Carp Liver Research Articles

Changes of hemoglobin resulted by distant hybridization contributed to increased hypoxia tolerance of allotriploid crucian carp

Hypoxia tolerance, one of the important goals of fish breeding, is beneficial for aquaculture and the transporting of fish. Based on the bisexual fertile allotetraploid crucian carp hybrid lineage obtained by distant hybridization, we successfully developed the allotriploid crucian carp via interploidy crossing with diploid red crucian carp. This allotriploid fish exhibited obvious hypoxia tolerance with lower values of dissolved oxygen at Pcrit (critical oxygen press) and 50 % ASR (aquatic surface respiration) than its original parents. Hemoglobin is the main vector of oxygen in vivo. This study examined the changes in amino acid sequences and natural protein conformation of hemoglobin, and found that the Hbα sequences of allotriploid crucian carp displayed obvious hybridity, including recombination and variation, when compared with its original parents. Moreover, the expression of hbα gene is higher in the liver and blood of allotriploid crucian carp than in its original parents. After acute anoxia treatment, the expression of gata1 gene, which served as the general switch for erythroid development, decreased in the blood of all the three kinds of fish. However, only in the allotriploid crucian carp hbα gene expression significantly decreased, coupled with the erythrocytes displaying an increased ratio of nuclei/cytoplasm. Taken together, this study suggested that changes in hemoglobin coupled with the erythrocyte morphological alterations under hypoxia increased the hypoxia tolerance ability of allotriploid crucian carp, which would provide a new perspective to guide fish breeding to obtain high-quality fish species with increased hypoxia tolerance.

Hepatocyte apoptosis is triggered by hepatic inflammation in common carp acutely exposed to microcystin-LR or chronically exposed to Microcystis

Cyanobacterial blooms pose a serious threat to the survival of fish because of the hepatotoxicity of microcystins produced by toxic cyanobacteria such as Microcystis. Many studies have investigated the hepatotoxicity of microcystins in common carp, a freshwater fish distributed worldwide, but the hepatotoxicity mechanism has not been fully clarified. The present study aimed to investigate the mechanism underlying the hepatic inflammatory response and hepatocyte apoptosis induced by acute microcystin-LR exposure via intraperitoneal injection (71 μg/kg and 119 μg/kg) or gavage (357.08 μg/kg) and chronic exposure to toxic Microcystis blooms. The results of acute exposure revealed that microcystin-LR caused an increase in serum transaminase activity and increased the levels of inflammatory factors and inflammatory mediators, inducing a significant inflammatory response in the liver of common carp. Moreover, biochemical detection revealed that hepatocyte apoptosis occurred in the fish. Moreover, chronic toxic Microcystis exposure also caused hepatic inflammation and subsequent apoptosis mediated by the tumour necrosis factor-α (TNF-α) pathway and the mitochondrial pathway similar to acute exposure. Therefore, our study suggests that the inflammatory response induced by microcystin-LR exacerbates apoptosis, likely mediated by TNF-α. In summary, both acute microcystin-LR exposure and chronic toxic Microcystis exposure can cause inflammation in the liver of common carp, which subsequently triggers hepatocyte apoptosis mediated by the TNF-α pathway and the mitochondrial pathway. This study helps elucidate the mechanism of liver damage induced by cyanobacterial blooms in natural water.

Microalgal astaxanthin ameliorates cypermethrin-induced necroptosis and inflammation via targeting mitochondrial Ca2+ homeostasis and the ROS-NF-κB-RIPK3/MLKL axis in carp hepatocytes (Cyprinus carpio)

