Flesh Shear Force, Cooking Loss, Muscle Antioxidant Status and Relative Expression of Signaling Molecules (Nrf2, Keap1, TOR, and CK2) and Their Target Genes in Young Grass Carp (Ctenopharyngodon idella) Muscle Fed with Graded Levels of Choline

Biochemical, Histological, and Transcriptomic Analyses Reveal Underlying Differences in Flesh Quality between Wild and Farmed Ricefield Eel (Monopterus albus)

The present study aimed to systematically investigate the underlying differences in flesh quality between wild and farmed Monopterus albus. Fifteen healthy M. albus per group with an average body weight of 45 g were sampled to analyze muscle parameters by biochemical indicators, histomorphology, and molecular biology. Compared with the wild fish, the farmed M. albus in flesh had lower crude protein, collagen, lysine, histidine, total amino acids, SFA, n-3 PUFA contents, and n-3/n-6 ratio (p < 0.05), and higher moisture, crude lipid, crude ash, MUFA, n-6PUFA, and total PUFA contents (p < 0.05). The thawing loss, drip loss, steaming loss, and boiling loss in the farmed group were significantly higher, and hardness, springiness, cohesiveness, gumminess, chewiness, and resilience were significantly lower than those in the wild group (p < 0.05). In addition, higher muscle fiber density and lower muscle fiber diameter were observed in wild M. albus (p < 0.05). In muscle transcriptome profiling, differentially expressed genes and enriched pathways are primarily associated with muscle development, protein synthesis, catabolism, lipid metabolism, and immunity. To the best of our knowledge, this is the first investigation that compares the flesh quality between wild and farmed M. albus in terms of biochemistry, histology, and molecular biology levels. Overall, wild M. albus had a higher nutritional value and texture quality than farmed M. albus.

Substituting Fish Meal with Tubiechong (Eupolyphaga sinensis) By-Product in the Diets of Largemouth Bass (Micropterus salmoides): Effects on Growth, Meat Quality, and Liver Health

A feeding trial was conducted to evaluate the effect of replacing 0% (control), 10% (T10), 20% (T20), 30% (T30), and 40% (T40) fish meal with a Tubiechong (Eupolyphaga sinensis) by-product in largemouth bass (Micropterus salmoides). Triplicate groups of 30 fish (5.36 ± 0.01 g) were fed two times daily to apparent satiation for 60 days. The experimental results showed that the Tubiechong by-product could improve the growth performance of largemouth bass by increasing the FBW, WGR, and SGR until the replacement ratio was 40%. The quadratic regression analysis showed that the proportion of the Tubiechong by-product was 20.79% and 20.91%, respectively, when WGR and SGR were the best. Concurrently, the meat quality in the replacement groups was higher, specifically, the lightness and white values were higher, and the water loss rates were lower (P < 0.05) than that in the control group. Moreover, the changes of the activities of CAT and GSH in the liver and T-AOC and GSH in serum could reveal the antioxidant capacity improvement of fish by the Tubiechong by-product. In the study, the replacement groups had lower T-CHO and HDL-C in serum (P < 0.05), indicating that the Tubiechong by-product had an active role in improving blood lipid and regulating lipid metabolism. Simultaneously, the replacement groups had a normal structure with central hepatocytes' nuclei and deviated from the center partly, while most of the hepatocytes were swollen in the control group with nuclear degeneration. The results showed that the Tubiechong by-product had a positive effect on the liver health of fish. Conclusively, the present study indicated that the partial dietary replacement of fish meal using the Tubiechong by-product (for up to 40% replacement level) in the diet of largemouth bass not only caused no adverse effects on fish health but also improved the growth performance, meat quality, antioxidant capacity, and hepatic health and is conducive to supplying nutritious, high-quality, and healthy aquatic products.

Cellular antioxidant mechanism of mannan-oligosaccharides involving in enhancing flesh quality in grass carp (Ctenopharyngodon idella)

BACKGROUND

Deterioration of flesh quality has bad effects on consumer satisfaction. Therefore, effects of safe mannan-oligosaccharides (MOS) on flesh quality of grass carp (Ctenopharyngodon idella) muscle were studied. A total of 540 healthy fish (215.85 ± 0.30 g) were randomly divided into six groups and fed six separate diets with graded levels of MOS (0, 200, 400, 600, 800 and 1000 mg kg^-1 ) for 60 days. This study aimed at investigating the benefits of dietary MOS on flesh quality (fatty acids, amino acids and physicochemical properties) and the protection mechanism regarding antioxidant status.

