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Autotetraploid Carassius auratus is a stable hereditary autotetraploid fish resulting from the hybridization of Carassius auratus red var. (RCC, ♀) × Megalobrama amblycephala (BSB, ♂), containing four sets of RCC chromosomes. However, the molecular mechanism underlying the determination of sex in this species remains largely unknown. Currently, there lacks a full understanding of the molecular mechanisms governing sex determination and specific molecular markers to differentiate sex in this species. In this study, 25,801,677 SNPs (Single-nucleotide polymorphism) and 6,210,306 Indels (insertion-deletion) were obtained from whole-genome resequencing of 100 individuals (including 50 female and 50 male). Further identification confirmed the candidate chromosomes as Chr46B, with the sex-determining region located at Chr46B: 22,500,000-22,800,000 bp. Based on the male-specific insertion (26 bp) within the candidate sex-determining region, a pair of sex-specific molecular markers has been identified. In addition, based on the screening of candidate sex-determining region genes and RT-qPCR validation analysis, ADAM10, AQP9 and tc1a were identified as candidate sex-determining genes. These findings provide a robust foundation for investigating sex determination mechanisms in fish, the evolution of sex chromosomes, and the development of monosex populations.

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Ginger polysaccharides (GP) promote growth and development in fish. However, the effects of GP on crucian carp remain unclear. The present study investigated the effects of GP on the growth performance, immunity, intestinal microbiota, and disease resistance in crucian carp. Four treatment groups were established with different concentrations of GP (0.1 %, 0.2 %, 0.4 %, and 0.8 %). GP was not added as the control group, and the feeding period lasted for 56 d, followed by a 96-h anti-infection treatment using Aeromonas hydrophila. The results showed that dietary GP significantly improved growth performance, especially in the 0.4 % GP group. Furthermore, GP administration notably increased serum lysozyme (LMZ) activity, digestive enzyme performance, and antioxidant capacity of crucian carp. Moreover, dietary inclusion of GP up-regulated the expression of tumour necrosis factor-α (TNF-α), interleukin-8 (IL-8), interferon-γ (IFN-γ), and nuclear factor kappa-B (NF-κB) genes while down-regulating IL-10 and transforming growth factor-ß (TGF-ß) gene expressions, thus promoting liver health in crucian carp. Additionally, incorporating GP into the diet regulated both the diversity and composition of the intestinal microbiota in crucian carp, explicitly enhancing the relative abundance of beneficial bacteria, such as Fusobacteriota and Firmicutes. Therefore, GP reduces the mortality of crucian carp infected with A. hydrophila. In conclusion, this study provides novel insights into the application of dietary GP in cultured fish and evaluates the value of traditional Chinese medicinal polysaccharides against pathogenic bacteria.

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Emerging technologies for cell-cultured fish meat as an environmentally friendly protein source for humans still have many obstacles, including large-scale production of high-quality cells, differentiation and bioassembly of cellular material, and improvement of the quality of meat products. Here, we used edible porous microcarriers as scaffolds to support scalable skeletal muscle cell expansion to prepare centimeter-scale cell-cultured fish (CCM) of Carassius auratus for the first time. The quality of CCM was assessed by analyzing the texture, nutrition, flavor, and safety. The results indicated that CCM demonstrated a softer texture than natural fish due to a high moisture content. CCM contained higher protein and lower fat contents, with no significant difference in energy from natural golden crucian carp meat (NGM). CCM had better digestible properties, and 17 volatile components were identified in CCM, ten cocontained compared to NGM. ELISA quantified penicillin, streptomycin, vitamin D, and insulin residues as risk factors in CCM. In conclusion, we utilized edible porous microcarriers to scale-up the expansion of Carassius auratus skeletal muscle cells and bioassembled high-quality CCM of Carassius auratus for the first time, which represents a state-of-the-art protocol applicable to different fish species and even to other economic animals and provides a theoretical basis for scaling up cell-cultured meat production.

