A comparative study on the immune response in the head and trunk kidney of yellow catfish infected with Edwardsiella ictaluri.

The teleost kidneys are anatomically divided into head kidney and trunk kidney, each performing distinct physiological functions. Although previous research has elucidated the role of the head kidney in immune responses, there is a paucity of literature on the comparative studies of the head and trunk kidney response to bacterial infection. Therefore, an Edwardsiella ictaluri infection model of yellow catfish was constructed to investigate and compare the immune responses between the two kidney types. The findings indicated that E. ictaluri infection induced significant pathological changes in both the head and trunk kidney. Despite variances in structure, both the head and trunk kidney of yellow catfish exhibit robust immune responses following E. ictaluri infection. Unexpectedly, the up-regulation level of IgM was found to be higher in the trunk kidney compared to the head kidney. Additionally, both the IgM+ and IgD+ B cells were increased after bacterial infection. This research elucidates the parallels and distinctions in immune functions between both the head and trunk kidney in fish, enriching the immune theory of the fish kidney, and also providing a theoretical basis for the immune response of teleost kidney against bacterial infections.

Molecular characterization, spatio-temporal expression patterns of crtc2 gene and its immune roles in yellow catfish (Pelteobagrus fulvidraco).

cAMP response element binding (CREB) protein 2 (CRTC2) is a transcriptional coactivator of CREB and plays an important role in the immune system. Thus far, the physiological roles of Crtc2 in teleost are still poorly understood. In this study, the crtc2 gene was identified and characterized from yellow catfish (Pelteobagrus fulvidraco; therefore, the gene is termed as pfcrtc2), and its evolutionary and molecular characteristics as well as potential immunity-related roles were investigated. Our results showed that the open reading frame of pfcrtc2 was 2346 bp in length, encoding a protein with 781 amino acids. Gene structure analysis revealed its existence of 14 exons and 13 introns. A phylogenetic analysis proved that the tree of crtc2 was clustered into five groups, exhibiting a similar evolutionary topology with species evolution. Multiple protein sequences alignment demonstrated high conservation of the crtc2 in various vertebrates with similar structure. Syntenic and gene structural comparisons further established that crtc2 was highly conserved, implying its similar roles in diverse vertebrates. Tissue distribution pattern detected by quantitative real-time PCR showed that the pfcrtc2 gene was almost expressed in all detected tissues except for eyes, with the highest expression levels in the gonad, indicating that Crtc2 may play important roles in various tissues. In addition, pfcrtc2 was transcribed at all developmental stages in yellow catfish, showing the highest expression levels at 12 h after fertilization. Finally, the transcriptional profiles of crtc2 were significantly increased in yellow catfishes injected with Aeromonas hydrophila or Poly I:C, which shared a consistent change pattern with four immune-related genes including IL-17A, IL-10, MAPKp38, and NF-κBp65, suggesting pfCrtc2 may play critical roles in preventing both exogenous bacteria and virus invasion. In summary, our findings lay a solid foundation for further studies on the functions of pfcrtc2, and provide novel genetic loci for developing new strategies to control disease outbreak in teleost.

Exploitation of multiple host-derived nutrients by the yellow catfish epidermal environment facilitates Vibrio mimicus to sustain infection potency and susceptibility.

Infection with Vibrio mimicus in the Siluriformes has demonstrated a rapid and high infectivity and mortality rate, distinct from other hosts. Our earlier investigations identified necrosis, an inflammatory storm, and tissue remodeling as crucial pathological responses in yellow catfish (Pelteobagrus fulvidraco) infected with V. mimicus. The objective of this study was to further elucidate the impact linking these pathological responses within the host during V. mimicus infection. Employing metabolomics and transcriptomics, we uncovered infection-induced dense vacuolization of perimysium; Several genes related to nucleosidase and peptidase activities were significantly upregulated in the skin and muscles of infected fish. Concurrently, the translation processes of host cells were impaired. Further investigation revealed that V. mimicus completes its infection process by enhancing its metabolism, including the utilization of oligopeptides and nucleotides. The high susceptibility of yellow catfish to V. mimicus infection was associated with the composition of its body surface, which provided a microenvironment rich in various nucleotides such as dIMP, dAMP, deoxyguanosine, and ADP, in addition to several amino acids and peptides. Some of these metabolites significantly boost V. mimicus growth and motility, thus influencing its biological functions. Furthermore, we uncovered an elevated expression of gangliosides on the surface of yellow catfish, aiding V. mimicus adhesion and increasing its infection risk. Notably, we observed that the skin and muscles of yellow catfish were deficient in over 25 polyunsaturated fatty acids, such as Eicosapentaenoic acid, 12-oxo-ETE, and 13-Oxo-ODE. These substances play a role in anti-inflammatory mechanisms, possibly contributing to the immune dysregulation observed in yellow catfish. In summary, our study reveals a host immune deviation phenomenon that promotes bacterial colonization by increasing nutrient supply. It underscores the crucial factors rendering yellow catfish highly susceptible to V. mimicus, indicating that host nutritional sources not only enable the establishment and maintenance of infection within the host but also aid bacterial survival under immune pressure, ultimately completing its lifecycle.

