Previously, we had shown that altering the highly unsaturated fatty acid(HUFA)/vitamin E ratios in sea bream (Sparus aurata) livers significantly affected their peroxidation status, with fish fed the diet rich in HUFA and low in vitamin E showing significantly higher values of lipid peroxidation products, without, however, significant effects on liver antioxidant defence enzyme activities. The aim of the present trial was to further characterise the biochemical indicators of peroxidative stress in juvenile sea bream. A high pro-oxidative stress was induced by feeding diets containing around 7% of the dry weight as n-3HUFA. The potential peroxidative stress was increased by oxidising the oil, increasing the peroxide value of the oil some 10-fold. These oils were fed without or with supplemental vitamin E (α-tocopherol acetate at 200 mg.kg -1 dry diet) giving four diets in total. Fish were sampled after 30 and 60 days of feeding the experimental diets. None of the diets had any serious deleterious effects on growth and mortality of the fish during the trial. Similarly, there were few significant effects due to dietary oxidised oil or supplementary vitamin E on liver lipid and fatty acid profiles of livers and, in particular, the proportions of HUFA were not decreased by dietary oxidised oil. The vitamin E content of the liver reflected the vitamin E contents of the diets but was also affected by dietary oxidised oil being reduced by oxidised oil in fish fed diets without supplemental vitamin E but, unexpectedly, increased by oxidised oil in fish fed diets supplemented with vitamin E. Liver TBARS levels were significantly lower in fish fed diets supplemented with vitamin E whereas dietary oxidised oil had no major effects on lipid peroxidation products. Catalase and superoxide dismutase activities were both increased in fish fed dietary oxidised oil and reduced by supplementary vitamin E after 30 days feeding.In contrast glutathione peroxidase was less affected by the diets, and the activities of glutathione-S-transferase and glutathione reductase were only reduced by dietary vitamin E after 60 days of feeding. However, all the enzyme activities were significantly affected by the duration of feeding, but the number of interactions between the three factors (time, oil and vitamin E) showed that the relationships were complicated. In conclusion, the present study showed that feeding diets containing oxidized oil significantly affected the activities of liver antioxidant defence enzymes and that dietary vitamin E partially abrogated these effects.Growth and survival of the fish were relatively unaffected suggesting that the responses in sea bream offered effective protection. However, the duration of feeding the diets of high pro-oxidative stress was observed to have a hitherto unknown effect, possibly the result of an adaptive process, but which requires further investigation.

This study was designed to investigate the requirements of Dentex dentex larvae for (n-3) highly unsaturated fatty acids (HUFA) at the Artemia feeding stage. Artemia were enriched using mixtures of ICES Experimental Emulsions ICES 50/0.6/C (500 mg/g (n-3) HUFA, 0.6 DHA/EPA ratio, based on ethyl esters) and ICES 0/-/C (based on coconut oil) and to give five dietary treatments which contained different levels of (n-3) HUFA from 0.72 to 6.23 as dry weight percentage. Optimal growth, as evidenced by total length, individual dry weight, specific growth rate and thermal growth coefficient, was achieved when dietary (n-3) HUFA was 3.97 on a dry weight basis. Larvae fed Artemia enriched with apparently super-optimal levels of (n-3) HUFA (5.67-6.23 %) showed significantly lower vitamin E contents and higher malondialdehyde (MDA) levels combined with their eyes having maximum (n-3) HUFA values and DHA/EPA ratios.Poorer performance of larvae was associated with increased dietary and larval MDA and decreased larval vitamin E, indicating increasing oxidation of (n-3) HUFA in Artemia and larval utilization of vitamin E with increasing levels of dietary (n-3) HUFA, particularly at supraoptimal levels of enrichment. The activities of antioxidant enzymes in the larvae was generally not greatly affected by the dietary treatments in this study. A balance is required between growth-promoting essential fatty acid (EFA) qualities of (n-3) HUFA and their potentially growth-inhibiting (prooxidant) qualities which must be counter-balanced with adequate dietary antioxidants.

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2Lipid peroxidation, specifically polyunsaturated fatty acid (PUFA) oxidation is highly deleterious, resulting in damage to cellular biomembranes, and may be a principal cause of several diseases in fish including jaundice and nutritional muscular dystrophy. Tissue lipid PUFA content and composition are critical factors in lipid peroxidation, as is the level of endogenous antioxidant molecules such as vitamin E. The primary objective of the present study was the characterization of antioxidant systems in a cultured juvenile marine fish, gilthead sea bream (Sparus aurata) with the underlying aim to understand how to avoid oxidation problems that may cause pathologies and disease and so to enhance growth and quality of early ongrowing stages. Juvenile sea bream were fed diets having either high or low levels of fish oil and supplemented or basal levels of vitamin E with PUFA/vitamin E ratios ranging from 117 ± 12 in the diet with low PUFA supplemented with vitamin E to 745 ± 48 in the diet with high PUFA with no additional vitamin E. None of the diets had serious deliterious effects on growth or survival of the fish, but the different dietary regimes were effective in significantly altering the PUFA/vitamin E ratios in the fish livers with values ranging from 5.7 ± 0.4 in fish fed the diet with low PUFA supplemented with vitamin E to 91.1 ± 13.2 in fish fed the diet with high PUFA with no additional vitamin E. This had effects on the peroxidation status of the fish as indicated by the significantly altered levels of in vivo lipid peroxidation products measured in liver, with fish fed the diet rich in PUFA and low in vitamin E showing significantly higher values of thiobarbituric acid reactive substances (TBARS) and isoprostanes. The isoprostane levels generally followed the same pattern as the TBARS levels supporting its value as an indicator of in vivo oxidative stress in fish, as it is in mammals.However, few significant effects on antioxidant enzyme activities were observed suggesting that more severe conditions may be required to affect these activities such as increasing the PUFA/vitamin E ratio or by increasing peroxidative stress through the feeding of oxidized oils.