Cypermethrin is a toxic pesticide that has infiltrated water bodies due to its widespread use. This contamination has led to detrimental effects on the immune organs of aquatic species, including fish. The natural fat-soluble orange-red carotenoid, astaxanthin (MAT), derived from microalgae, possesses anti-inflammatory, antioxidant, and immunomodulatory properties. To elucidate the mechanism of CY induced damage to carp liver cells and assess the potential protective effects of MAT, we established a carp hepatocyte model exposed to CY and/or MAT. Hepatocytes from carp (Cyprinus carpio) were treated with either 8 μM CY or 60 μM MAT for 24 h. Upon exposure CY, a significant increase in reactive oxygen species (ROS) was observed alongside a diminution in the activities of key antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), suggesting an impairment of cellular antioxidant capacity. Subsequently, acridine orange/ethidium bromide (AO/EB) staining and flow cytometry analysis revealed that hepatocytes exposed to CY exhibited a higher incidence of necroptosis, associated with an elevated mitochondrial Ca2+ concentration, which contributed to cellular dysfunction. Furthermore, exposure to CY also activated the ROS-NF-κB-RIPK3/MLKL signaling pathway, increasing the levels of necroptosis-related regulatory factors (RIP1, RIP3, and MLKL) in hepatocytes and the expression of inflammatory genes (IL-6, IFN-γ, IL-4, IL-1β, and TNF-α), which led to immune dysfunction in hepatocytes. The immunotoxic effects induced by CY were mitigated by MAT treatment, suggesting its potential in alleviating the aforementioned changes caused by CY. Overall, the data suggested that MAT therapy could enhance hepatocyte defenses against CY-induced necroptosis and inflammatory responses by regulating mitochondrial Ca2+ homeostasis and inhibiting the ROS-NF-κB-RIPK3/MLKL signaling cascade. This study elucidated the potential benefits of employing MAT to protect farmed fish from agrobiological hazards during CY exposure, underscoring the practical applications of MAT in aquaculture.

Curcumin attenuates ochratoxin A and hypoxia co-induced liver injury in grass carp (Ctenopharyngodon idella) by dual targeting endoplasmic reticulum stress and apoptosis via reducing ROS content

BackgroundOchratoxin A (OTA) is a toxin widely found in aquafeed ingredients, and hypoxia is a common problem in fish farming. In practice, aquatic animals tend to be more sensitive to hypoxia while feeds are contaminated with OTA, but no studies exist in this area. This research investigated the multiple biotoxicities of OTA and hypoxia combined on the liver of grass carp and explored the mitigating effect of curcumin (CUR).MethodsA total of 720 healthy juvenile grass carp (11.06 ± 0.05 g) were selected and assigned randomly to 4 experimental groups: control group (without OTA and CUR), 1.2 mg/kg OTA group, 400 mg/kg CUR group, and 1.2 mg/kg OTA + 400 mg/kg CUR group with three replicates each for 60 d. Subsequently, 32 fish were selected, divided into normoxia (18 fish) and hypoxia (18 fish) groups, and subjected to hypoxia stress for 96 h.ResultsCUR can attenuate histopathological damage caused by coming to OTA and hypoxia by reducing vacuolation and nuclear excursion. The alleviation of this damage was associated with the attenuation of apoptosis in the mitochondrial pathway by decreasing the expression of the pro-apoptotic proteins Caspase 3, 8, 9, Bax, and Apaf1 while increasing the expression of the anti-apoptotic protein Bcl-2, and attenuation of endoplasmic reticulum stress (ERS) by reducing Grp78 expression and chop levels. This may be attributed to the fact that the addition of CUR increased the levels of catalase (CAT) and glutathione reductase (GSH), increased antioxidant capacity, and ensured the proper functioning of respiratory chain complexes I and II, which in turn reduced the high production of reactive oxygen species (ROS), thus alleviating apoptosis and ERS.ConclusionsIn conclusion, our data demonstrate the effectiveness of CUR in attenuating liver injury caused by the combination of OTA and hypoxia. This study confirms the feasibility and efficacy of adding natural products to mitigate toxic damage to aquatic animals.

