Influence of dietary linseed oil as substitution of fish oil on whole fish fatty acid composition, lipid metabolism and oxidative status of juvenile Manchurian trout, Brachymystax lenok

In this study, juvenile Manchurian trout, Brachymystax lenok (initial weight: 6.43 +/- 0.02 g, mean +/- SE) were received for nine weeks with five types of diets prepared by gradually replacing the proportion of fish oil (FO) with linseed oil (LO) from 0% (LO0) to 25% (LO25), 50% (LO50), 75% (LO75), and 100% (LO100). The eicosapentaenoic (EPA) and docosahexaenoic (DHA) composition decreased with increasing inclusion level of LO (P < 0.05). With increasing LO inclusion level, triglyceride (TAG) content of serum increased significantly, however, there was a decrease in high-density lipoprotein cholesterol (HDL) (P < 0.05). LO substitution of FO up-regulated the gene expression level of lipid metabolism-related genes Fatty Acid Desaturases 6 (FAD6), Acetyl-Coa Carboxylase (ACCa), Sterol Regulatory Element Binding Protein 1 (SREBP-1), and Sterol O-Acyl Transferase 2 (SOAT2), and down-regulated the gene expression level of Peroxisome Proliferator-Activated Receptor a (PPARa) (P < 0.05). The SOD activities of both serum and liver in LO100 were significantly lower than in LO25 (P < 0.05). The CAT activity of the liver in LO100 was significantly lower than in LO0 and LO25 (P < 0.05). This study indicates that the Manchurian trout may have the ability to synthesize LC-PUFAs from ALA, and an appropriate LO in substitution of FO (<75%) could improve both the lipid metabolism and the oxidation resistance.