The Discovery of Tetracapsuloides bryosalmonae Infecting Enhanced Migratory Pacific Salmon Populations in the Great Lakes

Abstract

Simple Summary Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) salmon are important fish species in the Great Lakes region. We found them infected with a myxozoan parasite, Tetracapsuloides bryosalmonae, upon screening a high number of adult migratory Pacific salmon collected from fish weirs across multiple years and locations in Michigan. This microscopic parasite can cause Proliferative Kidney Disease (PKD), an important disease of salmonids, but the infected adult salmons examined in this study did not show clear signs of disease. Using several laboratory techniques (PCR, histology, immunohistochemistry, and sequence analysis), we confirmed the parasite presence in the kidney of fishes from a large watershed where it has not previously been detected. These findings show that T. bryosalmonae can infect Pacific salmon species in the Great Lakes, although its source, distribution, and effects on fish health remain unclear. Environmental conditions in the Great Lakes watershed are changing, creating more favorable conditions for T. bryosalmonae transmission, parasite development in freshwater bryozoans, and disease expression in salmonid hosts. Confirming the discovery of the regionally reportable myxozoan parasite T. bryosalmonae in fish hosts fills a long-standing gap in the salmonid disease surveillance of the Great Lakes fisheries.