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Aquaculture supplies the world food market with a significant amount of valuable protein. Highly productive aquaculture fishes can be derived by utilizing genome-editing methods, and the main problem is to choose a target gene to obtain the desirable phenotype. This paper presents a review of the studies of genome editing for genes controlling body development, growth, pigmentation and sex determination in five key aquaculture Salmonidae and Cyprinidae species, such as rainbow trout (Onchorhynchus mykiss), Atlantic salmon (Salmo salar), common carp (Cyprinus carpio), goldfish (Carassius auratus), Gibel carp (Carassius gibelio) and the model fish zebrafish (Danio rerio). Among the genes studied, the most applicable for aquaculture are mstnba, pomc, and acvr2, the knockout of which leads to enhanced muscle growth; runx2b, mutants of which do not form bones in myoseptae; lepr, whose lack of function makes fish fast-growing; fads2, Δ6abc/5Mt, and Δ6bcMt, affecting the composition of fatty acids in fish meat; dnd mettl3, and wnt4a, mutants of which are sterile; and disease-susceptibility genes prmt7, gab3, gcJAM-A, and cxcr3.2. Schemes for obtaining common carp populations consisting of only large females are promising for use in aquaculture. The immobilized and uncolored zebrafish line is of interest for laboratory use.

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Introdction: Aeromonas veronii is a significant pathogen to various aquatic life. Infections in fish can lead to high mortality rates, causing substantial economic losses in aquaculture. Vaccination is proposed as a substitute for antibiotics in aquaculture to decrease disease-related mortality and morbidity. Our study previously constructed a hisJ-deleted strain of A. veronii, which provided protective effect to Loach. Methods: To further assess the vaccine's applicability, this study evaluated its genetic stability and safety, and the immune protective effects in Carassius auratus through four distinct administration routes: intraperitoneal injection, intramuscular injection, oral administration, and immersion, to determine the efficacy of these administration routes. Results: The results showed that the vaccine remained genetically stable after 45 generations. Immunization via these administration routes was safe for Carassius auratus, with intraperitoneal and intramuscular injections causing stronger adverse reactions. Immersion immunization resulted in mild adverse reactions, and no significant adverse reactions were observed following oral immunization. Immunizing Carassius auratus at safe concentrations via these routes enhanced the phagocytic activity in serum, increased the levels of non-specific immune-related enzymes (ACP, AKP, C3, C4, LZM, SOD, and IgM), and improved specific serum antibody levels. It also elevated levels of cytokines related to inflammatory responses (IL-1ß, IL-10, TNF-α, TGF-ß) in organ tissues (liver, spleen, kidney, mid-post intestine, and gills). The survival rates of Carassius auratus were measured after challenging with the virulent strain A. veronii TH0426, resulting in the relative survival rates of 64% for Intraperitoneal vaccine group, 56% for Intramuscular vaccine group, 52% for oral vaccine group, and 48% for immersion vaccine group. Analysis of bacterial load in the liver, spleen, and kidney post-challenge showed a decreasing trend in the control group, indicating that the vaccine strain ΔhisJ could gradually restrict the rapid proliferation of bacteria in these tissues, thereby providing a certain level of immune protection against A. veronii. Discussion: In brief, the vaccine strain ΔhisJ can serve as a safe live attenuated vaccine for Carassius auratus, and this study lays the foundation for the development of live attenuated vaccines against Aeromonas veronii.

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An 88-day feeding trial was conducted to evaluate the effects of dietary inosine 5'-monophosphate (5'-IMP) on the growth performance and salinity and oxidative stress resistance in the juvenile gibel carp CAS III (Carassius auratus gibelio; initial body weight: 7.48 g). Four isonitrogenous and isoenergetic diets containing exogenous 5'-IMP were formulated. P1, P2, P3 and P4 were diets containing 5'-IMP at four concentrations (0, 1, 2 and 4 g kg-1). The four diets were randomly allotted to triplicate tanks in a recirculating system. After the feeding trial, six fish per tank were netted randomly and placed into 12‱ saline water to test their response to salinity stress. The results indicated that the feed conversion rate was enhanced by dietary supplementation with 5'-IMP. The appetite, plasma neuropeptide Y level and feeding rate of the P3 group were lower than those in the control treatment group. Dietary supplementation with 5'-IMP improved the osmoregulatory adaptation of gibel carp under acute salinity stress. Six hours after the salinity stress treatment, in the dietary 5'-IMP treatment group, the plasma cortisol and K+ concentrations were lower and the Na+/K+-ATPase activity was greater than that in the control group. Dietary supplementation with 5'-IMP promoted the expression of the glucocorticoid receptors NKA-α1b and NKCC and retarded the expression of Hsp70 in P4-treated gill filaments and kidneys. Dietary supplementation with 5'-IMP resulted in a stable oxidative-stress-resistant phenotype characterized by increased levels of cellular antioxidants, including SOD, catalase, glutathione peroxidase, glutathione reductase and MPO. The above results of the current study demonstrate that supplementation of 5'-IMP can promote feed utilization and have positive influences on the salinity and oxidative stress resistance of gibel carp.

