Complete replacement of dietary fish oil with a vegetable oil blend affect liver lipid and plasma lipoprotein levels in Atlantic salmon (Salmo salar L.)

To study how hepatic lipid turnover and lipid transport may be affected by complete replacement of dietary fish oil (FO) with a vegetable oil blend (VO) from start feeding until the adult stages, Atlantic salmon (Salmo salar L.) were fed either 100% FO- or 100% VO-based diets (55% rapeseed oil, 30% palm oil and 15% linseed oil) from start feeding until 22 months. Liver and plasma lipoprotein lipid class levels and lipoprotein fatty acid composition were analysed through the seawater phase, whereas liver fatty acid composition, plasma cholesterol, triacylglycerol (TAG) and protein levels were analysed through both freshwater and seawater stages. Further, enzyme activity of liver fatty acid spithetase (FAS), NADH-isocitrate dehydrogenase, malic enzyme, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and expression of the gene Peroxisome proliferator-activated receptor gamma (PPAR gamma) was analysed during both fresh water and seawater stages through the experiment. Dietary VO significantly increased salmon liver TAG and hence total liver lipid stores after 14 and 22 months of feeding. Further, after 22 months of feeding, plasma lipid levels and plasma low-density lipoprotein (LDL) levels were significantly decreased in VO-fed salmon compared with FO-fed fish. The same trend, although not statistically significant, was seen for plasma very low-density lipoprotein (VLDL). The activity of FAS was generally low throughout the experiment with the VO group having significantly lower activity after 16 months of feeding. The expression of PPAR gamma in livers increased prior to seawater transfer followed by a decrease, and then another increase towards the final sampling (22 months). Dietary vegetable oil replacement had no impact on PPAR gamma expression in salmon liver. In summary, liver TAG stores, plasma lipid and LDL levels were affected by dietary vegetable oil replacement in Atlantic salmon during a long-term feeding experiment. Current results indicate that high dietary vegetable oil inclusion increase hepatic TAG stores and decrease plasma lipid levels possible through decreased VLDL synthesis.