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The vertebrate mucosal barrier comprises physical and immune elements, as well as bioactive molecules, that protect organisms from pathogens. Vitamin D is a vital nutrient for animals and is involved in immune responses against invading pathogens. However, the effect of vitamin D on the mucosal barrier system of fish, particularly in the skin, remains unclear. Here, we elucidated the effect of vitamin D supplementation (15.2, 364.3, 782.5, 1167.9, 1573.8, and 1980.1 IU/kg) on the mucosal barrier system in the skin of grass carp (Ctenopharyngodon idella) challenged with Aeromonas hydrophila. Dietary vitamin D supplementation (1) alleviated A. hydrophila-induced skin lesions and inhibited oxidative damage by reducing levels of reactive oxygen species, malondialdehyde, and protein carbonyl; (2) improved the activities and transcription levels of antioxidant-related parameters and nuclear factor erythroid 2-related factor 2 signaling; (3) attenuated cell apoptosis by decreasing the mRNA and protein levels of apoptosis factors involved death receptor and mitochondrial pathway processes related to p38 mitogen-activated protein kinase and c-Jun N-terminal kinase signaling; (4) improved tight junction protein expression by inhibiting myosin light-chain kinase signaling; and (5) enhanced immune barrier function by promoting antibacterial compound and immunoglobulin production, downregulating pro-inflammatory cytokine expression, and upregulating anti-inflammatory cytokines expression, which was correlated with nuclear factor kappa B and the target of rapamycin signaling pathways. Vitamin D intervention for mucosal barrier via multiple signaling correlated with vitamin D receptor a. Overall, these results indicate that vitamin D supplementation enhanced the skin mucosal barrier system against pathogen infection, improving the physical and immune barriers in fish. This finding highlights the viability of vitamin D in supporting sustainable aquaculture. [ABSTRACT FROM AUTHOR]

In aquaculture, hypoxia poses a significant threat to fish growth and survival. Despite this, there is limited research on the impact of pantothenic acid (PA) in enhancing the anti-hypoxia stress capability of fish. The primary objective of this study was to explore the effects and potential mechanisms of PA in alleviating hypoxia-induced liver injury in sub-adult grass carp. To achieve this, six experimental diets containing varying levels of PA (0.08, 11.95, 24.95, 37.95, 50.95, and 63.95 mg/kg) were formulated and administered to grass carp (initial weight 696.22 ± 2.45 g) for 63 days. Following the dietary intervention, the fish were segregated into hypoxia and control groups and treated for 96 h. The findings revealed that optimal PA levels could enhance the growth performance of sub-adult grass carp and ameliorate the adverse impacts of hypoxia. First, optimal PA levels reduced serum levels of glutamate-oxaloacetate transaminase (GOT), glutamate-pyruvate transaminase (GPT), and lactate dehydrogenase (LDH), as well as mitigated hepatocyte vacuolization, improved liver and mitochondrial morphology, thereby alleviating hypoxia-induced liver injury. Furthermore, optimal PA levels were associated with increased contents of serum cortisol, glucose, liver glycogen, pyruvate, and the activities of Pantothenate kinase 2 (PanK2) and coenzyme A (CoA), while liver lactate content and LDH activity were reduced, indicating improvements in energy metabolism and PA utilization, potentially mediated by the down-regulation of hypoxia-inducible factor-1α (HIF-1α) mRNA level. Moreover, optimal PA levels decreased reactive oxygen species (ROS) and malondialdehyde (MDA) levels, enhanced liver antioxidant capacity, down-regulated autophagy-related gene mRNA levels, and up-regulated autophagy receptor protein 62 (p62) protein level, suggesting a reduction in oxidative damage and autophagy. Finally, a rise in levels of mitochondrial quality control-related mRNAs such as mitofusin 1/2 (MFN1/2), dynamin-related protein-1 (DRP-1), and nuclear respiratory factor 1/2 (Nrf-1/2) was observed, together with increment in the protein levels of PTEN induced putative kinase 1 (PINK1), BCL-2 interacting protein 3 (BNIP3) and FUN14 domain-containing protein 1 (FUNDC1). These alterations hinted at the role of PA in preserving mitochondrial homeostasis. In conclusion, PA exhibited a protective role against hypoxia-induced liver injury by enhancing liver energy metabolism, bolstering antioxidant defenses, suppressing autophagy, and maintaining mitochondrial homeostasis. Through an assessment of percentage weight gain (PWG) and liver ROS level, the requirements of PA for promoting growth and resilience to hypoxia-induced liver injury in sub-adult grass carp were determined to be 37.44 mg/kg and 42.57 mg/kg, respectively. • Optimal dietary PA levels alleviated hypoxia-induced liver injury of fish. • Optimal dietary PA levels helped ensure normal energy metabolism of fish under hypoxia. • Optimal dietary PA levels reduced liver oxidative damage and autophagy level in fish. • Optimal dietary PA levels helped maintain mitochondrial dynamic homeostasis in fish. [ABSTRACT FROM AUTHOR]

In this study, we investigated the functional roles and mechanisms of arginine in improving the muscle quality of sub-adult grass carp. We divided 450 healthy fish (661.60 ± 1.00 g) into six groups and fed them separate diets with increasing levels of arginine (3.51, 7.01, 10.51, 14.01, 17.51, and 21.01 g/kg) for 63 days. The results showed that optimal dietary arginine levels promoted grass carp growth and improved muscle lipid content, shear force (hardness), pH, hydrolyzed amino acid contents, and the chemical score of essential amino acids (protein quality). Suitable dietary arginine levels also decreased the proportion of hypertrophic fibers and increased the proportion of hyperplastic fibers. Furthermore, appropriate arginine supplementation increased the expression levels of MyoD, MyoG, Myf5, MRF4, MyHC, cyclin D1, cyclin B, cyclin E, WNT1, WNT3a, and β-catenin and decreased the expression levels of MSTN and GSK3β. In conclusion, appropriate arginine levels in the diet (10.51–14.01 g/kg) may promote the growth and muscle quality of grass carp while increasing the proportion of hyperplasia fibers and decreasing the proportion of hypertrophic fibers probably by regulating the WNT/β-catenin pathway to increase the expression levels of MRFs and cyclins. This study offers novel insights into the regulatory role of arginine in muscle fiber growth, which can facilitate the improvement of grass carp muscle quality. • Arg has a positive effect on sub-adult grass carp growth and muscle quality. • Arg improves the amino acid contents of fillets, which could meet the needs of human. • Arg improves muscle hardness is associated with changes in muscle fiber diameter and density in grass carp. • Arg promotes muscle fiber proliferation and differentiation via WNT signaling. [ABSTRACT FROM AUTHOR]

Flavobacterium columnare (F. columnare) is one of the deadliest fish pathogens causing bacterial gill rot disease in various freshwater fish species globally. Tea polyphenols (TPs) are an inexpensive product extracted from tea that have received much attention as a feed additive in aquaculture. The current study was designed to investigate the underlying mechanisms and protective effects of dietary TPs against F. columnare -induced gill injury via suppression of oxidative stress, apoptosis, and inflammation in grass carp. TPs were not supplemented to the diet (control) and were supplemented at 40, 80, 120, 160 or 200 mg/kg diet. The feeding experiment was carried out for 60 days, followed by a 3-Day F. columnare challenge test. The results showed that 120 mg/kg TPs in the diet exerted the following five protective effects in fish gill: (1) control gill-rot disease and improved histopathology, (2) inhibit excessive apoptosis, (3) enhance the activity of antioxidant enzymes and upregulate related gene expression via the Nrf2/Keap1 pathway, (4) increase the activity of immune enzymes, And (5) mediate inflammatory cytokine gene expression via the JAK/STAT3 pathway. Taken together, dietary supplementation with TPs is a compelling approach to protect the gill function of fish against F. columnare. • Tea polyphenols level reduced the incidence of rotten gill and protected gill morphology of grass carp. • Tea polyphenols attenuated the adverse effects induced by F. columnare of grass carp by enhancing antioxidant capacity, immunity and mediating excessive apoptosis and inflammatory response in gill. [ABSTRACT FROM AUTHOR]

This study investigated the effect of xylanase supplementation of a plant protein‐enriched diet on the growth performance and intestinal immune function of grass carp grow‐out (Ctenopharyngodon idella). Five hundred forty healthy grass carp grow‐out (232.74 ± 0.12 g) were fed diets containing graded levels of xylanase for 60 days. The fish were then challenged with Aeromonas hydrophila for 14 days. The results indicated that xylanase supplementation (a) improved fish growth performance and optimized the intestinal microflora; (b) increased lysozyme and acid phosphatase activities, complement and immunoglobulin M levels and antibacterial peptide hepcidin mRNA levels, thereby enhancing fish intestinal immune function; and (c) attenuated intestinal inflammation associated with the inhibition of the NF‐κB signalling pathway and activation of the TOR signalling pathway, resulting in the down‐regulation of pro‐inflammatory cytokines [except IL‐1β and IL‐12p40 in the distal intestine (DI) and IL‐6 in the proximal intestine (PI)] and up‐regulation of anti‐inflammatory cytokines [except IL‐4/13B and TGF‐β1 in the mid intestine (MI) and DI]. Finally, on the premise of a basal diet containing 45.8 g/kg araboxylans (AXs), the appropriate supplementation levels based on the ability to improve per cent weight gain (PWG) and prevent enteritis were estimated to be 1,527 and 1,608 U/kg, respectively. [ABSTRACT FROM AUTHOR]

To investigate the effect of dietary folic acid on fish flesh quality, muscle antioxidant status and the potential mechanism, young grass carp (Ctenopharyngodon idella) were fed diets containing 0.10–3.12 mg/kg diet of folic acid for 8 weeks. The results showed that optimum folic acid increased muscle contents of protein, lipid, pH, shear force, amino acids, unsaturated fatty acids, hydroxyproline and glutathione, whereas contents of moisture, cooking loss, lactate and saturated fatty acids and cathepsin L activity showed an opposite trend (p <.05). Moreover, optimum folic acid elevated antioxidant enzyme activities and mRNA levels, as well as NF‐E2‐related factor 2 and casein kinase 2 mRNA levels (p <.05). However, optimum folic acid decreased reactive oxygen species (ROS) content and Kelch‐like ECH‐associated protein 1a (Keap1a) and Keap1b mRNA levels (p <.05). Interestingly, excess folic acid induced negative effects on above‐mentioned parameters (p <.05). Summarily, this study indicated that optimum folic acid improved fish flesh quality and muscle antioxidant system associated with Nrf2‐Keap1 pathway. Based on muscle cathepsin L activity and ROS content, the folic acid requirements for young grass carp were 1.87 and 1.80 mg/kg diet, respectively, regarding to the flesh quality and antioxidant status. [ABSTRACT FROM AUTHOR]

The present study was mainly designed to evaluate the effect of potassium diformate (KDF) on growth performance, digestion and absorption capacity and intestinal microbes of juvenile grass carp (Ctenopharyngodon idella). Six experimental diets with KDF 0.0, 1.5, 3.0, 4.5, 6.0 and 7.5 g/kg were respectively fed to 1620 fish (5.73 ± 0.01 g) for 70 days. Results indicated that dietary KDF addition improved growth performance, intestinal growth and development, digestive enzymes and brush border enzymes activity. Additionally, mRNA levels of most amino acid transporters (AATs) and peptide transporter 1 (PepT1), and protein expressions of SLC7A1, SLC1A5 and SLC15A1 in intestine were up-regulated with addition of 3.0 g/kg KDF, which might be related to the activated TOR signaling pathway, as evident by the up-regulated mRNA levels of TOR and S6K1, the increased protein expression of phosphorylation TORSer2448, as well as the down-regulated mRNA level of 4EBP1. Furthermore, the 16S rRNA sequencing revealed that low dose of KDF addition enriched the abundances of Fusobacteria and Cetobacterium , and reduced the abundances of Proteobacteria and Ralstonia , which might be related to the reduced pH of intestine. In a word, this study using grass carp as a model provided novel evidence on the positive role and possible mechanisms of KDF in promoting fish growth. • KDF promoted the growth performance, intestinal growth and development of fish. • KDF enhanced digestion and absorption enzymes activity of fish. • KDF-up-regulated AATs expression might be related to TOR signaling pathway. • KDF-improved intestinal microbial structure of fish might be related to decreased pH. [ABSTRACT FROM AUTHOR]