Dietary Addition of Selenium Attenuates Cadmium-Induced Liver Injury in Grass Carp (Ctenopharyngodon idellus) by Reducing Oxidative Stress and Apoptosis

In order to investigate the effects of selenium (Se) against cadmium (Cd) toxicity, 180 healthy grass carp were separated into three groups and fed diets containing 0.147 (control group), 0.562, and 1.044 mg/kg of selenium Yeast throughout 60 days. In grass carp livers, malondialdehyde (MDA) content, antioxidant enzyme activities, and apoptosis-related gene expression were examined. As a result of acute exposure to cadmium, MDA content decreased significantly. With time, catalase (CAT), total superoxide dismutase (T-SOD), and glutathione peroxidase (GSH-Px) activities changed. The relative transcript levels of heavy metal scavenging genes abcc2 and mt2 were significantly reduced. The relative levels of expression of jnk, bax, caspase-3, caspase-8, and caspase-9 in apoptosis-associated factors were significantly elevated after cadmium exposure. Selenium-supplementation downregulated the expression of apoptosis-related factors. As compared to the control group, liver cells supplemented with selenium had a significantly lower apoptotic index. Comprehensive analysis showed that dietary selenium supplementation significantly attenuated cadmium-induced peroxidative damage and apoptosis in liver by increasing GSH-Px activity, and that cadmium toxicity could be alleviated by the addition of yeast selenium.

Fucoidan changes lipid accumulation in the liver of common carp (Cyprinus carpio) by modulating lipid and glucose metabolism

Fucoidan changes lipid accumulation in the liver of common carp (Cyprinus carpio) by modulating lipid and glucose metabolism

Immunometabolic interplay in Edwardsiella tarda-infected crucian carp (Carassius auratus) and in vitro identification of the antimicrobial activity of apolipoprotein D (ApoD) by utilization of multiomics analyses

Edwardsiella tarda is an intracellular pathogenic bacteria that can imperil the health of farmed fish. However, the interactive networks of immune regulation and metabolic response in E. tarda-infected fish are still unclear. In this investigation, we aimed to explore immunometabolic interplay in crucian carp after E. tarda infection by utilizing multiomics analyses. Crucian carp (Carassius auratus) receiving E. tarda infection showed increased levels of tissue damage and oxidative injury in liver. Multiomics analyses suggested that carbon and amino acid metabolism may be considered as crucial metabolic pathways in liver of crucian carp following E. tarda infection, while spaglumic acid, isocitric acid and tetrahydrocortisone were the crucial liver biomarkers. After that, a potential antimicrobial peptide (AMP) sequence called apolipoprotein D (ApoD) was identified from omics study. Then, tissue-specific analysis indicated that liver CaApoD showed the highest expression among isolated tissues. After Aeromonas hydrophila stimulated, CaApoD expressions increased sharply in immune-related tissues. Moreover, CaApoD fusion protein could mediate the in vitro binding to A. hydrophila and E. tarda, attenuate bacterial growth as well as diminish bacterial biofilm forming activity. These findings may have a comprehensive implication for understanding immunometabolic response in crucian carp upon infection.

Toxic effects of multi-walled carbon nanotubes and ZnO nanoparticle exposure on pathology and apoptosis on the liver of Cyprinus carpio

ZnO nanoparticles (ZnONPs) and carbon nanotubes (CNTs) are frequently used nanoparticles with unique features. Aquatic organisms are exposed to a combination of contaminants in natural water systems, so the combination effect of two or more nanomaterials has caused much concern. In this study, the toxicity to the liver of common carp was explored under four weeks of exposure to single ZnONPs or in combination with multi-walled CNTs (MWCNTs). The results demonstrated that ZnONPs induced pathological changes and apoptosis in the liver. In combination, decreased pathological changes were observed in the LSC-ZnONPs group (50 mg L-1 ZnONPs and 0.25 mg L-1 MWCNTs) at the microscopic level and ultrastructural level, and increased pathological changes in the HSC-ZnONPs group (50 mg L-1 ZnONPs and 2.5 mg L-1 MWCNTs). A 52% reduction in the percentage of TUNEL-positive nuclei in the LSC-ZnONPs group and a 33% increase in the HSC-ZnONPs group were observed compared to the ZnONPs group. The mRNA expression of apoptosis-related genes, including caspase3, BAX, and XBP1, were significantly up-regulated in the exposure groups, confirming the occurrence of apoptosis. Significantly decreased caspase 3 and BAX mRNA levels in the co-exposure groups were detected compared to the ZnONPs group. Nevertheless, the XBP1 mRNA level was significantly upregulated in the LSC-ZnONPs group, but downregulated in the HSC-ZnONPs group, indicating multiple signal pathways involved in the apoptosis. In conclusion, a low concentration of MWCNTs (0.25 mg L-1) decreased the toxic effect of ZnONPs on common carp, but a high concentration of MWCNTs (2.5 mg L-1) enhanced it. This study will contribute to developing future risk assessment and management strategies for nanomaterials.

