Effects of oxidised dietary fish oil and high-dose vitamin E supplementation on growth performance, feed utilisation and antioxidant defence enzyme activities of juvenile large yellow croaker (Larmichthys crocea).

This study was conducted to elucidate the effects of oxidised dietary lipids and high-dose vitamin E (VE) on growth performance and immune responses of large yellow croaker. Juvenile fish (initial average body weight of 7·82 (sem 0·68) g) were fed diets containing either fresh fish oil (fresh diet, peroxide value (POV)=1·72 mEq/kg) or fish oil oxidised to varying degrees (oxidised diets, POV=28·29-104·21 mEq/kg), with or without supplementary 600 mg VE/kg diet, for 10 weeks in floating cages. Growth was significantly lower and feed intake (g/100 g body weight per d) was higher in fish fed the oxidised diet. Supplementation with VE increased the growth of fish fed the oxidised diets, but significantly decreased the growth of fish fed the fresh diet. Hepatosomatic index increased with increasing dietary POV and decreased with VE supplementation. Hepatic catalase activity, superoxide dismutase (SOD) activity and malondialdehyde content were significantly higher in fish fed the oxidised diets, and these values decreased significantly following VE supplementation. However, hepatic SOD activity was enhanced by VE supplementation in fish fed the fresh diet. Air-exposure mortality was significantly increased by dietary POV, and this effect was inhibited by VE supplementation. These results suggest that dietary oxidised fish oil could stimulate the activities of antioxidant defence enzymes in stressed large yellow croaker. High-dose VE supplementation can alleviate oxidative stress of large yellow croaker fed oxidised fish oil, but can exert deleterious effects on fish in the absence of oxidative stress.