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Interleukin 8 (IL-8) is a critical chemokine regulating immune cells chemotaxis as well as their physiological or pathological activations. In fish cells, recombinant IL-8 proteins induced transcriptions of pro-inflammatory cytokines. However, the exact mechanisms underlying the function of fish IL-8 as a pro-inflammatory cytokine are still unclear. In this paper, we first prepared recombinant grass carp IL-8 (rgcIL-8) using an E. coli expression system, and later confirmed rgcIL-8 increased gene expression of il8, il1β and tumor necrosis factor alpha (tnfα) in grass carp head kidney leukocytes (HKLs). Using signaling pathway inhibitors, we demonstrated that rgcIL-8 regulated transcriptions of pro-inflammatory cytokines via MAPK and/or NF-κB signaling pathways. We cloned gcIL-8 specific receptor CXCR1 and subsequently discovered that gcIL-8 could increase the activity of NF-κB and the transcription of IL-1β via CXCR1. Simultaneously, antibody neutralization assay showed that endogenous IL-8 is partially relevant to the self-regulation of IL-1β. Moreover, rgcIL-8 led to the expression of inducible nitric oxide synthase gene, causing an accumulation of nitric oxide in the culture medium of HKLs, suggesting the potential of gcIL-8 to mediate inflammatory response. This study not only enriched the function of IL-8 in teleost, but also revealed it as a potential target for the inflammatory control in grass carp. This article is protected by copyright. All rights reserved.

BACKGROUND Enzyme injection is vital for improving the sensory attributes and processing characteristics of meat products by enhancing proteolysis. However, studies regarding the appropriate dose addition for accelerating protein degradation in grass carp are minimal. This study aimed to investigate the impact of Flavourzyme® on the flavor quality and antioxidant activity of salted grass carp via brine injection and brining. RESULTS Flavourzyme was added at doses of 0, 5, 10, 20, and 30 leucine aminopeptidase units (LAPU) per kilogram of raw meat. The results indicated that adding Flavourzyme promoted proteolysis, which was reflected by the enhanced total free amino acid content (from 3.7414 g kg-1 to 4.9160 g kg-1 in the brining group and from 3.8039 g kg-1 to 5.4061 g kg-1 in the injection group) and a decrease in salt soluble and insoluble protein (P

Following the discovery of heart regeneration in zebrafish, several more species within the Cyprinidae family have been found to have the same capability, suggesting heart regeneration may be conserved within this family. Although gonad regeneration has been observed in grass carp (Ctenopharyngodon idella), one of the largest cyprinid fish, the species’ response to cardiac injury has not been characterized. Surprisingly, we found cardiomyocytes do not repopulate the injured region following cryoinjury to the ventricle, instead exhibiting unresolved fibrosis and decreased cardiac function that persists for the 8-week duration of this study. Compared to other cyprinid fish studied, infiltration of macrophages is delayed and muted in this model. Additionally, fibroblasts are depleted following injury, a phenomenon not previously described in any cardiac model. This study shows that heart regeneration is not conserved among the Cyprinidae family and suggests the important role of non-fibroblasts in chronic fibrosis. Further study of these phenomenon may reveal the underlying differences between regeneration versus unresolved fibrosis in heart disease.Summary statementGrass carp, a member of the Cyprinidae family that includes regenerative zebrafish, do not regenerate functional cardiac tissue after cryoinjury. Instead, healing progresses through collagen deposition and scar formation.

In this work, the effect of processing stages including first soaking (FS), frying after first soaking (FFS), and second soaking (SS) on nonvolatile taste compounds of Shanghai smoked fish was investigated using high‐performance liquid chromatography (HPLC) and automatic amino acid analyzer. Results showed that the contents of free amino acids (FAAs) ranged from 396.94 to 585.79 mg/100 g and 5′‐inosine monophosphate (IMP, as main umami nucleotide) from 215.91 to 284.56 mg/100 g in Shanghai smoked fish, respectively. Moreover, the contents of Glu and Gly as main umami amino acids ranged from 1.64 to 107.32 mg/100 g and 61.61 to 108.88 mg/100 g, respectively. TAV values of IMP, Asp, and Glu in Shanghai smoked fish reached 11.38, 2.73, and 21.46, respectively. The obvious difference could be observed using principal component analysis (PCA) in three processing stages of Shanghai smoked fish. Therefore, probing into the nonvolatile flavor of Shanghai smoked fish could not only enrich the theoretical basis of flavor chemistry in freshwater fish fields, but probe into the formation mechanisms of taste compounds in further study., Removing the native unpalatable taste of grass carp is key for increasing its umami flavor and economic value. Therefore, the effect of processing stages including first soaking (FS), frying after first soaking (FFS), and second soaking (SS) on nonvolatile taste compounds of Shanghai smoked fish was investigated using high‐performance liquid chromatography (HPLC) and automatic amino acid analyzer.