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Tetracycline hydrochloride (TCH), a prevalent antibiotic in aquaculture for treating bacterial infections, poses challenges for on-site detection. This study employed the reversed-phase microemulsion method to synthesize a uniform nano metal-organic framework (MOF) material, europium-benzene-p-dicarboxylic acid (Eu-BDC), doped with Tb3+ to form a dual-emission fluorescence probe. By leveraging the combined a-photoinduced electron-transfer (a-PET) and inner filter effect (IFE) mechanisms, high-sensitivity TCH detection in Carassius auratus and Ruditapes philippinarum was achieved. The detection range for TCH is 0.380-75 µM, with a low limit of detection (LOD) at 0.115 µM. Upon TCH binding, Eu-BDC fluorescence rapidly decreased, while Tb3+ fluorescence remained constant, establishing a ratiometric fluorescence change. Investigation into the TCH quenching mechanism on Eu-BDC was conducted using time-dependent density functional theory (TD-DFT) calculations and fluorescence quenching kinetic equations, suggesting a mixed quenching mechanism. Furthermore, a novel photoelectric conversion fluorescence detection device (FL-2) was developed and evaluated in conjunction with high-performance liquid chromatography-diode-array detection (HPLC-DAD). This is the first dedicated fluorescence device for TCH detection, showcasing superior photoelectric conversion performance and stability that reduces experimental errors associated with smartphone photography methods, presenting a promising avenue for on-site rapid TCH detection.

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Infection by an emerging bacterial pathogen Rahnella aquatilis caused enteritis and septicemia in fish. However, the molecular pathogenesis of enteritis induced by R. aquatilis infection and its interacting mechanism of the intestinal microflora associated with microRNA (miRNA) immune regulation in crucian carp Carassius auratus are still unclear. In this study, C. auratus intraperitoneally injected with R. aquatilis KCL-5 was used as an experimental animal model, and the intestinal pathological changes, microflora, and differentially expressed miRNAs (DEMs) were investigated by multi-omics analysis. The significant changes in histopathological features, apoptotic cells, and enzyme activities (e.g., lysozyme (LYS), alkaline phosphatase (AKP), alanine aminotransferase (ALT), aspartate transaminase (AST), and glutathione peroxidase (GSH-Px)) in the intestine were examined after infection. Diversity and composition analysis of the intestinal microflora clearly demonstrated four dominant bacteria: Proteobacteria, Fusobacteria, Bacteroidetes, and Firmicutes. A total of 87 DEMs were significantly screened, and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that the potential target genes were mainly involved in the regulation of lipid, glutathione, cytosine, and purine metabolism, which participated in the local immune response through the intestinal immune network for IgA production, lysosome, and Toll-like receptor (TLR) pathways. Moreover, the expression levels of 11 target genes (e.g., TLR3, MyD88, NF-κB, TGF-ß, TNF-α, MHC II, IL-22, LysC, F2, F5, and C3) related to inflammation and immunity were verified by qRT-PCR detection. The correlation analysis indicated that the abundance of intestinal Firmicutes and Proteobacteria was significantly associated with the high local expression of miR-203/NF-κB, miR-129/TNF-α, and miR-205/TGF-ß. These findings will help to elucidate the molecular regulation mechanism of the intestinal microflora, inflammation, and immune response-mediated miRNA-target gene axis in cyprinid fish.

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Spatial and social cognition are two aspects of fish behaviour that have been subject to an increasing amount of research in recent years, but few have investigated potential behaviour overlaps. Testing the ability for an individual to socially learn a spatial task would bridge this gap in understanding. We provided naïve goldfish, Carassius auratus, the opportunity to observe a trained conspecific navigate a T-shaped maze, and then recorded how many trials it took for them to learn the maze, time taken per trial, motivation, and acceptance of the food reward. We also recorded how many trials it took a control group to learn the maze without the opportunity to observe a demonstrator. The observer group took significantly longer to learn the maze than the control group. Although the observer group were significantly less motivated (trials without a choice made), they were significantly more likely to accept the food reward. The social learning of reward acceptance was taking place, but the process of the demonstration disrupted the training of the spatial task, with possible explanations as the passenger effect and trade-off mechanism being discussed. Future studies are needed to determine whether goldfish can acquire spatial information socially; however, this study contributes to the feasibility of studying social learning of environmentally information in goldfish.

