LIPID-PEROXIDATION IN TURBOT (SCOPHTHALMUS-MAXIMUS) TISSUE - EFFECT OF DIETARY VITAMIN-E AND DIETARY N-6 OR N-3 POLYUNSATURATED FATTY-ACIDS

An experiment was performed on turbot juveniles to investigate the effects of dietary oil and alpha-tocopheryl acetate (alpha T) on muscle and the susceptibility of lipids to in vivo and in vitro peroxidation. Lipids were supplied by various feedstuffs as well as, at 5% of diet, by either cod liver oil (CLO) or peanut oil (PO) and alpha T was added at three different levels, the total amount being 20, 70 and 320 mg/kg feed. After 32 weeks of feeding, oxidation of lipids was determined in muscle by measuring thiobarbituric acid reactive substances (TBARS) before and after storage for 6 months at - 20 degrees C. The level of alpha T and the chemical composition of muscle were also assessed while vitamin E and C were assayed in liver. TBARS were also measured in the medium after in vitro incubation of muscle and liver homogenates with Fe2+ and ascorbic acid. This test was also performed after 46 weeks of feeding. Fatty acids were measured in addition to TEARS in three fish per diet. None of the parameters tested significantly altered the growth rate or the overall composition of muscle. In both tissues, alpha T levels were greatly influenced by dietary intake of alpha T, and to a lesser extent, by dietary lipid in muscle tissue only (which was lower in fish fed CLO). In the fresh tissue, TBARS were slightly higher in fish fed low dietary alpha T and in those fed CLO. In muscle, this phenomenon was accentuated after 6 months storage at - 20 degrees C. For both tissues, the in vitro release of TBARS was greater from homogenates of CLQ-fed fish than of PO-fed fish. An in vitro increase in TBARS was accompanied by a loss of polyunsaturated fatty acids and was found to be related to the degree of unsaturation of the fatty acids. This study demonstrates that dietary fish oil increases the susceptibility of turbot tissue to in vivo and in vitro fatty acid peroxidation, the in vitro test being more sensitive. alpha T supplementation limits this phenomenon, but in muscle complete compensation was observed only in fish fed PO, while in liver, complete inhibition was observed in fish fed both PO and CLO supplemented with 320 mg alpha T/kg. The comparison of liver and muscle indicates a better protection and a higher alpha T content in the former tissue, suggesting the better protection from peroxidation could be related to the alpha T/PUFA ratio.