Grass carp reovirus (GCRV) causes devastating viral haemorrhagic disease in farmed grass carp (Ctenopharyngon idellus). As novel molecular probes, aptamers have been widely applied in rapid diagnosis and efficient therapies against virus or diseases. In this study, three single-stranded DNA (ssDNA) aptamers were selected against GCRV-infected CIK cells via SELEX (systematic evolution of ligands by exponential enrichment technology). Secondary structures predicted by MFOLD indicated that aptamers formed stem-loop structures, and GVI-11 had the lowest ΔG value of -30.84 KJ/mol. Three aptamers could specifically recognize GCRV-infected CIK cells, with calculated dissociation constants (Kd) of 220.86, 176.63 and 278.66 nM for aptamers GVI-1, GVI-7 and GVI-11, respectively, which indicated that they could serve as specific delivery system for antiviral therapies. The targets of aptamers GVI-1, GVI-7 and GVI-11 on the surface of GCRV-infected cells could be membrane proteins, which were trypsin-sensitive. Furthermore, FAM-labelled aptamer GVI-7 could be applied to detect GCRV infection in vivo. It is the first time to generate and characterize aptamers against GCRV-infected cells. These aptamers have great potentials in development of rapid diagnosis technology and antiviral agents against GCRV infection in aquaculture.

Summary Microbial sulfate reduction and sulfur oxidation are vital processes to enhance organic matter degradation in sediments. However, the diversity and composition of sulfate‐reducing bacteria (SRB) and sulfur‐oxidizing bacteria (SOB) and their environmental driving factors are still poorly understood in aquaculture ponds, which received mounting of organic matter. In this study, bacterial communities, SRB and SOB from sediments of aquaculture ponds with different sizes of grass carp (Ctenopharyngodon idellus) were analysed using high‐throughput sequencing and quantitative real‐time PCR (qPCR). The results indicated that microbial communities in aquaculture pond sediments of large juvenile fish showed the highest richness and abundance of SRB and SOB, potentially further enhancing microbial sulfur cycling. Specifically, SRB were dominated by Desulfobulbus and Desulfovibrio, whereas SOB were dominated by Dechloromonas and Leptothrix. Although large juvenile fish ponds had relatively lower concentrations of sulfur compounds (i.e. total sulfur, acid‐volatile sulfide and elemental sulfur) than those of larval fish ponds, more abundant SRB and SOB were found in the large juvenile fish ponds. Further redundancy analysis (RDA) and linear regression indicated that sulfur compounds and sediment suspension are the major environmental factors shaping the abundance and community structure of SRB and SOB in aquaculture pond sediments. Findings of this study expand our current understanding of microbial driving sulfur cycling in aquaculture ecosystems and also provide novel insights for ecological and green aquaculture managements., In aquaculture pond sediments, sulfate‐reducing bacteria (SRB) produced AVS through sulfate reduction, and sulfur‐oxidizing bacteria was especially important to reduce AVS. High concentrations of sulfur compounds (TS, AVS, and ES) could inhibit SRB and sulfate reduction. Disturbance to sediments by fish activities could enhance the sulfate reduction and sulfur oxidation in sediments.

The research on the quality changes of grass carp during brine salting with 6%, 8%, and 10% salt additions was evaluated by chemical and physical indicators, as well as a sensory assessment and microbiological analysis. The NaCl content was proportional to salt addition and salting time. The increase of salt addition could lead to the increase of hardness and chewiness in which change trends were contrary to the pH within 24 hr. All K values were less than 10% during brine salting. The effect of 8% salt additions on free amino acids was relatively smaller. Higher levels of salt additions could inhibit bacterial growth. Combined with sensory assessment, equivalent umami concentration (EUC), and taste activity value (TAV) to analysis comprehensively, it was suggested that grass carp meat should be eaten at 4–8 hr of brine salting with 8% salt additions or processed for the next step, in which the grass carp meat had a better taste and quality., The quality changes of grass carp meat were studied over a period of 48 hr of brine salting with different salt additions (6%, 8%, and 10% (w/w)) by evaluating the K values, levels of free amino acids, EUC and TAV, as well as a sensory assessment, microbiological analysis, and electronic tongue evaluation. In addition to establish a firm theoretical foundation for quality control of grass carp during salting, these results would provide useful information for improving the nutritional value of aquatic products.

