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This study aimed to evaluate and select high aroma-producing strains for aroma improvement of a novel new fish sauce from channel catfish. Preliminary screening in the synthetic broth and secondary screening in fish frame hydrolysate were conducted for nine exogenous strains, including Lactiplantibacillus plantarum (LP), Pediococcus pentosaceus (PP), Latilactobacillus sakei (LS), Pichia fermentans (PF), Zygosaccharomyces rouxii (ZR), Wickerhamomyces anomalus (WA), Staphylococcus xylosus (SX), Staph. saprophyticus (SS) and Staph. carnosus (SC). In the broth, LP, PF, and SS exhibited superior growth, higher acid and alcohol tolerance than others in the same group (lactic acid bacteria, yeasts and staphylococci). Secondary screening in the fish frame hydrolysate demonstrated LP, PF, and SS displayed better performance in acid generation and reducing sugar consumption. HS-SPME-GC-MS analysis showed that the mixed culture of the three strains produced more alcohols and esters than other combinations. Sensory analysis revealed that the three-strains combination obviously improved the flavor profile of the fish frame hydrolysate relative to combinations with two strains and commercial fish sauce, especially the fruity and cheesy flavor. In summary, LP, PF, and SS can better adapt to the new fish sauce environment and have aroma enhancement potential. • L. plantarum, P. fermentans and S. saprophyticus were selected for channel catfish hydrolysate fermentation. • Each strain exhibited remarkable environmental adaptation than others. • A combination of three strains showed a better synergistic effect on flavor. • Co-inoculation imparted fruity and cheesy odors and reduced fishy odor. [ABSTRACT FROM AUTHOR]

Aeromonas hydrophila was a common bacterial pathogen in aquaculture resulting in considerable losses to the striped catfish aquaculture industry. As an emergent antimicrobial peptide (AMP), NK-lysin (NKL) had activity against various microorganisms. However, the antibacterial activity of NKL from striped catfish (Pangasianodon hypophthalmus) both in vitro and vivo remains unclear. In this study, the cDNA sequence of P. hypophthalmus NK-lysin gene (PhNK-lysin) was cloned and characterized. The amino acid sequence of PhNK-lysin contains a signal peptide sequence of 17 amino acid (aa) residues and a mature peptide composed of 130 aa. The saposin B domain of mature peptide comprised six conserved cysteines forming three putative disulfide bonds. Phylogenetic analysis revealed that the PhNK-lysin was most closely related to that of the channel catfish (Ictalurus punctatus) NK-lysin. The transcriptional levels of the PhNK-lysin were significantly upregulated in response to A. hydrophila infection in various tissues including heart, liver, spleen, head kidney, trunk kidney and gill. The synthetic PhNK-lysin-derived peptide consisting of 38aa showed antibacterial activity against Vibrio harveii , Aeromonas hydrophila and Escherichia coli. The MIC for V. harveii , A. hydrophila and E. coli were 15.625 μM, 250 μM and 31.25 μM respectively. Besides, the synthetic PhNK-lysin decreased the bacterial load of liver and trunk kidney in vivo as well as increased the survival rate of A. hydrophila infected striped catfish. Hence, these data suggest that PhNK-lysin had antimicrobial effect and protects the host from pathogenic infection. • A NK-lysin homolog was identified and characterized from striped catfish. • The transcriptional levels of the NKL gene were significantly upregulated in response to A. hydrophila infection. • The synthetic Pangasianodon hypophthalmus NK-lysin derived peptides exhibited antibacterial effect both in vivo and in vitro. [ABSTRACT FROM AUTHOR]