The present study evaluated the effects of enzymatically treated Artemisia annua L. (EA) on the growth performance, intestinal antioxidant capacity, and apical junctional complex (AJC) of adult grass carp. In this experiment, 375 healthy grass carp (initial body weight 673.96 ± 1.24 g) were selected and randomly divided into 5 treatments, and fish in each group were fed diets with different levels of EA (0, 400, 800, 1200, and 1600 mg/kg) 9 weeks. The results showed that compared with the control group (0 mg/kg EA diet), the EA supplementation in the diet increased the percentage of weight gain (PWG), specific growth rate (SGR), and feed intake (FI) (P < 0.05), indicating that dietary EA supplementation improved the growth performance of adult grass carp. The dietary EA supplementation also enhanced the digestion and absorption ability of adult grass carp, which might be reflected by improving the activities of hepatopancreas digestive enzymes (trypsin, chymotrypsin, lipase, and amylase) and intestinal brush border enzymes (alkaline phosphatase, Na+/K+-ATPase, and γ-glutamyl transpeptidase), but EA did not affect the creatine kinase enzyme activity. Meanwhile, we explored the effect of dietary EA addition on the structural integrity of the grass carp intestine. We observed that dietary EA supplementation improved the antioxidant capacity of the intestine which be reflected by increasing the activities levels of superoxide dismutase (SOD) and catalase (CAT), which might be related to the binding protein Keap1a (not Keap1b)/ NF-E2-related factor-2 (Nrf2) signaling pathway. In addition, dietary EA supplementation enhanced the integrity of AJC by increasing the mRNA levels of intestinal tight junction proteins (TJs) (except claudin 11 , claudin 12, claudin 15a) and adhere junction proteins (AJs) (E-cadherin , α-catenin , β-catenin , nectin , and afadin), which might be related to the Rho family GTPases (RhoA)/ Rho-associated protein kinase (ROCK)/ myosin light chain kinase (MLCK) signaling pathway. Collectively, dietary EA supplementation improved growth performance, digestion and absorption ability, and intestinal structural integrity in grass carp, which were associated with the activation of related signaling pathways and regulatory factors. Finally, by the growth indicator percent weight gain (PWG) and intestinal oxidative damage index protein carbonyl (PC), the optimum amounts of EA supplementation of adult grass carp (673–1726 g) were assessed to be 808.09 and 730.38 mg/kg diet, respectively. • Enzymatically treated Artemisia annua L. (EA) enhanced growth performance of fish. • EA increased the activities of digestive and brush border enzymes in fish. • EA improved the intestinal antioxidant capacity of fish. • EA enhanced the integrity of the intestinal apical junction complex of fish. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an important and essential mineral for fish. To investigate the effects of dietary P on gill immune and physical barrier function in grass carp (Ctenopharyngodon idella), fish were fed six graded levels of dietary available P (0.95–8.75 g/kg diet) for 60 days, and then sampled 3 days after a challenge test (exposure to water containing Flavobacterium columnare ; 1.0 × 108 colony-forming units (cfu)/ml for 3 h). P deficiency resulted in a decline in gill antimicrobial compound production, and liver-expressed antimicrobial peptide 2A (LEAP-2A), LEAP-2B, hepcidin and β-defensin-1 transcript abundance. P deficiency also decreased target of rapamycin transcript and protein expression and increased nuclear factor kappa B p65 mRNA expression, which because of their association with anti-inflammatory and pro-inflammatory cytokine gene expression, respectively, suggesting that P deficiency increased post-infection gill inflammation and could impair immune barrier function. Furthermore, P deficiency: (1) Enhanced Fas ligand /caspase-8 death receptor and Bcl-2associated X protein/apoptotic protease activating factor-1/caspase-9 mRNA expression (which is indicative of increased apoptosis). (2) Inhibited Kelch-like-ECH-associated protein 1b/NF-E2-related factor 2 mRNA expression, decreased the expression of antioxidant enzyme transcript levels and activities (with the exception of CuZnSOD mRNA expression), and increased ROS, malondialdehyde and protein carbonyl levels. This data suggests that protection against ROS-related damage was compromised with P deficiency. (3) Up-regulated myosin light chain kinase transcript levels, a response that was associated with the down-regulation zonula occludens 1 (but not ZO-2), occludin and claudin (except claudin-12) mRNA levels. This latter result suggesting that tight junction functional integrity (and thus, gill physical barrier function) was impaired. These data, combined with the fact that P deficiency led to opercular deformation and gill rot syndrome, suggest that insufficient dietary levels of this mineral (i.e. below ~5.75 mg/kg P) could increase the susceptibility of fishes to water borne pathogens. • P deficiency led to operculum deformation and then impaired fish gill health. • P deficiency promoted gill NF-κB, JNK, p38 MAPK and MLCK while suppressed TOR and Nrf2 signalling. • Signalling molecules TOR and Nrf2 protein levels were down-regulated by P deficiency. • P deficiency impaired fish gill health relating to gill immune and physical barrier function. [ABSTRACT FROM AUTHOR]

Abstract The present study was the first to investigate the effects of dietary vitamin A (VA) on the intestinal physical barrier function associated with oxidation, antioxidant system, apoptosis and cell-cellular tight junction (TJ) in the proximal (PI), mid (MI) and distal (DI) intestines of young grass carp (Ctenopharyngodon idella). Fish were fed graded levels of dietary VA for 10 weeks, and then a challenge test using an injection of Aeromonas hydrophila was conducted for 14 days. Results indicated that dietary VA deficiency caused oxidative damage to fish intestine partly by the reduced non-enzymatic antioxidant components glutathione (GSH) and VA contents as well as reduced antioxidant enzyme activities [not including manganese superoxide dismutase (MnSOD)]. Further results observed that the decreased antioxidant enzyme activities by VA deficiency were partly related to the down-regulation of their corresponding mRNA levels which were regulated by the down-regulation of NF-E2-related factor 2 (Nrf2) mRNA levels and up-regulation of kelch-like-ECH-associated protein (Keap1a) (rather than Keap1b) mRNA levels in three intestinal segments of fish. Meanwhile, VA deficiency up-regulated the mRNA levels of the apoptosis signalling [ caspase-3 , caspase-8 , caspase-9 (rather than caspase-7)] associated with the inhibition of the target of rapamycin (TOR) signalling pathway in three intestinal segments of fish. Additionally, VA deficiency decreased the mRNA levels of TJ complexes [ claudin-b, claudin-c, claudin-3, claudin-12, claudin-15a, occludin and zonula occludens-1 (ZO-1) in the PI, MI and DI, as well as claudin-7 and claudin-11a in the MI and DI] linked to the up-regulation of myosin light chain kinase (MLCK) signalling. These results suggested that VA deficiency impaired structural integrity in three intestinal segments of fish. Meanwhile, excessive VA also showed similar negative effects on these indexes. Taken together, the current study firstly demonstrated that VA deficiency impaired physical barrier functions associated with impaired antioxidant capacity, aggravated cell apoptosis and disrupted TJ complexes in the PI, MI and DI, but different segments performed different actions in fish. Based on protecting fish against protein oxidation, the optimal VA levels for grass carp were estimated to be 2622 IU/kg diet. Highlights • Vitamin A deficiency caused fish intestinal cell apoptosis and oxidative damage. • Vitamin A deficiency disrupted TJ complexs in different intestinal segments. • Vitamin A regulated Nrf2 and MLCK signalling pathways. • Effects of vitamin A on fish different intestinal segments are various. [ABSTRACT FROM AUTHOR]

This study was for the first time to investigate the effects of α-lipoic acid (LA) on growth and immune function of head kidney, spleen and skin in young grass carp ( Ctenopharyngodon idella ). A total of 540 healthy grass carp (with initial body weight at 216.59 ± 0.33 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of LA for 70 days. Un-supplemented group did not find LA and its concentrations in the other five diets were 203.25, 403.82, 591.42, 781.25 and 953.18 mg kg −1 , respectively. After the growth trial, fish were challenged with A. hydrophila for 14 days. The results showed that, compared with the un-supplemented group, optimal LA improved lysozyme (LZ) and acid phosphatase (ACP) activities, enhanced complement 3 (C3), C4 and immunoglobulin (Ig) M contents and up-regulated hepcidin, liver expressed antimicrobial peptide (LEAP)-2A, LEAP-2B and β-defensin-1 mRNA levels in the head kidney, spleen and skin of young grass carp; meanwhile, optimal LA up-regulated anti-inflammatory cytokines transforming growth factor (TGF)-β1, TGF-β2, interleukin (IL)-4/13A (not IL-4/13B), IL-10 and IL-11 mRNA levels partly related to target of rapamycin (TOR) signaling and down-regulated pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interferon (IFN)-γ2, IL-1β, IL-6, IL-8, IL-12p40 (not IL-12p35), IL-15 (not in the skin) and IL-17D mRNA levels partially associated with nuclear factor-kappa B (NF-κB) signaling in the head kidney, spleen and skin of young grass carp. Above results indicated that optimal LA enhanced the immune function of head kidney, spleen and skin in fish. Interestingly, excessive LA decreased the growth and impaired the immune function of head kidney, spleen and skin in fish. Finally, on the basis of the percent weight gain (PWG), the ability against skin hemorrhage and lesion, the IgM content in the head kidney and the LZ activity in the spleen, the optimal dietary LA levels were estimated to be 315.37, 382.33, 353.19 and 318.26 mg kg −1 diet, respectively. [ABSTRACT FROM AUTHOR]

In aquaculture, the occurrence of enteritis has increased and dietary nutrition is considered as one of the major strategies to solve this problem. In the present study, we assume that dietary phosphorus might enhance intestinal immune barrier and physical barrier function to reduce the occurrence of enteritis in fish. To test this assumption, a total of 540 grass carp ( Ctenopharyngodon idella ) were investigated by feeding graded levels of available phosphorus (0.95–8.75 g/kg diet) and then infection with Aeromonas hydrophila . The results firstly showed that phosphorus deficiency decreased the ability to combat enteritis, which might be related to the impairment of intestinal immune barrier and physical barrier function. Compared with optimal phosphorus level, phosphorus deficiency decreased fish intestinal antimicrobial substances activities or contents and down-regulated antimicrobial peptides mRNA levels leading to the impairment of intestinal immune response. Phosphorus deficiency down-regulated fish intestinal anti-inflammatory cytokines mRNA levels and up-regulated the mRNA levels of pro-inflammatory cytokines [except IL-1β and IL-12p35 in distal intestine (DI) and IL-12p40] causing aggravated of intestinal inflammatory responses, which might be related to the signalling molecules target of rapamycin and nuclear factor kappa B. In addition, phosphorus deficiency disturbed fish intestinal tight junction function and induced cell apoptosis as well as oxidative damage leading to impaired of fish intestinal physical barrier function, which might be partially associated with the signalling molecules myosin light chain kinase, c-Jun N-terminal protein kinase and NF-E2-related factor 2, respectively. Finally, based on the ability to combat enteritis, dietary available phosphorus requirement for grass carp (254.56–898.23 g) was estimated to be 4.68 g/kg diet. [ABSTRACT FROM AUTHOR]