RESULTS

Optimal MOS could improve tenderness (27.4%), pH (5.5%) while decreasing cooking loss (16.6%) to enhance flesh quality. Meanwhile, optimal MOS improved flavor inosine 5'-monophosphate (IMP) of 11.8%, sweetness and umami-associated amino acid, healthy unsaturated fatty acid (UFA) of 14.9% and n-3 polyunsaturated fatty acids (n-3 PUFAs) especially C20:5n-3 (15.8%) and C22:6n-3 (38.3%). Furthermore, the mechanism that MOS affected pH, tenderness and cooking loss could be partly explained by the reduced lactate, cathepsin and oxidation, respectively. The enhanced flesh quality was also associated with enhanced antioxidant ability concerning improving antioxidant enzymes activities and the corresponding transcriptional levels, which were regulated through NF-E2-related factor 2 (Nrf2) and target of rapamycin (TOR) signaling. Based on pH_24h , cooking loss, shear force and DHA (docosahexaenoic acid, C22:6n-3), optimal MOS levels for grass carp were estimated to be 442.75, 539.53, 594.73 and 539.53 mg kg^-1 , respectively.

CONCLUSION

Dietary MOS is a promising alternative strategy to improve flesh quality of fish muscle. © 2022 Society of Chemical Industry.

A comparative study on the tolerance of tilapia (Oreochromis niloticus) to high carbohydrate and high lipid diets

A 12-wk trial was conducted to compare the tolerance of tilapia to high carbohydrate and high lipid diets. Three isonitrogenous and isoenergetic diets, whose carbohydrate and lipid levels were the following: 35.0% and 8% (control), 44.2% and 4% (D1, high carbohydrate), and 25.8% and 12% (D2, high lipid), respectively. Three hundred tilapias (27 ± 0.11 g) were fed the diets for 10 wk (4 replicates per group); 72 fish from the D1 group were continually fed the D1 (D1D1) and 72 fish from the D2 were continually fed the D2 (D2D2) diet for 2 wk (3 replicates each group) to evaluate the tilapia's capacity to tolerate high carbohydrate and high lipid diets, respectively. Another 36 fish from D1 group were continually fed D2 (D1D2) for comparison with D1D1 and D2D2 groups. In phase 1, hepatosomatic index, liver triglycerides (TG), glucose tolerance (GT) and crude protein in the whole body in D1 group were higher than those in D2 group (P < 0.05). During phase 2, D1D1 group had lower feed intake and weight gain, as well as lower serum total protein and albumin than that of D2D2 group (P < 0.05), while its liver glycogen was significantly higher than that in D1D2 and D2D2 groups (P < 0.05). Moreover, serum glucose and GT were higher in D1D1 and D1D2 groups than those in D2D2 group (P < 0.05). By contrast, D2D2 group had significantly higher intraperitoneal fat, subcutaneous adipose tissue (SCAT) and liver TG than those in D1D1 group (P < 0.05). The mRNA expression of brain npy, hepatic nrf2, gst1 and hepatic transcriptomic data showed that immune-related genes (gama, mrc2, mhc2 and cd163), were downregulated in D1D1 group compared to D2D2 and D1D2 groups. Taken together: 1) tilapia have higher tolerance to a high lipid diet than high carbohydrate diet; 2) despite retention of glucose tolerance, the continuous feeding of D1 diet impaired tilapia's appetite, weight gain rate and host immune response; 3) specific distribution of fat in intraperitoneal regions, SCAT and liver may be a risk-avoidance strategy in tilapia in response to a continuous D2 diet.

