The role of vitamin E in polyunsaturated fatty acid synthesis and alleviating endoplasmic reticulum stress in sub-adult grass carp (Ctenopharyngodon idella).

Vitamin E (VE) is an essential lipid-soluble vitamin that improves the fish flesh quality. However, the underlying molecular mechanisms remain unclear. This study aimed to investigate the effects of VE on growth performance and flesh quality in sub-adult grass carp (Ctenopharyngodon idella). A total of 450 fish (713.53 ± 1.50 g) were randomly divided into six treatment groups (three replicates per treatment) and fed for nine weeks with different experimental diets (dietary lipid 47.8 g/kg) that contained different levels of VE (5.44, 52.07, 96.85, 141.71, 185.66, and 230.12 mg/kg diet, supplemented as dl-α-tocopherol acetate). Notably, the treatment groups that were fed with dietary VE ranging from 52.07 to 230.12 mg/kg diet showed improvement in the percent weight gain, special growth rate, and feed efficiency of grass carp. Moreover, the treatment groups supplemented with dietary VE level of 141.71, 185.66, and 230.12 mg/kg diet showed enhancement in crude protein, lipid, and α-tocopherol contents in the muscle, and the dietary levels of VE ranging from 52.07 to 141.71 mg/kg diet improved muscle pH24h and shear force but reduced muscle cooking loss in grass carp. Furthermore, appropriate levels of VE (52.07 to 96.85 mg/kg diet) increased the muscle polyunsaturated fatty acid content in grass carp. Dietary VE also increased the mRNA levels of fatty acid synthesis-related genes, including fas, scd-1, fad, elovl, srebp1, pparγ, and lxrα, and up-regulated the expression of SREBP-1 protein. However, dietary VE decreased the expression of fatty acid decomposition-related genes, including hsl, cpt1, acox1, and pparα, and endoplasmic reticulum stress-related genes, including perk, ire1, atf6, eif2α, atf4, xbp1, chop, and grp78, and down-regulated the expression of p-PERK, p-IRE1, ATF6, and GRP78 proteins. In conclusion, dietary VE increased muscle fatty acid synthesis, which may be partly associated with the alleviation of endoplasmic reticulum stress, and ultimately improves fish flesh quality. Moreover, the VE requirements for sub-adult grass carp (713.53 to 1590.40 g) were estimated to be 124.9 and 122.73 mg/kg diet based on percentage weight gain and muscle shear force, respectively.

Role of creatine supplementation on the myofibre characteristics and muscle protein synthesis of grass carp (Ctenopharyngodon idellus).

To assess the role of dietary creatine on myofibre characteristics and protein synthesis in muscle, we fed grass carp (Ctenopharyngodon idellus, initial body weight: 88·47 ± 1·44 g) creatine-supplemented diets (1·84, 5·91, 8·48 and 15·44 g/kg diet) for 8 weeks. Creatine supplementation did not affect growth performance, but significantly increased creatine contents in muscle and liver. At 8·48 g/kg, creatine decreased the activities of alanine transaminase and aspartate aminotransferase in serum and improved hardness and chewiness of muscle due to shorter myofibre mean diameter, higher myofibre density and the frequencies of the diameters of classes I and III and collagen content, longer sarcomere length and upregulated mRNA levels of slow myosin heavy chains. Creatine supplementation upregulated the mRNA expressions of myogenic regulatory factors. The 8·48 g/kg creatine-supplemented diet significantly increased the contents of protein, total amino acids (AA), essential AA and free flavour AAs in muscle, the protein levels of insulin-like growth factor I, myogenic differentiation antigen and PPAR-γ coactlvator-1α in muscle and stimulated the phosphorylation of target of rapamycin (TOR) pathway in muscle. In summary, 8·48 mg/kg creatine improved fish health and skeletal muscle growth and increased hardness and protein synthesis in muscle of grass carp by affecting myofibre characteristics and the TOR signalling pathway. A second-order regression model revealed that the optimal dietary creatine supplementation of grass carp ranges between 8·48 and 12·04 g/kg.

Dietary effects of aucubin on growth and flesh quality of grass carp (Ctenopharyngodon idellus) based on metabolomics.

