Comparison of susceptibility to Kabatana takedai (Microspora) among salmonid fishes

Abstract

Kabatana takedai (Microspora) is known as an enzootic pathogen of salmonids in limited water systems such as the Chitose River in Hokkaido, northern Japan. In this study, susceptibility to K. takedai was compared among masu salmon Oncorhynchus masou originating from the Chitose River, Shiribetsu River and Shari River, and rainbow trout O. mykiss from Shizuoka Prefecture, Japan. After exposure of fish to the Chitose River water, cysts of K. takedai in the heart and trunk muscle were examined by microscopy. Prevalence and intensity of infection were not considerably different among the three populations of masu salmon, whereas rainbow trout was more susceptible to K. takedai than masu salmon, particularly in the heart. A newly developed PCR test showed the higher percentage of fish with pre-cyst stage of K. takedai in the heart of rainbow trout than in masu salmon, suggesting that K. takedai established the cardiac infection at early stages more in rainbow trout than in masu salmon. A histopathological observation indicated that K. takedai infection in the heart caused granulomatous inflammation characterized by fibrinoid degeneration, but there was no difference in the progress of the inflammation between the two fish species. © 2007 The Japanese Society of Fish Pathology.