Experimental and natural host specificity of Loma salmonae (Microsporidia)

The microsporidian Loma salmonae (Putz, Hoffman & Dunbar, 1965) Morrison & Sprague, 1981 has caused significant gill disease in Pacific salmon Oncorhy nchus spp. Host specificity of the parasite was examined experimentally by per os challenge of selected salmonids and non-salmonids with infective chi nook salmon O. tshawytscha gill material. Pink Oncorhynchus gorbuscha and c hum salmon O. keta, brown Salmo trutta and brook trout Salvelinus fontinali s, and chinook salmon (controls) were positive, whereas Atlantic salmon Sal mo salar and Arctic char Salvelinus alpinus were negative. In addition, no non-salmonids were susceptible to experimental exposure. Wild Pacific salmo n species in British Columbia, Canada, were examined for L. salmonae during their fresh water life history stages (smolts, prespawning, spawning). All stages were infected, although infections in smolts were only detectable u sing a L. salmonae-specific PCR test. Many previous Loma spp. described fro m Oncorhychus spp. are likely L. salmonae based on host, parasite morpholog y, and site of infection.