Effects of dietary lipid level and vegetable oil on fatty acid metabolism in Atlantic salmon (Salmo salar L.) over the whole production cycle

Abstract

Changes in fatty acid metabolism in Atlantic salmon (Salmo salar) induced by vegetable oil (VO) replacement of fish oil (FO) and high dietary oil in aquaculture diets can have negative impacts on the nutritional quality of the product for the human consumer, including altered flesh fatty acid composition and lipid content. A dietary trial was designed to investigate the twin problems of FO replacement and high energy diets in salmon throughout the entire production cycle. Salmon were grown from first feeding to around 2 kg on diets in which FO was completely replaced by a 1:1 blend of linseed and rapeseed oils at low (14-17%) and high (25-35%) dietary oil levels. This paper reports specifically on the influence of diet on various aspects of fatty acid metabolism. Fatty acid compositions of liver, intestinal tissue and gill were altered by the diets with increased proportions of C 18 polyunsaturated fatty acids and decreased proportions of n-3 highly unsaturated fatty acids (HUFA) in fish fed VO compared to fish fed FO. HUFA synthesis in hepatocytes and enterocytes was significantly higher in fish fed VO, whereas β-oxidation was unaltered by either dietary oil content or type. Over the entire production cycle, HUFA synthesis in hepatocytes showed a decreasing trend with age interrupted by a large peak in activity at seawater transfer. Gill cell prostaglandin (PG) production showed a possible seasonal trend, with peak activities in winter and low activities in summer and at seawater transfer. PG production in seawater was lower in fish fed the high oil diets with the lowest PG production generally observed in fish fed high VO. The changes in fatty acid metabolism induced by high dietary oil and VO replacement contribute to altered flesh lipid content and fatty acid compositions, and so merit continued investigation to minimize any negative impacts that sustainable, environmentally-friendly and cost-effective aquaculture diets could have in the future.Abbreviations: FO, fish oil; HUFA, highly unsaturated fatty acids acids (carbon chain length ≥ C 20 with ≥ 3 double bonds); LO, linseed oil; RO, rapeseed oil; VO, vegetable oil.3

Long-chain polyunsaturated fatty acid synthesis in fish: Comparative analysis of Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.) Δ6 fatty acyl desaturase gene promoters

“…The activity of the LC-PUFA biosynthesis pathway was significantly lower in liver and intestine from salmon being fed EPA and DHA in the form of fish oil compared to fish fed vegetable oils that are devoid of LC-PUFA (Tocher et al, 1997(Tocher et al, , 2003c. There is also a significant correlation between the activity of the LC-PUFA biosynthetic pathway and dietary n-3 LC-PUFA levels (Tocher et al, 2003b).…”

Criteria for Safe Use of Plant Ingredients in Diets for Aquacultured Fish

“…One that has gained significant interest in salmonid feeds is linseed oil. As it contains more than 50% of the fatty acids as linolenic acid (LNA,18:3n-3) it has been explored as a potential for increasing the content of n-3 HUFA in salmonid fish flesh (Tocher et al 2003a;Bendiksen and Jobling 2004).…”

“…A natural consequence of this is that increases in n-6 HUFA in PI following increased feeding of 18:2n-6 should cause major increases in the production of this series of eicosanoids. Indeed most available literature do point to this in salmonids while Norwegian Scientific Committee for Food Safety Vitenskapskomiteen for mattrygghet (VKM) 81 07/604 -final increases in n-3 HUFA or linseed oil (18:3n-3) will inhibit the production of n-6 eicosanoids (Ashton et al 1994;Bell et al 1996a;Balfry and Higgs 2001;Tocher et al 2003b;Gjøen et al 2004). The question then remains if increasing the n-6 PUFA in plant oil supplemented diets will enhance the immune response as seen in mammals and reduce the likelihood of infections.…”

“…A standard inclusion of soybean lecithin may also be advisable. These and other variants of mixtures of oil sources have been explored in recent years with some success in salmonid fish Bell et al 2003b;Tocher et al 2003a). Such mixtures do not seem to be necessary for marine fish.…”

Docosahexaenoic acid in Arctic charr (Salvelinus alpinus): The importance of dietary supply and physiological response during the entire growth period

“…Therefore, the present results suggested that juvenile Arctic charr are more efficient at retaining dietary DHA and/or the amount of DHA synthesised de novo is higher compared to adult Arctic charr. Tocher et al (2003) found that endogenous synthesis of DHA was higher in juvenile Atlantic salmon (parr) compared to older Atlantic salmon (smolt). During later stages of development, fish allocate energy to gonadal maturation (Izquiredo et al, 2001;Mourente and Odriozola, 1990;Wiegand 1996) and thus retention of DHA in somatic tissues may be reduced in sexually mature adults.…”