The reduction of fishmeal in aquafeeds has been the concern of researchers. Replacing fishmeal with plant proteins affects intestinal function and inflammation, but the interaction between the intestinal responses and gut microbiota remains unclear. In this study, juvenile channel catfish (Ictalurus punctatus) was fed with four diets in which enzymatic rice protein (RP) replaced fishmeal at levels of 0 (FM), 2.5% (RP2.5), 5.0% (RP5.0), and 7.5% (RP7.5) for 8 weeks to solve the problem mentioned above. Quantification of intestinal morphology showed that 2.5% or 5.0% RP significantly increased villus length and goblet cell number, accompanied by higher activities of intestinal trypsin, alkaline phosphatase (AKP), and Na+/K+-ATPase (NKA) in RP2.5 group (P < 0.05). In contrast, 7.5% RP slightly damaged the intestinal mucosa and significantly reduced the activities of amylase, AKP, and NKA, as well as decreased serum complement 4 (C4) and immunoglobulin M (IgM). Noteworthy, RT-qPCR showed that 2.5% RP significantly down-regulated intestinal mRNA expression level of il8 , while up-regulated mif , tlr4 , tlr7 , tgfβ3 , and cldn2. In contrast, 7.5% RP up-regulated the mRNA expression levels of il1β , il8 , and mif , while down-regulated cldn3d. Analysis of gut microbiota showed that 2.5% RP increased the relative abundance of Bacteroidetes and significantly activated potential functions of gut microbiota involved in carbohydrate metabolism. The 7.5% RP increased the diversity of the gut microbiota, accompanied by a significant increase in the relative abundance of conditionally pathogenic bacteria such as Vibrio , Serratia , and Aeromonas (classified as Proteobacteria). Notably, Vibrio was the biomarker species with the greatest difference between the FM and RP7.5 groups (genus level). Correlation analysis indicated that Vibrio may affect immunity through the C4 pathway and further lead to gut inflammation and digestive impairment. Taken above, these results indicated that RP could affect intestinal morphology, digestion, and inflammation, and interact with the composition and potential function of gut microbiota. The low RP supplement (2.5%) improved intestinal morphology and digestion, while high supplement (7.5%) disrupted gut microbiota homeostasis, resulting in damage to intestinal mucosa and inflammatory response. • Replacing 2.5% of fishmeal with RP improved gut morphology and digestion. • The 7.5% RP supplement resulted in damaged intestinal mucosa, decreased digestion, and inflammatory responses. • The 7.5% RP induced gut inflammation by affecting the abundance and predicted function ofpathogenic bacteria. [ABSTRACT FROM AUTHOR]

IL-26 is a crucial inflammatory cytokine that participates in defending host cells against infections. We initially cloned and identified the cDNA sequences of interleukin (IL)-26 in channel catfish (Ictalurus punctatus). The open reading frame (ORF) of Ip IL-26 was 537 bp in length, encoding 178 amino acids (aa). Constitutive expression of Ip IL-26 was observed in tested tissues, with the highest level found in the gill and spleen. To explore the function of Ip IL-26 in channel catfish, different stimuli were used to act on both channel catfish and channel catfish kidney cells (CCK). The expression of Ip IL-26 could be up-regulated by bacteria and viruses in multiple tissues. In vitro , recombinant Ip IL-26 (r Ip IL-26) could induce the expression levels of inflammatory cytokines such as TNF-α, IL-1β, IL-6, IL-20, and IL-22 playing vital roles in defending the host against infections. Our results demonstrated that Ip IL-26 might be an essential cytokine, significantly affecting the immune defense of channel catfish against pathogen infections. • The cDNA sequences of Ip IL-26 was cloned and constitutively expressed in all tissues. • In vivo, Ip IL-26 expression can be up-regulated in different immune tissues after stimulated by bacteria and viruses. • In vitro, r Ip IL-26 can defend host against infections by inducing the expression of inflammatory cytokines. [ABSTRACT FROM AUTHOR]

