DAO 37:205-208 (1999)  -  doi:10.3354/dao037205

Resistance to reinfection in chinook salmon Oncorhynchus tshawytscha to Loma salmonae (Microsporidia)

M. L. Kent1,*, S. C. Dawe1, D. J. Speare2

1Fisheries and Oceans Canada, Pacific Biological Station, Nanaimo, British Columbia V9R 5K6, Canada
2Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada

ABSTRACT: Chinook salmon Oncorhynchus tshawytscha were experimentally infected per os with Loma salmonae and held in flow-through seawater tanks at 12 to 14°C. The fish exhibited 100% infection when first examined at 7 wk post initial exposure (p.e.), and by 20 wk p.e. they had completely recovered from gill infections. The recovered fish were then re-exposed the following week. All of these fish showed strong protection to new L. salmonae infections, while naïve fish exposed to the same inoculum developed the infection. Most of the re-exposed fish exhibited a few free spores or spores within phagocytes in the kidney interstitium at 20 to 29 wk p.e., but xenomas were not detected in either the gills or visceral organs. The kidney is the primary site of reticulo-endothelial activity, and thus these spores were likely deposited in the kidney by entrapment by fixed macrophages. It is possible that these spores provide immunologic stimuli to reinforce the resistance to new L. salmonae infections.

KEY WORDS: Loma · Oncorhynchus · Resistance

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