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

Abstract

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 (ACCα), 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 (PPARα) (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.

Insect (black soldier fly larvae) oil as a potential substitute for fish or soy oil in the fish meal-based diet of juvenile rainbow trout (Oncorhynchus mykiss)

“…Substitution of FO with alternative oils has been reported to change the fatty acid composition of fish tissue and quality of the fillet ( Peng et al., 2017 ; Turchini and Francis, 2009 ; Yang et al, 2020 ; Yu et al., 2019 ). In the current study, it was evident that the muscle and liver fatty acid composition mirrored that of the diet with fish fed the SO and BSLO-based diets having the highest 18:2n-6 and 18:3n-3 and 14:0, 16:0, and total SFA, respectively, than trout fed the FO diet.…”

“…Also, turbot fed a palm oil-based diet had a higher deposition of ARA and DHA than SO fed fish ( Peng et al., 2017 ). Contrarily, replacement of FO with linseed oil (LO) resulted in a lower whole-body of LC-PUFA in Manchurian trout ( Yu et al., 2019 ). The lower EPA and n-3:n-6 ratio seen in the BSLO groups compared to FO are consistent with other studies where fish were fed vegetable oil ( Mu et al., 2020 ; Peng et al., 2017 ; Yang et al, 2020 ; Yu et al., 2019 ).…”

“…Contrarily, replacement of FO with linseed oil (LO) resulted in a lower whole-body of LC-PUFA in Manchurian trout ( Yu et al., 2019 ). The lower EPA and n-3:n-6 ratio seen in the BSLO groups compared to FO are consistent with other studies where fish were fed vegetable oil ( Mu et al., 2020 ; Peng et al., 2017 ; Yang et al, 2020 ; Yu et al., 2019 ). Furthermore, the close proximity in PCA of fish fed SO and BSLO signifies that BSLO has a comparable fatty acids composition and is suitable for use in place of SO in trout feeds.…”

“…On the other hand, no effect on glucose concentration was recorded when Jian carp was fed BSLO as replacement for SO ( Li et al., 2016 ), and this may be due to use of plant oil as a control, which possibly has bioactive compounds. SOD, CAT and GPx are important antioxidant defense enzymes which help to protect cells against reactive oxygen species-triggered damage in fish ( Fawole et al., 2020 ; Shamna et al., 2020 ; Yu et al., 2019 ). In the present study, the activity of SOD was found to be higher in BSLO + BA fed trout compared to the other dietary groups.…”

“…In addition, the concentration of unsaturated fatty acid (linoleic, 18:2n-6, and linolenic, 18:3n-3) in BSL oil is closely related to that of soybean oil (SO), and this could be effectively utilized by freshwater fish to biosynthesize n-3 and n-6 LC-PUFA due to their endogenous capability ( Tocher, 2003 ). The nutritional modulation and accumulation of LC-PUFA in fish is related to the biosynthesis and decomposition of fatty acids by enzymes associated with fatty acid metabolism and pertinent transcription factors ( Yu et al., 2019 ). Fatty acid synthase (FAS), one of the main lipogenic enzymes, catalyzes the synthesis of long-chain saturated fatty acids (LC-SFA) from acetyl CoA and malonyl-CoA in the presence of nicotinamide adenine dinucleotide phosphate (NADPH) ( Dong et al., 2014 ), while fatty acid-binding proteins (FABP) aid in the transport of fatty acids into cells ( Torstensen et al., 2009 ).…”