Epitheliocystis in lake trout Salvelinus namaycush (Walbaum) is associated with a β-proteobacteria.
Lake trout Salvelinus namaycush (Walbaum) raised for stocking experienced yearly (2011-13) winter epizootics of epitheliocystis. Affected fish were dispersed on the bottom of the tank, had decreased feed and fright response, and mortality often reached 40%. Peak mortality occurred within 3 weeks of the appearance of clinical signs, and outbreaks typically lasted 6 weeks. Affected fish had no gross lesions but histologically had branchial epithelial necrosis and lamellar hyperplasia, with small to large numbers of scattered epithelial cells containing 10- to 20-μm inclusions. A longitudinal study was undertaken of one annual outbreak, and lamellar hyperplasia was most closely associated with mortality. The number of inclusions was statistically greater (P < 0.05) before and during peak mortality, but inclusions were present in low numbers before clinical signs occurred. Results of histochemical staining, immunohistochemistry and transmission electron microscopy supported the presence of a β-proteobacteria rather than a Chlamydiales bacterium within inclusions. PCR primers to identify Chlamydiales did not give consistent results. However, the use of universal 16S rDNA bacterial primers in conjunction with laser capture microdissection of inclusions demonstrated that a β-proteobacteria was consistently associated with affected gills and is more likely the cause of the disease in lake trout.
Fish Pathology Laboratory, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada.
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Contador
Ontario Ministry of Natural Resources, Peterborough, ON, Canada.
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Methner
Fish Pathology Laboratory, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada.
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Ryerse
Fish Pathology Laboratory, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada.
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Huber
Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada.
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Lillie
Department of Pathobiology and Veterinary Science, University of Connecticut, Storrs, CT, USA.
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Frasca
Fish Pathology Laboratory, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada.
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Lumsden
D000818:Animals; D004848:Epithelium / Q000382:microbiology*; D005393:Fish Diseases / Q000382:microbiology* / Q000401:mortality / Q000473:pathology; D005880:Gills / Q000382:microbiology* / Q000473:pathology / Q000648:ultrastructure; D006965:Hyperplasia / Q000382:microbiology / Q000401:mortality / Q000473:pathology / Q000662:veterinary; D007150:Immunohistochemistry; D008137:Longitudinal Studies; D046529:Microscopy, Electron, Transmission; D009336:Necrosis / Q000382:microbiology / Q000401:mortality / Q000473:pathology / Q000662:veterinary*; D020560:Proteobacteria / Q000235:genetics / Q000502:physiology*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D014337:Trout / Q000382:microbiology*
D012336:RNA, Ribosomal, 16S
16s rDNA; epitheliocystis; histopathology; lake trout; laser capture microdissection; β-proteobacteria