Response signatures of intestinal microbiota and gene transcription of yellow catfish (Pelteobagrus fulvidraco) to Aeromonas hydrophila infection.

Bacterial intestinal inflammation is a common disease of yellow catfish (Pelteobagrus fulvidraco) in high-density aquaculture. Understanding the interactions between host and intestinal bacteria is helpful to intestinal inflammatory disease control. Here, we constructed a model of intestinal inflammation after Aeromonas hydrophila infection in yellow catfish, and characterized variations in gene expression and microbiome in the gut through high-throughput sequencing. Furthermore, host gene-microbiome interactions were identified. Histology observation showed disordered distribution of columnar epithelial cells and decrease of goblet cells in intestine. A total of 4741 genes showed differentially expression, mostly in comparisons between 12 hpi group with each other groups respectively, including control, 24 hpi and 48 hpi groups. These genes were enriched in immune-related pathways including the IL-17 signaling pathway, triggering strong inflammatory response at the invading stage within 12 h. Subsequently, the host strengthened energy consumption by activating carbohydrate and lipid metabolism pathways to repair the intestinal mucosal immune defense line. In addition, fish with A. hydrophila infection show decreased richness of gut microbial, reduced relative abundance of probiotics including Akkermansia, and elevated pathogenic bacteria such as Plesimonas. An integrative analysis identified A. hydrophila-related genes, such as il22 and stat3, for which expression level is close associated with the shift of A. hydrophila-related bacteria relative abundance, such as Akkermansia and Cetobacterium. Aside from picturing the variations of intestine gene expression and mucosal microbiome of yellow catfish coping with A. hydrophila infection, our study probed the underlying host-microbe interactions in A. hydrophila infection induced intestinal inflammatory, providing new insights for disease control in aquaculture.

Enrofloxacin pharmacokinetics in yellow catfish (Pelteobagrus fulvidraco): A comparative analysis of oral, intramuscular, and bath administration.

Enrofloxacin (ENR) residues in yellow catfish (Pelteobagrus fulvidraco) often exceed the standard due to excessive use. This study explored the pharmacokinetics of ENR and its metabolite ciprofloxacin (CIP) in yellow catfish following a single dose of 10 mg/kg body weight via intramuscular injection (IM), oral gavage (PO), or a 5-h drug bath at 10 mg/L and 25°C. High-performance liquid chromatography-mass spectrometry was used to determine the ENR and CIP concentrations in various tissues. The highest ENR concentration occurred with IM administration, peaking at 4.124 mg/L in the plasma, 8.359 mg/kg in the kidney, 6.272 mg/kg in the liver, and 5.192 mg/kg in the muscle. However, PO administration resulted in the longest metabolic time, with elimination half-lives of 56.47 h in plasma, 86.43 h in the kidney, 76.25 h in the liver, and 64.75 h in muscle. Additionally, the area under the concentration-time curve values for IM, PO, and bath administration in yellow catfish plasma were 108.36, 88.96, and 22.08 mg·h/L, respectively. These results indicate the effectiveness of all three administration methods in treating bacterial diseases in yellow catfish. The selection of an appropriate administration method depends on the minimal inhibitory concentration of ENR against pathogenic bacteria. Yellow catfish subjected to PO and IM administration require longer resting periods before they can be marketed than those receiving drug bath administration.

