Outbreaks of coldwater disease in wild ayu and pale chub

Abstract

A bacterial disease occurred in wild ayu Plecoglossus altivelis and pale chub Zacco platypus from July to November in 1993 in Gonokawa River, Hiroshima Prefecture, Japan. Two types of gliding bacteria were isolated from diseased ayu and pale chub showing ulceration or erosion of the body surface. Both types of bacteria formed yellowish colonies on modified Cytophaga agar within 14 days at 8°C. Based on their biochemical characteristics, one was identified as Cytophaga psychrophila and the other was classified as an unknown species of Cytophaga. These two Cytophaga species were also serologically differentiated from each other. The representative strains of both types were pathogenic to ayu and pale chub in challenge tests. As C. psychrophila was dominantly isolated, the species is considered as the main pathogen in this epizootic.