Constructs bearing the cecropin B gene from the moth Hyalophora cecropia , driven by the cytomegalovirus (CMV) promoter, or the common carp beta-actin (β-actin) promoter were transferred to channel catfish, Ictalurus punctatus via electroporation. One F 3 channel catfish family transgenic for cecropin transgene driven by the CMV promoter, and one F 1 channel catfish family transgenic for cecropin transgene driven by the common carp β-actin promoter were produced. F 3 and F 1 individuals exhibited enhanced disease resistance when challenged in tanks with Edwardsiella ictaluri , the causative agent of enteric septicemia of catfish (ESC). Inheritance of the transgene by the F 1 and F 3 generation was 15% and 60%, respectively. Growth rates of the cecropin transgenic and non-transgenic full siblings (controls) channel catfish were not different (P > 0.05). All transgenic fish showed significant resistance to infection by ESC at day 3 and day 4 post exposure (P = 0.005). No correlation was detected between body weight and time to death for all genetic groups (P = 0.34). Results of our study confirmed that genetic enhancement of E. ictaluri resistance can be achieved by cecropin transgenesis in channel catfish. In addition to survival rate, improving survival time is essential because the extension of survival time gives a better chance to apply treatments to stop the bacterial infection. • Genetic enhancement of E. ictaluri resistance can be achieved by transgenesis. • Non-transgenic channel catfish survived less time than cecropin-transgenic. • No correlation was detected between weight and time to death for all genotypes. [ABSTRACT FROM AUTHOR]

Glutamine synthetase (GS) plays a crucial role in the regulation of glutamine synthesis in fish which is a very effective ammonia detoxification strategy. In this study, the full-length GS was cloned from the liver of yellow catfish. The full-length cDNA sequence of GS was 1928 bp in length and encoded 371 amino acids. The amino acid sequence of GS showed high homology (99%) with that of channel catfish. The highest mRNA expression of GS was found in the brain of yellow catfish. Acute ammonia stress (96 h LC50) significantly increased ammonia levels in plasma, liver, and brain, and GS gene expression was significantly up-regulated in the liver and brain. RNA interference inhibited the GS mRNA expression level in primary cultured hepatocytes after acute ammonia stress and reduced hepatocyte survival rate. It is suggested that GS plays a key role in ammonia detoxification in yellow catfish by regulating glutamine synthesis. • The full-length cDNAs sequences of GS from yellow catfish was 1928 bp. • GS RNAi reduced survival of hepatocyte after ammonia stress. • GS plays a key role in ammonia detoxification of yellow catfish. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the partial replacement of fish meal by Saccharomyces cerevisiae culture on growth performance, immunity, composition and function of intestinal microbiota and disease resistance in channel catfish (Ictalurus punctatus). Two equal nitrogen and energy diets were prepared including a basal diet (containing 10% fish meal, Control) and an experimental diet (replacing 20% of the fish meal of the basal diet with yeast culture, RFM). Channel catfish were fed with the diets for 12 weeks. The results showed that weight gain and condition factor were significantly increased, and FCR was significantly decreased in RFM group (P < 0.05). The gene expression of intestinal HIF1α was significantly increased in RFM group (P < 0.05), while the expressions of NF-κB in the intestine and liver were significantly decreased (P < 0.05). The relative abundance of Firmicutes tended to increase, and the Turicibacter had an upward trend (0.05 < P < 0.2). In addition, the survival rate of channel catfish was significantly increased in RFM group after challenged with Aeromonas veronii Hm091 and Aeromonas hydrophila NJ-1 (P < 0.05). Compared with intestinal microbiota of channel catfish of control group, intestinal microbiota of channel catfish of RFM group significantly increased the expression of HIF1α , and decreased the expression of IL-1β and TNF-α (P < 0.05) in germ-free zebrafish. Intestinal microbiota induced by RFM diet also significantly increased disease resistance to Aeromonas veronii Hm091 and Aeromonas hydrophila NJ-1. In conclusion, replacement of fish meal by the yeast culture improved the growth, immunity and disease resistance of channel catfish, and intestinal microbiota of channel catfish induced by the yeast culture played a critical role in these effects. • RFM diet increased growth performance, gut and liver health of channel catfish. • RFM diet enhanced the resistance of channel catfish to A. Veronii and A. hydrophila. • Intestinal microbiota induced by RFM diet played a critical role in probiotic effects of Saccharomyces cerevisiae by using the germ-free zebrafish model. [ABSTRACT FROM AUTHOR]