This aim of this study was to investigate the effects of dietary aucubin on the growth, flesh quality, and metabolomics of grass carp (Ctenopharyngodon idella). Five diets were designed with the aucubin inclusion of 0 (control diet), 0.2, 0.4, 0.6, and 0.8 g/kg (Auc-0.2, Auc-0.4, Auc-0.6, Auc-0.8) and were fed to grass carp with an initial body weight of 17.0 ± 0.2 g for 60 d. The results indicated that dietary aucubin did not significantly affect the growth performance of grass carp (P > 0.05). Compared to the control, dietary supplementation with 0.2 to 0.8 g/kg aucubin increased flesh hardness, chewiness, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and the contents of total free amino acids (TFAA) and n-3 polyunsaturated fatty acids (n-3 PUFA) (P < 0.05). The contents of malondialdehyde (MDA) and lactic acid (LD) in the flesh were significantly decreased by the addition of 0.4 to 0.6 g/kg aucubin and by the addition of 0.6 to 0.8 g/kg aucubin (P < 0.05), respectively, while the content of delicious amino acids (DAA) was significantly enhanced by the addition of 0.4 to 0.8 g/kg aucubin (P < 0.05). Moreover, the contents of collagen and C22:6n3 (DHA) in the flesh of the Auc-0.8 group were significantly higher than those of the control (P < 0.05). In the metabolomics profiling of flesh, 133 and 135 named differential metabolites were identified in the Auc-0.4 and Auc-0.8 groups, respectively, compared to the control, and these metabolites were found to be involved in the second-grade pathways of "lipid metabolism" and "amino acid metabolism". Regarding gene expression, the mRNA levels of CuZn-SOD, CAT, COL1A1, COL1A2, Smad4, and FAS in flesh were upregulated in the Auc-0.4 and Auc-0.8 groups, and the expression levels of GPx, Nrf2, and TGF-ß1 mRNA were also upregulated in the Auc-0.8 group (P < 0.05). In summary, dietary aucubin did not promote growth, but improved the flesh quality of grass carp, which might be associated with the TGF-ß/Smad and Nrf2 pathways. The recommended supplementation level of aucubin in the diet of grass carp was 0.6 to 0.8 g/kg.

Aucubin is an iridoid glycoside that is widely distributed in green plants and exhibits various biological activities such as antioxidant, anti-inflammatory, and protecting the liver. In previous studies, we explored the effects of different dietary levels of iridoids including geniposide and geniposide acid, on the flesh quality of grass carp. As aucubin shares a similar chemical structure to that of geniposide and geniposide acid, it was speculated that aucubin might exhibit the same function of promoting flesh quality in fish. Our study was conducted to explore the effects on the growth and flesh quality of grass carp. We found that dietary aucubin did not affect the growth of grass carp but improved flesh quality by increasing the contents of collagen, free amino acids, and n-3 PUFA; increasing the activities of CAT, SOD, and GPx; and decreasing the contents of MDA and PC in flesh, which might be associated with the TGF-ß/Smad and Nrf2 pathways.

Transcriptomic and biochemical analyses revealed the improved growth, lipid metabolism, and flesh quality of grass carp (Ctenopharyngodon idellus) by dietary Eucommia ulmoides bark and leaf supplementation.

The objective of this study was to investigate the dietary effects of Eucommia ulmoides bark and leaf (EB, EL) supplementation on the growth, lipid metabolism, flesh quality, and transcriptome of grass carp (Ctenopharyngodon idellus). EB and EL were individually added to the basal diet (control) at concentrations of 20 g/kg and 40 g/kg, respectively, and then the three diets were fed to grass carp (59.7 ±â€…0.3 g) for 60 d. The results showed that the weight gain was improved, and the feed conversion ratio was decreased by supplementation with EB and EL (P < 0.05). Compared to the control, the EB and EL groups showed higher flesh hardness; water-holding capacity; and collagen, docosahexaenoic acid (DHA), and n-3 polyunsaturated fatty acids (n-3PUFAs) contents and lower mesenteric lipid and muscle crude lipid contents (P < 0.05). Moreover, dietary EB and EL supplementation increased the activities of superoxide dismutase and glutathione peroxidase and decreased the contents of malondialdehyde and protein carbonyl in flesh (P < 0.05). In muscle transcriptome profiling, a total of 979, 1980 differentially expressed genes (DEGs) were identified, and 29, 199 Gene Ontology (GO) terms and 13, 39 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were significantly enriched in the EB and EL groups, respectively. Some key pathways and genes involved in promoting growth, lipid metabolism and flesh quality were obtained, including mTOR and PPAR signaling pathways, muscle cytoskeleton- and extracellular matrix-related genes (myosin and collagen), etc. Overall, dietary EB and EL supplementation improved the growth, lipid metabolism, and flesh quality of grass carp, and several potential pathways and genes were identified behind the improvement mechanism of EB and EL supplementation.

As a traditional herb, Eucommia ulmoides (E. ulmoides) has been utilized in East Asia for at least 2 000 years. In recent years, E. ulmoides has been applied in the culture of fish for its functions of promoting growth, lipid metabolism, and flesh quality. However, the underlying molecular mechanism of improving growth, lipid metabolism, and flesh quality is not well understood. Our study showed that the improvement of flesh quality is the combined effect of antioxidant capacity, muscle texture, water-holding capacity, and nutritional composition. Additionally, several potential pathways and differentially expressed genes were identified through RNA sequencing to further study the improvement mechanism of dietary E. ulmoides bark and leaf supplementation on growth, lipid metabolism, and flesh quality in fish.