Molecular characterization of a teleost-specific toll-like receptor 22 (tlr22) gene from yellow catfish (Pelteobagrus fulvidraco) and its transcriptional change in response to poly I:C and Aeromonas hydrophila stimuli.

Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs) that can recognize pathogen-associated molecular patterns (PMPs) and play important roles in the innate immune system in vertebrates. In this study, we identified a teleost-specific tlr22 gene from yellow catfish (Pelteobagrus fulvidraco) and its immune roles in response to different pathogens were also determined. The open reading frame (ORF) of the tlr22 was 2892 bp in length, encoding a protein of 963 amino acids. Multiple protein sequences alignment, secondary and three-dimensional structure analyses revealed that TLR22 is highly conserved among different fish species. Phylogenetic analysis showed that the phylogenetic topology was divided into six families of TLR1, TLR3, TLR4, TLR5, TLR7 and TLR11, and TLR22 subfamily was clustered into TLR11 family. Meanwhile, synteny and gene structure comparisons revealed functional and evolutionary conservation of the tlr22 gene in teleosts. Furthermore, tlr22 gene was shown to be widely expressed in detected tissues except barbel and eye, with highest expression level in liver. The transcription of tlr22 was significantly increased in spleen, kidney, liver and gill tissues at different timepoints after Poly I:C infection, suggesting TLR22 plays critical roles in defensing virus invasion. Similarly, the transcription of tlr22 was also dramatically up-regulated in spleen, kidney and gill tissues with different patterns after Aeromonas hydrophila infection, indicating that TLR22 is also involved in resisting bacteria invasion. Our findings will provide a solid basis for the investigation the immune functions of tlr22 gene in teleosts, as well as provide useful information for disease control and treatment for yellow catfish.

Transport stress induces innate immunity responses through TLR and NLR signaling pathways and increases mucus cell number in gills of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂).

Transport stress poses a threat to most teleost fish in production, causing mass losses to the aquaculture industry. Fish gills are a mucosa-associated lymphoid tissue in direct contact with water, and they represent an ideal tissue type to study mechanisms of transport stress. In this study, hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) were exposed to simulated transport stress for 16 h and then allowed to recover for 96 h. Gill tissues and blood samples were collected at 0 h, 2 h, 4 h, 8 h, and 16 h of transport stress and after 96 h of recovery, as well as from fish in a control group at the same sampling times. The activities of alkaline phosphatase, acid phosphatase, and superoxide dismutase and the total antioxidant capacity first increased and then decreased during the 16 h transport treatment. Exposure to 16 h of transport stress resulted in decreased serum triglyceride and total cholesterol contents, increased serum glucose content, increased activities of alanine aminotransferase and aspartate transaminase, and more mucus cells, compared with the control group. Transcriptome analysis revealed differential expression of 1525 genes (803 down-regulated and 722 up-regulated) between the control and 16 h transportation groups. Functional analyses revealed that the differentially expressed genes were enriched in immune response, signal transduction, and energy metabolism pathways. We found that tlr5, tnfɑ, hsp90ɑ, il-1ß, map2k4, il12ba were clearly up-regulated and arrdc2, syngr1a were clearly down-regulated following 8 h and/or 16 h simulated transport after qRT-PCR validation. These findings suggested that Toll- and NOD-like receptor signaling pathways potentially mediate transport stress. Transport stress altered innate immunity responses and energy use in the gill tissues of hybrid yellow catfish. After 96 h of recovery, only alanine aminotransferase and alkaline phosphatase activities and the number of mucus cells had returned to control levels. We speculate that for juvenile yellow catfish to recover to a normal state, a recovery period of more than 96 h is required after 16 h of transportation. These results provide new perspectives on the immune response of yellow catfish under transport stress and theoretical support for future optimization of their transportation.

Molecular characteristics, polymorphism and expression analysis of mhc â ¡ in yellow catfish(pelteobagrus fulvidraco)responding to Flavobacterium columnare infection.