The purpose of the study was to investigate the effects of Eucommia ulmoides leaf extract (ELE) on the common occurrence of liver steatosis, chronic inflammation, oxidative stress, disturbance of gut microbiota, and disease susceptibility in high-fat diet-fed channel catfish. Channel catfish fed three diets, including a high-fat diet (11% crude fat) and ELE-supplemented diets containing 1‰ or 2‰ ELE for 4 weeks. The results showed the contents of liver triacylglycerol of 1‰ and 2‰ ELE groups were reduced, and ELE treatments decreased the expression of lipogenesis related genes (srebp-1c, pparγ, and acc-1), and increased the expression of lipolysis related genes (pparα). In addition, the supplementation of ELE improved the inflammatory response of the liver and intestine. ELE could improve the destruction of intestinal morphology structure and increase the expression level of hif-1a and tight junction proteins (Occludin, Claudin2, Claudin15). 2‰ ELE significantly enhanced the antioxidant capacity of intestine by increasing the activity of SOD enzyme. Moreover, the supplement of ELE significantly increased the abundance of Cetobacterium and Romboutsia (p < 0.05). Compared with the control group, the expression of immune factor nf-κb had a significant decrease, and il-1β showed a tendency to decrease in the ELE supplement groups after pathogenic bacteria challenge. In conclusion, the ELE alleviated fatty liver disease and inflammation response, improved the oxidative capacity and physiological structure of intestine, and improved the structure of intestinal microbiota and disease resistance in HFD-fed channel catfish. • Dietary ELE supplementation alleviated liver steatosis induced by high-fat diet. • Dietary ELE supplementation improved liver and gut health of channel catfish. • Dietary ELE supplementation improved the intestinal microbiota structure of channel catfish. • Dietary ELE supplementation enhanced disease resistance of channel catfish. [ABSTRACT FROM AUTHOR]

In this work, we describe the complete repertoire of channel catfish, Ictalurus punctatus , IFNs and IFN receptor genes. Based on multiple genomic and transcriptomic resources we identified 16 type I IFN genes, which represent the six type I IFN subgroups previously defined in salmonids (a-f.) No representatives of subgroup h previously only found in percomorphs were identified. An expansion in copy numbers of subgroup d IFN genes was of particular interest, as this has not been reported in other fish species to date. Furthermore, we confirmed the presence of two type II ifn genes encoding orthologs of IFNγ and the teleost-specific IFNγRel. Six homologs of IFN type I receptor genes were found in an array that shows conserved synteny with human chromosome 21. Three homologs of type II IFN receptor genes were also identified. These type I and type II receptor sequences are compatible with the dual type I IFN receptors, and the potentially more complex type II IFN receptors described in teleosts. Our data provide a comprehensive resource for future studies of channel catfish innate antiviral immunity. • Sixteen interferon type I and two type II genes are present in channel catfish. • The 16 type I interferons belong to six subgroups (a, b, c, d, e, f). • Interferon subgroup d is expanded in channel catfish with 5 copies. • Six homologs of interferon type I and three of type II receptor genes are found in channel catfish. [ABSTRACT FROM AUTHOR]

• F. columnare recombinant DnaK protein vaccine with or without an immersion adjuvant confers protection against columnaris disease. • The benefit of using an immersion adjuvant is the reduction of immunization time required to achieve that protection. [ABSTRACT FROM AUTHOR]

Aeromonas veronii is associated with food spoilage and some human diseases, such as diarrhea, gastroenteritis, hemorrhagic septicemia or asymptomatic and even death. This research investigated the mechanism of the growth, biofilm formation, virulence, stress resistance, and spoilage potential of Bacillus subtilis lipopeptide against Aeromonas veronii. Lipopeptides suppressed the transmembrane transport of Aeromonas veronii by changing the cell membrane's permeability, the structure of membrane proteins, and Na+/K+-ATPase. Lipopeptide significantly reduced the activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) by 86.03% and 56.12%, respectively, ultimately slowing Aeromonas veronii growth. Lipopeptides also restrained biofilm formation by inhibiting Aeromonas veronii motivation and extracellular polysaccharide secretion. Lipopeptides downregulated gene transcriptional levels related to the virulence and stress tolerance of Aeromonas veronii. Furthermore, lipopeptides treatment resulted in a considerable decrease in the extracellular protease activity of Aeromonas veronii , which restrained the decomposing of channel catfish flesh. This research provides new insights into lipopeptides for controlling Aeromonas veronii and improving food safety. [Display omitted] • Lipopeptides reduced Aeromonas veronii biofilm formation. • Lipopeptides reduce the virulence and resistance of Aeromonas veronii. • Lipopeptides inhibit the spoiling potential of Aeromonas veronii. [ABSTRACT FROM AUTHOR]