Evaluating dynamic effects of dietary glycerol monolaurate on the productive performance and flesh quality of large yellow croaker (Larimichthys crocea).

The effects of GML (Glycerol monolaurate) supplementation with two level (0.5 and 1.0 g kg-1) on the productive performance and flesh quality of large yellow croaker (360 per group) were investigated during feeding (23,50-days) and fasting stage (23,70-days). The GML supplementation significantly increased body weight after 23-days and crude protein, inosinic acid, and yellowness after 50-days. Moreover, it increased hardness, springiness, and chewiness by increasing the collagen content, myofiber density, and decreasing myofiber diameter. The high GML supplementation increased the total free amino acids, delicate amino acids, monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (n-3 PUFA), and EPA + DHA, whereas it decreased the content of saturated fatty acids/unsaturated fatty acids (SFA/UFA). During fasting, better body shape and color were shown were shown at high GML supplementation. Conclusively, high dose GML supplementation exerted promising effects on the productive performance and flesh quality of large yellow croaker.

Dietary l-carnitine supplementation recovers the increased pH and hardness in fillets caused by high-fat diet in Nile tilapia (Oreochromis niloticus).

The wide use of high-fat diet (HFD) causes negative effects on flesh quality in farmed fish. l-carnitine, a lipid-lowering additive, enhances mitochondrial fatty acid ß-oxidation. However its roles in alleviating the effects of HFD on flesh quality in fish are unknown. We fed Nile tilapia with medium-fat diet (MFD, 6% dietary lipid), high-fat diet (HFD, 12% dietary lipid) and HFCD supplemented with l-carnitine (HFCD + 400 mg/kg l-carnitine) for 10 weeks. The HFD-fed fish had higher fat deposition, pH value, myofiber density and flesh hardness than those fed on MFD. However, feeding the fish with the HFCD improved lipid catabolism, which increased significantly lactic acid content and myofiber diameter in muscle, thus reduced pH and hardness values. HFCD also reduced endoplasmic reticulum stress and myofiber apoptosis caused by HFD in the fish. Our study suggests that dietary l-carnitine supplementation alleviates the negative effects of HFD on flesh quality of farmed fish.

Interactive effects of dietary quercetin nanoparticles on growth, flesh antioxidant capacity and transcription of cytokines and Aeromonas hydrophila quorum sensing orchestrating genes in Nile tilapia (Oreochromis niloticus).

Recently, the concept of incorporating natural products into nanocarriers has been intended to promote fish growth and health via modulating their stability and bioavailability. In this concern, the potential role of reformulated quercetin into nanocarriers was examined, for the first time, on Nile tilapia's performance and immunity, flesh quality and antioxidant indices and disease resistance. Five hundred fish assigned into five experimental groups with formulated diets containing quercetin nanoparticles (QT-NPs) at levels of 0, 100, 200, 300 and 400 mg/kg were challenged with Aeromonas hydrophila (A. hydrophila) after 12 weeks feeding trial. Fish final body weight gain and feed efficiency were significantly maximized in groups enriched with 300 and 400 mg/kg of QT-NPs. Significant reduction in total saturated fatty acids and an elevation in polyunsaturated fatty acids' contents were noticed in fish fed higher QT-NPs doses. The levels of Hydrogen peroxide, reactive oxygen species and malondialdehyde, the markers of meat antioxidant capacity, were reduced by higher inclusion levels of QT-NPs. Accordingly, serum activities and transcriptional levels of GSH-Px, CAT and SOD genes were increased with elevated QT-NPs levels. Immune responses mediated by upregulation of IL-10 and TGF-ß and downregulation of IL-1ß, IL-8 and TNF-α mRNA levels were found to be positively affected by QT-NPs. Dietary QT-NPs downregulated the expression of ahyI and ahyR quorum sensing genes conferring protection against A. hydrophila challenge. This study concluded that supplementation of quercetin in encapsulated nanoparticles could improve its efficacy making it as a compelling approach to improve fish performance and as a promising drug candidate against A. hydrophila virulence.

Creatine improves the flesh quality of Pacific white shrimp (Litopenaeus vannamei) reared in freshwater.