To investigate the effects of dietary quercetin on growth, antioxidation, and flesh quality of grass carp, Ctenopharyngodon idella, six diets were prepared with quercetin inclusion rates of 0 (control diet), 0.1, 0.2, 0.4, 0.6, and 0.8 g/kg. Grass carp with a body weight of 13.3 ± 0.1 g were fed with one of the six diets for 60 days. The weight gain (WG) showed a quadratic relationship with dietary quercetin levels; the supplementation of 0.4 g/kg quercetin significantly improved WG (+4.73%) and decreased feed conversion ratio (−0.06) (p

Total dissolved gas (TDG) supersaturation in the upper Yangtze River caused by high spill rates upstream of hydroelectric dams has become a serious environmental problem in recent years. TDG supersaturation downstream of the Xiangjiaba Dam was investigated during flood periods in 2014 and 2015. Alongside this, an in situ study was conducted to evaluate the impacts of TDG supersaturation on grass carp (Ctenopharyngodon idellus) and rock carp (Procypris rabaudi). TDG supersaturation levels ranged from 115% to 131% in 2014 and from 118% to 128% in 2015. During 2014, TDG supersaturation first decreased and then increased and finally remained relatively stable. In contrast, the TDG supersaturation level remained between 122–126% for a relatively long time in the 2015 study period. During 2014, grass carp confined to water depths of 0–1 and 1–2 m began to die after 45 hr of exposure, and most grass carp died between 90 and 130 hr when TDG supersaturation level was greater than 127%. The first observed death during 2015 occurred after 30‐hr exposure. The survival of rock carp was greater than 50% when they were restricted to water depths of 0–1 m. Only three rock carp died when they were confined to water depths of 0–2 m, and no dead fish were recorded at water depths of 0–3 m.

To investigate the effects of supplemental nutrient additives in broad bean‐based diets on growth, flesh quality, and collagen gene expression of grass carp, five diets were prepared, including complete formula diet (control), soaked broad bean (SBB), and three broad bean‐based diets containing 80% broad bean without (BBD1) or with the supplementation of methionine (BBD2), and methionine+vitamins+minerals (BBD3), and were fed to grass carp (171.9 ± 1.1 g), Ctenopharyngodon idellus, for 84 days. The results showed that broad bean‐based diets significantly increased weight gain (WG) and reduced the feed conversion ratio (FCR) of grass carp when compared to the SBB (p .05). Grass carp fed the BBD3 diet had lower steaming loss of flesh, higher muscle fiber density, and higher collagen content in muscle and skin than the control (p

In the present study, interferon (IFN) regulatory factor (IRF) 9 gene (irf9) was identified and characterized in common carp Cyprinus carpio. The predicted protein sequence of Irf9 contains a DNA binding domain (DBD) that possess five tryptophans, an IRF association domain (IAD) and two nuclear localisation signals (NLS). Alignment of Irf9 of C. carpio with the corresponding Irf9 proteins of other species showed that the DBD is more highly conserved than the IAD. The putative Irf9 protein sequence of C. carpio shares higher identities with teleosts (53.8-82.3%) and lower identities with mammals (30.2-31.0%). Phylogenetic studies of the putative amino-acid sequence of IRF9 based on the neighbour-joining method showed that Irf9 of C. carpio has the closest relationship with the grass carp Ctenopharyngodon idella. Tissue distribution analysis showed that irf9 transcripts were detectable in all examined tissues with the highest expression in the skin and the lowest expression in the head kidney. Poly I:C and Aeromonas hydrophila stimulation up-regulated irf9 expression in the spleen, head kidney, foregut and hindgut at different time intervals. In addition, irf9 was induced by Poly I:C and lipopolysaccharides (LPS) in vitro. These results indicate that Irf9 participates in antiviral and antibacterial immunity. Transfection of irf9 up-regulated the expression of cytokines, including type I IFN, protein kinase R (PKR), interferon-stimulated gene (ISG)15 and tumour necrosis factor (TNF)α in epithelioma papulosum cyprini cells (EPC) upon poly I:C and LPS stimulation. A dual-luciferase reporter assay revealed that Irf9 has no effect on NF-κB activation. The present study on Irf9 provides new insights into the IFN system of C. carpio and a valuable experimental platform for future studies on the immune system of fish.

