Effect of partial substitution of dietary fish oil by vegetable oils on desaturation and β-oxidation of [1-C]18:3n-3 (LNA) and [1-C]20:5n-3 (EPA) in hepatocytes and enterocytes of European sea bass (Dicentrarchus labrax L.)

The increasing worldwide aquaculture output and concomitant decrease in the stocks of feedgrade fish used for fish oil production has made fish oil replacement in feeds a priority for the aquaculture industry. The regulation of fatty acid metabolism in fish is important in order to determine strategies for the best use of plant oils in diets for commercially important cultured fish species. We have studied the desaturation/elongation and β-oxidation of C-linolenic (LNA) and C-eicosapentaenoic (EPA) acids in hepatocytes and pyloric caecal enterocytes in European sea bass fed diets with partial substitution (60%) of fish oil (FO) with vegetable oils (rapeseed, linseed and palm oil) blended in different proportions, for 64 weeks. The rate of desaturation of C‐LNA was very low in hepatocytes from all treatments and no significant differences were observed among treatments. The rate of desaturation of C‐LNA in enterocytes was higher than that in hepatocytes but still low (less than 5% of total radioactivity recovered). The desaturation of C‐EPA in enterocytes was also higher than in hepatocytes, but again was low and no significant differences were found among treatments. The rates of ß‐oxidation of C-LNA and C-EPA were much higher than the rates of desaturation in both hepatocytes and enterocytes, however, no significant differences were observed in either hepatocytes or enterocytes among treatments. The rates of β-oxidation of C-LNA were considerably higher than those of C-EPA in both hepatocytes and enterocytes. In conclusion, European sea bass (a carnivorous marine fish), showed very low desaturation and elongation of LNA to EPA and DHA, and EPA to DHA, higher β−oxidation of LNA than EPA, and all desaturation and oxidation activities were significantly higher in enterocytes than in hepatocytes. A second major conclusion is that no clear quantitative nutritional effects on the desaturation/elongation and β−oxidation activities in either hepatocytes or enterocytes of sea bass were observed upon the inclusion of vegetable oils in the diet.