Polyunsaturated fatty acid metabolism in three fish species with different trophic level

Abstract

Reducing the dependency of fishfeed for marine ingredients and species diversification are both considered crucial factors for the sustainable development of aquaculture. The substitution of fish oil (FO) by vegetable oils (VO) in aquafeeds is an economically feasible solution. However, such substitution may compromise the fish flesh content of essential n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) and, therefore, its nutritional value for human consumption. Likewise, there is a wide range of strategies to select new target species for sector diversification, among which, the capacity to biosynthesize n-3 LC-PUFA from their C18 precursors abundant in VO might be considered as a fair preliminary strategy. Therefore, the aim of the present study was to analyze the metabolic fate of [1-14C] labeled 18:2n-6, 18:3n-3, 20:5n-3 and 22:6n-3 in isolated hepatocytes and enterocytes from wild individuals of three fish species with different trophic level: the marine herbivorous salema (Sarpa salpa), the strict carnivorous sand sole (Pegusa lascaris) and the omnivorous thicklip grey mullet (Chelon labrosus). These species were selected for their phylogenetic proximity to consolidated farmed species such as gilthead seabream (Sparus aurata), senegalese sole (Solea senegalensis), and golden grey mullet (Liza aurata), respectively. The study also assessed the molecular cloning, functional characterization and tissue distribution of the fatty acyl elongase (Elovl) gene, elovl5, involved in the biosynthetic metabolism of n-3 LC-PUFA. The three species were able to biosynthesize docosahexaenoic acid (22:6n-3). S. salpa seems to have similar biosynthetic capacity than S. aurata, with a fatty acyl desaturase 2 (Fads2), with Δ6, Δ8 and Δ5 activities. P. lascaris showed a wider Fads2 activity repertory than S. senegalensis, including Δ4 and residual Δ6/Δ5 activities. In C. labrosus, both Δ8 and Δ5 activities but not the Δ6 described for L. aurata were detected in the incubated cells. Elongation from C18 and C20 precursors to C20 and C22 products occurred in hepatocytes and enterocytes as well as in the functional characterization of Elovl5 by heterologous expression in yeast. Elovl5 showed a species specific expression pattern, with the highest rates observed in the liver, gut and brain in S. salpa and P. lascaris, and in the brain for C. labrosus. In summary, the LC-PUFA biosynthesis capacity from S. salpa, P. lascaris and C. labrosus greatly resembled that of their phylogenetic closer species. The three studied species could be further explored as candidates for the aquaculture diversification from their potential ability to biosynthesize LC-PUFA.