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Alkaline stress poses a significant challenge to the healthy growth of fish. Ginger polysaccharide (GP) is one of the main active substances in ginger and has pharmacological effects, such as anti-oxidation and immune regulation. However, the physiological regulatory mechanism of GP addition to diet on alkalinity stress in crucian carp remains unclear. This study aimed to investigate the potential protective effects of dietary GP on antioxidant capacity, gene expression levels, intestinal microbiome, and metabolomics of crucian carp exposed to carbonate (NaHCO3). The CK group (no GP supplementation) and COG group (NaHCO3 stress and no GP supplementation) were set up. The GPCS group (NaHCO3 stress and 0.4% GP supplementation) was stressed for seven days. Based on these data, GP significantly increased the activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), acid phosphatase (ACP), and alkaline phosphatase (AKP) in carp under alkalinity stress (p < 0.05) and decreased the activity of malon dialdehyde (MDA) (p < 0.05). GP restored the activity of GSH-PX, ACP, and AKP to CK levels. The expression levels of tumor necrosis factor ß (TGF-ß), tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), and interleukin 8 (IL-8) genes were decreased, and the expression levels of determination factor kappa-B (NF-κB) and interleukin 10 (IL-10) genes were increased (p < 0.05). Based on 16 S rRNA high-throughput sequencing, GP improved the changes in the intestinal microbial diversity and structural composition of crucian carp caused by NaHCO3 exposure. In particular, GP increased the relative abundance of Proteobacteria and Bacteroidetes and decreased the relative abundance of Actinobacteria. The metabolic response of GP to NaHCO3 exposed crucian carp guts was studied using LC/MS. Compared to the COG group, the GPCS group had 64 different metabolites and enriched 10 metabolic pathways, including lipid metabolism, nucleotide metabolism, and carbohydrate metabolism. The addition of GP to feed can promote galactose metabolism and provide an energy supply to crucian carp, thus alleviating the damage induced by alkalinity stress. In conclusion, GP can mitigate the effects of NaHCO3 alkalinity stress by regulating immune function, intestinal flora, and intestinal metabolism in crucian carp. These findings provide a novel idea for studying the mechanism of salt-alkali tolerance in crucian carp by adding GP to feed.

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With the gradual decline in freshwater resources, the space available for freshwater aquaculture is diminishing and the need to maximize saline water for aquaculture is increasing. This study aimed to elucidate the impact mechanisms of the disruption of the glutamate pathway on serum metabolism and ammonia excretion in crucian carp (Carassius auratus) under carbonate alkaline stress. A freshwater control group (C group), a 20 mmol/L NaHCO3 stress group (L group), and a 40 mmol/L NaHCO3 stress group (H group) were established. After 30 days of exposure, methionine sulfoximine (MSO) was injected to block the glutamate pathway metabolism, and the groups post-blocking were labeled as MC, ML, and MH. Ultra-high-performance liquid chromatography coupled with the quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) metabolomics technique was employed to detect changes in the composition and content of crucian carp serum metabolites. Significant differential metabolites were identified, and related metabolic pathways were analyzed. The results revealed that, following the glutamate pathway blockade, a total of 228 differential metabolites (DMs) were identified in the three treatment groups. An enrichment analysis indicated significant involvement in glycerophospholipid metabolism, arachidonic acid metabolism, sphingolipid metabolism, purine metabolism, arginine and proline biosynthesis, pantothenate and CoA biosynthesis, glutathione metabolism, and fatty acid degradation, among other metabolic pathways. The results showed that ROS imbalances and L-arginine accumulation in crucian carp after the glutamate pathway blockade led to an increase in oxidative stress and inflammatory responses in vivo, which may cause damage to the structure and function of cell membranes. Crucian carp improves the body's antioxidant capacity and regulates cellular homeostasis by activating glutathione metabolism and increasing the concentration of phosphatidylcholine (PC) analogs. Additionally, challenges such as aggravated ammonia excretion obstruction and disrupted energy metabolism were observed in crucian carp, with the upregulation of purine metabolism alleviating ammonia toxicity and maintaining energy homeostasis through pantothenate and CoA biosynthesis as well as fatty acid degradation. This study elucidated the metabolic changes in crucian carp under carbonate alkaline stress after a glutamate pathway blockade at the cellular metabolism level and screened out the key metabolic pathways, which provide a scientific basis for further in-depth studies on the ammonia excretion of freshwater scleractinian fishes under saline and alkaline habitats at a later stage.

