From 1983 to 1984, detections of
Vibrio anguillarum from reared fry and fingerlings of ayu (
Plecoglossus altivelis) and their environment were made at Hiroshima and Okayama prefectural fish hatcheries by a two-step incubation method using alkaline peptone water (APW) and BTB teepol agar. The concentration of NaCl of APW was modified to 0.5% from 3% of the original method (MUROGA
et al., 1984), because 0.5% NaCl APW gave a higher detection rate than 3% NaCl APW when sea water reared fish were used as materials.
Vibrio anguillarum was detected frequently from fish and waters at both hatcheries, however, only a few isolates proved virulent for Japanese eel (
Anguilla japonica) and/or ayu. In order to find a method for estimating pathogenicity of isolates, O-serotype, proteolytic activity of the extracellular products, and resistance to normal ayu serum were examined, but none of these factors proved available for the indicator of pathogenicity.
The organism was also detected in rotifer (
Brachionus plicatilis), a food for ayu fry, at a high density (10
7 CFU/g wet weight), thus the contaminated rotifer was thought to be a source of the infection or carriage of
V. anguillarum in reared ayu.
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