The major histocompatibility complex (MHC) is an important component of the immune system of vertebrates, which plays a vital role in presenting extrinsic antigens. In this study, we cloned and characterized the mhc ⅡA and mhc ⅡB genes of yellow catfish Pelteobagrus fulvidraco. The open reading frames (ORFs) of mhc ⅡA and mhc ⅡB genes were 708 bp and 747bp in length, encoding 235 and 248 amino acids, respectively. The structure of mhc ⅡA and mhc ⅡB includes a signal peptide, an α1/ß1 domain, an α2/ß2 domain, a transmembrane region and a cytoplasmic region. Homologous identity analysis revealed that both mhc ⅡA and mhc ⅡB shared high protein sequence similarity with that of Chinese longsnout catfish Leiocassis longirostris. mhc ⅡA and mhc ⅡB showed similar expression patterns in different tissues, with the higher expression level in spleen, head kidney and gill and lower expression in liver, stomach, gall bladder and heart. The mRNA expression level of mhc ⅡA and mhc ⅡB in different embryonic development stages also showed the similar trends. The higher expression was detected from fertilized egg to 32 cell stage, low expression from multicellular period to 3 days post hatching (dph), and then the expression increased to a higher level from 4 dph to 14 dph. The mRNA expression levels of mhc ⅡA and mhc ⅡB were significantly up-regulated not only in the body kidney and spleen, but also in the midgut, hindgut, liver and gill after challenge of Flavobacterium columnare. The results suggest that Mhc Ⅱ plays an important role in the anti-infection process of yellow catfish P. fulvidraco.

Responses of functional miRNA-mRNA regulatory modules to a high-fat diet in the liver of hybrid yellow catfish (Pelteobagrus fulvidraco × P. vachelli).

Fatty liver disease is common in cultured yellow catfish as a result of high fat contents in feeds. However, little is known about the mechanism by which the excessive deposition of liver fat causes fatty liver disease. Hybrid yellow catfish (Pelteobagrus fulvidraco♀ × P. vachelli♂) were fed a high-fat diet (HFD) or a normal-fat diet (NFD) for 60 days. Compared with the NFD group, the HFD group showed lower growth performance, higher hepatosomatic and viscerosomatic indexes, increased hepatic triglyceride and cholesterol contents, and more and larger lipid droplets in liver tissue. Whole transcriptome mRNA libraries and microRNA libraries from fish in the NFD and HFD groups were constructed by high-throughput sequencing. Twelve miRNAs were differentially expressed (DE) between the HFD and NFD groups. Seven negatively correlated DE miRNA-DE mRNA pairs were selected, and the expression patterns of both were confirmed using qRT-PCR. Hybrid yellow catfish showed mediated oxidative degradation of liver glucose and fatty acid peroxidation, regulation of antioxidant enzyme activity, and various immune and inflammatory responses to fat deposition and stress. These findings have important biological significance for protecting the liver against stress, as well as economic significance for establishing healthy aquaculture conditions.

Effects of Dietary Glycinin on Oxidative Damage, Apoptosis and Tight Junction in the Intestine of Juvenile Hybrid Yellow Catfish, Pelteobagrus fulvidraco ♀ × Pelteobaggrus vachelli ♂.

The objective of this study was to examine the influences of glycinin for growth and intestinal structural integrity related to oxidative damage, apoptosis and tight junction of juvenile hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × Pelteobaggrus vachelli ♂). Fish (initial weight, 1.02 ± 0.01 g) were fed diets containing five different levels of glycinin at 0%, 2%, 4%, 6%, and 8% for 8 weeks. The results demonstrated that dietary glycinin levels had a negative correlation with final weight, feed intake, protein efficiency ratio and survival rate of the experiment fish. When the level of dietary glycinin exceeded 4%, the structural integrity of the posterior intestine was observably impaired, characterized by disordered and exfoliated margin of intestinal villi, blurred and broken boundaries of tight junctions, damaged organelles and cell vacuolation. Levels of 4-8% dietary glycinin depressed the total antioxidant capacity and total superoxide dismutase activities of posterior intestine. Furthermore, a high level of dietary glycinin linearly and quadratically down-regulated the mRNA expressions of Claudin-1, Occludin and ZO-1, while it linearly and significantly up-regulated the mRNA expressions of Bax, Cyt C, Caspase 3, Caspase 9 and p53 in the posterior intestine. In conclusion, dietary 4-8% glycinin impaired the morphological structure of the posterior intestine by inducing oxidative stress and cell apoptosis, and eventually impeded the growth performance of juvenile hybrid yellow catfish.

