2015 年 50 巻 3 号 p. 97-104
We studied the epidemiology of Flavobacterium psychrophilum in ayu from Lake Biwa for establishing control measures to bacterial cold water disease (BCWD). During 1998-2011, 12,743 wild ayu were collected from coastal (set net and gill net), offshore (offshore scoop net) and inflow river (fishing weir) areas of Lake Biwa. We employed a nested-PCR technique targeting 16S rRNA gene for the detection of F. psychrophilum in the gills and kidney of ayu. Prevalence of the bacterium was greatest when the water temperature of Lake Biwa was 18-21°C, which coincides with the optimum temperature for multiplication of F. psychrophilum. The prevalence of F. psychrophilum in the gills was higher in fish from fishing weirs and set nets maintained in net cages than in fish just after catch with the other fishing techniques. This suggests that rearing ayu in net cages at high densities following catch by fishing weirs and set nets can advance infection with the bacterium among the captured fish which will be used for seedlings in aquaculture or releasing in rivers. Control measures for the captured ayu must be conducted in reliable ways to prevent spread of the disease after release and in aquaculture.
