Effects of Water Temperature on Infection of the Microsporidian Kabatana takedai in Salmonids

Effects of water temperature on infection of the microsporidian Kabatana takedai were investigated in salmonids under field and experimental conditions. “Cysts” of K. takedai appeared in the heart and the skeletal muscle of wild juvenile masu salmon Oncorhynchus masou from the Chitose River, Hokkaido, during summer in 2003 and 2004, when the river water temperature exceeded 15°C. Following the exposure of naive juvenile sockeye salmon Oncorhynchus nerka to river water (18-19°C) for 3 days, the fish were transferred to separate tanks where the temperatures were set to 11, 13, 15 and 17°C. Prevalence of infection reached more than 70% in the 13, 15 and 17°C groups, but in the 11°C group, it remained less than 30%. However, shifting a part of the 11°C group to 18°C increased the prevalence to 71 % by 23 days after the elevation of the temperature. When juveniles were exposed to 11°C river water and subsequently kept at 9°C for 42 days, no development of K. takedai occurred even after the temperature was elevated to 15°C. These results indicate that temperature manipulation is partially effective as a preventive method of K. takedai infection.