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The present study was conducted to investigate the effects of dietary fructo-oligosaccharide (FOS) (0, 1, 2 and 3 %) supplementation on the growth performance, haemato-immunological parameters, cultivable autochthonous (non-adherent) intestinal microbiota and stress resistance of common carp (Cyprinus carpio) fry (3·23 (sem 0·14) g). These parameters were measured after feeding the carp fry with the experimental diets for 7 weeks. Dietary FOS supplementation had no significant effects on the growth performance and food intake of carp fry compared with the control treatment. It also had no significant effects on the following haematological parameters: erythrocyte count; leucocyte counts (WBC); haematocrit; Hb; mean corpuscular volume; mean corpuscular Hb content; mean corpuscular Hb concentration. However, WBC and respiratory burst activity were significantly affected by dietary FOS supplementation. Evaluation of the cultivable autochthonous intestinal microbiota revealed a significant increase in the levels of total viable heterotrophic aerobic bacteria and lactic acid bacteria in fish fed diets supplemented with 2 and 3 % FOS. Furthermore, dietary FOS supplementation significantly increased the survival rate and stress resistance of carp fry compared with the control treatment. These results encourage conducting further research on the administration of FOS and other prebiotics in carp fry studies.

This study investigated whether Bacillus subtilis can provide protection for grass carp against oxidative stress damage induced by Aeromonas hydrophila . A total of 240 healthy grass carp ( Ctenopharyngodon idellus ) (average weight of 71.42 ± 4.36g) were randomly divided into four groups with three replicates: control group, A. hydrophila group, B. subtilis + A. hydrophila group, and A. hydrophila + B. subtilis group. After challenge with A. hydrophila , the lipid oxidative damage, antioxidant defenses, and the gene expression of inflammatory cytokines of the grass carp were investigated. Our results showed that A. hydrophila caused lipid oxidative damage, led to significant decreases in antioxidant defenses, and induced inflammatory responses of grass carp. However, the grass carp group fed the probiotic B. subtilis diet for 42 days before the challenge and the group fed the probiotic B. subtilis diet immediately after the challenge both showed (i) a reduced level of oxidative stress with a decrease in the level of MDA; (ii) an increase in antioxidant defenses, including an increase in total antioxidant capacity (T-AOC), increased activities of SOD and CAT, increased levels of GSH, and upregulated gene expression of antioxidant enzymes (SOD, CAT, and Gpx); and (iii) an improved immune response with the level of antiinflammatory cytokines IL-10 messenger RNA (mRNA) upregulated and the levels of pro-inflammatory cytokines TNF-α, IL-1β, and IL-8 mRNA downregulated. Based on this study, B. subtilis can provide effective protection of fish against oxidative stress damage induced by A. hydrophila infection.

Gut microbiota of invasive Asian silver carp (SVCP) and indigenous planktivorous gizzard shad (GZSD) in Mississippi river basin were compared using 16S rRNA gene pyrosequencing. Analysis of more than 440 000 quality-filtered sequences obtained from the foregut and hindgut of GZSD and SVCP revealed high microbial diversity in these samples. GZSD hindgut (GZSD_H) samples ( n =23) with >7000 operational taxonomy units (OTUs) exhibited the highest alpha-diversity indices followed by SVCP foregut ( n =15), GZSD foregut ( n =9) and SVCP hindgut (SVCP_H) ( n =24). UniFrac distance-based non-metric multidimensional scaling (NMDS) analysis showed that the microbiota of GZSD_H and SVCP_H were clearly separated into two clusters: samples in the GZSD cluster were observed to vary by sampling location and samples in the SVCP cluster by sampling date. NMDS further revealed distinct microbial community between foregut to hindgut for individual GZSD and SVCP. Cyanobacteria, Proteobacteria , Actinobacteria and Bacteroidetes were detected as the predominant phyla regardless of fish or gut type. The high abundance of Cyanobacteria observed was possibly supported by their role as the fish’s major food source. Furthermore, unique and shared OTUs and OTUs in each gut type were identified, three OTUs from the order Bacteroidales , the genus Bacillariophyta and the genus Clostridium were found significantly more abundant in GZSD_H (14.9–22.8%) than in SVCP_H (0.13–4.1%) samples. These differences were presumably caused by the differences in the type of food sources including bacteria ingested, the gut morphology and digestion, and the physiological behavior between GZSD and SVCP.