Severe acute respiratory syndrome (SARS)‐like coronavirus sequences were identified in two separate complementary DNA (cDNA) pools. The first pool was from a Carassius auratus (crusian carp) cell line and the second was from Ctenopharyngodon idella (grass carp) head kidney tissue. BLAST analysis suggests that these sequences belong to SARS‐like coronaviruses, and that they are not evolutionarily conserved in other species. Investigation of the submitting laboratories revealed that two laboratories from the Institute of Hydrobiology at the Chinese Academy of Sciences in Wuhan, China performed the research and submitted the cDNA libraries to GenBank. This institution is very close in proximity to the Wuhan South China Seafood Wholesale Market where SARS‐CoV‐2 first amplified in the human population. It is possible that these sequences are an artifact of the bioinformatics pipeline that was used. It is also possible that SARS‐like coronaviruses are a common environmental pathogen in the region that may be in aquatic habitats., Highlights SARS‐like coronavirus sequences were found in two carp cDNA pools from separate laboratories in Wuhan, China.

In this study, a full-sib population of Ctenopharyngodon idella was constructed and approximately 500 C. idella individuals were sampled at four early developmental stages (hatching, first feeding, juvenile fish and young fish). Four DNA pools were constructed and subjected to next-generation sequencing. On the basis of the identification of single nucleotide polymorphisms (SNP), changes in gene and genotype frequencies during the developmental progress of C. idella were revealed, which indicates that death during the early developmental stage is not a random process. These findings will establish the basis for further studies performed for identifying superior alleles or genotypes as target markers for molecular breeding.

Background A decreasing freshness occurrs in Ctenopharyngodon (C.) idellus during post-mortem storage. In the present study, chitosan-glucose Maillard reaction products (CG-MRPs) were prepared by heating chitosan and glucose at different reaction temperatures and then used for preserving the freshness and quality of C. idellus fillets during cold storage (4 °C). Results High temperature enhanced the chitosan-glucose Maillard reaction and promoted the accumulation of melanoidins and intermediate compounds. The reducing power of CG-MRPs increased with an increasing reaction temperature. CG-MRPs inhibited the microbial growth rate and retarded the oxidation of proteins, lipids and nucleotides in C. idellus fillets by suppressing total bacterial count, total volatile basic nitrogen, thiobarbituric acid reactive substances and K values during cold storage. Furthermore, CG-MRPs prolonged shelf-life. The fillets treated with the CG-MRPs prepared at 120 °C showed an especially longer shelf-life (7 days). The preservative effect of CG-MRPs on fillets was the result of antibacterial components (melanoidins, reductone and furfural) in CG-MRPs and a reducing power against the oxidative degradation of proteins, nucleotides and lipids in C. idellus fillets. Conclusion The present study demonstrates that, for C. idellus fillets, treatment with CG-MRPs prepared at 120 °C for 40 min could be a feasible approach for maintaining the freshness of C. idellus fillets and prolonging shelf-life during cold storage. © 2018 Society of Chemical Industry.

Currently, serological assays for grass carp reovirus genotype II (GCRV-II) diagnosis are not available. In this study, an indirect enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against GCRV-II was developed. The structural protein VP38 of GCRV-II was used as the coating antigen. Monoclonal antibodies (mAb) against IgM of grass carp labelled with HRP were used as a secondary antibody. The antigen concentration and serum dilution were optimized using chess board titration. Furthermore, the specificity of indirect ELISA assay was confirmed by cross check with sera positive for other grass carp pathogens. In comparison with results obtained from indirect immunofluorescence assay (IFA) and Western blot by testing of 60 serum samples to evaluate the sensitivity and specificity of the ELISA, agreement between 90% and 96.7% was reached, respectively. A serological survey was performed using the assay with grass carp field serum samples. The seropositive rate of the 242 serum samples was 69.8%. In conclusion, the developed indirect ELISA is a very specific and sensitive test that will be useful for large-scale serological surveys to detect indirectly GCRV II infections as well as to monitor the changes of antibody level after immunization.