Interactive effects of vitamin C and E supplementation on growth performance, fatty acid composition and reduction of oxidative stress in juvenile Japanese flounder Paralichthys olivaceus fed dietary oxidized fish oil

A study was conducted to determine the interactive effects of vitamin C (VC) and E (VE) supplementation on growth, fatty acid composition and oxidative status of Japanese flounder juveniles. Fish (initial average body weight of 1.1 ± 0.1 g) in triplicate were fed five test diets for 60 days. Control diet contained fresh fish oil (FFO, 8.9 meq/kg) with 100 mg α-tocopherol (α-Toc) equivalents/kg of VE and 500 mg ascorbic acid (AsA) equivalents/kg of VC (FFO100E/500C). The other four diets contained oxidized fish oil (OFO, 167.8 meq/kg) with varying levels of VE (mg/kg) and VC (mg/kg) (OFO100E/500C, OFO200E/500C, OFO100E/1000C and OFO200E/1000C). Fish fed FFO100E/500C and OFO100E/500C had no differences in body weight gain (BWG). However, fish fed OFO200E/1000C diet had a significantly lower BWG than FFO100E/500C. Fish fed OFO200E/500C and OFO100E/1000C showed no differences in thiobarbituric acid-reactive substance values compared with FFO100E/500C. Increasing the levels of VC and VE supplementation increased liver AsA and α-Toc contents, respectively. Liver α-Toc content was significantly increased with incremental dietary VC levels, indicating a sparing effect of VC on liver α-Toc content of fish. Increasing the levels of dietary VC and VE supplementations decreased concentrations of 20:5n-3, 22:5n-3 and 22:6n-3 in fish liver. Fish fed OFO100E/500C and OFO200E/1000C diets showed higher oxidative stress condition than those fed FFO100E/500C. In conclusion, dietary VC and VE supplementation could maintain normal growth and health condition of juvenile Japanese flounder fed OFO. However, high doses of both vitamin supplements induced fish lipid peroxidation under oxidative stress condition