Pathology associated with an aquareovirus in captive juvenile Atlantic halibut Hippoglossus hippoglossus and an experimental treatment strategy for a concurrent bacterial infection.
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, Truro, Canada. cusackrr@gov.ns.ca
R R
RR
Cusack
D B
DB
Groman
A M
AM
MacKinnon
F S
FS
Kibenge
D
D
Wadowska
N
N
Brown
D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D000891:Anti-Infective Agents, Local / Q000627:therapeutic use; D017756:Aquaculture; D001424:Bacterial Infections / Q000150:complications / Q000188:drug therapy / Q000662:veterinary*; D002478:Cells, Cultured; D002700:Chloramines / Q000627:therapeutic use; D004357:Drug Synergism; D005393:Fish Diseases / Q000188:drug therapy / Q000401:mortality* / Q000473:pathology* / Q000821:virology; D005412:Flatfishes / Q000821:virology; D008099:Liver / Q000473:pathology; D010118:Oxytetracycline / Q000627:therapeutic use; D012087:Reoviridae / Q000302:isolation & purification*; D012088:Reoviridae Infections / Q000150:complications / Q000188:drug therapy / Q000473:pathology / Q000662:veterinary*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D014105:Tosyl Compounds / Q000627:therapeutic use
D000900:Anti-Bacterial Agents; D000891:Anti-Infective Agents, Local; D002700:Chloramines; D014105:Tosyl Compounds; C016300:chloramine-T; D010118:Oxytetracycline