Environmental endocrine disrupting chemical 4-tert-butylphenol induced calcium overload and subsequent autophagy impairment via miRNA-363/CACNA1D Axis in epithelioma papulosum cyprini cells

Environmental endocrine disrupting chemical 4-tert-butylphenol (4-tBP), a widely-utilized surfactant in various industries, poses potential risks to aquatic organisms. Our previous sequencing results suggested that 4-tBP-induced common carp liver injury might be associated with Ca2+ signaling and autophagy. However, the intricate involvement of these pathways in 4-tBP-induced cytotoxic mechanisms remained unexplored. To bridge these knowledge gaps, this study focused on epithelioma papulosum cyprini (EPC) cells, a significant cell type in fish biology. Initial observations showed that 4-tBP induced a dose-dependent perturbation in Ca2+ levels. Further investigations, with siRNA and L-type Ca2+ channel agonist (BAYK8644), identified L-type calcium channel gene CACNA1D as a critical regulator of 4-tBP-induced Ca2+ overload. Predictive analysis using miRanda platform suggested a potential interaction between miR-363 and CACNA1D, which was subsequently verified through dual-luciferase reporter gene assays. We then established miR-363 mimic/inhibitor models, along with miR-363 and CACNA1D co-suppression models in EPC cells. Through TEM observation, immunofluorescence assay, Ca2+ staining, and qRT-PCR analysis, we evaluated the role of miR-363/CACNA1D axis in modulating the effects of 4-tBP on Ca2+ signaling and autophagy. Results showed that miR-363 inhibitor exacerbated 4-tBP-induced increase in CALM2, CAMKII, Calpain2, and p62 expression and also led to decrease in ATG5, ATG7, and LC3b expression. In contrast, miR-363 mimic notably alleviated these changes. Notably, siRNA CACNA1D effectively modulating miR-363 inhibitor's effect. Our study revealed that 4-tBP induced Ca2+ overload and subsequent autophagy impairment via miR-363/CACNA1D axis. These findings illuminated a profound understanding of molecular mechanisms underlying 4-tBP-induced cytotoxicity and spotlighted a potential therapeutic target.

Synergistic toxic effects of copper sulfate and trichlorfon on the health and intestinal microbiota of gibel carp Carassius auratus gibelio

In the high-density pond aquaculture of gibel carp (Carassius auratus gibelio) in China, copper sulfate (CuSO4) and trichlorfon (Tri) are commonly used, either in combination or alternately, to prevent and control various diseases and harmful algae. Despite their widespread use, there is a lack of studies on the toxic effects of CuSO4 and Tri on gibel carp, particularly regarding their combined application. This study assessed the effects of exposure to CuSO4 (0.5 mg/L) and Tri (0.5 mg/L), both individually and in combination, on gibel carp over 21 days. Histopathological assessments revealed significant structural damage to the liver and intestines in gibel carp exposed to either CuSO4 or Tri alone, with co-exposure notably intensifying these effects. Analysis of antioxidant enzyme activities revealed a substantial reduction in the liver and intestines, concurrent with a significant rise in the oxidative stress marker malondialdehyde in both single and combined exposure groups. Moreover, quantitative PCR analyses indicated a downregulation of immune-related genes post-exposure, with the combined treatment causing more severe suppression. This suppressed immune response correlated with a reduced ability to resist infection by the pathogenic bacterium Aeromonas hydrophila, particularly in the combined exposure group. This indicates that long-term exposure to CuSO4 and Tri, particularly in combination, induces significant oxidative stress damage in the liver and intestinal tissues, suppresses immune function, and reduces disease resistance. Additionally, 16S rRNA sequencing of the intestinal microbiota revealed that CuSO4 and Tri exposure altered the diversity and composition of intestinal microbial communities, potentially bringing both benefits and drawbacks. These findings underscore the need for careful management of CuSO4 and Tri in aquaculture to mitigate their adverse impacts, especially when used in combination for an extended period.