Glycocholic acid supplementation improved growth performance and alleviated tissue damage in the liver and intestine in Pelteobagrus fulvidraco fed a high-pectin diet.

In a study on the anti-nutritional effect of dietary fiber, it was noticed that a high-pectin diet (PEC diet) caused growth retardation, hepatic cholestasis, steatosis, fibrosis, and enteritis accompanied by decreased glycocholic acid (GCA) in Pelteobagrus fulvidraco. This study was conducted to investigate the potential alleviating effects of supplementation with GCA. A PEC diet and a diet supplemented with 0.6 g kg-1 GCA based on the PEC diet (named the GCA diet) were formulated and randomly fed to juvenile Pelteobagrus fulvidraco. Compared to fish that were fed the PEC diet for 7 days, the GCA content in liver increased significantly in fish fed the GCA diet, the incidence of abnormal liver color, gallbladder somatic index (GBSI), total bile acid concentration in serum and liver, and the expression of arnesoid X receptor gene (fxr) upregulated and genes involved in bile acid (BA) synthesis and uptake in liver decreased significantly. After 56 days, the SGR, the expression of fxr and genes involved in BA synthesis and transportation in the liver, the serum content of total bilirubin, total protein, and globulin were significantly higher, while the hepatosomatic index, GBSI, liver lipid and collagen content, and the incidence of distal intestine tissue damage were lower in fish fed the GCA diet than in those fed the PEC diet. These results suggested that GCA improved growth performance and alleviated hepatic cholestasis and tissue damage to the liver and intestine induced by a high-pectin diet, which might occur through activating FXR.

Transcriptome profiling reveals differential expression of immune-related genes in gills of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) under hypoxic stress: Potential NLR-mediated immune response.

Fish gills are the primary organ that respond to sudden changes in the dissolved oxygen (DO) level in the aquatic environment. Hypoxic stress impairs the normal function of gill tissues. However, little is known about the mechanisms of the response of yellow catfish gills to hypoxic stress. In this study, we compared transcriptomic and physiological changes in gill tissues of hybrid yellow catfish (Tachysurus fulvidraco ♀ × Pseudobagrus vachellii ♂) between a hypoxia-treated group (DO: 1.5 mg/L) and a control group (DO: 6.5 mg/L). In fish in the hypoxia-treated group, gill filaments underwent adaptive changes, and the number of vacuoles in gill tissues increased. Exposure to hypoxic conditions for 96 h resulted in increased anaerobic metabolism and decreased antioxidant and immune capacity in gill tissues. Transcriptome analyses revealed 1556 differentially expressed genes, including 316 up-regulated and 1240 down-regulated genes, between fish in the hypoxia-treated and control groups. Functional analyses indicated that the main pathway enriched with differentially expressed genes was immune response, followed by energy metabolism and signal transduction. Under hypoxic stress, the transcript levels of genes involved in the NOD-like receptor signaling pathway initially increased rapidly but then decreased over time, suggesting that the NOD-like receptor-mediated immune response plays an essential role in hypoxia tolerance and resistance in hybrid yellow catfish. Our results provide novel insights into which immune-related genes and pathways are activated under hypoxic stress, and reveal details of early adaptation of the immune response and defense mechanisms under hypoxic stress.

Effect of dietary histamine on intestinal morphology, inflammatory status, and gut microbiota in yellow catfish (Pelteobagrus fulvidraco).