The present study evaluated the effect of dietary sodium butyrate (SB) supplementation on the growth and immune function in the proximal intestine (PI), middle intestine (MI) and distal intestine (DI) of young grass carp ( Ctenopharyngodon idella ). The fish were fed one powdery sodium butyrate (PSB) diet (1000.0 mg kg −1 diet) and five graded levels of microencapsulated sodium butyrate (MSB) diets: 0.0 (control), 500.0, 1000.0, 1500.0 and 2000.0 mg kg −1 diet for 60 days. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila . The results indicated that optimal SB supplementation improved the fish growth performance (percent weight gain, specific growth rate, feed intake and feed efficiency) and intestinal growth and function (intestine weight, intestine length, intestinal somatic index, folds height, trypsin, chymotrypsin, lipase and amylase activities), increased beneficial bacteria lactobacillus amount and butyrate concentration, decreased baneful bacteria Aeromonas and Escherichia coli amounts, reduced acetate and propionate concentrations, elevated lysozyme and acid phosphatase activities, increased complement (C3 and C4) and immunoglobulin M contents, and up-regulated β-defensin-1 (rather than DI), hepcidin, liver expressed antimicrobial peptide 2B (LEAP-2B) (except LEAP-2A), Mucin2, interleukin 10 (IL-10), IL-11 (rather than PI), transforming growth factor β1 (rather than PI), transforming growth factor β2 (rather than PI), IL-4/13A, IL-4/13B and inhibitor of κBα (IκBα) mRNA levels, whereas it down-regulated tumor necrosis factor α, interferon γ2, IL-1β (rather than PI), IL-6, IL-8, IL-15 (rather than PI), IL-17D (rather than PI), IL-12p35, IL-12p40 (rather than PI or MI), nuclear factor kappa B p65 (NF-κB p65) (except NF-κB p52), c-Rel (rather than PI or MI), IκB kinase β (IKKβ) (rather than PI), IKKγ (except IKKα), p38 mitogen-activated protein kinase (p38MAPK) and MAPK kinase 6 mRNA levels in three intestinal segments of young grass carp ( P < 0.05), suggesting that SB supplementation improves growth and intestinal immune function of fish. Furthermore, according to the positive effect, MSB was superior to PSB on improving growth and enhancing intestinal immune function of fish, and based on feed efficiency of young grass carp, the efficacy of MSB was 3.5-fold higher than that of PSB. Finally, based on percent weight gain, protecting fish against enteritis morbidity and lysozyme activity, the optimal SB supplementation (MSB as SB source) of young grass carp were estimated to be 160.8, 339.9 and 316.2 mg kg −1 diet, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The present study explored the effects of glutamine on hydrogen peroxide (H2O2)-induced oxidative stress in isolated carp enterocytes. In order to select an optimal H2O2 concentration to induce oxidative stress in enterocytes, cultures were treated with different concentrations of H2O2 (0–100 μM) for 16 h. The results showed that exposure to H2O2 increased lactate dehydrogenase activity and malondialdehyde levels in a dose-dependent manner in the culture medium, suggesting increase toxicity of H2O2. Thus, 100 μM was an appropriate concentration for inducing oxidative stress. We then examined the cytoprotective effects of glutamine under conditions of oxidative stress. Cells were treated with glutamine (0–20 mM) in the presence of H2O2 (100 μM) for 16 h. The control cells were kept in the glutamine-free MEM only. Results showed that glutamine completely blocked H2O2-stimulated release of lactate dehydrogenase. Furthermore, glutamine reduced H2O2-induced increase in malondialdehyde level and protein carbonyls content to the level seen in the control culture. In addition, glutamine treatment completely prevented the decrease in Na+-K+-ATPase, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione S-transferase activities as well as reduced glutathione concentration and the ratio between reduced and oxidized glutathione induced by H2O2. No significant difference was observed between cells incubated with glutamine in the presence of H2O2 and control cells in values for most of the markers mentioned above. Complete protection was obtained at a concentration of glutamine as small as 4 mM. The present results indicate that glutamine is effective in protecting against H2O2-induced oxidative stress in carp intestinal epithelial cells. [Copyright &y& Elsevier]

In this study, the impact and underlying mechanisms of zinc (Zn) on the immune function of the head kidney, spleen and skin of grass carp were investigated. A 60-day growth test was first conducted by feeding diets containing seven different Zn levels, Zn lactate (10.71, 30.21, 49.84, 72.31, 92.56 and 110.78 mg Zn/kg diet) and Zn sulfate (56.9 mg Zn/kg diet); after that, selected test fish were subjected to 14-day Aeromonas hydrophila. The findings indicated that, in comparison to the group with Zn deficiency, (1) the optimal Zn level decreased parenchymal cell lysis and necrosis, cellular vacuolar degeneration and iron-containing haemoflavin in head kidney and spleen; (2) the optimal Zn level significantly increased the levels of lysozyme, complement proteins C3 and C4, immunoglobulin IgM, and the transcript levels of antimicrobial peptides in head kidney, spleen and skin; (3) the optimal Zn level demonstrated a mitigating effect on inflammatory responses, partially attributed to the downregulation of pro-inflammatory cytokines mRNA levels and the upregulation of anti-inflammatory cytokines mRNA levels in head kidney, spleen and skin. These effects may partially mediated by the signaling pathways [IKKα, β, γ/IκBα/NF-κB] and [TOR/(S6K1, 4E-BP1)] in the respective tissues; (4) the results of this study indicate that Zn lactate exhibited superior efficacy compared to Zn sulfate in augmenting the immune response of head kidney, spleen and skin, as assessed through various health parameters. The aforementioned findings suggest that the inclusion of dietary Zn has a positive impact on the immune function of head kidney, spleen and skin. Using the acid phosphatase (ACP) levels observed in head kidney, spleen and skin, we have ascertained the optimal quantities of Zn in grass carp diets to be 70.59, 67.99 and 65.31 mg/kg, respectively. • Zinc enhanced immune parameter of fish. • Zinc regulated inflammatory response in immune organ of fish. • Zinc activated TOR and NF-κB signaling pathways to regulate immune response. • Zn lactate was found to be more effective than Zn sulfate. • 65.31–70.59 mg/kg zinc may be added into the feed to improve immunity of fish. [ABSTRACT FROM AUTHOR]

Zearalenone (ZEA) is a prevalent mycotoxin with high toxicity in animals. In order to study its effect on juvenile grass carp (Ctenopharyngodon idella), six diets supplemented with different levels of ZEA (0, 535, 1041, 1548, 2002, and 2507 μg/kg diet) for 10 weeks were studied to assess its toxicity on intestinal structural integrity and potential mechanisms of action. Our report firstly proved that ZEA led to growth retardation and body deformity, and impaired the intestinal structural integrity of juvenile grass carp, as revealed by the following findings: (1) ZEA accumulated in the intestine and caused histopathological lesions; (2) ZEA resulted in oxidative injury, apoptosis, and breached tight junctions in the fish intestine, which were probably associated with Nuclear factor-erythroid 2-related factor 2 (Nrf2), p38 mitogen activated protein kinases (p38MAPK), and myosin light chain kinase (MLCK) signaling pathways, respectively. ZEA had no influence on the antioxidant gene levels of Kelch-like ECH associating protein 1 (Keap1)b (rather than Keap1a), glutathione-S-transferase (GST)P1, GSTP2 (not in the distal intestine (DI)), tight junctions occludin, claudin-c (not in the proximal intestine (PI)), or claudin-3c (not in the mid intestine (MI) or DI). [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the effects of dietary pyridoxine (PN) deficiency on intestinal antioxidant capacity, cell apoptosis and intercellular tight junction in young grass carp ( Ctenopharyngodon idella ). A total of 540 young grass carp (231.85 ± 0.63 g) were fed six diets containing graded levels of PN (0.12–7.48 mg/kg diet) for 10 weeks. At the end of the feeding trial, the fish were challenged with Aeromonas hydrophila for 2 weeks. The results showed that compared with the optimal PN level, PN deficiency (1) increased the contents of reactive oxygen species (ROS), malondialdehyde (MDA) and protein carbonyl (PC), decreased the activities and mRNA levels of antioxidant enzymes such as copper, zinc superoxide dismutase (CuZnSOD), catalase (CAT), glutathione peroxidase (GPx), glutathione- S -transferase (GST) and glutathione reductase (GR) ( P  < .05); (2) up-regulated the mRNA levels of cysteinyl aspartic acid-protease-3 (caspase-3), caspase-7, caspase-8, caspase-9, Bcl-2 associated X protein (Bax), apoptotic protease activating factor-1 (Apaf-1) and Fas ligand (FasL), and down-regulated the mRNA levels of inhibitor of apoptosis proteins (IAP), B-cell lymphoma protein-2 (Bcl-2) and myeloid cell leukaemia-1 (Mcl-1) ( P  < .05); (3) down-regulated the mRNA levels of ZO-1, occludin [only in middle intestine (MI)], claudin-b, claudin-c, claudin-f, claudin-3c, claudin-7a, claudin-7b and claudin-11, and up-regulated the mRNA levels of claudin-12 and claudin-15a ( P  < .05), which might be partly linked to Kelch-like-ECH-associated protein 1a (Keap1a)/NF-E2-related factor 2 (Nrf2), p38 mitogen-activated protein kinase (p38MAPK) and myosin light chain kinase (MLCK) signalling in the intestines of fish. However, the activities and mRNA levels of MnSOD, the mRNA levels of Keap1b, c-Jun N-terminal protein kinase (JNK) and claudin-15b in three intestinal segments, and the mRNA levels of occludin in the proximal intestine (PI) and distal intestine (DI) were not affected by graded levels of PN. These data indicate that PN deficiency could disturb the intestinal physical barrier function of fish. Additionally, based on the quadratic regression analysis for MDA content and GST activity, the dietary PN requirements for young grass carp were estimated as 4.85 and 5.02 mg/kg diet, respectively. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of dietary sodium butyrate (SB) supplementation on the intestinal physical barrier function of young grass carp ( Ctenopharyngodon idella ). The fish were fed one powdery sodium butyrate (PSB) diet (1000.0 mg kg −1 diet) and five graded levels of microencapsulated sodium butyrate (MSB) diets: 0.0 (control), 500.0, 1000.0, 1500.0 and 2000.0 mg kg −1 diet for 60 days. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila to explore the effect of SB supplementation on intestinal physical barrier function and the potential mechanisms in fish. The results showed that optimal SB supplementation: (1) down-regulated the cysteine-aspartic protease-2 (caspase-2), caspase-3 (rather than PI), caspase-7, caspase-8 (rather than PI), caspase-9, fatty acid synthetase ligand (FasL), apoptotic protease activating factor-1 (Apaf-1), B-cell lymphoma 2 associated X protein (Bax) and c-Jun Nterminal protein kinase (JNK) mRNA levels, up-regulated the B-cell lymphoma protein-2 (Bcl-2) (rather than PI), inhibitor of apoptosis proteins (IAP) and myeloid cell leukemia-1 (Mcl-1) mRNA levels in the intestine ( P < 0.05), inhibited the intestinal cell apoptosis, maintained the intestine cell structure integrity; (2) increased NF-E2-related factor 2 (Nrf2) mRNA levels and nucleus protein levels, and down-regulated kelch-like-ECH-associated protein (Keap1b) (rather than Keap1a) mRNA levels in the intestine, up-regulated copper/zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase 1a (GPx1a), GPx1b, GPx4a, GPx4b, glutathione S-transferases R (GSTR), GSTP1, GSTP2, GSTO1, GSTO2 and glutathione reductase (GR) mRNA levels in the intestine, increased the corresponding antioxidant enzymes activity ( P < 0.05), thus enhancing the ability of scavenging free radicals and decreasing the reactive oxygen species (ROS) content, decreasing the lipid and protein peroxidation, as well as alleviating oxidative damage; (3) down-regulated the molecule myosin light-chain kinase (MLCK) mRNA levels in the intestine, and up-regulated the occludin, zonula occludens-1 (ZO-1), ZO-2, claudin-b, claudin-c, claudin-f, claudin-3c (rather than PI), claudin-7a, claudin-7b and claudin-11 mRNA levels, down-regulated claudin-12, claudin-15a and claudin-15b mRNA levels ( P < 0.05), thus maintaining the structural integrity between cells. This study suggests that SB supplementation could improve fish intestinal physical barrier function. Furthermore, according to the positive effect, MSB was superior to PSB on improving intestinal physical barrier function of fish. Finally, based on protein carbonyl content in the PI, the optimal SB supplementation (MSB as SB source) for young grass carp was estimated to be 338.8 mg kg −1 diet. [ABSTRACT FROM AUTHOR]

The current study explored the protective effect of leucine on antioxidant status, apoptosis and tight junction damage in the gill of grass carp ( Ctenopharyngodon idella Val.). The trial was conducted by feeding grass carp with six graded level of leucine (7.1, 8.9, 11.0, 13.3, 15.2 and 17.1 g kg −1 diet) for 8 weeks. The fish were fed to apparent satiation 4 times per day. The results indicated that compared with the leucine deficiency group, 8.9–11.3 g leucine kg −1 diet supplementations decreased protein carbonyl (PC), malondialdehyde (MDA) and ROS contents, which may be partially attributed to the improvement of antioxidant status in the gill by increasing hydroxyl radical capacity and anti-superoxide radicals, glutathione contents and the activities and mRNA levels of Cu/Zn superoxide dismutase (SOD1), glutathione peroxidase (GPx), catalase (CAT), glutathione-S-transferase (GST) and glutathione reductase (GR), that referring to the up-regulation of nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA expression. Moreover, leucine deficiency induced DNA fragmentation via the up-regulation of caspase-3, caspase-8 and caspase-9 expressions and down-regulation of target of rapamycin and ribosomal S6 protein kinase 1 expressions. Furthermore, leucine deficiency increased interleukin-1β (IL-1β), interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α) mRNA expression and decreased IL-10 and transforming growth factor β (TGF-β), which was partly related to nuclear factor κB (NF-κB) and its inhibitor (IκB). In contrast, the relative mRNA expression of IL-1, IL-8 and TNF-α was down-regulated with 8.9–11.3 g leucine kg −1 diet supplementations. Finally, the relative mRNA expression of tight junction protein, including occludin, zonula occludens-1, claudin b, claudin 3 and claudin 12 was up-regulated with leucine diet supplementations. Our results indicate that leucine protected the fish gill structural integrity partially because of the inhibition of apoptosis, the improvement of antioxidant status, the regulation of tight junction protein and related signalling molecules mRNA expressions in the fish gill. [ABSTRACT FROM AUTHOR]