Ultrastructural investigation of iron oxide nanoparticles accumulation in the liver of common carp (Cyprinus carpio Linnaeus, 1758)

In recent years, the intensive production of nanoparticles with a wide application has led to their transfer to the environment, including the water ecosystem. The accumulation of nanoparticles in fish, causing various pathological changes in the host, raises certain concerns. In the current study, we investigated the penetration and bioaccumulation of Fe3O4 nanoparticles, in the liver of common carp (Cyprinus carpio Linnaeus, 1758). Common carp juveniles were exposed to Fe3O4 nanoparticles at concentrations of 10 and 100 mg. After 7 days, their livers were examined by light and transmission electron microscopes. Compared to normal fish's liver, after using a small concentration (10 mg) of nanoparticles, changes were observed in erythrocytes, hepatocytes, intracellular canaliculi, and bile ducts of the liver. At a high concentration (100 mg), the intensity of changes increased significantly. The liver's capsule was damaged, and a considerable number of hepatocytes were completely destroyed. Additionally, the walls of blood vessels and biliary ductule walls was notably disturbed. It was found that the intensity of pathologies occurring in the liver, increases proportionally with higher concentrations of nanoparticles. Confirmation via electron microscopic methods revealed that Fe3O4 nanoparticles, when administered with food to common carp, enter the fish's liver through erythrocytes localized in the lumen of blood vessels. From there, they traverse through the endothelium of vessels, proceed to hepatocytes, including cytoplasmic organelles, intracellular canaliculi, biliary ductules, and eventually reach the bile ducts. Fe3O4 nanoparticles in all structural elements of fish liver was up to 20 nm. Therefore, high concentrations of nanoparticles in the environment harms the bodies of aquatic organisms, including fish. The changes identified in the liver of common carp in the present study are valuable information in assessing possible risks to other components of the aquatic ecosystem and organisms.

Dietary additive ferulic acid alleviated oxidative stress, inflammation, and apoptosis induced by chronic exposure to avermectin in the liver of common carp (Cyprinus carpio)

Avermectin (AVM) has been utilized extensively in agricultural production since it is a low-toxicity pesticide. However, the pollution caused by its residues to fisheries aquaculture has been neglected. As an abundant polyphenolic substance in plants, ferulic acid (FA) possesses anti-inflammatory and antioxidant effects. The goal of the study is to assess the FA's ability to reduce liver damage in carp brought on by AVM exposure. Four groups of carp were created at random: the control group; the AVM group; the FA group; and the FA + AVM group. On day 30, and the liver tissues of carp were collected and examined for the detection of four items of blood lipid as well as the activity of the antioxidant enzymes catalase (CAT), glutathione (GSH) and malondialdehyde (MDA) in carp liver tissues by biochemical kits, and the transcript levels of indicators of oxidative stress, inflammation and apoptosis by qPCR. The results showed that liver injury, inflammation, oxidative stress, and apoptosis were attenuated in the FA + AVM group compared to the AVM group. In summary, dietary addition of FA could ameliorate the hepatotoxicity caused by AVM in carp by alleviating oxidative stress, inflammation, apoptosis in liver tissues.