The toxic effect of dietary histamine on the intestine of aquatic animals has been demonstrated, but reports on the morphological observation of the intestine are limited. Thus, a feeding trial was conducted to determine the effect of dietary histamine on intestinal histology, inflammatory status and gut microbiota of yellow catfish (Pelteobagrus fulvidraco). Here, we showed that histamine-rich diets caused severe abnormality and damage to the intestine, including a decreased villi length and reduced villi number. In addition, the quantitative real-time PCR (qRT-PCR) demonstrates that histamine-rich diets increased the expression of pro-inflammatory genes (Tnfα, Il1ß, and Il8) and decreased the expression of an anti-inflammatory gene (Il10). Furthermore, the alpha-diversity (observed OTUs, Chao1, Shannon and Simpson) and beta-diversity (non-metric multidimensional scaling, with the stress value of 0.17) demonstrated that histamine-rich diets caused alterations in gut microbiota composition and diversity. Co-occurrence networks analysis of the gut microbiota community showed that the histamine influenced the number and the relationship between bacteria species in the phyla of Acidobacteria, Proteobacteria, and Bacteroidetes, which caused the instability of the intestinal microbiota community. Additionally, random forest selected six bacterial species as the biomarkers to separate the three groups, which are Lachnospiraceae Blautia (V520), Bacteroidales S24.7 (V235), Chloroplast Streptophyta (V368), Actinomycetales Streptomycetaceae (V152), Clostridia Clostridiales (V491) and Paraprevotellaceae Prevotella (V245). Finally, Pearson correlation analysis demonstrated that V520, V235, and V491 were negatively correlated with pro-inflammatory factors (Tnfα, Il1ß, and Il8) and positively correlated with an anti-inflammatory factor (Il10), which indicated that V520, V235, and V491 might be anti-inflammatory. These findings improved our understanding of the toxic effect of dietary histamine to intestinal histological damage, the induction of mucosa inflammatory status, and the alteration of gut microbiota.

Immunogenicity study of OmpU subunit vaccine against Vibrio mimicus in yellow catfish, Pelteobagrus fulvidraco.

The outer membrane protein U (OmpU) is a conserved outer membrane protein in a variety of pathogenic Vibrio species and has been considered as a vital protective antigen for vaccine development. Vibrio mimicus (V. mimicus) is the pathogen causing ascites disease in aquatic animals. In this study, the prokaryotically expressed and purified His-tagged OmpU of V. mimicus (His-OmpU) was used as a subunit vaccine. The formalin inactivated V. mimicus, purified His tag (His-tag), and PBS were used as controls. The vaccinated yellow catfish were challenged with V. mimicus at 28 days post-vaccination, and the results showed that the His-OmpU and inactivated V. mimicus groups exhibited much higher survival rates than the His-tag and PBS groups. To fully understand the underlying mechanism, we detected the expression levels of several immune-related genes in the spleen of fish at 28 days post-vaccination and 24 h post-challenge. The results showed that most of the detected immune-related genes were significantly upregulated in His-OmpU and inactivated V. mimicus groups. In addition, we performed the serum bactericidal activity assay, and the results showed that the serum from His-OmpU and inactivated V. mimicus groups exhibited much stronger bactericidal activity against V. mimicus than those of His-tag and PBS groups. Finally, the serum agglutination antibody was detected, and the antibody could be detected in His-OmpU and inactivated V. mimicus groups with the antibody titers increasing along with the time post-vaccination, but not in His-tag or PBS group. Our data reveal that the recombinant OmpU elicits potent protective immune response and is an effective vaccine candidate against V. mimicus in yellow catfish.

Ammonia stress disrupts intestinal microbial community and amino acid metabolism of juvenile yellow catfish (Pelteobagrus fulvidraco).

Ammonia has adverse effects on aquatic animals, which is also widely distributed in natural aquatic environments and intensive aquaculture systems. The intestine is a primary defensive line for aquatic animals, the accumulation of ammonia in the aquatic environment can cause irreversible damage to intestinal function. In this study, we investigated the effects of acute ammonia stress on the reaction characteristics of digestive function, amino acid metabolism, and the variation in the intestinal microbiota of juvenile yellow catfish (Pelteobagrus fulvidraco). Thus, the yellow catfish was placed in water with the addition of ammonia at 0 (control), 14.6, and 146 mg/L total ammonia nitrogen for 96-h. The present study observed that ammonia accumulated in the intestine and muscle (ammonia contents in the intestine and muscle increased) and induced the activities of protein digestive enzymes dysfunction (pepsin increased while trypsin decreased). Ammonia stress changed various amino acids composition (proline, arginine, lysine, histidine, phenylalanine, tyrosine, leucine, isoleucine, valine, alanine, glutamic acid, tyrosine, and aspartic acid contents were increased in muscle) and increased the activities of alanine aminotransferase and aspartate aminotransferase in muscle. Furthermore, through 16 S rRNA gene analysis, ammonia stress-induced reduction in diversity, richness, and evenness and structure of microbiota alteration in the intestine. At the phylum level, the abundance of Fusobacteria increased while Firmicutes and Actinobacteria decreased significantly. At the genus level, the abundance of beneficial microbiota Cetobacterium significantly increased after ammonia stress. In conclusion, activation of amino acid synthesis in muscle may be involved in ammonia detoxification after severe ammonia stress. The accumulation of ammonia can disrupt the intestinal digestive function and intestinal microbiota community. The Cetobacterium may be a new potential positive factor in the resistance of ammonia toxicity.

