Data of the current study show that, based on weight gain, FI, FER and survival, vitamin E requirement of Nile tilapia was not affected by dietary lipid levels and supplementation of 50 mg of vitamin E/kg diet (analyzed average value of 112 mg/kg)was sufficient for Nile tilapia fed diets containing an equal mixture of corn oil and menhaden fish oil ranging from 6 to 14%. However, regardless of the dietary levels of vitamin E, increasin g the level of supplemental lipid to 14% resulted in decreased feed efficiency and accumulation of body lipid. Liver content of α-tocopherol increased with increasing dietary level of vitamin E, decreased with increasing dietary levels of lipid and became significantly lower at 14% supplemental lipid. Hematological values and HSI were unaffected by dietary levels of lipid or vitamin E. Dietary lipid levels had no effect on serum lysozyme but an increase in serumprotein and a decrease in serum alternative complement activity were observed at 14% and 10 or 14% dietary lipid, respectively. Increasing supplemental levels of vitamin E to 100 or 200 mg/kg diet positively affected serum lysozyme and complement activity but had no influence on serum protein. Even though some immune parameters evaluated were affected by dietary levels of lipid and vitamin E, at levels used, these
dietary nutrients appear to be of no benefit in increasing resistance of Nile tilapia to S. iniae.