This study isolated CFI gene from Pelteobagrus fulvidraco and named it PfCFI. The cDNA of PfCFI is 2374 bp long, including a 52 bp 5′ untranslated sequence, a 222 bp 3′ untranslated sequence, and an open reading frame (ORF) of 2100 bp encoding polypeptide consisting of 699 amino acids. Phylogenetic analysis revealed that the PfCFI was closely related to CFI of Ictalurus punctatus. Real-time quantitative reverse transcription-PCR (qRT-PCR) analysis indicate that there is the PfCFI gene which expressed in all the rest of tested tissues in varied levels, and mainly distributed in liver and least in heart. The reseachers induce the expressions level of PfCFI gene in liver, spleen, head kidney and blood at different points in time after challenged with lipopolysaccharide (LPS), and polyriboinosinic polyribocytidylic acid (poly I:C), respectively. Together these results suggested that CFI gene plays an important role in resistance to pathogens in yellow catfish immunity. • A complement factor I gene was characterized from yellow catfish Pelteobagrus fulvidraco. • The expression profiles of PfCFI in various tissues were investigated. • The mRNA expression levels of PfCFI were performed in response to Poly I:C or LPS challenge. [ABSTRACT FROM AUTHOR]

Sustainability of channel catfish, Ictalurus punctatus ♀ × blue catfish, Ictalurus furcatus ♂ hybrid aquaculture relies on new innovative technologies to maximize fry output. Transplanting spermatogonial stem cells (SSCs) from blue catfish into channel catfish hosts has the potential to greatly increase gamete availability and improve hybrid catfish fry outputs. Cryopreservation would make these cells readily accessible for xenogenesis, but a freezing protocol for blue catfish testicular tissues has not yet been fully developed. Therefore, the objectives of this experiment were to identify the best permeating [dimethyl sulfoxide (DMSO), ethylene glycol (EG), glycerol, methanol] and non-permeating (lactose or trehalose with egg yolk or BSA) cryoprotectants, their optimal concentrations, and the best freezing rates (−0.5, −1.0, −5.0, −10 ° C/min until −80 ° C) that yield the highest number of viable type A spermatogonia cells. Results showed that all of these factors had significant impacts on post-thaw cell production and viability. DMSO was the most efficient permeating cryoprotectant at a concentration of 1.0 M. The optimal concentration of each cryoprotectant depended on the specific cryoprotectant due to interactions between the two factors. Of the non-permeating cryoprotectants, 0.2 M lactose with egg yolk consistently improved type A spermatogonia production and viability beyond that of the 1.0 M DMSO control. The overall best freezing rate was consistent at −1 °C/min, but similar results were obtained using −0.5 °C/min. Overall, we recommend cryopreserving blue catfish testicular tissues in 1.0 M DMSO with 0.2 M lactose and egg yolk at a rate of either -0.5 or −1 °C/min to achieve the best cryopreservation outcomes. Continued development of cryopreservation protocols for blue catfish and other species will make spermatogonia available for xenogenic applications and genetic improvement programs. • Effects of cryoprotectants and freezing rates were evaluated. • Optimal concentration varied by cryoprotectant. • 1.0 DMSO with 0.2 M lactose and egg yolk was the best treatment combination. • Freezing rate of −1 °C/min was more effective than −5 or −10 °C/min. • Cryopreservation protocol established for blue catfish Type A spermatogonia cells. [ABSTRACT FROM AUTHOR]