An environmental DNA (eDNA) analysis method has been recently developed to estimate the distribution of aquatic animals by quantifying the number of target DNA copies with quantitative real-time PCR (qPCR). A new quantitative PCR technology, droplet digital PCR (ddPCR), partitions PCR reactions into thousands of droplets and detects the amplification in each droplet, thereby allowing direct quantification of target DNA. We evaluated the quantification accuracy of qPCR and ddPCR to estimate species abundance and biomass by using eDNA in mesocosm experiments involving different numbers of common carp. We found that ddPCR quantified the concentration of carp eDNA along with carp abundance and biomass more accurately than qPCR, especially at low eDNA concentrations. In addition, errors in the analysis were smaller in ddPCR than in qPCR. Thus, ddPCR is better suited to measure eDNA concentration in water, and it provides more accurate results for the abundance and biomass of the target species than qPCR. We also found that the relationship between carp abundance and eDNA concentration was stronger than that between biomass and eDNA by using both ddPCR and qPCR; this suggests that abundance can be better estimated by the analysis of eDNA for species with fewer variations in body mass.

Carp are the backbone of a growing aquaculture industry. They facilitate scientific progress as a model species in laboratories, cause concern for ecosystem managers as an invasive species, and mesmerize anglers as big game. In addition, ornamental koi carp fascinate hobby breeders. Biology and Ecology of Carp covers all these facets of this freshw

Background Grass carp is an important farmed fish in China that is affected by serious disease, especially hemorrhagic disease caused by grass carp reovirus (GCRV). The mechanism underlying the hemorrhagic symptoms in infected fish remains to be elucidated. Although GCRV can be divided into three distinct subtypes, differences in the pathogenesis and host immune responses to the different subtypes are still unclear. The aim of this study was to provide a comprehensive insight into the grass carp response to different GCRV subtypes and to elucidate the mechanism underlying the hemorrhagic symptoms. Results Following infection of grass carp, GCRV-I was associated with a long latent period and low mortality (42.5%), while GCRV-II was associated with a short latent period and high mortality (81.4%). The relative copy number of GCRV-I remained consistent or decreased slightly throughout the first 7 days post-infection, whereas a marked increase in GCRV-II high copy number was detected at 5 days post-infection. Transcriptome sequencing revealed 211 differentially expressed genes (DEGs) in Group I (66 up-regulated, 145 down-regulated) and 670 (386 up-regulated, 284 down-regulated) in Group II. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed significant enrichment in the terms or pathways involved in immune responses and correlating with blood or platelets. Most of the DEGs in Group I were also present in Group II, although the expression profiles differed, with most DEGs showing mild changes in Group I, while marked changes were observed in Group II, especially the interferon-related genes. Many of the genes involved in the complement pathway and coagulation cascades were significantly up-regulated at 7 days post-infection in Group II, suggesting activation of these pathways. Conclusion GCRV-I is associated with low virulence and a long latent period prior to the induction of a mild host immune response, whereas GCRV-II is associated with high virulence, a short latent period and stimulates a strong and extensive host immune response. The complement and coagulation pathways are significantly activated at 7 days post-infection, leading to the endothelial cell and blood cell damage that result in hemorrhagic symptoms.

The gut–liver axis is essential in animal disease and health. However, the role of the gut–liver axis in the anti-disease mechanism of disease-resistant grass carp (DRGC) derived from the backcross of female gynogenetic grass carp (GGC) and male grass carp (GC) remains unclear. This study analyzed the changes in gut histopathology, fecal intestinal microflora and metabolites, and liver transcriptome between GC and DRGC. Histological analysis revealed significant differences in the gut between DRGC and GC. In addition, microbial community analyses indicated that hybridization induced gut microbiome variation by significantly increasing the proportion of Firmicutes and Bacteroidota in DRGC. Metabolomic data revealed that the hybridization-induced metabolic change was probably characterized by being related to taurocholate and sphinganine in DRGC. Transcriptome analysis suggested that the enhanced disease resistance of DRGC was primarily attributed to immune-related genes (SHMT2, GOT1, ACACA, DLAT, GPIA, TALDO1, G6PD, and FASN). Spearman’s correlation analysis revealed a significant association between the gut microbiota, immune-related genes, and metabolites. Collectively, the gut–liver axis, through the interconnected microbiome–metabolite–gene pathway, may play a crucial role in the mechanism of greater disease resistance in DRGC, offering valuable insights for advancing the grass carp cultivation industry.

