Eicosapentaenoic Acid, Arachidonic Acid and Eicosanoid Metabolism in Juvenile Barramundi Lates calcarifer

Abstract

A two part experiment was conducted to assess the response of barramundi (Lates calcarifer; initial weight=10.3±0.03g; mean±S.D.) fed one of five diets with varying eicosapentaenoic acid (diets 1, 5, 10, 15 and 20g/kg) or one of four diets with varying arachidonic acid (1, 6, 12, 18g/kg) against a fish oil control diet. After 6weeks of feeding, the addition of EPA or ARA did not impact on growth performance or feed utilisation. Analysis of the whole body fatty acids showed that these reflected those of the diets. The ARA retention demonstrated an inversely related curvilinear response to either EPA or ARA. The calculated marginal utilisation efficiencies of EPA and ARA were high (62.1 and 91.9% respectively) and a dietary ARA requirement was defined (0.012g/kg0.796/day). The partial cDNA sequences of genes regulating eicosanoid biosynthesis were identified in barramundi tissues, namely cyclooxygenase 1 (Lc COX1a, Lc COX1b), cyclooxygenase 2 (Lc COX2) and lipoxygenase (Lc ALOX-5). BothLc COX2andLc ALOX-5expression in the liver tissue were elevated in response to increasing dietary ARA, meanwhile expression levels ofLcCOX2and the mitochondrial fatty acid oxidation gene carnitine palmitoyltransferase 1 (LcCPT1a) were elevated in the kidney. A low level of EPA increased the expression ofLc COX1bin the liver. Consideration should be given to the EPA to ARA balance for juvenile barramundi in light of nutritionally inducible nature of the cyclooxygenase and lipoxygenase enzymes.