Yellowtail Seriola quinqueradiata fed a non-fish meal diet and control fish fed a standard fish meal diet were reared in neighboring net-cages under the same natural environmental conditions. The growth and food consumption of the fish fed the non-fish meal diet (NFM fish) were similar to the fish fed the control diet (control fish). Mortality due to a natural infection with Pasteurella piscicida occurred among NFM fish, but not among control fish during 55 days of feeding experiment. Plasma total cholesterol, free cholesterol and phospholipid of NFM fish were significantly lower than those of control fish. This result indicates that the decrease in the levels of plasma lipid components may be a good indicator of reduced disease resistance in yellowtail.