This study investigated the effects of dietary protein levels on disease resistance, immune function and structural integrity in the head kidney, spleen and skin of grass carp ( Ctenopharyngodon idella ). A total of 540 grass carp (264.11 ± 0.76 g) were fed six diets containing graded levels of protein (143.1, 176.7, 217.2, 257.5, 292.2 and 322.8 g digestible protein kg −1 diet) for 8 weeks. After the growth trial, fish were challenged with Aeromonas hydrophila for 14 days. The results indicated that optimal levels of dietary protein: (1) (1) increased the lysozyme (LA) and acid phosphatase (ACP) activities and the complement 3 (C3) and C4 contents, up-regulated antimicrobial peptides, anti-inflammatory cytokines, inhibitor of κBα, target of rapamycin and ribosomal protein S6 kinases 1 mRNA levels, whereas down-regulated pro-inflammatory cytokines, nuclear factor kappa B (NF-κB) P65, IKKβ, IKKγ, eIF4E-binding proteins (4E-BP) 1 and 4E-BP2 mRNA levels in the head kidney, spleen and skin of grass carp ( P < 0.05), suggesting that optimal level of dietary protein could enhance immune function in the head kidney, spleen and skin of fish; (2) increased the activities and mRNA levels of antioxidant enzymes, enhanced the glutathione content, decreased reactive oxygen species, malondialdehyde (MDA) and protein carbonyl contents, and up-regulated the mRNA levels of NF-E2-related factor 2, B-cell lymphoma protein-2, inhibitor of apoptosis proteins, myeloid cell leukemia-1 and tight junction complexes, whereas down-regulated Kelch-like-ECH-associated protein (Keap) 1b, cysteinyl aspartic acid-protease 3, 8, 9, Fas ligand, apoptotic protease activating factor-1, Bcl-2 associated X protein and myosin light chain kinase mRNA levels in the head kidney, spleen and skin of grass carp ( P < 0.05), indicating that optimal level of dietary protein could improve structural integrity in the head kidney, spleen and skin of fish. Finally, based on the skin hemorrhage and lesion morbidity, LA activity and MDA content, the optimal levels of dietary protein for grass carp (264 g-787 g) were estimated to be 241.45 g kg −1 diet (217.68 g digestible protein kg −1 diet), 301.68 g kg −1 diet (265.48 g digestible protein kg −1 diet) and 307.84 g kg −1 diet (272.71 g digestible protein kg −1 diet), respectively. [ABSTRACT FROM AUTHOR]

A 105-day feeding trial was carried out to investigate the effects of dietary curcumin (CM) supplementation on growth performance, digestive enzyme activities, and intestinal antioxidant capacity of c rucian carp ( Carassius auratus ). A total of 585 crucian carp with average initial weight of 76.3 ± 0.10 g were fed three diets supplemented with 0 (basal group), 1, or 5 g kg − 1 CM. Fish fed the diet supplemented with 5 g kg − 1 CM showed significantly higher final body weight (FW), percent weight gain (PWG), and feed efficiency (FE) compares to those fed the basal or 1 g kg − 1 CM diet ( P < 0.05). Feed intake and body composition were not significantly different among dietary groups ( P > 0.05). The hepatopancreas weight, hepatopancreas protein content, intestinal weight, intestinal somatic index, intestine protein content, trypsin and lipase activities in hepatopancreas and intestine, amylase activity in hepatopancreas, Na + , K + -ATPase (NKA), alkaline phosphatase (AKP), gamma-glutamyl transpeptidase (γ-GT), and creatine kinase (CK) activities in intestine were significantly increased with dietary CM supplementation at 5 g kg − 1 ( P < 0.05). Fish fed the 5 g kg − 1 CM diet showed significantly lower malondialdehyde and protein carbonyl contents in the intestine ( P < 0.05). Superoxide anion and hydroxy radical scavenging ability, glutathione reducase (GR), catalase (CAT), total superoxide dismutase (T-SOD), glutathione peroxidase (GPx), and glutathione- S -transferase (GST) activities, and glutathione (GSH) content in the intestine were significantly increased with increased CM. The relative mRNA expressions of trypsin, lipase, NKA, AKP, γ-GT, CK, SOD1, CAT, GPx, GST, and GR in intestine were significantly up-regulated by dietary CM supplementation at 5 g kg − 1 . These results suggested that dietary CM supplementation increased intestinal antioxidant capacity, digestive and absorptive ability, and promoted fish growth. [ABSTRACT FROM AUTHOR]

An 8 week experiment was conducted to assess the effect of dietary thiamin on meat quality of grass carp. Totally, 540 fish were randomly distributed into 18 cages (1.4 m × 1.4 m × 1.4 m) each containing 30 fish in three replicates. Test fish were fed with respective diets for four times daily: 0.12 (thiamin un‐supplemented diet), 0.43, 0.83, 1.25, 1.62 and 2.04 mg thiamin/kg diet. Results revealed that optimum dietary thiamin improves grass carp flesh quality in five aspects: (1) increased nutritional quality (fillet protein, lipid contents) was associated with increasing target of rapamycin and casein kinase 2 expression, (2) improved flesh flavour via increasing the flavour amino acids contents (Glu, Asp, Gly, Ala, Leu and Ile), (3) elevated fillet healthcare components contents (especially docosahexaenoic acid and eicosapentaenoic acid contents), (4) improved sensory characteristics (pH, firmness, water‐holding capacity) of flesh and (5) enhanced flesh antioxidative capacity by elevating the activities and expression of antioxidant enzymes, which was involved in elevating Nrf2 expression and down‐regulating Keap1a and Keap1b expression. Dietary thiamin affected fish flesh quality correlated with changes in muscle flavour, healthcare components, sensory characteristics, antioxidant capacity, target of rapamycin and Nrf2 expression. [ABSTRACT FROM AUTHOR]

Hypoxia is becoming a non-negligible issue in aquaculture. The studies of dietary lipids mainly focused on growth performance, immune and meat quality of fish. There were scarce reports that dietary lipids can help fish resist stress, especially hypoxia stress. The objective of this study was to investigate the effects of dietary lipids on hypoxia-caused liver injury, oxidative damage, apoptosis, endoplasmic reticulum (ER) stress and autophagy of grass carp (Ctenopharyngodon idella), as well as make sure the lipid requirement of grass carp to resist hypoxia. Grass carp were fed diets containing six graded lipid levels (0%, 1.2%, 2.4%, 3.6%, 4.8% and 6.0%) for 60 days and exposed to hypoxia or normoxia for 96 h respectively. As shown in our results of grass carp, diets with proper lipid levels relieved hypoxia-induced adverse effects: (1) alleviated liver injury [decreased lactic dehydrogenase (LDH), glutamic oxalacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) activity, as well as reduced hepatic cellular vacuolation (HCV) and improved ER morphology]; (2) diminished liver oxidative damage [decreased reactive oxygen species (ROS), malondialdehyde (MDA) and protein carbonyl (PC) contents] and inhibited liver apoptosis (decreased caspase-3, −8 and − 9 activity); (3) relieved liver ER stress which might have connection with the inhibition of glucose regulated protein 78 (GRP78) -protein kinase R-1ike ER kinase (PERK) - eukaryotic translation initiation factor 2 subunit alpha (eIF2α) - activating transcription factor 4 (ATF4) and GRP78 - activating transcription factor 6 (ATF6) - X-box binding protein 1 (XBP1) pathways, rather than inhibition of inositol-requiring kinase1α (IRE1) pathway; (4) inhibited liver autophagy which might be related to the inhibition of the initiation [unc-51 like autophagy activating kinase 1 (ULK1)], elongation and closure [autophagy-related protein 5 (ATG5), autophagy-related protein 12 (ATG12) and light chain3II protein (LC3II)] of autophagosomes, rather than the inhibition of mitophagy and sequestosome 1 (P62) mediated degradation of substrates. In all, diets with proper lipid levels might be helpful to relieve hypoxia-induced adverse effects (injury, oxidative damage, apoptosis, ER stress and autophagy in the liver) on grass carp. Based on ROS and MDA contents of grass carp liver, we determined the optimal lipid levels to resist hypoxia-induced liver damage were 3.59% and 3.05%, respectively. • Proper dietary lipidlevels alleviated hypoxia-induced liver injury of fish. • Proper dietary lipids relieved hypoxia-induced liver oxidative damage in fish. • Proper dietary lipid levels relieved hypoxia-induced liver apoptosis of fish. • Proper dietary lipid levels relieved hypoxia-induced liver ER stress of fish. • Proper dietary lipid levels relieved hypoxia-induced liver autophagy of fish. [ABSTRACT FROM AUTHOR]

[Display omitted] • Niacin deficiency decreased the growth performance of fish. • Niacin deficiency affected muscle amino acid and fatty acid compositions of fish. • Niacin deficiency exerted negative impacts on flesh physicochemical properties. • Niacin deficiency may quicken flesh pH drop by promoting glycolysis. • Niacin deficiency impaired mitochondrial homeostasis. Energy metabolism exerts profound impacts on flesh quality. Niacin can be transformed into nicotinamide adenine dinucleotide (NAD), which is indispensable to energy metabolism. To investigate whether niacin deficiency could affect energy metabolism and flesh quality, six diets with graded levels of 0.49, 9.30, 21.30, 33.30, 45.30 and 57.30 mg/kg niacin were fed to grass carp (Ctenopharyngodon idella) for 63 days. The results showed that niacin deficiency declined flesh quality by changing amino acid and fatty acid profiles, decreasing shear force, increasing cooking loss and accelerating pH decline. The accelerated pH decline might be associated with enhanced glycolysis as evident by increased hexokinase (HK), pyruvate kinase (PK) and lactic dehydrogenase (LDH) activities, and mitochondrial dysfunction as evident by destroyed mitochondrial morphology, impaired respiratory chain complex I and antioxidant ability. Based on PWG and cooking loss, the niacin requirements for sub-adult grass carp were 31.95 mg/kg and 29.66 mg/kg diet, respectively. [ABSTRACT FROM AUTHOR]

The mucosal barrier of vertebrates comprises a unique array of physical elements and bioactive molecules that act in concert to protect the host against pathogens. Vitamin D (VD), an essential nutrient for animals, along with its receptor (VDR), plays a major role in immunity. However, the correlation between VD/VDR and the mucosal barrier system remains unclear. Here, we employed the fish gill as a model and evaluated the role of VD as a dietary supplement in modifying this typical mucosal barrier system. Varies levels of VD (15.2, 364.3, 782.5, 1167.9, 1573.8, and 1980.1 IU/kg) were formulated and fed to grass carp (Ctenopharyngodon idella) for 70 d. Subsequently, fish were challenged with Flavobacterium columnare , a pathogen in epithelial tissues. Following infection, dietary VD alleviated gill rot and damage caused by F. columnare. Further investigations demonstrated that VD improved physical barrier function by elevating the antioxidant capacity and tight junction barriers, and moderated excessive apoptosis. The promoted physical barrier function was related to nuclear factor E2-related factor 2 and myosin light-chain kinase signaling. Additionally, VD treatment enhanced the immune barrier function by boosting disease resistance, producing antibacterial compounds and immunoglobulins, downregulating pro-inflammatory cytokines, and upregulating the gene expression of anti-inflammatory cytokines, which correlated with nuclear factor kappa B and the target of rapamycin signaling pathways. Thus, VD strengthened pathogen defenses in the gill mucosal barrier system. This finding supports the rationale for VD intervention in infectious diseases and will be critical for the viability of sustainable practices in aquaculture. • Knowledge of the relationship between the VD and VDR isoforms is lacking in fish. • We evaluated the effects of VD along with VDR in regulating the gill mucosal barrier. • VD improved barrier functions via multiple signaling correlated with VDRa. • VD intervention for infections is vital for sustainable development of aquaculture. [ABSTRACT FROM AUTHOR]