MiRNAs-Modulation of Nrf2 Signaling Networks in Regulation Oxidative Stress of Chinese Perch Skeletal Muscle After Fasting Treatment

Nrf2 is an important transcription factor involved in the antioxidant response and is widely expressed in animal tissues. The function of Nrf2 is regulated by its negative regulator Keap1 by inducing its cytoplasmic degradation. Recent studies have suggested that Nrf2 is also regulated post-transcriptionally via miRNAs. However, to date, how miRNAs regulate Nrf2 in fish skeletal muscles is unknown. In this study, the full-length cDNAs with 2398 bp of the Nrf2 was firstly cloned by SMART RACE amplification tools from Chinese perch. The Nrf2 gene structure and its 3'-UTR region for possible miRNA binding sites, as well as its spatial expression profile were assayed. Then, we employed TargetScan Fish tool MiRNAnome to predict putative sites for five miRNAs including miR-181a-5p, MiR-194a, MiR-216a, miR-459-5p, and miR-724. Using qRT-PCR assay, we found that Nrf2 mRNA levels have negative correlation with all five miRNAs expression in muscle of nutritionally deprived fish, and that ectopic expression of miR-181a-5p alone reduces Nrf2 mRNA levels. Luciferase reporter assay in a heterologous cell system revealed that each of the five miRNAs reduced Nrf2 expression, suggesting a direct regulatory mechanism. Moreover, the miR-181a-5p suppression using specific antagomir led to a significant increase in Nrf2 expression in vivo. At the same time, the expression levels of the antioxidant enzymes CAT, ZnSOD, GPx, GSTA, and GSTA genes increased significantly after injecting miR-181a-5p antagomir. Taken together, these findings provide evidence that miRNAs are involved in the Nrf2 signaling networks in regulation of oxidative stress in fish, at least in Chinese perch muscle.

Enzyme-treated soy protein supplementation in low protein diet improved flesh tenderness, juiciness, flavor, healthiness, and antioxidant capacity in on-growing grass carp (Ctenopharyngodon idella)

An 8-week feeding trial was conducted to investigate the effects of enzyme-treated soy protein (ETSP) supplementation in low protein diets on growth performance as well as flesh sensory quality and healthiness in on-growing grass carp. A total of 540 on-growing grass carp (initial average weight 325.72 ± 0.60 g) were fed six diets, which included a normal protein diet (28% crude protein) and five low protein diets (26% crude protein) supplemented with graded levels of ETSP (0.0, 0.8, 1.2, 1.6, and 2.0%). The results showed that reducing dietary protein by 2% decreased percentage weight gain, feed intake, and flesh flavor (aspartic acid, glutamic acid, histidine, and 5'-inosinic acid contents) and healthiness-related indices (linolenic acid (LA) and docosahexaenoic acid (DHA) contents and polyunsaturated fatty acids to saturated fatty acids ratio). Under the condition of reducing dietary protein by 2%, 0.8-1.2% ETSP supplementation restored above parameters to levels equal or superior to those in 28% crude protein diet group. Although reducing dietary protein by 2% did not deteriorate flesh tenderness and juiciness, 0.8-1.2% ETSP supplementation in low protein diets also improved the two indices compared with 28% crude protein diet. Moreover, ETSP-improved flesh quality was partly related to increased muscle antioxidant enzymes activities and their mRNA levels. In addition, ESTP-enhanced antioxidant enzyme mRNA levels were partly associated with the upregulation of NF-E2-related factor 2 (Nrf2) and target of rapamycin (TOR) signaling. Collectively, 0.8-1.2% ETSP supplementation in low protein diets improved growth performance as well as flesh sensory quality and healthiness in on-growing grass carp.

Dietary vegetable choline improves hepatic health of Nile tilapia (Oreochromis niloticus) fed aflatoxin-contaminated diet

