Antioxidant effect of dietary tocopherol and ascorbic acid on growth and survival of Litopenaeus vannamei postlarvae

The nutritional effect of vitamin E in diets for Litopenaeus vannamei postlarve (PL19) was investigated. Four formulated diets with different combinations of alpha-tocopheryl acetate (alpha-TA), ascorbic acid (AA) and highly unsaturated fatty acids (HUFA) were tested, using four replicates. No significant differences in survival were observed among treatments after 34 days of feeding. However, shrimp fed with a diet containing 2% fish oil (low n-3 HUFA content), 200 mg.kg(-1) alpha-TA and 100 mg.kg(-1) AA (diet H/E/C) showed significantly better growth than those fed a diet supplemented with 5% fish oil (high n-3 HUFA content), 200 mg.kg(-1) alpha-TA and 100 mg.kg(-1) AA (diet H+/E/C). Shrimp fed with a diet containing 5% fish oil, 900 mg.kg(-1) alpha-TA and 100 mg.kg(-1) AA (diet H+/E+/C) showed a significantly higher tissue level of n-6 PUFA than postlarvae fed diet H+/E/C. No definite conclusion could be drawn about a possible interaction between alpha-TA and AA, since a comparison of the diet containing 5% fish oil, 200 mg.kg(-1) alpha-TA and 700 mg.kg(-1) AA (H+/E+/C+) and the diet H+/E/C did not show any significant differences in any of the measured parameters. The antioxidative status of the shrimp tissue (measured by means of the thiobarbituric acid (TBA) assay and expressed as nM malonaldehyde (MA) per gramme dry weight) was equal for all treatments. Nevertheless, there was a slightly lower MA value with the diet H+/E/C+, indicating that AA may be an effective antioxidant in the aqueous phase and at the water/lipid interface of the tissue. The tissue levels of alpha-T and AA were highly dependent on the amounts in diets and no correlation between alpha-T and AA incorporation could be observed.