Lipid metabolism in Tinca tinca and its n-3 LC-PUFA biosynthesis capacity

Carps, barbels and other cyprinids are the major contributors to freshwater aquaculture at global scale. Nevertheless, freshwater fish aquaculture needs to diversify their production in order to offer consumers new species. Tench (Tinca tinca) is a freshwater species with great interest for the diversification of continental aquaculture. However, up to date, no commercial formulated diet exists for this species in order to optimize their nutritional requirements and the quality of its final product. Using multiple methodological approaches, the aim of this study was to evaluate the long chain polyunsaturated fatty acid (LC-PUFA) metabolism of T. tinca. Firstly, the molecular cloning and functional characterisation by heterologous expression in yeast of a desaturase (Fads2) and two elongases (Elov12 and Elov15) involved in LC-PUFA biosynthesis, and the analysis of gene expression among tissues were performed. Secondly, in order to confirm the LC-PUFA biosynthesis capacity of isolated hepatocytes and enterocytes, cells were incubated with [1-C-14] labelled linoleic acid (18:2n-6, LA), linolenic acid (18:3n-3, ALA) and eicosapentaenoic acid (20:5n-3, EPA). In yeast, Fads2 showed a Delta 6/Delta 5 bi-functional activity. Elovl2 was more active over C-20 and C-22 substrates, whereas Elov15 was over C-18 and C-20. Liver displayed the highest expression for the three target genes (fads2, elovl2 and elovl5). Incubated cells also showed Fads2 bifunctional activity as well as elongation products in concordance with yeast heterologous expression results. Importantly, our results demonstrated that tench is able to biosynthesise docosahexaenoic acid (DHA) from 18:3n-3 in both hepatocytes and enterocytes, a capacity that seems to explain in part the surprisingly high levels of DHA found in the fish flesh compared to its dietary supply. Tench is a promising freshwater species with a potential capacity to endogenously increase its flesh DHA contents, reducing the impact that the usage of fish oils from forage fisheries may have on the aquaculture industry.