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Trimethylamine (TMA) is an organic amine with strong pungent smell which is an indicator gas for evaluating fish freshness according to the international standard. In this work, as-synthesize α-Fe2O3 solid nanocubes (NCs), α-Fe2O3 nucleoshell NCs and α-Fe2O3 hollow NCs were used as sensing material to develop an outstanding TMA gas sensor. The response of the α-Fe2O3 hollow NCs sensors towards 20 ppm TMA at 230 ℃ was 6.3. Meanwhile, these sensors showed exceptional response/recovery time, low limit of detection, great selectivity, and outstanding linear relationship. Furthermore, the analysis of gases released during the decomposition of Carassius auratus (0-10 days) was conducted, which demonstrated the assessment of TMA by α-Fe2O3 hollow NCs sensor can evaluate the freshness of Carassius auratus. Such a novel sensor signifies the outstanding application potential in efficient gas-sensing properties of TMA, which will make the tremendous contribution for Carassius auratus product evaluation in the future.

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Gibberellic acid (GA3), one of the most plant growth stimulator, is widely applied in agricultural regions and in beer industry. However, GA3 residue remained in soil and water can cause toxicity to all organisms. In this study, we investigated the mechanisms of GA3-induced hepatic injury in gibel carp (Carassius auratus gibelio). We found that GA3 exposure caused oxidative stress, endoplasmic reticulum stress (ERS), and apoptosis. The gibel carp exposed to GA3 exhibited significant alteration in erythrocyte nuclei. GA3 induced liver damage, as indicated by increasing the aminopherase activities. GA3 led to oxidative stress by increasing malondialdehyde content and decreasing the activities of CAT and GPx. GA3 stimulated ERS and increased the expression of grp78, perk, eif2s1α, chop, atf4, ire1α, xbp1, and atf6. Additionally, GA3 down-regulated the level of anti-apoptotic gene Bcl-2 and up-regulated the levels of pro-apoptotic genes bax and caspase-3. Overall results demonstrated that GA3 caused hepatic injury in gibel carp by increasing oxidative stress, ERS, and apoptosis.

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CD4-1 found in bony fish contains four extracellular immunoglobulin (Ig)-like domains similar to that of mammalian CD4, which is crucial for the activation of CD4+ helper T-cell. However, there is limited knowledge regarding the molecular markers, immune functions and regulation mechanism of CD4-1 in teleosts due to their vast diversity. In this study, we cloned and characterized two isoforms of Qihe crucian carp CD4-1, designated as CaCD4-1.1 and CaCD4-1.2. We further explored their expression responses upon stimulation with Aeromonas veronii, and the regulation of their immune responses against A. veronii by NF-κB. The ORF of CaCD4-1.1 and CaCD4-1.2 cDNA encoded 477 and 466 amino acids, respectively. Both proteins contained seven conserved cysteine residues in the extracellular domain, and a CCC motif in their cytoplasm, respectively. However, CaCD4-1.1 exhibited a relatively limited similarity with CaCD4-1.2 in the ectodomain. The quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed that the mRNA expression of CaCD4-1.1 and CaCD4-1.2 exhibited differential constitutive expression across all examined tissues. Furthermore, the expression level of CD4-1.2 was higher than that of CD4-1.1 in the gills, head kidney, and spleen of Qihe crucian carp subjected to A. veronii challenge, while it was lower in the trunk kidney. Inhibition of NF-κB activity resulted in a decrease in the expression levels of CD4-1.1 and CD4-1.2 mRNA in the gill, while inducing an increase in expression levels in the spleen, in accordance with the observed ultrastructural changes in both organs. Interestingly, the impact of NF-κB on the mRNA expression level of CD4-1.1 appears to be stronger than that of CD4-1.2. Our results suggest that CaCD4-1.1 and CaCD4-1.2 could be expressed on T cells and antigen-sampling cells that exhibit similar characteristics to mammalian M cells, respectively, and differentially regulated by NF-κB in adaptive immune responses against bacterial infection. This research contributes to a better understanding of the crucial role of CD4-1 in the immune response of Qihe crucian carp and provide novel insights for the prevention and treatment of fish diseases in aquaculture.

