Data of the current study showthat, 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, increasing 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 serumlysozymebut an increase in serumprotein
and a decrease in serumalternative complement activitywere 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.