An identified PfHMGB1 promotes microcystin-LR-induced liver injury of yellow catfish (Pelteobagrus fulvidraco).

Microcystin-LR (MC-LR) is a potent hepatotoxin that can cause liver inflammation and injury. However, the mode of action of related inflammatory factors is not fully understood. PfHMGB1 is an inflammatory factor induced at the mRNA level in the liver of juvenile yellow catfish (Pelteobagrus fulvidraco) that were intraperitoneally injected with 50 µg/kg MC-LR. The PfHMGB1 mRNA level was highest in the liver and muscle among 11 tissues examined. The full-length cDNA sequence of PfHMGB1 was cloned and overexpressed in E. coli, and the purified protein rPfHMGB1 demonstrated DNA binding affinity. Endotoxin-free rPfHMGB1 (6-150 µg/mL) also showed dose-dependent hepatotoxicity and induced inflammatory gene expression of primary hepatocytes. PfHMGB1 antibody (anti-PfHMGB1) in vitro reduced MC-LR (30 and 50 µmol/L)-induced hepatotoxicity, suggesting PfHMGB1 is important in the toxic effects of MC-LR. In vivo study showed that MC-LR upregulated PfHMGB1 protein in the liver. The anti-PfHMGB1 blocked its counterpart and reduced ALT/AST activities after MC-LR exposure. Anti-PfHMGB1 partly neutralized MC-LR-induced hepatocyte disorganization, nucleus shrinkage, mitochondria, and rough endoplasmic reticula destruction. These findings suggest that PfHMGB1 promotes MC-LR-induced liver damage in the yellow catfish. HMGB1 may help protect catfish against widespread microcystin pollution.

Dietary pectin caused great changes in bile acid profiles of Pelteobagrus fulvidraco.

To reveal the impact of dietary fiber (DF) on the bile acid (BA) profiles of fish, yellow catfish (Pelteobagrus fulvidraco) were fed a diet containing 300 g kg-1 dextrin (CON diet, control) or pectin (a type of soluble DF, PEC diet) for 7 days, and then the BA profiles were analyzed by UHPLC-MS/MS. A total of 26 individuals of BAs were detected in the fish body, with 8, 10, 14, and 22 individuals of BAs detected in the liver, serum, bile, and hindgut digesta, respectively. The conjugated BAs (CBAs) of fish were dominated by taurine CBAs (TCBAs). The concentrations of free BAs (FBAs) and the value of FBAs/CBAs in the bile of fish fed the PEC diet were nearly 5 and 7 times higher, respectively than those in fish fed the CON diet. The value of glycine CBAs/TCBAs in the liver, serum and bile of fish fed the PEC diet was significantly lower, and in the hindgut digesta was higher than that of fish fed the CON diet (P < 0.05). These results suggested that dietary pectin greatly changed the BA profiles of Pelteobagrus fulvidraco, attributed to inhibition of reabsorption of BAs. Therefore, attention should be paid to the impact on BA homeostasis when replacing fishmeal with DF-rich plant ingredients in the fish diet.

Intraperitoneal injection of genistein affects the distribution and metabolism of cholesterol in female yellow catfish Tachysurus fulvidraco.

