Effect of dietary vitamin E and lipids on some immune parameters of turbot (Scophthalmus maximus L.)
The effect of dietary vitamin E and dietary lipids on growth and immune parameters of juvenile turbot (Scophthalmus maximus) were investigated in a series of experiments. The aims of the studies were to maximise immune function through dietary modulation to counteract stress induced immunodepression resulting from high stocking densities. In the first experimental trial, the vitamin E requirement for an optimum immune response was studied and revealed that vitamin E depletion induced poor health status, lower growth with some mortalities occurring at the end of the trial. However, supplementation of the diets with high levels of α-tocopherol although ensuring better growth did not significantly enhance most of the parameters measured at the end of the trial. The second trial aimed to test regimes coupling fresh or oxidised oil and low or high vitamin E supplementation. The results showed that vitamin E had a role in preventing peroxidation as high vitamin E supplementation improved some of the immunological parameters measured compared to fish fed with the same oxidised oil but low levels of vitamin E. By contrast low levels of vitamin E did not induce pathological conditions in fish fed with fresh oil showing the importance of dietary lipid in the evaluation of vitamin E requirements. Following this investigation another feeding trial was designed to look at the interaction of polyunsaturated fatty acids (PUFAs) and α-tocopherol on the immune parameters of juvenile turbot. Although liver lipid composition was affected by the diets and growth was enhanced by high vitamin E levels and a high ratio of (n-3)/(n-6) PUFAs no significant differences could be attributed to the lipid quality in the immunological parameters measured. Vitamin E supplementation enhanced the proliferation of kidney leucocytes when stimulated with lipopolysaccharide. These studies give some information on the requirements for vitamin E and lipid quality of juvenile turbot.