Effects of dietary vitamin E level on growth performance, feed utilization, antioxidant capacity and nonspecific immunity of largemouth bass, Micropterus salmoides

An 8-week feeding trial was conducted to explore the optimal dietary vitamin E requirement of largemouth bass. The fish (7.54 +/- 0.04 g) were fed diets containing grade level of vitamin E, 14.24 (the basal diet), 79.53, 118.70, 176.32 and 225.32 mg/kg diet, to apparent satiation twice daily. Results showed that the supplementation of vitamin E significantly enhanced the specific growth rate, which may be related to the elevated feed intake, feed efficiency ratio and protein efficiency ratio. The increase of dietary vitamin E from 14.24 to 118.70 mg/kg diet significantly increased the activity of total superoxide dismutase, consistent with the variation of liver vitamin E content. However, the supplementation of vitamin E significantly decreased the malondialdehyde content. The activity of lysozyme, respiratory burst activity and classical complement pathway were all improved with the supplementation of vitamin E, and fish fed the diet with 118.70 mg/kg vitamin E obtained the highest value. Meanwhile, the red blood cell and haemoglobin followed the similar pattern with the above nonspecific immune indexes. Based on the above results, the optimal dietary vitamin E should be estimated to be 73-108 mg/kg diet through the analysis of broken-line regression.