloramine-T alone had a significantly elevated mortality rate compared to controls. Despite supportive medical therapy, mortality levels in treated and untreated groups remained elevated, supporting the hypothesis that the primary pathogen was of viral origin. This is the first report of elevated mortalities in Atlantic halibut associated with an aquareovirus.


KEY WORDS: Aquareovirus · Atlantic halibut · Fish diseases · Oxytetracycline · Chloramine-T · Pathology · Fish treatments


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