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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.

Ferulic acid (FA) is one of a common ingredients in Chinese herbal medicine. FA has the interesting property of promoting growth and improving meat quality in livestock, but the mechanism is not understood. This study evaluated both safety and mechanism of efficacy in zebrafish model. At 15 μg/mL or above, FA led to pericardial oedema and delayed growth in zebrafish embryos. Dietary FA promoted growth and feed assimilation in male adult zebrafish. Genes related to myogenic development (myod1, myog and myf5) were significantly upregulated by FA and muscle fibre width in skeletal muscle was increased. At 20 µg/g, FA significantly increased number of goblet cells in zebrafish intestinal tissue, and gut microbiota composition also changed. Based on 16s rRNA gene sequences, 20 μg/g FA decreased Firmicutes and increased Bacteroides. 20 μg/g FA also stimulated the expression of PPAR‐α, a gene associated with fat metabolism, and decreased the expression of PPAR‐β and PPAR‐γ. These gene expression changes were beneficial to fatty acid synthesis and metabolism and decreased fat deposition. Our overall results indicated that FA can be a safe growth promotor in fish particularly in skeletal muscles. [ABSTRACT FROM AUTHOR]

This study aimed to assess the effects of different linolenic acid (LNA, 18:3n‐3) and linoleic acid (LA, 18:2n‐6) ratios in diet on growth performance, fatty acid composition in muscle and liver and non‐specific immunity in serum, liver and intestines of juvenile Manchurian trout (Brachymystax lenok). With casein, soybean meal and corn protein meal as main protein sources, a vegetable oil‐based (VO‐based) diet with iso‐nitrogen (40%) and iso‐lipid (18.5%) was prepared by adding different proportions of linseed oil, corn oil and palm oil. The LNA/LA ratio in the VO‐based diets was 0.02, 0.55, 1.06, 1.61 and 2.17 (constant composition of LNA and LA). The control group (CON) used fish oil (FO) as the sole lipid source. Healthy juvenile Manchurian trout (body weight: 7.00 ± 0.07 g) were fed in a recirculating aquaculture system for 9 weeks. The results showed that VO‐based diets did not affect the growth of Manchurian trout, but decreased DHA and EPA levels in the dorsal muscle of Manchurian trout. Levels of LA, arachidonic acid (ARA) and n‐6 polyunsaturated fatty acids (PUFA) of liver in VO‐based diets were significantly higher than those in CON diet and decreased with an increasing LNA/LA ratio in the diet. The composition of LNA, DHA, EPA and n‐3 PUFA of dorsal muscle and liver in VO‐based diets increased with increasing LNA/LA ratio. In the liver and proximal intestine (PI), lysozyme (LZM) activity increased with the increasing LNA/LA ratio in the VO‐based diet. However, it decreased in the mid‐intestine (MI) and distal intestine (DI). Acid phosphatase (ACP) activity in liver was significantly high when the LNA/LA ratio in the diet was 1.06 (p <.05). Alkaline phosphatase (AKP) activity in the MI increased with the increasing dietary LNA/LA ratio. The LNA/LA ratio in the diet did not affect the growth of Manchurian trout juveniles, and a diet with an LNA/LA ratio between 0.55 and 1.06 was beneficial for non‐specific immunity in Manchurian trout. [ABSTRACT FROM AUTHOR]

In order to study the effects of linseed oil substitution on the growth, body composition, tissue fatty acid composition, flesh nutritional value and immune indices of juvenile Manchurian trout, five feed types containing different levels of linseed oil (LO) mixed with fish oil (FO) were prepared: 0 (0 LO); 250 g/kg (25 LO); 500 g/kg (50 LO); 750 g/kg (75 LO); and 1000 g/kg (100 LO); and fed to juvenile Manchurian trout (initial weight 6.43 ± 0.02 g) for 9 weeks. The results showed that substitution of FO with 750 g/kg LO did not affect the growth of juvenile trout, with protein content in the dorsal muscle, and lipid content in the liver not showing any significant difference (p > 0.05). The highest lipid content found in muscle samples occurred for the 25 LO diet. The fatty acid composition found in the dorsal muscle and the liver of the Manchurian trout reflects the fatty acid composition in the diet, where the relative amount of linolenic acid (ALA), linoleic acid (LA) and docosahexaenoic acid (DHA) found in these organs has a positive linear correlation with their relative composition in the diet (p < 0.05). As the amount of LO in the diet was increased, the composition of ALA found in the sampled organs increased, while the composition of DHA and eicosapentaenoic acid (EPA) decreased. At the same time, the index of atherogenicity (IA) and thrombogenicity (IT) of the muscle samples from the 75 LO and 100 LO diets was significantly lower than for the 0 LO and 25 LO diets (p < 0.05), while the flesh lipid quality (FLQ) in the 100 LO diet was significantly lower than for the other diets (p < 0.05). The aspartate transaminase (AST) activity decreased initially, and then increased, as the level of LO replacement for FO was increased, with the 25 LO diet being significantly lower than for other groups (p < 0.05). The alanine aminotransferase (ALT) activity in serum samples from the 100 LO diet was higher than that from other diets. The lysozyme (LZM) activity in both serum and liver tissue first increased to a peak for the 25 LO and 50 LO diets, respectively, and then decreased as the level of LO was further increased. There was no significant change in the alkaline phosphatase (AKP) activity in the liver samples; however, the acid phosphatase (ACP) activity decreased significantly from the highest value for 0 LO feed group. In conclusion, the composition of fatty acids in the dorsal muscle and the liver was found to be modified by the diets, and with the diet containing less than 750 g/kg LO, being both beneficial for growth, and improved immunity, while maintaining the nutritional value of the lipid content in the dorsal muscle during the 9‐week period. [ABSTRACT FROM AUTHOR]