Silybin mitigated liver and brain damage after difenoconazole exposure: Crosstalk between oxidative stress, inflammation, ferroptosis and apoptosis

Long-term residue of difenoconazole (DFZ) in the environment caused multiple organ damage to aquatic organisms. Due to the potential hepatoprotective and neuroprotective properties of silybin (SIL), we hypothesized that SIL could alleviate growth inhibition, liver, and brain damage in carp induced by DFZ exposure. The in vivo experiments were divided into the Control group, the SIL group, the DFZ group and the DFZ + SIL group. The exposure concentration of DFZ was 0.39 mg/L, and the therapeutic dose of SIL was 400 mg/kg. The whole experiment lasted for 30 days. SIL was also found to reduce hepatic injury and lipid metabolism based on H&E staining, oil red O staining, and measurement of serum and liver tissue levels of ALT, AST, LDH, TG, and TC. Similarly, SIL reduced brain damage after DFZ exposure, according to H&E staining and detection transcription level of the ZO-1, ZO-2, occludin, and Claudin7 in carp brain. In terms of mechanism, the results showed that SIL inhibited the excessive production of ROS in liver and brain tissues, increased the activity of antioxidant enzymes (T-AOC, SOD, CAT) and resist oxidative stress. Also, SIL promoted the production of anti-inflammatory factors (TGF-β1 and IL-10) and inhibited the expression of pro-inflammatory factors (TNF-α and IL-6) to reduce the inflammatory response in liver and brain tissues caused by DFZ. ln terms of ferroptosis, by lowering iron levels, upregulating ferroptosis-related genes (GPX4, SIC7A11, GCLC), and downregulating the expression of NCOA4, STEAP3, COX2, and P53, SIL was able to inhibit ferroptosis of liver and brain tissues of carp. In addition, SIL restored the reduced mitochondrial membrane potential (MMP) level and inhibited apoptosis as measured by MMP level detection, TUNEL staining, and apoptosis gene transcript levels. In this study, we analyzed the interactions between genes and proteins associated with oxidative stress, inflammation, ferroptosis and apoptosis using the String database and ranked the nodes in the network using the Cytoscape plugin Cytohubba, and found that P53, Caspase3, TNF-α, IL-6 and Bcl-2 were the key hub genes. Our study not only revealed the multiple pharmacological activities of SIL, but also provided a reference for the prevention and reduction pesticide hazards to aquatic organisms.

Single and combined effects of high-fat diet and ammonia nitrogen on oxidative stress, lipid accumulation and inflammation in liver of grass carp Ctenopharyngodon idella

The current study aims to investigate the role of high-fat diet (HFD) and ammonia nitrogen (AN) in the fatty liver disease progression in farmed fish. In the present study, grass carp were fed the normal fat diet or HFD for 4 weeks to set up the Control group, HFD group, AN group and HFD + AN group. In the AN group and HFD + AN group, grass carp were exposed to 0.52 mg/L NH3-N for the last week. The results show that HFD feeding had no effect on the growth of grass carp but AN stress significantly inhibited it. Further, the HFD feeding and AN challenge both significantly increased the level of alanine aminotransferase (ALT) and reduced the total antioxidant capacity (T-AOC) significantly. Moreover, a further aggravated liver injury appeared in HFD-fed grass carp after AN challenge, as evidenced by the significant increasing of the level of ALT, AST and malondialdehyde (MDA) and marked reducing of glutathione (GSH) and T-AOC. Moreover, the results of Oil Red O and TG contents in liver all indicate that HFD and AN challenge both promoted the lipid accumulation in grass carp liver. Corresponding to this, the results of genes and protein related to lipid metabolism reveal that AN challenge dramatically inhibited lipid hydrolysis, lipophagy and fatty acid oxidation in HFD-fed grass carp liver but the single HFD feeding or AN challenge did not have this effect. Moreover, the single HFD feeding and AN challenge both promoted fatty acid transport to the liver and lipid synthesis in grass carp liver. In summary, the HFD feeding and AN challenge both can disturb the lipid metabolism in grass carp liver. In parallel, the results of expression levels of genes and protein related to inflammation indicate that the single HFD feeding might not significantly contribute to the inflammation in grass carp liver, but the single AN challenge apparently promoted the inflammatory process. Most importantly, inflammatory progression in liver was further aggravated in the HFD-fed grass carp after AN challenge compared to grass carp with only AN stress, mostly evidenced by the increased levels of inflammatory factors (il1β, il2, TNF-α, etc.). In summary, AN challenge significantly promoted the lipid accumulation and inflammatory process in the liver of HFD-fed grass carp, which might have further aggravated liver injury.