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The present investigation deals with the accounts of a novel species of ciliate parasite belonging to the genus Paratrichodina namely, Paratrichodina indiana n. sp. identified from the respiratory organ of goldfish Carassius auratus at Nadia district of West Bengal, India. 276 fish have been collected for parasitological examination from various fish farm of West Bengal, India. The parasitological investigation was conducted using the AgNO3 impregnation technique, which was supplemented by a taxonomic description, morphological variations and data comparison with previously documented closely related species. Paratrichodina indiana n. sp. is a small-sized trichodinid, measures uniquely 19.21 ± 1.6 µm in body diameter, with prominent adhesive disc measure 15.55 ± 1.22 µm. The current investigation supports the first record of the genus from C. auratus and adds one new species to the genus Paratrichodina, as well as report of a new host, region and prevalence rates.

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Polyvalent antibodies can resist multiple bacterial species, and immunoglobulin Y (IgY) antibody can be economically prepared in large quantities from egg yolk; further, IgY polyvalent antibodies have application value in aquaculture. The outer membrane proteins (OMPs) PF1380 and ExbB of Pseudomonas fluorescens were expressed and purified, and the corresponding IgY antibodies were prepared. PF1380, ExbB, and the corresponding IgY antibodies could activate the innate immune responses of chicken and Carassius auratus. The passive immunization to C. auratus showed that the IgY antibodies of PF1380 and ExbB had an immune protection rate, down-regulated the expression of antioxidant-related factors (MDA, SOD, GSH-Px, and CAT) to reduce the antioxidant reaction, down-regulated the expression of inflammation-related genes (IL-6, IL-8, TNF-α, and IL-1ß) to reduce the inflammatory reaction, maintained the integrity of visceral tissue structure, and reduced apoptosis and damage of tissue cells in relation to P. fluorescens and Aeromonas hydrophila infections. Thus, the IgY antibodies of PF1380 and ExbB could be considered as passive polyvalent vaccine candidates in aquaculture.

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Encapsulation of DNA vaccines onto carriers enhances the immunogenicity of an antigen. Specifically, biodegradable polymers offer sustained release of vaccines which is crucial for any targeted delivery approach. Poly (lactic-co-glycolic) acid (PLGA) microspheres were used to load a DNA vaccine having a targeted gene of outer membrane protein (OMP) of Aeromonas hydrophila to clone and construct a DNA vaccine using a eukaryotic expression vector system (pVAX1-OMP DNA) and delivery in Carassius auratus against A. hydrophila infection. PLGA microspheres were prepared by emulsion technique oil-in-water and characterized by a High-Resolution Scanning Electron Microscope (HR-SEM). The results of PLGA-pVAX1-OMP DNA microspheres shows that average of 100-150 µm particle size and a loading efficiency (LE) of 68.8 %. Results indicate that C. auratus fed with PLGA-pVAX1-OMP DNA microspheres revealed a significant improvement in innate immune response, which includes, myeloperoxidase activity, respiratory burst and total immunoglobulin level compared with control group fish. The immune-related gene, IL1ß, IL10, TGF, c-type, and g-type lysozyme also showed significantly higher expression after immunization. Furthermore, dietary supplementation of the PLGA-pVAX1-OMP DNA (G III) group exhibited a significantly higher survival rate (78 %) than the control group of fish. These results help us to understand the of mechanism of DNA vaccine administrated feed through PLGA nanoparticles resistance to infection by regulating systemic and innate immunity in Carassius auratus.

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Perfluorocaproic acid (PFHxA) has received much attention as an emerging pollutant linked to neurological problems in humans and fish. However, the potential mechanism remains unknown. In this study, the pathological damage to tissue sections demonstrated that perfluorocaproic acid caused brain tissue damage, and the increased antioxidant index malondialdehyde (MDA) and decrease in superoxide Dismutase (SOD), acid phosphatase (ACP), alkaline phosphatase (AKP), glutathione peroxidase (GSH-Px), Catalase (CAT), and Lysozyme (LZM) that perfluorocaproic acid activated antioxidant stress and caused brain damage. Transcriptome sequencing discovered 1,532 divergent genes, 931 upregulated, and 601 down-regulated. Furthermore, according to GO enrichment analysis, the differently expressed genes were shown to be involved in biological processes, cellular components, and molecular functions. The MAPK, calcium, and Neuroactive ligand-receptor interaction were considerably enriched in the KEGG enrichment analysis. We then analyzed qRT-PCR and chose ten essential differentially expressed genes for validation. The qRT-PCR results followed the same pattern as the RNA-Seq results. In conclusion, our study shows that perfluorocaproic acid exposure causes oxidative stress in the brain. It establishes a theoretical foundation for future research into genes linked to perfluorocaproic acid toxicity.

