High dietary intake of α-tocopherol acetate enhances the non-specific immune response of gilthead seabream (Sparus aurata L.)

To determine the effects of three high levels of dietary intake of α-tocopherol acetate (vitamin E) on the non-specific immune response of gilthead seabream (Sparus aurata L.), specimens were fed a commercial diet (100 mg α-tocopherol kg−1) as control, or vitamin E supplemented diets (600, 1200 or 1800 mg α-tocopherol acetate kg−1) for 15, 30 or 45 days. Growth, serum α-tocopherol levels, natural haemolytic complement activity and head–kidney leucocyte migratory, respiratory burst and phagocytic activities were studied at each of the assay times. A positive correlation between α-tocopherol acetate intake and serum α-tocopherol levels was observed, the increase being linked to both the dosage and length of treatment. Specimens fed the diet supplemented with 600 mg vitamin E kg−1showed no enhancement in any of their immune parameters, while those fed the diet supplemented with 1200 mg vitamin E kg−1presented a slightly higher (but not statistically significant) specific growth rate than fish fed the other diets. In addition, serum haemolytic activity and the phagocytosis of head–kidney leucocytes were enhanced by the dietary intake of 1200 mg vitamin E kg−1after 30 and 45 days of treatment, although leucocyte migration and respiratory burst activity remained unaffected. The highest vitamin E dietary dose used, 1800 mg kg−1, unexpectedly provoked no immunostimulation. These results indicate that a moderate level of vitamin E in the diet (1200 mg kg−1) stimulates the seabreamʹs non-specific immune system after 30 days of administration. Lower or higher vitamin E concentrations may not be so effective, because of an imbalance in the vitamin E ratio with other antioxidants. The proposed dietary levels of vitamin together with the indicated administration time could be useful for reducing the susceptibility of farmed fish to infectious diseases.