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Unlike the case of mammals, teleost fish generally have poor ability to utilize carbohydrate, and the clearance of glucose from the plasma is sluggish. In this study, after a 8‐week feeding trial, we conducted a glucose tolerance test to hypothesize that the capability of grass carp (Ctenopharyngodon idellus) to clear a glucose load is associated with its nutrient history of different carbohydrate‐to‐lipid ratio diets (CHO:L: 1.52%, 5.84% and 34.84%) through glycogen synthesis and glucose metabolic key enzymes. Our results showed that after a glucose load, the plasma glucose of fish fed with high CHO:L‐ratio diet (34.84%) first declined to baseline conditions, and the peak value of liver and muscle glycogen content was significantly higher in high CHO:L‐ratio but lower in low CHO:L group (1.52%). In addition, after glucose administration, hepatic GK (glucokinase) activity of fish fed with high CHO:L‐ratio diet increased more significantly than that of the other groups, and PEPCK (phosphoenolpyruvate carboxykinase) activity obviously decreased in low CHO:L‐ratio group. The results indicated that a long‐term adaptation to the high CHO:L‐ratio diet can improved the glucose tolerance of C. idellus through the promotion of glycogen synthesis and GK activity. [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]

The current study aimed to investigate the effects and mechanisms of dietary soybean β-conglycinin in immune function and oxidative damage among different intestinal segments of juvenile grass carp (Ctenopharyngodon idella). 240 fish (13.77 ± 0.10 g) were fed control or 8% β‐conglycinin diet for 7 weeks. Dietary β-conglycinin caused inconsistent suppression effects on the innate immune by decreasing complement component, lysozyme, antimicrobial peptide and acid phosphatase among different intestinal segments. Meanwhile, dietary β-conglycinin caused inflammation in the mid and distal intestine by raising pro-inflammatory cytokines and declining anti-inflammatory cytokines mRNA levels, while more serious in the distal intestine than in the mid intestine. Furthermore, dietary β-conglycinin regulating inflammatory cytokines might be associated with transcription factors nuclear factor-κB P65 (NF-κB P65) nucleus translocation and target of rapamycin (TOR) phosphorylation in the distal intestine but only related to TOR phosphorylation in the mid intestine. Interestingly, in the proximal intestine, dietary β-conglycinin decreased both pro-inflammatory and anti-inflammatory cytokines mRNA level, and did not affect NF-κB P65 nucleus translocation and TOR phosphorylation. For oxidative damage, dietary β-conglycinin exposure elevated both malondialdehyde (MDA) and protein carbonyl (PC) contents in the distal intestine, which might be attributed to the suppression of the Mn-SOD, catalase (CAT) and glutathione peroxidase (GPx) activities. In the mid intestine, dietary β-conglycinin only increased PC content in association with the low activities of CAT, GPx and glutathione peroxidase (GR). Unexpectedly, in the proximal intestine, dietary β-conglycinin did not significantly change MDA and PC contents while decreased antioxidant enzyme activities. Furtherly, dietary β-conglycinin affect the antioxidant enzyme activity might be regulated by the varying pattern of nuclear factor-erythroid 2-related factor 2 (Nrf2) nucleus translocation among these three intestinal segments. In summary, dietary β-conglycinin caused intestinal inflammation and oxidative damage in association with NF-κB, TOR and Nrf2 signaling molecules, which were varying among the three intestinal segments of grass carp. • β-conglycinin didn't induce proximal intestine inflammation and oxidative damage. • β-conglycinin-caused mid intestine inflammation related to TOR phosphorylation. • β-conglycinin-caused distal intestine inflammation relied on NF-κB and TOR signals. • β-conglycinin-caused mid and distal intestine oxidative damage depend on Nrf2 signal. [ABSTRACT FROM AUTHOR]

This study aims to explore the effects of dietary betaine (BET) supplementations in low methionine (Met) diet on the growth performance and intestinal immune function of on-growing grass carp (Ctenopharyngodon idella). A total of 540 on-growing grass carp (210 ± 0.68 g) were fed with a normal Met diet and five diets containing graded levels of BET supplementations (0, 1.6, 3.2, 4.8 and 6.4 g kg−1) in low Met diet for 60 days. Subsequently, a challenge test was conducted by injection with Aeromonas hydrophila for 14 days. Results showed that, compared with BET0 group, appropriate BET supplementations (1) could enhance the abilities of fish against enteritis, intestinal lysozyme activities (LZ), acid phosphatase activities (ACP), complement 3 (C3) and C4 contents and IgM contents, and up-regulate the transcript abundances of liver-expressed antimicrobial peptide (LEAP) -2A , LEAP-2B , LEAP-1 / hepcidin and β-defensin-1 (P <.05); (2) could down-regulate intestinal pro-inflammatory cytokines TNF-α , IL-1β , IFN-γ2 , IL-6 and IL-8 mRNA levels partly related to [IKK β, γ/IκBα/NF-κBp65, c-Rel] signaling pathway; (3) could up-regulate intestinal anti-inflammatory cytokine transforming growth factor (TGF) -β1 , IL-4/13A and IL-10 mRNA levels partly related to the target of rapamycin (TOR) [TOR/(S6K1, 4E-BP1 and 4E-BP2)] signaling pathway. Furthermore, BET could spare part methionine (Met) and the actually comprehensive efficacy of BET relative to DL-Met was estimated to be 113.14% for on-growing grass carp (body weight 210–776 g) based on percent weight gain (PWG). Finally, based on PWG and LZ, the appropriate BET supplementations for on-growing grass carp (body weight 210–776 g) were estimated to be 4.28 and 4.51 g kg−1 diet, respectively. In general, dietary BET supplementations in low Met diet boosted the growth performance and enhanced the immune function in the intestines of on-growing grass carp. • Betaine supplementations in low Met diet boosted fish growth performance. • Betaine supplementations ameliorated enteritis morbidity and histopathological deteriorations. • Betaine supplementations modulated NF-κB and TOR pathways in fish intestines. • The actual efficacy of BET relative to DL-Met was estimated to be 113.14% (based on PWG). [ABSTRACT FROM AUTHOR]