Leucine is an essential amino acid for fish. The ability of leucine to resist stress in fish has not been reported. Nitrite is a common pollutant in the aquatic environment. Therefore, we investigated the effects of dietary leucine on growth performance and nitrite-induced liver damage, mitochondrial dysfunction, autophagy, and apoptosis for sub-adult grass carp. A total of 450 grass carp (615.91 ± 1.15 g) were selected and randomly placed into 18 net cages. The leucine contents of the six diets were 2.91, 5.90, 8.92, 11.91, 14.93, and 17.92 g/kg, respectively. After a 9-week feeding trial, the nitrite exposure experiment was set up for 96 h. These results indicated that dietary leucine significantly promoted FW, WG, PWG, and SGR of sub-adult grass carp (P < 0.05). Appropriate levels of dietary leucine (11.91–17.92 g/kg) decreased the activities of serum parameters (glucose, cortisol, and methemoglobin contents, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and lactate dehydrogenase), the contents of reactive oxygen species (ROS), nitric oxide (NO) and peroxynitrite (ONOO−). In addition, appropriate levels of dietary leucine (11.91–17.92 g/kg) increased the mRNA levels of mitochondrial biogenesis genes (PGC-1α, Nrf1/2, TFAM), fusion-related genes (Opa1, Mfn1/2) (P < 0.05), and decreased the mRNA levels of caspase 3, caspase 8, caspase 9, fission-related gene (Drp1), mitophagy-related genes (Pink1, Parkin) and autophagy-related genes (Beclin1, Ulk1, Atg5, Atg7, Atg12) (P < 0.05). Appropriate levels of dietary leucine (8.92–17.92 g/kg) also increased the protein levels of AMP-activated protein kinase (AMPK), prostacyclin (p62) and decreased the protein levels of protein light chain 3 (LC3), E3 ubiquitin ligase (Parkin), and Cytochrome c (Cytc). Appropriate levels of leucine (8.92–17.92 g/kg) could promote growth performance and alleviate nitrite-induced mitochondrial dysfunction, autophagy, apoptosis for sub-adult grass carp. Based on quadratic regression analysis of PWG and serum GPT activity, dietary leucine requirements of sub-adult grass carp were recommended to be 12.47 g/kg diet and 12.55 g/kg diet, respectively. [Display omitted] • Leucine could alleviate nitrite-induced liver damage of grass carp. • Leucine alleviated liver damage probably via reducing nitrite-induced autophagy, apoptosis, and mitochondrial dysfunction. • Based on PWG and serum GPT, leucine requirement was determined to be 12.47 g/kg and 12.55 g/kg diet for sub-adult grass carp. [ABSTRACT FROM AUTHOR]

Taurine is abundantly present in fishmeal, while plant protein sources typically contain minimal to no taurine. This disparity in taurine content may explain variations in fish quality traits caused by the dietary substitution of fishmeal with plant protein sources. This research explored whether taurine supplementation to non-fishmeal (NFM) diet could improve fillet quality and muscle antioxidant capacity in grass carp. A total of 540 fish (255.74 ± 0.65 g) were distributed among six groups. One of them was provided with a fishmeal (FM) diet, while the remaining five groups received NFM diets, formulated with incremental concentrations of crystalline taurine (0, 0.5, 1.0, 1.5, 2.0 g/kg) for 60 days. Our data showed that, in comparison with the un-supplemented group, the optimal taurine supplementation to NFM diet yielded the following findings: (1) increased fillet nutritional values by improving crude protein content, free amino acid and fatty acid compositions; (2) improved fillet physicochemical properties by improving water holding capacity (WHC), tenderness, and preventing pH decline; (3) enhanced antioxidant enzymes activities and gene expressions through nuclear factor-erythroid 2-related factor 2 (Nrf2) signaling pathway. Additionally, this optimal NFM diet showed to be competitive with FM diet in terms of fillet quality. According to quadratic regression curves of ROS production and polyunsaturated fatty acids (PUFA) content, the optimal taurine supplementation levels in NFM diet for on-growing grass carp were 1.12 and 1.18 g/kg diet, respectively. • The addition of taurine to non-fishmeal (NFM) diets resulted in enhanced nutritional values and improved physicochemical properties of the fillet. • Taurine supplementation to NFM diet improved muscle antioxidant status. • NFM diet supplemented with appropriate taurine was competitive with fishmeal diet in terms of fillet quality. [ABSTRACT FROM AUTHOR]

The present study was designed to assess the possible protective effects of arginine (Arg) against lipopolysaccharide (LPS) induced inflammatory response in juvenile Jian carp ( Cyprinus carpio var. Jian) in vivo and in enterocytes in vitro . Firstly, inflammatory response was established by exposing enterocytes to different concentrations of LPS for 24 h. Secondly, the protective effects of Arg against subsequent LPS exposure were studied in enterocytes. Finally, we investigated whether dietary Arg supplementation could attenuate immune challenge induced by LPS in vivo . The result indicated that 10 mg/L LPS could induced inflammatory response in enterocytes. Cells exposed to LPS (10–30 mg/L) alone for 24 h resulted in a significant increase in lactate dehydrogenase release (LDH) ( P < 0.05). The cell viability, protein content, alkaline phosphatase activity were decreased by LPS ( P < 0.05). Moreover, LPS exposure significantly increased TNF-α, IL-1β, and IL-6 mRNA expression in vitro ( P < 0.05). However, pre-treatment with Arg remarkably prevented the increase of TNF-α, IL-1β, and IL-6 by inhibiting the excessive activation of TLR4-Myd88 signaling pathway through down-regulating TLR4, Myd88, NFκB p65, and MAPK p38 mRNA expression ( P < 0.05). Interestingly, the experiment in vivo showed that Arg pre-supplementation could attenuate immune challenge induced by LPS via TLR4-Myd88 signaling pathway, and thus protect fish against LPS-induced inflammatory response. In conclusion, all of these results indicated pre-supplementation with Arg decreased LPS induced immune damage and regulated TLR4-Myd88 signaling pathway in juvenile Jian carp in vivo and in enterocytes in vitro . [ABSTRACT FROM AUTHOR]

Hypoxia in water environment is one of the important problems faced by intensive aquaculture. Under hypoxia stress, the effects of dietary thiamine were investigated on grass carp gill tissue damage and their mechanisms. Six thiamine diets with different thiamine levels (0.22, 0.43, 0.73, 1.03, 1.33 and 1.63 mg/kg) were fed grass carp (Ctenopharyngodon idella) for 63 days. Then, 96-hour hypoxia stress test was conducted. This study described that thiamine enhanced the growth performance of adult grass carp and ameliorated nutritional status of thiamine (pyruvic acid, glucose, lactic acid and transketolase). Additionally, thiamine alleviated the deterioration of blood parameters [glutamic oxalacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), glucose, cortisol, lactic dehydrogenase (LDH), erythrocyte fragility, and red blood cell count (RBC count)] caused by hypoxia stress, and reduced reactive oxygen species (ROS) content and oxidative damage to the gills. In addition, thiamine alleviated endoplasmic reticulum stress in the gills, which may be related to its inhibition of RNA-dependent protein kinase-like ER kinase (PERK)/eukaryotic translation initiation factor-2α (eIF2α)/activating transcription factor4 (ATF4), inositol-requiring enzyme 1 (IRE1)/X-Box binding protein 1 (XBP1) and activating transcription factor 6 (ATF6) pathways. Furthermore, thiamine maintaining mitochondrial dynamics balance was probably related to promoting mitochondrial fusion and inhibiting mitochondrial fission, and inhibiting mitophagy may involve PTEN induced putative kinase 1 (PINK1)/Parkin-dependent pathway and hypoxia-inducible factor (HIF)-Bcl-2 adenovirus E1B 19 kDa interacting protein 3 (BNIP3) pathway. In summary, thiamine alleviated hypoxia stress in fish gills, which may be related to reducing endoplasmic reticulum stress, regulating mitochondrial dynamics balance and reducing mitophagy. The thiamine requirement for optimum growth [percent weight gain (PWG)] of adult grass carp was estimated to be 0.81 mg/kg diet. Based on the index of anti-hypoxia stress (ROS content in gill), the thiamine requirement for adult grass carp was estimated to be 1.32 mg/kg diet. [Display omitted] • Hypoxia stress causes gill damage in fish. • Thiamine alleviates hypoxia-induced gill oxidative damage in fish. • Thiamine alleviates hypoxia-induced gill ER stress in fish. • Thiamine regulates hypoxia-induced gill mitochondrial fusion-fission in fish. • Thiamine alleviates hypoxia-induced gill mitophagy in fish. [ABSTRACT FROM AUTHOR]

Lactobacillus rhamnosus is a probiotic, which not only promotes the growth of animals, but also has anti-inflammatory effects. However, the mechanism by which Lactobacillus rhamnosus regulates intestinal immunity is not well comprehended. Hence, the study aimed to research how Lactobacillus rhamnosus affects the intestinal immunity using juvenile grass carp (Ctenopharyngodon idella) as a model. We selected 1800 juvenile grass carp for testing. They were divided into six treatments and fed with six gradients of Lactobacillus rhamnosus GCC-3 (0.0, 0.5, 1.0, 1.5, 2.0, 2.5 g/kg) for 70 days. Enteritis was subsequently induced with dextroside sodium sulfate. Results indicated that dietary Lactobacillus rhamnosus GCC-3 addition improved growth performance. Meanwhile, appropriate levels of Lactobacillus rhamnosus GCC-3 alleviated excessive inflammatory response by down-regulating the expression of TLR4 and NOD receptors, up-regulating the expression of TOR, and then down-regulating the expression of NF-κB. Additionally, appropriate Lactobacillus rhamnosus GCC-3 improved intestinal immunity by reducing pyroptosis triggered by NLRP3 inflammasome and mediated by GSDME. Furthermore, 16 S rRNA sequencing showing appropriate levels of Lactobacillus rhamnosus GCC-3 increased Lactobacillus and Bifidobacterium abundance and decreased Aeromonas abundance. These results suggest that Lactobacillus rhamnosus GCC-3 can alleviate intestinal inflammation through down-regulating NF-κB and up-regulating TOR signaling pathways, as well as by inhibiting pyroptosis. • GCC-3 may inhibited the TLR4/NF-κB and NOD/NF-κB to alleviate intestinal inflammation. • GCC-3 may alleviated intestinal inflammation by inhibiting pyroptosis. • GCC-3 improved gut microbiota composition and diversity. • The appropriate amount of GCC-3 in juvenile grass carp diet was 1.0–1.5 g/kg. [ABSTRACT FROM AUTHOR]

In this study, fish were fed six diets containing different levels of pyridoxine (PN) for 10 weeks, and then infected with Aeromonas hydrophila for 2 weeks. The results showed that dietary supplementation with PN had a powerful effect on the inhibition of skin haemorrhage and lesion morbidity, and the enhancement of immunity after fish were infected with A. hydrophila. For example, PN increased the levels of immunoglobulin M (IgM), acid phosphatase (ACP), complement 3 (C3), lysozyme (LZ), C4, antimicrobial peptides, target of rapamycin (TOR), anti‐inflammatory cytokines, ribosomal protein S6 kinases 1 (S6K1) and inhibitor of κBα (IκBα), while decreasing the levels of proinflammatory cytokines [except interleukin‐12 p40 (IL‐12p40)], eIF4E‐binding proteins (4E‐BP), IκB kinase β (IKKβ) and nuclear factor κB p65 (NF‐κBp65) in grass carp skin. Additionally, dietary supplementation with PN increased the levels of tight junction proteins (not claudin‐15 and claudin‐12), antioxidant enzymes [except manganese superoxide dismutase (MnSOD) activity and gene expression, glutathione peroxidase 4a (GPx4a) and GPx4b gene expression], NF‐E2‐related Factor 2 (Nrf2), myeloid cell leukaemia‐1 (Mcl‐1) and inhibitor of apoptosis proteins (IAP), while decreasing the levels of malondialdehyde (MDA), reactive oxygen species (ROS), protein carbonyl (PC), Kelch‐like ECH‐associating protein 1a (Keap1a) myosin light chain kinase (MLCK), cysteinyl aspartic acid protease‐9 (caspase‐9), caspase‐8, caspase‐7, caspase‐3, Bcl‐2‐associated X protein (Bax), p38 mitogen‐activated protein kinase (p38MAPK) and apoptotic protease‐activating factor 1 (Apaf‐1) in grass carp skin. In summary, dietary PN can enhance the immunity of fish skin via elevated immune substances, an eased inflammatory response and an improved barrier integrity. [ABSTRACT FROM AUTHOR]

