2023 Volume 58 Issue 4 Pages 164-170
In Japan, Bacterial cold-water disease (BCWD) is an economically important fish disease, occurring in ayu Plecoglossus altivelis altivelis not only at aquaculture farms but also in rivers. In this study, an epizootiological study of BCWD was conducted to understand the route of infection in ayu and the source of the causative agent, Flavobacterium psychrophilum in rivers. We used a genotyping system with a combination of four PCR-restriction fragment length polymorphisms (PCR-RFLP). For five years from 2014 to 2018, various fish, mainly ayu, were caught and sampled in the Kanna River, Gunma Prefecture, Japan. A total of 852 isolates of F. psychrophilum from these fish species were used as PCR-RFLP genotyping samples. Nine PCR-RFLP genotypes were identified among these isolates, some of which were the typical epizootic types for ayu in this river, while species-specific genotypes exist in other fish species. In addition, fish species other than ayu, decoy ayu, and land-locked ayu were suspected as reservoirs of epizootic F. psychrophilum genotypes for ayu in the Kanna River. These results provide the basis for an epizootiological assessment of the transmission dynamics of ayu BCWD not only in the Kanna River but also in rivers in general.
