Outbreaks of phaeohyphomycosis in the chinook salmon (Oncorhynchus tshawytscha) caused by Phoma herbarum |
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Authors: | Mohamed Faisal Ehab Elsayed Scott D. Fitzgerald Victor Silva Leonel Mendoza |
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Affiliation: | (1) Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, S-114 Plant Biology Building, East Lansing, MI 48824, USA;(2) Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University, East Lansing, MI 48824, USA;(3) Faculty of Veterinary Medicine, Cairo University, Egypt;(4) Medical Technology Program, College of Natural Science, 322 North Kedzie Laboratory, Michigan State University, East Lansing, MI 48824, USA |
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Abstract: | Phoma herbarum has been associated with two outbreaks of systemic mycosis in hatchery-reared chinook salmon (Oncorhynchus tshawytscha) fingerlings. Affected fish exhibited abnormal swimming behavior, exophthalmia, multiple rounded areas of muscle softening, protruded hemorrhagic vents, and abdominal swelling. In all affected fish, swimbladders were filled with whitish creamy viscous fungal mass, surrounded by dark red areas in swimbladder walls, kidneys, and musculature. Clinical and histopathological examinations suggest that the infection may have started primarily in the swimbladder and then spread to the kidneys, gastrointestinal tract, and surrounding musculature. Consistent microscopical findings included broad septate branched fungal hyaline hyphae, 5–12 μm in diameter within the swimbladder, stomach, and often within and adjacent to blood vessels. Profuse growths of woolly brown fungal colonies were obtained from swimbladders and kidneys on Sabouraud medium. On corn meal agar the formation of pycnidia, characteristic of Phoma spp., was detected within 10 days of incubation. Morphological and molecular analyses identified this fungus as Phoma herbarum. This report underscores systemic fungal infections as a threat to raceway-raised salmon. |
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Keywords: | chinook salmon Oncorhynchus tshawytscha phaeohyphomycosis Phoma herbarum Michigan |
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