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We confirmed antioxidant-related gene expression, bioaccumulation, and cell damage following exposure to various microplastics in vivo and in vitro in the goldfish Carassius auratus. Exposure of C. auratus to a 500 µm fiber-type microplastic environment (MF; 10 and 100 fibers/L) and two sizes (0.2 and 1.0 µm) of beads (MB; 10 and 100 beads/L) for 120 h increased superoxide dismutase (SOD) mRNA expression in the liver until 24 h followed by a decrease. Whereas, catalase (CAT) mRNA expression increased from 12 h to the end of the in vivo experiment. In vitro experiments were conducted with diluted microfibers (1 and 5 fibers/L) and microbeads (1 and 5 beads/L) using cultured liver cells. The results of SOD and CAT mRNA expression analysis conducted in vitro showed a tendency similar to those of experiments conducted in vivo. The H2O2 level increased in the high-concentration experimental groups compared with that in the low-concentration groups of 0.2-µm beads. In addition, the H2O2 level increased in both MF and MB groups from 12 h of exposure. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in plasma were used as indicators of liver damage in fish. The ALT and AST levels increased up to 120 h after exposure. Caspase-3 (casp-3) mRNA expression was higher in the MB group than in the MF group. We visually confirmed liver casp-3 mRNA signals using in situ hybridization. The degree of DNA damage in the MF and MB high-concentration groups increased with the exposure time. The tail length and percent of DNA in the tail of the MB group were significantly higher than those of the MF group, confirming that DNA damage was greater in the MB group. Both fiber- and bead-type microplastics induced oxidative stress in C. auratus, but the bead-type induced greater stress than the fiber-type.

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Lead (Pb) is a hazardous pollutant in water environments that can cause significant damage to aquatic animals and humans. In this study, crucian carp (Carassius auratus) were exposed to waterborne Pb for 96 h; then, histopathological analysis, quantitative qPCR analysis, and 16S high-throughput sequencing were performed to explore the effects of Pb on intestinal bioaccumulation, structural damage, oxidative stress, immune response, and microbiota imbalance of C. auratus. After Pb exposure, the intestinal morphology was obviously damaged, including significantly increasing the thickness of the intestinal wall and the number of goblet cells and reducing the depth of intestinal crypts. Pb exposure reduced the mRNA expressions of Claudin-7 and villin-1 while significantly elevated the level of GST, GSH, CAT, IL-8, IL-10, IL-1, and TNF-α. Furthermore, 16S rRNA analysis showed that the Shannon and Simpson indices decreased at 48 h after Pb exposure, and the abundance of pathogenic bacteria (Erysipelotrichaceae, Weeksellaceae, and Vibrionaceae) increased after Pb exposure. In addition, the correlation network analysis found that Proteobacteria were negatively correlated with Firmicutes and positively correlated with Bacteroidetes. Functional prediction analysis of bacteria speculated that the change in intestinal microbiota led to the PPAR signaling pathway and peroxisome function of the intestine of crucian carp was increased, while the immune system and membrane transport function were decreased. Finally, canonical correlation analysis (CCA) found that there were correlations between the intestinal microbiota, morphology, antioxidant factors, and immune factors of crucian carp after Pb exposure. Taken together, our results demonstrated that intestinal flora dysbiosis, morphological disruption, oxidative stress, and immune injury are involved in the toxic damage of Pb exposure to the intestinal structure and function of crucian carp. Meanwhile, Pb exposure rapidly increased the abundance of pathogenic bacteria, leading to intestinal disorders, further aggravating the damage of Pb to intestinal structure and function. These findings provide us a basis for the link between gut microbiome changes and heavy metal toxicity, and gut microbiota can be used as biomarkers for the evaluation of heavy metal pollution in future.