Creatine improves flesh quality on mammalian but studies on crustaceans are scarce. In the present study, diets with six levels of creatine (1.23, 2.58, 5.12, 8.28, 14.12, 24.49 g kg-1 diet) were hand-fed to juvenile Litopenaeus vannamei (IBW: 1.50 ± 0.02 g) reared in freshwater for 46 days. Results showed creatine supplementation did not affect the growth performance (FBW: 17.04 ± 1.28 g) or the content of guanidinoacetic acid in muscle and hepatopancreas whereas significantly increased muscular creatine content. Diet with 8.28 g kg-1 creatine significantly increased muscular hardness and chewiness by decreasing myofiber diameter and increasing myofiber density. Additionally, creatine downregulated the mRNA expression of fast sMyHC1, sMyHC2, sMyHC6a and upregulated slow sMyHC5 and sMyHC15 mRNA expression. Muscular protein, collagen, total amino acid and flavor amino acid contents increased with creatine supplementation. In conclusion, the diet with 8.28 g kg-1 creatine improved the flesh quality of L. vannamei.

Effects of dietary arginine supplementation on growth performance, flesh quality, muscle antioxidant capacity and antioxidant-related signalling molecule expression in young grass carp (Ctenopharyngodon idella).

Growth performance, flesh quality, antioxidant status and antioxidant-related signalling molecule expression in the muscle of young grass carp, which were fed graded levels of arginine (6.9-24.5 g/kg diet) for eight weeks, were investigated. Muscle protein, lipid and nitric oxide contents, shear force, hydroxyproline concentration, and pH were significantly improved by appropriate arginine. Cooking loss, lactate content, cathepsins activities, malondialdehyde and protein carbonyl contents exhibited an opposite tendency. Additionally, optimum arginine significantly enhanced glutathione content and the activities and gene expression of copper/zinc superoxide dismutase, catalase and glutathione peroxidase in muscle. Moreover, the expression levels of glutamate-cysteine ligase, target of rapamycin, ribosome protein S6 kinase 1, casein kinase 2 and NF-E2-related factor 2 in muscle were significantly elevated by appropriate arginine. However, optimum arginine significantly decreased Kelch-like ECH-associated protein 1 mRNA levels in muscle. In conclusion, arginine improved the flesh quality and muscle antioxidant capacity and regulated antioxidant-related signalling molecule expression.

Effects of Dietary Lipid Source and Level on Growth Performance, Blood Parameters and Flesh Quality of Sub-adult Olive Flounder (Paralichthys olivaceus).

This study was conducted to investigate the effects of dietary lipid source and level on growth performance, blood parameters, fatty acid composition and flesh quality of sub-adult olive flounder Paralichthys olivaceus. Eight experimental diets were formulated to contain 5% squid liver oil (SLO), 5% linseed oil (LO), 5% soybean oil (SO), a mixture of 1% squid liver oil, 2% linseed oil and 2% soybean oil (MIX), no lipid supplementation with high protein level (LL-HP), 10% squid liver oil (HL-SLO), a mixture of 1% squid liver oil, 4.5% linseed oil and 4.5% soybean oil (HL-VO), and 1% squid liver oil with high starch level (LL-HC), respectively. Two replicate groups of fish (average initial weight of 296 g) were fed the diets for 17 wks. After 5 wks, 11 wks and the end of the feeding trial, five fish from each tank were randomly sampled for analysis of body composition. At the end of the feeding trial, final mean weight of fish fed the LL-HP diet was significantly (p<0.05) higher than that of fish fed the HL-VO diet, but did not differ significantly from those of fish fed the SLO, LO, SO, MIX, HL-SLO and LL-HC diets. Fish fed the LL-HP diet showed significantly higher feed efficiency than fish fed the LO, HL-SLO and HL-VO diets. Feed efficiency of fish fed the LO, SO and MIX diets were similar to those of fish fed the SLO and HL-SLO diets. Fish fed the HL-SLO diet showed significantly higher total cholesterol content in plasma compared with other diets. Fatty acid composition of tissues was reflected by dietary fatty acid composition. The highest linoleic (LA) and linolenic acid (LNA) contents in the dorsal muscle were observed in fish fed the SO and LO diets, respectively, regardless of feeding period. The highest eicosapentaenoic acid (EPA) content in the dorsal muscle was observed in fish fed the LL-HP and LL-HC diets after 11 and 17 weeks of feeding, respectively. Fish fed the SLO and HL-SLO diets showed higher docosahexaenoic acid (DHA) content than that of other treatments after 11 and 17 weeks of feeding, respectively. Dietary inclusion of vegetable oils reduced n-3 HUFA contents in the dorsal muscle and liver of fish. The n-3 HUFA contents in tissues of fish fed the SLO and HL-SLO diets were higher than those of fish fed other diets, except for the LL-HP and LL-HC diets. Hardness, gel strength, chewiness and cohesiveness values of dorsal muscle in fish were significantly affected by dietary lipid source. The results of this study indicate that fish oil in fish meal based diets for sub-adult olive flounder could be replaced by soybean oil and linseed oil without negative effects on growth and feed utilization.