Abstract
The relation between the streptococcicosis and the food quality was ascertained by our epidemiological reserch. The food species, quality and the way of melting for frozen food were considered to be very important promoting factors of the disease. The methods for the preventions against the disease were proposed based on a few experiments as follows:
1. It was supposed that the cultured fishes were infected oraly through foods which were polluted by the pathogenic bacteria. To prevent the pollution by pathogen and it's growth, 1) washing and melting food fish by clean water, 2) feeding frozen food without melting and 3) feeding processed food (pellet) were proposed.
2. It was also clarified that the deteriolated food and unbalanced nutrition were not good in maintaining the resistancy of fishes against the disease. Inorder to maintain the food quality and nutritional balance, unmelted food and vitamin mixture were used and then it was observed that the resistancy of host was remarkably increased.
3. The resistancy of host was also influenced by organic pollution of water so that the water quality must be maintained in good condition.
It is relatively difficult to recover yellowtail from the streptococcicosis by drags, but the preventions above mentioned are effective in early stage of disease in population level, so that the early detection and diagnosis of the disease in the fish farm is especially important. In Kochi Prefecture, the improvement of culture equipment and hygienic education have been tried among the farmer of yellowtail culture.
