Regulation of genes related to lipid metabolism in Atlantic salmon (Salmo salar L.)

Fish is a vital source of highly valuable omega-3 (n-3) fatty acids (FA) in the human diet. With declining commercial fisheries, aquaculture fish constitute a growing proportion in human consumption. Sustainable development of aquaculture dictates that the fish feed used not solely is based on fish oil (FO) but also contain increasing levels of vegetable oil (VO). The replacement of FO with VO influences FA composition in fish tissues with the decrease of the n-3 highly unsaturated fatty acids (HUFAs), as main consequence rendering a fish less beneficial for human health. Accordingly the last decade of salmonid research has been focusing on increasing the amount of HUFAs in fish fed VO diets. Part of this focus has been on the addition of bioactive compounds to VO diets. In this thesis 2 studies are presented trying to shed more light on the potential positive effects of bioactive compounds.Paper I examine in vivo the effects of sesamin inclusion on Atlantic salmon (Salmo salar L.) fed VO-based diets with different n-6/n-3 FA ratios. Fish were fed for 4 months. In Paper II in vitro effects of bioactive compounds (genistein, lipoic acid, sesamin/episesamin and sesamin) were investigated in Atlantic salmon primary hepatocytes. Analyses were made 12h and 48h after addition of bioactive compounds, with most effects seen after 48h. In both studies, the FA composition and expression of genes involved in transcription, lipid uptake, desaturation, elongation and β-oxidation were examined.Genes involved in transcription regulation, β-oxidation, elongation and desaturation were affected by addition of bioactive compounds in both in vivo and in vitro experiments. Effects on the FA composition were found, but no clear affect on the DHA content. High level of sesamin supplementation had negative effect on growth rate and live weight.