Pathology associated with an
aquareovirus in captive juvenile Atlantic halibut Hippoglossus
hippoglossus and an experimental treatment strategy for a concurrent
bacterial infection
R.R. Cusack, D.B. Groman, A.-M. MacKinnon, F.S.B. Kibenge, D. Wadowska, N. Brown-2001
Diseases of Aquatic Organisms, 44(1): 7-16
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.
(Veterinary Pathology, Nova Scotia Department of
Fisheries and Aquaculture, PO Box 550, Truro, Nova Scotia B2N 5E3, Canada,
E-mail: cusackrr@gov.ns.ca)