人為経口感染におけるハマチの連鎖球菌症の経過

抄録

To clarify the process of streptococcicosis of yellowtail, the symptom, pathogen incidence, and mortality were recorded with time elapse using peroral inoculation of the bacteria. The incubation period was usually one to 3 days, rarely within one day. The pathogen increased tremendously to more than 10⁴ cfu/g on hte 4th or 5th day after inoculation, when viable bacteria were counted in the blood and liver of the inoculated fish.
The symptoms usually appeared more than 3 days after inoculation except redness inside the operculum, which often appeared within a day after inoculation. The seriously infected and dead fish were usually observed on the 5th day after inoculation. There was little time lag between the spread of pathogen to the different organs and the appearance of symptoms. The progress of the disease was very variable. Some inoculated fish died within a few days after the symptoms appeared while others died soon after the symptoms appeared. Some inoculated fish also recovered before showing serious symptoms.
The inoculated fish reared under good environmental conditions and given high quality food were not seriously infected. They tend to be more resistant to the disease, however, it was still not possible to prevent the occurrence of the disease. On the other hand, the inoculated fish reared in poor environmental conditions and fed with low quality food soon died after the appearance of serious symptoms.