An 8-week feeding trial was conducted to investigate the effects of dietary soy protein concentrate (SPC) levels on growth, blood biochemical indexes, non-specific immune enzyme activity, and nutrient apparent digestibility for juvenile Litopenaeus vannamei (initial weight 0.44 ± 0.002 g). They were formulated by replacing 0% (the control), 10%, 20%, 30%, 40%, 60%, and 80% of fish meal (FM) protein with SPC (designed FM, S11, S22, S33, S44, S55, and S66, respectively). With the replacement level of SPC in the diet was higher than 30%, weight gain (WG) and specific growth rate (SGR) for juvenile Litopenaeus vannamei significantly decreased (P < 0.05) with SPC increasing, but feed conversion ratio (FCR) significantly increased (P < 0.05). When the replacement level was above 40%, the protein efficiency ratio (PER), survival rate (SR), apparent digestibility of dry matter, and energy significantly decreased (P < 0.05). On the contrary, the content of triglyceride glucose (TG) in serum was increased significantly (P < 0.05). Apparent digestibility for crude protein and total lipid were significantly higher at higher fishmeal inclusion (0 and 10% SPC replacement) and significantly lower at lower fishmeal inclusion (< 70%) (P < 0.05). In conclusion, with reference to all the parameters, SPC can be used to replace up to 30% of fishmeal protein in shrimp feeds and so the total fishmeal exceeds 70% be used to cater to shrimps' dietary needs. [ABSTRACT FROM AUTHOR]

Ochratoxin A (OTA) is a prevalent contaminant in fish feed, posing a threat to aquatic health. Curcumin (Cur), a widely used feed additive renowned for its antioxidant and anti-inflammatory functions, has emerged as a potential solution. Gills are one of the mucosal immune organs in fish. Adding a natural product to feed is one of the most popular strategies to alleviate mycotoxin. At present, it is unknown whether dietary Cur can alleviate the damage to the fish gill barrier caused by ochratoxin A in the diet. Here, we explored the mitigation effects of Cur on the physical, chemical, and immune barriers of gills in grass carp damaged by OTA. This study employed 720 juvenile grass carp (initial average body weight: 11.06 ± 0.05 g) were randomly assigned into 4 groups: the control group (devoid of OTA and Cur), the 1.2 mg/kg OTA group, the 400 mg/kg Cur group, with three replicates per treatment (180 fish) over a 60-day period. Results demonstrated that Cur supplementation could significantly counter OTA-induced damage to the gill barrier through distinct mechanisms: (1) Inhibition of OTA absorption while promoting efflux transporters mRNA expression, thereby diminishing OTA residuals. (2) Enhancement of the physical barrier by fortifying antioxidant defenses, reducing apoptosis, and strengthening tight junctions. (3) Improvement of the chemical barrier by elevating goblet cells, immune components, and antimicrobial peptides. (4) Enhanced the immune barrier by suppressing toll-like receptor 4 and nuclear factor-κB signaling pathways, leading to reduced expression of pro-inflammatory factors and increased T cell differentiation-related genes. In conclusion, Cur emerges as an effective agent in alleviating OTA-induced gill immune function, enhancing physical, chemical, and immune barriers. This study provides a valuable theoretical foundation and practical significance for employing Cur to mitigate the mucosal immune toxicity of OTA in fish. • Curcumin alleviates OTA-induced gill histological injury by reducing OTA residues. • Curcumin alleviates the gills physical, chemical and immune barrier of OTA damage. • There is a potential regulatory network affected by Cur: Nrf2/RhoA/MAPK/Mucin/ NFκB. [ABSTRACT FROM AUTHOR]

Potassium diformate (KDF) is a green and safe feed additive to replace antibiotics in animal. Although a few studies have found that KDF improved disease resistance, the specific mechanisms have not been explored in depth. Therefore, the study aims to examine the effects of KDF on immune defense substances, inflammatory process, T cell differentiation, and related molecular expression in fish. The juvenile grass carp were selected from six groups after feeding graded levels of KDF (0.0, 1.5, 3.0, 4.5, 6.0 and 7.5 g/kg) for 70 days. Then 6-day challenge experiment was performed by intraperitoneal injection Aeromonas hydrophila. Appropriate levels of KDF increased the lysozyme and acid phosphatase activities, the complement 3 and complement 4 contents in the head kidney and spleen of juvenile grass carp. Meanwhile, Appropriate addition levels of KDF down-regulated the abundances of TNF-α, IL-2, IL-6, IL-8, IL-1β, IL-12, IL-22, IL-17D, T-bet and RORγt (RORγ2) mRNA and up-regulated the abundances of TGF-β, IL-4, IL-10, GATA3, FOXP3, CD4, MHCIIα and MHCIIβ mRNA in the head kidney and spleen. Besides, appropriate levels of KDF down-regulated the mRNA levels of IKKγ (not IKKα) , IKKβ, NF-κB p65 (not p52) , STAT1, STAT4 , and the protein level of NF-κB p65, up-regulated the mRNA levels of IκBα, JAK1, JAK2, JAK3, STAT3b1, STAT3b2 (not STAT3a) , STAT5b, STAT6, and the protein level of p-STAT3Tyr705. The appropriate levels of KDF enhanced the immune defense and mediated the inflammatory process that might be related to T cell differentiation probably via JAK-STATs and NF-κB signalings in fish. • KDF enhanced immune parameter of fish. • KDF regulated inflammatory response in immune organ of fish. • KDF activated JAK-STATs and NF-κB signaling pathways to regulate immune response. • 4.96–5.07 g/kg KDF may be added into the feed to improve immunity of fish. [ABSTRACT FROM AUTHOR]

Quenching enzymes have attracted wide attention as one of the alternatives to antibiotics because their positive effects on inhibiting pathogenic microorganism. Therefore, the objective of this study was to investigate the impact of dietary quenching enzyme AiiO-AIO6 on the growth performance, digestion and absorption capacity, intestinal structural integrity, and gut microbiota composition in juvenile grass carp. Healthy grass carp (4.73 ± 0.01 g) were assigned to 36 fish tanks (1.2 × 0.6 × 0.9 m), randomly divided into 6 groups, and fed on six diets with different levels of AiiO-AIO6 (0, 2.5, 5.0, 7.5, 10.0 and 12.5 U/g feed) for a duration of 10 weeks. The present findings demonstrated that dietary AiiO-AIO6 supplementation positively influenced the final body weight (FBW), specific growth rate (SGR), percent weight gain (PWG), and feed intake (FI) of juvenile grass carp. Moreover, our results indicated that the appropriate dietary AiiO-AIO6 supplementation promoted the number of goblet cells and improved the activities of chymotrypsin, trypsin, lipase, amylase, Na+-K+-ATPase, γ-GT and CK, which ultimately contributed to the enhancement of digestion and absorption capacity of juvenile grass carp. Additionally, the present study further found that dietary AiiO-AIO6 supplementation up-regulated the relative mRNA levels of tight junctions (TJs) and adhesive junctions (AJs) proteins, including ZO-1, occludin, claudin-b, −c, −f, −7a, −7b, −11, −12 , α-catenin, nectin, afadin, and E-cadherin , thereby enhancing the physical barrier function, potentially attributed to the reduction in abundance of intestinal pathogenic bacteria, such as Pseudomonas. Ultimately, the optimal level of AiiO-AIO6 for juvenile grass carp, as determined by the percent weight gain (PWG), was found to be 4.5 U/g. • Quenching enzyme AiiO-AIO6 enhanced the growth performance of fish. • Quenching enzyme AiiO-AIO6 improved intestinal development, digestion and absorption capacity of fish. • Quenching enzyme AiiO-AIO6 promoted the intestinal physical barrier function of fish. • Dietary AiiO-AIO6 affected the structure of intestinal microbiota. [ABSTRACT FROM AUTHOR]

This study was performed to determine effects of dietary isoleucine (Ile) on growth performance, and intestinal immunological and physical barrier function of hybrid catfish Pelteobagrus vachelli × Leiocassis longirostris. Six hundred and thirty fish (33.11 ± 0.09 g) were randomly divided into seven experimental groups with three replicates each, and respectively fed seven diets with 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile kg−1 diets for 8 weeks. The results showed improvement of growth performance, feed intake, feed utilization, relative gut length (RGL), and intestinal fold height and width by dietary Ile (P < 0.05). Meanwhile, dietary Ile (12.5 g kg−1 diet) improved the activities of lysozyme (LZM), acid phosphatase, alkaline phosphatase and the contents of complement 3 (C3), C4, and immunoglobulin M (IgM) (P < 0.05). The c-type-lectin, c-LZM, g-LZM, and hepcidin mRNA expressions in the intestine were up-regulated in fish fed diets with 10.0–20.0 g Ile kg−1 diet (P < 0.05). Dietary Ile (10.0–12.5 g Ile kg−1 diet) increased intestinal β-defensin mRNA expression partially in association with Sirt1/ERK/90RSK signaling pathway. Dietary Ile (12.5–15.0 g Ile kg−1 diet) decreased oxidative damage and improved antioxidant ability by increasing activities and expressions of superoxide dismutase, glutathione peroxidase, and glutathione reductase, glutathione-S-transferase (P < 0.05). The occludin, ZO-1, ZO-2, claudin3, and claudin 7 mRNA expressions in the intestine were up-regulated in fish fed diets with 10.0 and 12.5 g Ile kg−1 diet (P < 0.05), whereas the myosin light chain kinase gene expression was decreased in fish fed diets with 7.5–17.5 g Ile kg−1 diet. Dietary Ile (10–12.5 g Ile kg−1 diet) decreased apoptotic responses by reducing the expression of caspase3 and caspase 9 via the AKT/TOR signaling pathway. Based on the quadratic regression analysis of PWG, the dietary Ile requirement of hybrid catfish was estimated to be 12.43 g Ile kg−1 diet, corresponding to 32.05 g Ile kg−1 dietary protein. Collectively, dietary Ile improved growth performance and immunological and physical barrier function of intestine in hybrid catfish. • Ile improved growth performance and intestinal immune barrier of hybrid catfish. • Ile regulated intestinal antioxidant status and tight junctions function in fish. • Ile decreased enterocytes apoptosis via AKT-FOXO3a signaling pathway in fish. [ABSTRACT FROM AUTHOR]

The present research evaluated the effects of graded levels of dietary fibre on growth, digestive and absorptive capacities, and the potential underlying mechanisms in on‐growing grass carp (Ctenopharyngodon idella). Grass carp (123.00 ± 0.70 g) were fed diets with graded levels of neutral detergent fibre (NDF: 97.8, 119.0, 140.2, 159.4, 181.2 and 201.6 g/kg diet) for 60 days. Besides, a 2‐week digestion experiment was conducted to explore the effect of dietary fibre on the apparent digestibility coefficients (ADC) of feed. The results showed that optimum dietary fibre level (140.2 or 159.4 g/kg diet) increased feed intake, per cent weight gain, specific growth rate and the ADC of dietary protein (p <.05); increased the activities of digestive and brush border enzyme; and up‐regulated intestinal amino acid transporter mRNA levels (SLC1A5 and SLC6A19b, p <.05) partially associated with activation of TOR signalling pathway. However, high dietary fibre levels (NDF levels ≥181.2 g/kg diet) were not conducive to the digestion and absorption of nutrients, resulting in the decline of growth performance. Thus, based on the quadratic regression analysis for per cent weight gain and feed efficiency, the optimum (143.9 and 134.5 g/kg diet) and maximum tolerance (189.8 and 171.2 g/kg diet) levels of dietary NDF were estimated for on‐growing grass carp. [ABSTRACT FROM AUTHOR]

Tea polyphenols (TP) are functional feed additives (antioxidants) derived from tea. Research to date has not investigated the impacts of TP on flavour quality, healthcare components, and physicochemical parameters of fish flesh. This study aimed to investigate whether dietary TP in growing grass carp could provide high quality fish flesh. 540 fish (187.49 ± 0.66 g) were fed six diets with different concentrations of TP (0, 40, 80, 120, 160 and 200 mg / kg) for 60 days to determine the effects of TP on flesh quality. The results demonstrated that appropriate dietary TP supplementation benefits growing grass carp in the following respects: (1) promoting performance of growth and nutritional value of fish, (2) enhancing flavour of flesh by increasing the levels of umami-taste free amino acids (glutamic acid and aspartic acid) (3) increasing healthcare components of flesh particularly eicosapentaenoic acid (EPA 20:5n-3) and docosahexaenoic acid (DHA 22:6n-3), (4) improving physicochemical properties (firmness,pH, water-holding capacity) of flesh. The present research explores, for the first time, the effects of TP on enhancing the collagen content, which is partly correlated with the upregulation of type I collagen synthesis genes Col1α1 and Col1α2 , mediated through transforming growth factor-β1 (TGF-β1) by Smad pathway in fish muscle. Based on growth performance (percentage weight gain) and fish flesh quality indices (EPA, DHA, shear force, and pH), the appropriate dietary supplementation of TP in growing grass carp were assessed to be 103.01, 116.30, 106.60, 141.15 and 113.49 mg/kg, using quadratic regression analysis. In summary, TP is a promising feed additive to improve fish flesh quality. • Tea polyphenols promoted growth performance of fish. • Tea polyphenols enhanced flavour of fish flesh. • Tea polyphenols enhanced healthcare component of fish flesh. • Tea polyphenols enhanced collagen content by regulating TGF-β1/Smads signalling pathways in fish flesh. [ABSTRACT FROM AUTHOR]

