| Summary: | This study was carried out for the purpose of establishing control methods for furunculosis affecting propagated salmon in Japan. We determined the distribution and prevalence of A. salmonicida among asymptomatic adult chum (Oncorhynchus keta), pink (O. gorbuscha) and masu salmon (O. masou) returning to rivers on the island of Hokkaido and on the mainland of Honshu. During 1979-2002, a total of 22,109 chum, pink and masu salmon were collected from the rivers in Hokkaido and Honshu. We isolated A. salmonicida from the chum salmon in 21 of the 34 rivers examined and the overall prevalence was 12.2 % in the infected stocks. The prevalence of the agent in pink salmon and masu salmon was 4.6 % and 1.4 % respectively. Using CBB medium, we also examined the chum salmon from the Chitose River catching site. The prevalence of the agent on gill surface was high (50%) at the catching site and decreased among fish in the holding pond in the river. The bacteria appear to be spread during fish migration in the river and during transportation of the fish from the capture site to the holding pond. Recently, the agent was isolated from the gill surface of chum salmon caught off the coast of the eastern part of Hokkaido, but the prevalence was low (1.7%). To control furunculosis in salmonids, the fish should be held for maturation in ponds under conditions of low density and the fish should be disinfected to prevent spread of furunculosis before placement in the holding pond. 10th International Symposium for Veterinary Epidemiology and Economics. 17-21 November 2003. Vina Del Mar, Chile.
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