Based on previous finding that the incidence of disease was higher in yellowtail fed with defrosted food that in those give unthawed food, the feeding experiment on frozen diet was tried using various food fishes. Yellowtail accepted the unthawed food without any trouble. The property of the frozen diet to float on water was useful to locate left over food and to monitor activity of the fish. The experimental group fed with unthawed diet had the best growth rate and feeding efficiency compared with the other experimental groups given thawed diet. The survival rate was also very high in the group given unthawed food. Washing treatment and adding ethoxyquine or vitamin mixture to the diet were also effective comparet with the control group. Even if old frozen food was used, the group fed with unthawed diet had better growth rate and feeding efficiency than the other groups. Based on the results, it is recommended that feeding yellowtail on unthawed diet should be applied as a practical control for bacterial infection and water pollution in yellowtail culture.