The immune function of immune organs is extremely crucial for maintaining organism health status, which ultimately affects fish growth. Our previous study has found that dietary supplementation of (2-carboxyethyl)dimethylsulfonium Bromide (Br-DMPT) in non-fish meal (NFM) diet could promote the growth of grass carp (Ctenopharyngodon idella), whereas the underlying reason or mechanism for this results is largely unclear. Herein, we further explored whether dietary supplementation of Br-DMPT promoted fish growth is connected with the enhanced immune function in the immune organs (the head kidney, spleen and skin). In this study, 540 fish (216.49 ± 0.29 g) were irregularly distributed to six groups with three replicates (30 fish replicate−1) and fed corresponding diets group containing a fish meal (FM) diet group and five different NFM diets supplemented with gradational Br-DMPT (0–520.0 mg/kg level) group for 60 days. After the 60-days feeding trial, 8 fish from each replicate were selected and then conducted a challenge test with A. hydrophila for 14 days. Our results indicated that in the NFM diets, appropriate Br-DMPT: (1) significantly decreased the morbidity of skin haemorrhage and lesion after A. hydrophila infection (P < 0.05). (2) significantly improved the innate and adaptive immune components (lysozyme, complement 3, immunoglobulin M and antibacterial peptides et al.) (P < 0.05). (3) increased the gene expressions of main anti-inflammatory cytokines partially by referring to TOR signalling pathway, and decreased the gene expressions of main pro-inflammatory cytokines partially by referring to NF-kB signalling pathway (P < 0.05). Strikingly, no statistical difference could be found in the most of above immune parameters between 260.0 mg/kg Br-DMPT diet group and FM diet group (P > 0.05). Taken together, in non-fish meal diet, appropriate supplementation of Br-DMPT could improve the disease resistance capacity, non-specific immunity and ameliorate inflammation, and simultaneously could mitigate these adverse effects induced by the non-fish meal diet in fish immune organs. Moreover, this study may be helpful to decipher the underlying mechanisms of how Br-DMPT promote fish growth by immune organs and also provide scientific theoretical evidence for the future application of Br-DMPT as a new immunopotentiator in aquaculture industry. • 1、 Appropriate Br-DMPT supplementation enhanced skin disease resistance of fish. • 2、 Appropriate Br-DMPT supplementation improved non-specific immunity of immune organs in fish. • 3、 Appropriate Br-DMPT supplementation alleviated inflammation response involving cytokines of immune organs in fish. • 4、 Appropriate Br-DMPT supplementation modulated NF-κB and TOR signalling in fish immune organs. [ABSTRACT FROM AUTHOR]

This research investigates the influences of dietary mannan oligosaccharides (MOS) on the head-kidney and spleen immune function in on-growing grass carp (Ctenopharyngodon idella) and its related mechanism. Fish were fed during 60 days at different levels of MOS (0, 200, 400, 600, 800 and 1000 mg kg−1). Subsequently, 14 days after the feeding trial was injected intraperitoneally with Aeromonas hydrophila , the immune function was studied. The results are as follows: (1) appropriate MOS supplementation could increase the content of antibacterial compound and immunoglobulin (Ig), up-regulate antimicrobial peptides transcriptional levels in these two organs; (2) appropriate MOS supplementation attenuated inflammatory response in these two organs by regulating cytokines (pro- and anti-inflammatory cytokines) and related signalling pathways (NF-κB and TOR). The interesting points though, was, no differences were found in liver-expressed antimicrobial peptide (LEAP)-2A, interleukin (IL) -8 , IL-4 / 13B , IκB kinase (IKK) α and nuclear factor kappa B (NF-κB) p52 gene expression in these two organs. Consequently, the present research suggests that MOS supplementation can enhance head-kidney and spleen immune function. Finally, we obtained these appropriate MOS dose (538.5 and 585.8 mg kg−1) by quadratic regression analysis of lysozyme activity (head-kidney) and phosphatase activity (spleen), respectively. • Mannan oligosaccharide (MOS) supplementation increasing antimicrobial substance in fish head kidney and spleen. • MOS supplementation attenuated the damaging effect of Aeromonas hydrophila infection on the fish head kidney and spleen. • MOS supplementation reduced the inflammatory in fish head kidney and spleen by regulating TOR and NF-κB signalling pathway. [ABSTRACT FROM AUTHOR]

Glycinin is a major protein and antinutritional factor of soybean. However, how dietary glycinin affect intestinal immune function of fish were largely unknown. In this study, we used juvenile grass carp as a model to investigate the impacts of glycinin on intestinal immune function of fish and involved mechanisms. We set three treatments including control, glycinin and glycinin + glutamine in this trial. For immune components, results revealed that compared with control group, glycinin group had lower acid phosphatase activities in the foregut, midgut and hindgut, lower C3 and C4 content, and lower mRNA abundances of IgM, IgZ, hepcidin, LEAP-2A, LEAP-2B and β-defensin-1 in the midgut and hindgut rather than foregut of grass carp. For pro-inflammatory cytokines and relevant signaling, glycinin elevated mRNA abundances of IL-1β, IL-8, IL-12p35, IL-12p40 and IL-17D in the midgut and IL-1β, IFN-γ2, IL-6, IL-8, IL-12p35, IL-12p40 and IL-17D in the hindgut, and increased protein abundances of PKC-ζ and nuclear NF-κB p65 in the midgut and hindgut in comparison to control. For anti-inflammatory cytokines and relevant signaling, glycinin reduced mRNA abundances of TGF-β1, TGF-β2, IL-4/13B (rather than IL-4/13A), IL-10 and IL-11 in the midgut and hindgut, and reduced p -mTOR (Ser 2448), p-S6K1 (Thr 389) and p-4EBP1 (Thr 37/46) protein abundances in the midgut and hindgut rather than foregut. Co-administration of glutamine with glycinin could partially enhance intestinal function and reduce intestinal inflammation compared with glycinin treatment. Concluded, glycinin decreased intestinal immune components and caused intestinal inflammation associated with PKC-ζ/NF-κB and mTORC1 signaling. • Glycinin decreased intestinal immune components of grass carp. • Glycinin upregulated pro-inflammatory cytokines associated with PKCζ/NF-κB p65 signaling. • Glycinin downregulated anti-inflammatory cytokines associated with mTORC1 signaling. [ABSTRACT FROM AUTHOR]

A 56 days feeding trial was conducted to investigate the effects of enzyme-treated soy protein (ETSP) supplementation in low protein diets on immune function of immune organs (head kidney, spleen and skin) 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%). At the end of feeding period, a challenge test was performed by infection with Aeromonas hydrophila for two weeks. The results indicated that (1) reducing dietary protein content from 28 to 26% decreased antibacterial substances and aggravated inflammatory responses of above three immune organs; (2) under the condition of reducing protein level in diet, 0.8–1.2% ETSP supplementation reversed these above adverse effects on immune function of above three immune organs; (3) suitable ETSP supplementation-decreased inflammatory responses were partly associated with [IκB kinase β (IKKβ)/inhibitor of κBα (IκBα)/nuclear factor kappa B (NF-κB) p65 and p52 or NF-κB p65] signaling and [target of rapamycin (TOR)/(S6K1, 4E-BP)] signaling in above three immune organs. (4) On the basis of C3 content (head kidney), C4 content (spleen) and skin hemorrhage and lesion, the optimal ETSP supplementation levels in low protein diets were estimated to be 1.48%, 1.61% and 1.03%, respectively. In summary, ETSP supplementation in low protein diets improved immune function of head kidney, spleen and skin in on-growing grass carp. • Reducing dietary protein by 2% decreased immune function of fish immune organs. • ETSP supplementation enhanced antibacterial substances in fish immune organs. • ETSP supplementation alleviated inflammatory responses in fish immune organs. • ETSP supplementation regulated NF-κB and TOR signaling pathway. [ABSTRACT FROM AUTHOR]

In this study, the protective effects and potential mechanisms of (2-Carboxyethyl) dimethylsulfonium Bromide (Br-DMPT) were evaluated in relation to the gill health status of on-growing young grass carp (Ctenopharyngodon idella). A total of 450 grass carp (216.49 ± 0.29 g) were randomly distributed into five treatments of three replicates each (30 fish per replicate) and were fed diets supplemented with gradational Br-DMPT (0–520.0 mg/kg levels) for 60 days. Subsequently, the fish were challenged with Flavobacterium columnare for 3 days, and the gills were sampled to evaluate antioxidant status and immune responses evaluation. Our results showed that, when compared to the control group, dietary supplementation with appropriate Br-DMPT levels resulted in the following: (1) decreased gill rot morbidity and improved gill histological symptoms after exposure to F. columnare (P < 0.05); (2) improved activities and gene expression levels (except GSTP2 gene) of antioxidant enzymes and decreased oxidative damage parameter values (reactive oxygen species, malondialdehyde and protein carbonyl) (P < 0.05), which may be partially associated with the nuclear factor-erythroid 2-related factor 2 (Nrf2) signalling pathway (P < 0.05); (3) increased lysozyme (LZ) and acid phosphatase (ACP) activities and complement 3 (C3), C4 and immunoglobulin M (IgM) contents, and upregulated genes expressions of antibacterial peptides (liver-expressed antimicrobial peptide-2A , -2B , hepcidin , β-defensin and mucin2) (P < 0.05); (4) upregulated gene expressions of anti-inflammatory cytokines (except IL--4/13B) that may be partially to the TOR/(S6K1, 4E-BP1) signalling pathway, and downregulated gene expressions of pro-inflammatory cytokines (except IL-12P35) may be partially to the IKK β, γ/IκBα/NF-kB) signalling pathway (P < 0.05). Taken together, our results indicate that dietary supplementation with appropriate amounts of Br-DMPT may effectively protect on-growing grass carp from F. columnare by strengthening gill antioxidant capacity and immunity. Furthermore, based on measures of combatting gill rot, antioxidant indices (MDA) and immune indices (LZ), the dietary Br-DMPT supplementation levels for on-growing grass carp are recommended to be 291.14, 303.38 and 312.01 mg/kg diet, respectively. • Appropriate Br-DMPT supplementation enhanced gill disease resistance of fish. • Appropriate Br-DMPT supplementation improved gill non-specific immunity and antioxidant ability of fish. • Appropriate Br-DMPT supplementation alleviated gill inflammation response involving cytokines of fish. • Appropriate Br-DMPT supplementation modulated Nrf2, NF-κB and TOR signaling in fish gill. [ABSTRACT FROM AUTHOR]

The effects of dietary pyridoxine (PN) on the gill immunity, apoptosis, antioxidant and tight junction of grass cap (Ctenopharyngodon idella) were investigated in this study. Fish were fed semi-purified diets containing graded levels of PN for 10 weeks, and then challenged with Flavobacterium columnare by bath immersion exposure for 3 days. The results indicated that compared with the optimal PN level, PN deficiency resulted in a decline in the antimicrobial compound production of gill. In addition, PN deficiency up-regulated the pro-inflammatory cytokines and down-regulated the anti-inflammatory cytokines gene expression, which might be associated with the enhanced nuclear factor κB p65 and the inhibited target of rapamycin signalling pathways, respectively, suggesting that PN deficiency could impair gill immune barrier function. Furthermore, PN deficiency (1) induced cell apoptosis, which may be partly associated with the (apoptotic protease activating factor-1, Bcl-2 associated X protein)/caspase-9 and c-Rel/tumor necrosis factor α (rather than FasL)/caspase-8 mediated apoptosis pathway. (2) Inhibited Kelch-like ECH-associating protein 1a/NF-E2-related factor 2 mRNA expression, decreased the mRNA expression and activities of antioxidant enzymes, increased the levels of reactive oxygen species, protein carbonyl and malondialdehyde. (3) Increased the mRNA expression level of myosin light chain kinase, which may be result in the down-regulation of tight junction complexes such as zonula occludens 1, occludin and claudins (expect claudin-12 and claudin-15). These results suggest that PN deficiency could impair gill physical barrier function. In summary, dietary PN deficiency could cause the impairment of gill barrier function associated with immunity, apoptosis, antioxidant and tight junction, which may result in the increased the susceptibility of fish to pathogenic bacteria. Moreover, based on the gill rot morbidity, LZ activity and MDA content, the dietary PN requirements for grass cap were estimated to be 4.85, 4.78 and 4.77 mg kg−1 diet, respectively. • Dietary pyridoxine deficiency impaired immune function of fish gill. • Dietary pyridoxine deficiency impaired apoptosis, antioxidant system and intercellular tight junction of fish gill. • Dietary pyridoxine regulated the signalling of NF-κB, TOR, p38MAPK, Nrf2 and MLCK in fish. [ABSTRACT FROM AUTHOR]

