The following results were obtained from investigation about the dynamics of V. anguillarum in process of artificial seedling production of ayu (Plecoglossus altivelis).
When ayu reared in sea water, serotype A strains of V. anguillarum were detected from fish and other samples at the first half and serotype C strains were isolated from fish and other samples at the latter half in rearing periods. Continuously, when these fish were transferred to fresh water ponds, there was recognized occurrence of the vibriosis caused by serotye A strains again.
Among the serotype A strains were isolated from ayu reared in sea water and fresh water ponds, were demonstrated some differences in biochemical characteristics. Pathogenicity of the isolates was confirmed using ayu and amago (Oncorhynchus rhodurus).
Serotype A strains from ayu reaed in sea water ponds were observed excellent growth in 2-3% NaCl concentration at 20°C, but serotype C strains did not. Serotype A strains from ayu reared in fresh water ponds were shown favourable growth in 1% NaCl concentration at 20 c.
As V. anguillarum was never detected from both the new sea water and the newly hatched ayu in our survey, the source of V. anguillarum seemed to be rotifer.
Drug bathing of rotifers before administrate it to fish considered to be one of the useful control method of the vibriosis in seedling production of ayu.
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