Global fish production from aquaculture has rapidly grown over the past decades, and grass carp shares the largest portion. However, hemorrhagic disease caused by grass carp reovirus (GCRV) results in tremendous loss of grass carp (Ctenopharyngodon idella) industry. During the past years, development of molecular biology and cellular biology technologies has promoted significant advances in the understanding of the pathogen and the immune system. Immunoprophylaxis based on stimulation of the immune system of fish has also got some achievements. In this review, authors summarize the recent progresses in basic researches on GCRV; viral nucleic acid sensors, high-mobility group box proteins (HMGBs); pattern recognition receptors (PRRs), Toll-like receptors (TLRs) and retinoic acid inducible gene I- (RIG-I-) like receptors (RLRs); antiviral immune responses induced by PRRs-mediated signaling cascades of type I interferon (IFN-I) and IFN-stimulated genes (ISGs) activation. The present review also notices the potential applications of molecule genetic markers. Additionally, authors discuss the current preventive and therapeutic strategies (vaccines, RNAi, and prevention medicine) and highlight the importance of innate immunity in long term control for grass carp hemorrhagic disease.

In aquaculture, viral diseases pose a significant threat and can lead to substantial economic losses. The primary defense against viral invasion is the innate immune system, with interferons (IFNs) playing a crucial role in mediating the immune response. With advancements in molecular biology, the role of non-coding RNA (ncRNA), particularly microRNAs (miRNAs), in gene expression has gained increasing attention. While the function of miRNAs in regulating the host immune response has been extensively studied, research on their immunomodulatory effects in teleost fish, including silver carp (Hyphthalmichthys molitrix), is limited. Therefore, this research aimed to investigate the immunomodulatory role of microRNA-30b-5p (miR-30b-5p) in the antiviral immune response of silver carp (Hypophthalmichthys molitrix) by targeting cytokine receptor family B5 (CRFB5) via the JAK/STAT signaling pathway. In this study, silver carp were stimulated with polyinosinic-polycytidylic acid (poly (I:C)), resulting in the identification of an up-regulated miRNA (miR-30b-5p). Through a dual luciferase assay, it was demonstrated that CRFB5, a receptor shared by fish type I interferon, is a novel target of miR-30b-5p. Furthermore, it was found that miR-30b-5p can suppress post-transcriptional CRFB5 expression. Importantly, this study revealed for the first time that miR-30b-5p negatively regulates the JAK/STAT signaling pathway, thereby mediating the antiviral immune response in silver carp by targeting CRFB5 and maintaining immune system stability. These findings not only contribute to the understanding of how miRNAs act as negative feedback regulators in teleost fish antiviral immunity but also suggest their potential therapeutic measures to prevent an excessive immune response.

Gut microbiota has shown tight and coordinated connection with various functions of its host such as metabolism, immunity, energy utilization, and health maintenance. To gain insight into whether gut microbes affect the metabolism of fish, we employed fast-growing transgenic common carp (Cyprinus carpio L.) to study the connections between its large body feature and gut microbes. Metagenome-based fingerprinting and high-throughput sequencing on bacterial 16S rRNA genes indicated that fish gut was dominated by Proteobacteria, Fusobacteria, Bacteroidetes and Firmicutes, which displayed significant differences between transgenic fish and wild-type controls. Analyses to study the association of gut microbes with the fish metabolism discovered three major phyla having significant relationships with the host metabolic factors. Biochemical and histological analyses indicated transgenic fish had increased carbohydrate but decreased lipid metabolisms. Additionally, transgenic fish has a significantly lower Bacteroidetes:Firmicutes ratio than that of wild-type controls, which is similar to mammals between obese and lean individuals. These findings suggest that gut microbiotas are associated with the growth of fast growing transgenic fish, and the relative abundance of Firmicutes over Bacteroidetes could be one of the factors contributing to its fast growth. Since the large body size of transgenic fish displays a proportional body growth, which is unlike obesity in human, the results together with the findings from others also suggest that the link between obesity and gut microbiota is likely more complex than a simple Bacteroidetes:Firmicutes ratio change.