Genistein is an abundant phytoestrogen in soybean. This study aimed to determine the effects of genistein on cholesterol distribution and metabolism in female yellow catfish. Three hundred fish (49.2 ± 1.4 g) were randomly divided into five treatments and received intraperitoneal injections as follows: (1) blank, no injection; (2) control, vehicle only; (3) E2, 17ß-estradiol at 10 µg·g-1 body weight; (4) low genistein doses, genistein at 10 µg·g-1 body weight; (5) high genistein doses, genistein at 100 µg·g-1 body weight. Both high and low genistein doses significantly reduced (p < 0.05) serum TC and LDL-C 24 h after injection. Moreover, the high genistein doses significantly reduced (p < 0.05) serum HDL-C. Both high and low doses of genistein significantly increased (p < 0.05) hepatic TC. Only high genistein doses significantly increased (p < 0.05) ovary TC. In the liver, both high and low genistein doses significantly increased (p < 0.05) protein and mRNA expression of ldlr. Meanwhile, high genistein doses significantly decreased (p < 0.05) mRNA expression of hmgcr. In ovary tissue, high genistein doses significantly decreased (p < 0.05) mRNA expression of cyp11a1. These results suggested that genistein affected the cholesterol distribution in female yellow catfish. Both high and low doses of genistein reduced cholesterol content in blood and increased its content in the liver by increasing the uptake of blood cholesterol. Meanwhile, high genistein doses may inhibit hepatic cholesterol synthesis. Additionally, high genistein doses could increase cholesterol transfer from serum into the ovary and disturb cholesterol conversion to pregnenolone.

Effects of acute hypoxia and reoxygenation on oxygen sensors, respiratory metabolism, oxidative stress, and apoptosis in hybrid yellow catfish "Huangyou-1".

The regulation mechanism of the hybrid yellow catfish "Huangyou-1" was assessed under conditions of hypoxia and reoxygenation by examination of oxygen sensors and by monitoring respiratory metabolism, oxidative stress, and apoptosis. The expressions of genes related to oxygen sensors (HIF-1α, HIF-2α, VHL, HIF-1ß, PHD2, and FIH-1) were upregulated in the brain and liver during hypoxia, and recovered compared with control upon reoxygenation. The expressions of genes related to glycolysis (HK1, PGK1, PGAM2, PFK, and LDH) were increased during hypoxia and then recovered compared with control upon reoxygenation. The mRNA levels of CS did not change during hypoxia in the brain and liver, but increased during reoxygenation. The mRNA levels of SDH decreased significantly only in the liver during hypoxia, but later increased compared with control upon reoxygenation in both tissues. Under hypoxic conditions, the expressions of genes related to oxidative stress (SOD1, SOD2, GSH-Px, and CAT) and the activity of antioxidant enzymes (SOD, CAT, and GSH-Px) and MDA were upregulated compared with control. The expressions of genes related to apoptosis (Apaf-1, Bax, Caspase 3, Caspase 9, and p53) were higher than those in control during hypoxic exposure, while the expressions of Bcl-2 and Cyt C were decreased. The findings of the transcriptional analyses will provide insights into the molecular mechanisms of hybrid yellow catfish "Huangyou-1" under conditions of hypoxia and reoxygenation. Overall, these findings showed that oxygen sensors of "Huangyou-1" are potentially useful biomarkers of environmental hypoxic exposure. Together with genes related to respiratory metabolism, oxidative stress and apoptosis occupy a quite high position in enhancing hypoxia tolerance. Our findings provided new insights into the molecular regulatory mechanism of hypoxia in "Huangyou-1."

The protective effects of selenium on chronic ammonia toxicity in yellow catfish (Pelteobagrus fulvidraco).

Ammonia is toxic to most fish, and its negative effects can be eliminated by nutritional manipulation. In this study, triplicate groups of yellow catfish (0.58 ± 0.03 g) were fed diets supplemented with 0, 0.30 and 0.60 mg selenium (Se) kg-1 diet for 56 days under three ammonia contents (0.00, 5.70 and 11.40 mg L-1 total ammonia nitrogen). The results showed that ammonia toxicity could affects growth (weight gain, feed efficiency ratio, Se contents in muscle and whole body declined) and survival, leads to oxidative stress (total antioxidant capacity, superoxide dismutase, catalase and glutathione peroxidase activities declined and malondialdehyde accumulation), immunosuppression (lysozyme activity, 50% hemolytic complement, immunoglobulin M, respiratory burst and phagocytic index declined) and cytokines release (TNF, IL 1 and IL 8 elevated), induces up-regulation of antioxidant enzymes (Cu/Zn-SOD, Mn-SOD, CAT and GPx), cytokines (TNFα, IL 1 and IL 8) and pro-apoptotic genes (p53, Bax, Cytochrome c, Caspase 3 and Caspase 9) transcription, and down-regulation of anti-apoptotic gene Bcl2 transcription. The dietary Se supplementation could mitigate the adverse effect of ammonia poisoning on fish growth, oxidative damage, immunosuppression and apoptotic.