Aflatoxin B_{1 (}AFB₁) is one of the most important mycotoxins due to its hepatotoxic and carcinogenic effects on animals. The effect of dietary supplementation with vegetable choline (VC) at 400, 800, and 1200 mg/kg against the deleterious effects of AFB₁ (2 ppm/kg diet) in the liver of Nile tilapia (Oreochromis niloticus) was studied. The experimental period was 81 days, and the diet with VC was offered to the fish for 60 days prior to challenge with AFB₁. Diets with AFB₁ were tested in three replications and animals were analyzed at days 14 and 21 of dietary intake. The addition of VC to tilapia diet increased body weight (days 30 and 60 pre-challenge and day 21 post-challenge). The group fed aflatoxin-contaminated diet presented significantly reduced antioxidant enzymes and increased reactive oxygen species (ROS) levels, thiobarbituric acid reactive species (TBARS) levels, and protein carbonyl (PC) content in the liver. Dietary supplementation with VC at 800 and 1200 mg/kg demonstrated a significant protective effect, avoiding the increase of ROS, TBARS, and PC levels in the liver of tilapia from the aflatoxin contaminated groups. Thus, dietary VC supplementation may be used in tilapia to increase antioxidant status and reduce the negative effects caused by AFB₁ toxicity. Based on the findings, it is recommended to use VC as a food supplement for Nile tilapia in order to avoid AFB₁ toxication. In addition, decreased aflatoxin toxicity can be attributed to the VC antioxidant property.

Soybean isoflavones improve the health benefits, flavour quality indicators and physical properties of grass carp (Ctenopharygodon idella)

Health benefits, flavour quality indicators and physical properties were analysed after feeding grass carp graded concentrations of soybean isoflavones (SIF) (0, 25, 50, 75, 100 and 125 mg/kg) for 60 days. The results demonstrated that optimal dietary SIF supplementation improved the protein and total PUFA content, especially healthcare n-3 PUFA (C18: 3n-3, EPA and DHA), and increased the flavour-related free amino acid [especially umami amino acid] and 5'-inosine monophosphate content, improving the health benefits and flavour quality indicators in the muscle of grass carp. In addition, optimal dietary SIF supplementation (25 or 50 mg SIF/kg diet) enhanced some physical properties [water-holding capacity and tenderness] and increased the collagen content; however, it reduced cathepsin activity and apoptosis. SIF supplementation enhanced the glutathione content and the activity of antioxidant enzymes (except CuZnSOD) by regulating their gene expression. The gene expression could be regulated by NF-E2-related factor 2 (Nrf2) signalling in the muscle of grass carp. We demonstrated that optimal dietary SIF supplementation elevated the health benefits, flavour quality indicators and physical properties of fish muscle.

Dietary choline regulates antibacterial activity, inflammatory response and barrier function in the gills of grass carp (Ctenopharyngodon idella)

An 8-week feeding trial was conducted to determine the effects of graded levels of choline (197-1795 mg/kg) on antibacterial properties, inflammatory status and barrier function in the gills of grass carp. The results showed that optimal dietary choline supplementation significantly improved lysozyme and acid phosphatase activities, complement component 3 (C3) content, and the liver expressed antimicrobial peptide 2 and Hepcidin mRNA levels in the gills of fish (P < 0.05). In addition, appropriate dietary choline significantly decreased the oxidative damage, which might be partly due to increase copper, zinc superoxide dismutase (Cu/Zn-SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR) activities and increased glutathione content in the gills of fish (P < 0.05). Moreover, appropriate dietary choline significantly up-regulated the mRNA levels of interleukin 10 and transforming growth factor β1, Zonula occludens 1, Occludin, Claudin-b, c, 3 and 12, inhibitor of κBα, target of rapamycin, Cu/Zn-SOD, CAT, GR, GPx, GST and NF-E2-related factor 2 in the gills of fish (P < 0.05). Conversely, appropriate dietary choline significantly down-regulated the mRNA levels of pro-inflammatory cytokines, tumor necrosis factor α, interleukin 8, interferon γ, interleukin 1β, and related signaling factors, nuclear factor kappa B p65, IκB kinase β, IκB kinase γ, myosin light chain kinase and Kelch-like-ECH-associated protein 1a (Keap1a) in the gills of fish (P < 0.05). However, choline did not have a significant effect on the mRNA levels of IκB kinase α, Claudin-15 and Keap1b in the gills of fish. Collectively, appropriate dietary choline levels improved gill antibacterial properties and relative gene expression levels of tight junction proteins, and decreased inflammatory status, as well as up-regulated the mRNA levels of related signaling molecules in the gills of fish. Based on gill C3 content and AHR activity, the dietary choline requirements for young grass carp (266.5-787.1 g) were estimated to be 1191.0 and 1555.0 mg/kg diet, respectively.