Bacterial cold-water disease in ayu (Plecoglossus altivelis altivelis) inhabiting rivers in Japan

Abstract

Ayu or sweetfish, Plecoglossus altivelis altivelis, is commercially important to inland fisheries in Japan and popular as a summer delicacy owing to its unusually sweet flavor. Ayu is also a popular recreational fishing species, especially for anglers using the Japanese fishing method "tomozuri."Bacterial cold-water disease (BCWD) was first recorded in an ayu farm in the Tokushima Prefecture in 1987 (Wakabayashi et al., 1994;Inouye, 2000). The cause of this occurrence was believed to be the introduction of ayu from Lake Biwa because BCWD was detected only a few days after landlocked ayu stock from Lake Biwa was transported to the farm (Wakabayashi, 2009). In 1993, BCWD spread to ayu populations in Gonokawa River in Hiroshima Prefecture (Iida and Mizokami, 1996). Subsequently, BCWD epizootics in ayu populations were reported in most rivers in Japan, and a close relationship was found to exist between the occurrence of BCWD and the release and use as a decoy of landlocked ayu stocks from Lake Biwa (Inouye, 2000;Taniguchi, 2002;Imura, 2003). According to the Japanese government statistics site e-Stat (https://www.estat.go.jp/en), the commercial catch of ayu in 2020 has decreased by 88.3% compared with the maximum catch of 16,414 tons in 1991. In the manuscript, the current knowledge of BCWD in ayu, which inhabits Japanese rivers, was compiled. Types of native and stock ayuTwo forms of native ayu exist, amphidromous and landlocked ayu, with an assumed genetic distance and divergence time of approximately 100,000 years (Nishida, 1985).

Host specificity and virulence of Flavobacterium psychrophilum: a comparative study in ayu (Plecoglossus altivelis) and rainbow trout (Oncorhynchus mykiss) hosts

“…F. psychrophilum has currently a worldwide distribution and salmonids, especially rainbow trout and Atlantic salmon, are particularly affected species. However, F. psychrophilum has been frequently associated to diseased ayu (an Osmeriformes fish) in farms and rivers [ 4 ]. In addition, F. psychrophilum has been occasionally isolated from other non-salmonid freshwater fish [ 1 ].…”

“…In addition, F. psychrophilum has been occasionally isolated from other non-salmonid freshwater fish, such as carp, sturgeon, sea lamprey, and eel [ 1 , 3 ]. Ayu ( Plecoglossus altivelis ), an Osmeriformes, also appears highly susceptible to BCWD [ 4 , 5 ]. Ayu is an important fish species in Japan, famous for game fishing (Tomozuri for anglers) but also produced in fish farms for human consumption.…”

“…Ayu is an important fish species in Japan, famous for game fishing (Tomozuri for anglers) but also produced in fish farms for human consumption. F. psychrophilum has been frequently associated with diseased ayu in farms and rivers in Japan and is responsible for heavy mortality and severe economic losses [ 4 ]. F. psychrophilum isolation from cultured ayu was also reported in Korea [ 6 ].…”