Growth, feed utilization, and quantitative histological assessment of the distal intestine and liver of common carp (Cyprinus carpio L.) fed formulated diets containing grains of different soybean cultivars

Growth, feed utilization, and quantitative histological assessment of the distal intestine and liver of common carp (Cyprinus carpio L.) fed formulated diets containing grains of different soybean cultivars

QseC regulates chemotaxis, biofilm formation, motility, and virulence in Aeromonas veronii TH0426

Aeromonas veronii is an important fish and human pathogen that causes significant economic losses in aquaculture. The two-component system QseBC has been shown to regulate virulence in various pathogens, but its functional role in A. veronii is unclear. In this study, we constructed in-frame deletion mutants of qseC in A. veronii TH0426 and complemented strains to determine the effects on pathogenesis-related phenotypes and global gene expression. Deletion of qseC did not significantly impact growth curves or colony morphology compared to wild-type A. veronii TH0426. However, the ΔqseC mutant displayed impaired swimming motility, with flagella staining and TEM images showing severe flagella detachment compared to intact flagella in wild-type cells. Crystal violet assays and confocal microscopy revealed that deletion of qseC significantly increased biofilm formation in A. veronii, with the ΔqseC mutant forming 2.07 times more biofilm than wild-type. Altered structural parameters indicative of increased heterogeneity were observed in the ΔqseC biofilm compared to wild-type using ISA analysis. Furthermore, the ΔqseC mutant showed enhanced adhesion to and invasion of epithelioma papulosum cyprini (EPC) cells in vitro. Using a zebrafish infection model, the ΔqseC mutant exhibited attenuated virulence with an 8.5-fold increase in LD50 value compared to wild-type A. veronii TH0426. Bacterial load enumeration in the blood, liver, spleen, and kidney of ΔqseC-infected carp over a 48-h period revealed significantly reduced bacterial counts compared to wild-type. In vivo competition assays indicated the ΔqseC mutant had reduced fitness in carp tissues compared to wild-type A. veronii. RNA sequencing revealed 2364 differentially expressed genes in the ΔqseC mutant compared to wild-type strain TH0426. KEGG pathway enrichment analysis indicated these genes were involved in chemotaxis, flagellar assembly, biofilm formation, protein secretion, and other pathways. Overall, this study demonstrates that QseC plays a vital regulatory role in controlling chemotaxis, flagellar motility, biofilm formation and virulence in the fish and human pathogen A. veronii.

Histopathology and micronuclei induction as pollution biomarkers in common carp, Cyprinus carpio from southern Iraq

This study aimed to assess the histopathological alterations and micronuclei induction in the gill, kidney and liver of common carp, Cyprinus carpio from Al-Huwaizah Marshes, Al-Hammar Marshes and Al-Sweap River. Thirty C. carpio were sampled at each locality using monofilament gillnets. Most prominent histopathological alterations recorded in the gill included formation venous sinus in primary lamellae, oedema, curling and distortion of primary lamellae fusion of secondary lamellae, hyperplasia of epithelial cells, necrosis, curling of secondary lamellae, severe dilation of lamellar capillaries, clavate lamellae formation at the tip of secondary lamellae, a proliferation of cartilage tissue in primary lamellae and lifting of the lamellar epithelium whereas congestion, fibrosis with proliferative inflammation, necrosis area, degenerated cells, vacuolar degeneration, vacuolation, nuclear pyknosis, hypertrophy of hepatocytes were reported in the liver. In the kidney, the most pronounced changes were necrosis of the hematopoietic tissue, hyaline droplet and activation of melanomacrophage centres. A higher prevalence of alterations was observed in the population from Al-Huwaizah Marshes, however, Al-Hammar population exhibited severe pathologies. Micronuclei frequency was significantly higher at Al-Huwaizah Marsh (p < 0.05) with low frequency being recorded at Al-Sweap River. This study attests to the effectiveness of histopathology and micronucleus induction as potential tools for discriminating the health of populations from different water bodies.