The present study aimed to explore the effects of phytic acid (PA) on the antimicrobial activity and inflammatory response in three immune organs (head kidney, spleen and skin) of on-growing grass carp (Ctenopharyngodon idella). To achieve this goal, we first conducted a 60-day growth trial by feeding fish with graded levels of PA (0, 0.8, 1.6, 2.4, 3.2 and 4.0%). Then, the fish were challenged with Aeromonas hydrophila for 6 days. Compared with the control group, the following results were obtained regarding supplementation with certain levels of PA in the diet. (1) There was an increase in skin haemorrhage and lesion morbidity in fish. (2) There was a decrease in activities or contents of immune factors, including lysozyme (LZ), complement 3 (C3), C4 and immunoglobulin M (IgM), and there was downregulation of gene expression levels of hepcidin, liver-expressed antimicrobial peptide 2A (LEAP-2A), LEAP-2B, and β-defensin-1 in immune organs. (3) There was upregulation in the gene expression of the following pro-inflammatory cytokines: tumour necrosis factor α (TNF-α), interleukin 1β (IL-1β) (except in the spleen), interferon γ2 (IFN-γ2), IL-6 (except in the spleen), IL-8, IL-12p40, IL-15 and IL-17D. These changes were partly related to the nuclear factor kappa B (NF-κB) signalling pathway, but downregulation of mRNA levels of anti-inflammatory cytokines (transforming growth factor β1 (TGF-β1), TGF-β2, IL-413/A, IL-413/B, IL-10 (except in the skin) and IL-11) occurred in a manner partially related to the target of rapamycin (TOR) signalling pathway. Finally, based on the broken-line analysis of skin haemorrhage and lesion morbidity and IgM content in the head kidney, the maximum tolerance levels of PA for on-growing grass carp (120.56–452.00 g) were estimated to be 1.79 and 1.31% of the diet, respectively. • Compared with the control group (0% phytic acid): • Phytic acid level ≥ 2.4% increased fish skin haemorrhage and lesion morbidity. • Certain levels of phytic acid suppressed the antimicrobial activity of head kidney, spleen and skin. • Certain levels of phytic acid aggravated the inflammation of head kidney, spleen and skin in fish. [ABSTRACT FROM AUTHOR]

This study was carried out to investigate the effects of dietary pyridoxine (PN) on the antioxidant status, apoptosis, intercellular integrity and immune function of head kidney and spleen in young grass carp (Ctenopharyngodon idella). Results showed that compared with the optimal PN level, (a) PN deficiency decreased antioxidant enzyme activities and down‐regulated the mRNA levels of antioxidant enzymes, NF‐E2‐related factor 2 (Nrf2), myeloid cell leukaemia‐1 (Mcl‐1) and tight junction proteins, whereas it increased the contents of reactive oxygen species (ROS), malondialdehyde (MDA) and protein carbonyl (PC), and up‐regulated the mRNA levels of cysteinyl aspartic acid‐protease (caspase), Fas ligand (FasL), p38 mitogen‐activated protein kinase (p38MAPK) and myosin light chain kinase (MLCK) in the head kidney and spleen of fish (p <.05). (b) PN deficiency decreased lysozyme (LZ) and acid phosphatase (ACP) activities, and complement contents, and down‐regulated the mRNA levels of antibacterial peptides, anti‐inflammatory cytokines, inhibitor of κBα (IκBα) and target of rapamycin (TOR), whereas it up‐regulated the mRNA levels of pro‐inflammatory cytokines and nuclear factor kappa B p65 (NF‐κBp65) in the head kidney and spleen of fish (p <.05). (c) Dietary PN requirements of grass carp based on the malondialdehyde content and lysozyme activity were estimated as 4.97 and 4.99 mg/kg diet, respectively. [ABSTRACT FROM AUTHOR]

To investigate effects of vitamin A (VA) on fish immune function and structural integrity in the head kidney and spleen of fish, total of 540 on-growing grass carp (Ctenopharyngodon idella) were divided into six groups, feeding graded levels of VA (0, 600, 1200, 1800, 2800 and 3800 IU/kg diet) for 70 days. Results showed that dietary VA deficiency depressed antibacterial ability and aggravated inflammatory response partially linked to nuclear factor κB p65 (NF-κB p65) and target of rapamycin (TOR) signaling pathways in the head kidney and spleen of fish. Meanwhile, VA deficiency caused oxidative damage, apoptosis and disruption of tight junctions (TJs), which were partially attributed to the down-regulation of NF-E2-related factor 2 (Nrf2) signaling mediated antioxidant ability, the up-regulation of p38 mitogen-activated protein kinase (p38MAPK) signaling mediated apoptosis and myosin light chain kinase (MLCK) signaling mediated disruption of tight junctions (TJs). Taken together, current study firstly demonstrated that VA deficiency decreased the immune function and damaged the structural integrity of the head kidney and spleen in fish. • Vitamin A deficiency impaired immunity in the head kidney and spleen of fish. • Vitamin A deficiency disrupted the structural integrity of systemic immune organs in fish. • Vitamin A regulated p38MAPK, NF-κB, TOR, Nrf2 and MLCK signaling pathways. [ABSTRACT FROM AUTHOR]

The present study evaluated the effects of (2-Carboxyethyl)dimethylsulfonium Bromide (Br-DMPT) supplementation on the intestinal immune function and potential mechanisms of on-growing grass carp (Ctenopharyngodon idella) by feeding fish (initial weight 216.49 ± 0.29 g) five diets with gradational Br-DMPT (0–520 mg/kg diet) concentrations for 60 days and then infecting them with Aeromonas hydrophila for 14 days. Our results firstly indicated that compared with the control group, appropriate Br-DMPT supplementation increased the number of beneficial bacteria Lactobacillus and Bifidobacterium and enteritis resistance, decreased the number of detrimental bacteria Aeromonas and E. coli , and relieved the intestinal histopathological symptoms of fish. In addition, compared with the control group, appropriate Br-DMPT supplementation (1) increased lysozyme (LZ) and acid phosphatase (ACP) activities, as well as complement 3 (C3), C4 and immunoglobulin M (IgM) content; (2) upregulated the mRNA levels of anti-microbial substance: liver expressed anti-microbial peptide (LEAP) -2A, LEAP-2B, hepcidin, β-defensin-1 and Mucin2; (3) partially downregulated the mRNA levels of pro-inflammatory cytokines [interleukin 1β (IL-1β), IL-6, IL-8, IL-12p40, IL-15, IL-17D, tumour necrosis factor α (TNF-α) and interferon γ2 (IFN-γ2)] by inhibiting [IKKβ/IκBα/(NF-κBp65 and c-Rel)] signalling; and (4) partially upregulated the mRNA levels of anti-inflammatory cytokines [IL-4/13A, IL-10, IL-11, transforming growth factor (TGF)-β1] by activating [TOR/(S6K1 and 4E-BP)] signalling. The aforementioned results indicated that appropriate amount of Br-DMPT exerted a positive effect on the regulation of intestinal immune function in fish. Finally, based on enteritis morbidity, the IgM content and the lysozyme activity in the PI, the appropriate levels of Br-DMPT supplementation for on-growing grass carp were established as 295.43, 301.73 and 320.36 mg/kg diet, respectively. • Appropriate Br-DMPT supplementation enhanced enteritis resistance of fish. • Appropriate Br-DMPT supplementation increased intestinal innate and adaptive immune components of fish. • Appropriate Br-DMPT supplementation alleviated the intestinal inflammation response involving cytokines. • Appropriate Br-DMPT supplementation modulated NF-κB and TOR signaling in the intestine of fish. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of dietary biotin deficiency on the growth performance and immune function of the head kidney, spleen and skin in on-growing grass carp (Ctenopharyngodon idella). A total of 540 on-growing grass carp (117.11 ± 0.48 g) were fed six diets containing increasing levels of biotin (0.012, 0.110, 0.214, 0.311, 0.427 and 0.518 mg/kg diet) for 70 days. Subsequently, a challenge experiment was performed by infecting them with Aeromonas hydrophila for six days. Our results showed that compared with the appropriate biotin level, (1) biotin deficiency (0.012 mg/kg diet) reduced the activities of lysozyme (LZ) and acid phosphatase (ACP), decreased the contents of complement 3 (C3), C4 and immunoglobulin M (IgM), as well as reduced the mRNA levels of antimicrobial peptides in the head kidney, spleen and skin of on-growing grass carp; (2) biotin deficiency reduced the mRNA levels of anti-microbial substances: liver-expressed antimicrobial peptide (LEAP) -2A, LEAP-2B, hepcidin, β-defensin-1 and mucin 2 in the head kidney, spleen and skin of on-growing grass carp; (3) biotin deficiency increased the mRNA levels of pro-inflammatory cytokines interleukin 1β (IL-1β), IL-6, IL-8, IL-12p40, IL-15, IL-17D, tumour necrosis factor α (TNF-α) and interferon γ2 (IFN-γ2) partially in association with nuclear factor-kappa B (NF-κB) signalling and reduced anti-inflammatory IL-4/13A, IL-10, IL-11 and transforming growth factor β1 (TGF-β1) mRNA levels partially in association with target of rapamycin (TOR) signalling in the head kidney, spleen and skin of on-growing grass carp. Interestingly, biotin deficiency had no effect on the expression of IL-12p35, IL-4/13B, TGF-β2, 4E-BP1 (skin only) or IKKα in the head kidney, spleen and skin of on-growing grass carp. In conclusion, the results indicated that biotin deficiency impaired the immune function of the head kidney, spleen and skin in fish. Finally, based on the percent weight gain (PWG), the ability to prevent skin haemorrhages and lesions, the LZ activity in the head kidney and the C4 content in the spleen, the optimal dietary biotin levels for on-growing grass carp (117–534 g) were estimated as 0.210, 0.230, 0.245 and 0.238 mg/kg diet, respectively. • Biotin deficiency decreased growth performance and skin disease resistance of fish. • Biotin deficiency depressed non-specific and specific immune components in fish. • Biotin deficiency aggravated fish inflammation response involving cytokines. • Dietary biotin regulated NF-κB and TOR signalling of fish immune organs. [ABSTRACT FROM AUTHOR]

Deoxynivalenol (DON) is a common mycotoxin existed in animal feed, and lead to significant economic loss due to its negative impacts on animal growth performance and animal health. The gill is a primary mucosal immune organ in teleosts, and the structural integrity of the gill is closely relevant with fish healthy growth. Hence, this study assessed the influences of DON on the gill structural integrity of juvenile grass carp, Ctenopharyngodan idella (initial average weight 12.17 ± 0.01 g), when offered with six different diets which contained various content of DON (27, 318, 636, 922, 1243 and 1515 μg/kg diet) for 60 days. Our research firstly systematically elaborated that DON caused histopathological lesions, oxidative injury, reduction of antioxidant ability, apoptosis as well as damages of tight junctions in fish gills. Comparing these data to the control, we found that DON at dose of more than 318 μg/kg diet led to oxidative injury, apoptosis and disruption of tight junctions in fish gill, which were likely to be relevant with Nrf2, JNK and MLCK signalling pathways, respectively. It was worth noting that DON was not found to affect the gene expressions of Keap1b (rather than Keap1a), claudin-b, claudin-3c and claudin-15b (not claudin-15a) in fish gills. Furthermore, based on MDA and T-AOC activities in the gill, the maximum permissible levels of DON were evaluated to be 375.60 as well as 412.91 μg/kg diet in grass carp, respectively. • Deoxynivalenol (DON) caused oxidative damage and declining antioxidant capacity in the fish gill. • DON aggravated apoptosis in the fish gill. • DON disrupted tight junctions in the fish gill. • DON regulated Nrf2, JNK and MLCK signalling. • DON did not affect Keap1b, claudin-b, claudin-3c and claudin-15b in fish gill. [ABSTRACT FROM AUTHOR]