Detection of Vibrio anguillarum from wild fingerlings of ayu Plecoglossus altivelis.

Abstract

From 1979 to 1983, detection of Vibrio anguillarum from wild fringerlings of ayu Plecoglossus altivelis were made by selective enrichment in alkaline peptone water and subsequent plating on BTB teepol agar. The detection rate was 0.08%, 2.5%, 6% and 17% from the fingerlings in Lake Biwa (freshwater lake), Lake Hamana (sea-water lake), the coastal sea of Hiwasa, and the estuary of the Hiwasa river, Respectively. It was found that the fingerlings caught in sea water or blackish water harbored V. anguillarum at highter rates than those caught in the freshwater lake, and the pathogen was detected exclusively in the later period of the season for the fingerling collection in both freshwater and marine environments. Among 54 isolates of V. anguillarum, 32 isolates were confirmed to be virulent for eels and most of the virulent strais belonged o the serotype J-O-1, J-O-2, or J-O-3. On the other hand, most of the avirulent strains could not be classified into any of the three serotypes. Based on these results, it was deduced that V. anguillarum is introduced into freshwater ayu farms through the fingerlings themselves.