The effect of fipronil exposure on the activity of biotransformation enzymes and histology in the liver of grass carp

Fipronil (FPN) is an insecticide used in agriculture. This study focused on the biotransformation process and the histopathological effects of FPN in the liver of grass carp. Fish were exposed to environmental concentrations of FPN (3, 6, and 10 ug l-1) for up to 14 d. The alterations in phase I and II biotransformation enzyme activity (ethoxyresorufin-O-deethylase [EROD] and glutathione-S-transferase [GST]), malondialdehyde (MDA) content, and histopathology in the liver were studied on the 1st, 3rd, 7th, and 14th days. Results showed that EROD (dose-dependent) and GST activity (time-dependent) increased. The MDA content increased in a time- and dose-dependent manner. The most common types of hepatological damage were steatosis, vein dilatation, pyknosis, and increased melanomacrophage centers, probably due to oxidative stress originating from biotransformation enzyme activity (R2 = 0.88 for GST and MDA). The degree of tissue change (DTC) at the highest dose indicated moderate damage to the liver (R2 = 0.82 for GST and DTC). Nevertheless, the level of EROD and GST activity and MDA content indicated complex interactions among various phase I and phase II biotransformation enzymes which should be investigated in future studies with more replications.

Grass carp (Ctenopharyngodon idella) SIRT3 enhances MAVS-mediated antiviral innate immunity in response to GCRV infection

Grass carp (Ctenopharyngodon idella) is a widely cultivated freshwater fish in the world, which occupies a leading position in China's aquaculture industry. However, the outbreak of hemorrhagic disease resulted from grass carp reovirus (GCRV) infection causes tremendous loss in grass carp production. In this study, we cloned the cDNA of grass carp SIRT3 (gc-SIRT3) and found that it is highly conserved across species and abundantly expressed in grass carp liver. Upon GCRV infection, the expression of gc-SIRT3 is dynamically changed. In addition, grass carp SIRT3 positively regulates the expression of antiviral genes depending on its enzymatic activity. Mechanistically, gc-SIRT3 interacts with gc-MAVS to enhance the MAVS-mediated antiviral response. Furthermore, SIRT3 inhibition in zebrafish or grass carp larvae with the specific inhibitor, 3-TYP, attenuates the antiviral ability against GCRV infection. Our findings may provide clues for understanding the function of SIRT3 in antiviral innate immunity.

Consumption of toxic benthic cyanobacteria by two common demersal fish: Growth, antioxidant and liver histopathology responses

Benthic freshwater cyanobacteria have the potential to produce toxins. Compared with more extensively studied plankton species, little is known about the impact of harmful benthic cyanobacteria on aquatic organisms. As demersal fish are usually in direct contact with benthic cyanobacteria, it is important to understand their interactive effects. This study investigated the physio-chemical responses of two demersal fish (Xenocypris davidi and Crucian carp) after exposure to benthic Oscillatoria (producing cylindrospermopsin, 2 × 106 cells/mL) for 7 days. Interestingly, benthic Oscillatoria had less adverse effects on X. davidi than C. carp. The two demersal fish effectively ingested Oscillatoria, but Oscillatoria cell sheathes could not be fully digested in C. carp intestines and led to growth inhibition. Oscillatoria consumption induced oxidative stress and triggered alterations in detoxification enzyme activities in the X. davidi liver. Superoxide dismutase (SOD) and glutathione reductase (GR) activities significantly increased in the C. carp liver, but catalase (CAT) and detoxification enzymes glutathione S-transferase (GST) and glutathione (GSH) activities were insignificantly changed. This suggested that C. carp may have a relatively weak detoxification capacity for toxic Oscillatoria. Oscillatoria ingestion led to more pronounced liver pathological changes in C. carp, including swelling, deformation, and loss of cytoskeleton structure. Simultaneously, fish consumption of Oscillatoria increased extracellular cylindrospermopsin concentration. These results provide valuable insights into the ecological risks associated with benthic cyanobacteria in aquatic ecosystems.