Channel catfish (Ictalurus punctatus) vaccinated with pcDNA3.1-IAg52b plasmid DNA vaccine encoding immobilization antigen genes of Ichthyophthirius multifiliis (Ich) produced anti-Ich antibodies and were partially protected (20% survival) in a previous study. Here we evaluated whether a higher dose or two doses of pcDNA3.1-IAg52b vaccine could provide better protection for catfish against Ich. Fish were distributed into 6 groups and vaccinated using following schemes: 1.10 μ g pcDNA3.1-IAg52b fish−1, 2.20 μ g pcDNA3.1-IAg52b fish−1, 3. two doses of 10 μ g pcDNA3.1-IAg52b fish−1 with 7 days between doses, 4.20 μ g pcDNA3.1 fish−1 (mock-vaccinated control), 5.15,000 live theronts fish−1 (positive control), and 6. non-vaccinated and non-challenge control. Parasite infection levels, serum anti-Ich antibody levels, fish mortality and immune-related gene expression were determined during the trial. Fish vaccinated with a single dose of 20 μ g pcDNA3.1-IAg52b fish−1 or two doses of 10 μ g fish−1 had higher anti-Ich antibody levels than fish receiving a single dose of 10 μ g fish−1. Survival was significantly higher in fish receiving 20 μ g vaccine fish−1 (35.6%) or 2 doses of 10 μ g fish−1 (48.9%) than fish injected with a single dose of 10 μ g fish−1 (15.6%) or mock-vaccinated control (0%). Fish vaccinated at the dose 20 μ g fish−1 had higher expression of vaccine DNA in muscle than fish vaccinated with 10 μ g fish−1. Fish vaccinated with the DNA vaccine showed higher up-regulation than mock-vaccinated control in the expression of IgM, CD4, MHC I and TcR-α genes during most of time points after vaccination. Further studies are needed to improve efficacy of DNA vaccines by using multiple antigens in the DNA vaccines. • Vaccinated fish showed higher anti-Ich antibody and survival than control fish. • Fish had higher vaccine DNA expression when vaccinated 20 μ g than 10 μ g per fish. • Fish had higher survival when received 20 μ g DNA vaccine than 10 μ g per fish. • Fish vaccinated with DNA vaccines increased immune gene expression. [ABSTRACT FROM AUTHOR]

MiR-155 is reported as immune regulated miRNA in mammalian corresponding to immunity, antibacterial and antiviral effects regulation. However, the roles and mechanisms of the miRNA have remained largely undefined. We herein comprehensively investigated the functions of miR-155 in vitro and in vivo by miR-155 mimics, agomir and antagomir in Cyprinus carpio and Ictalurus punctatus , with the target genes in the SOSC1 pathway certified in I. punctatus via luciferase reporter assays. Results showed that the miR-155 regulated the expressions of cytokines, including TNF-α, IFN-γ, IL-1β, IL-6 and IL-10. Further research confirmed SOSC1 as one of the targets of the miRNA, and the JAK1/STAT3/SOSC1 signal pathway involved in the miR-155 effects on the expression of immune cytokines as well. Additionally, the changes of TLR2 in fish may also be related to miR-155 along with its target SOCS1, and the TLR2/MyD88 pathway may partly participate in the effects of the miR-155 on the cytokines. The research here confirmed that the miR-155 can regulate cytokines expression by SOSC1 signal pathways of fish in vitro and in vivo, which would provide resources for understanding and studying about immune regulation in fish. • Firstly investigated the immune functions of miR-155 of fish in vitro and in vivo. • Proved the miR-155 regulating immune cytokines expressions in different fishes. • Certified the SOSC1 as the target of miR-155 by Luciferase reporter assay. • Certified JAK1/STAT3/SOSC1 pathway being involved in the miR-155 immune effects. • Certified TLR2/MyD88 pathway being correlated to the immune effects of miR-155. [ABSTRACT FROM AUTHOR]

Channel catfish (Ictalurus punctatus) is an important aquaculture species in China. In channel catfish, diseases such as haemorrhagic, sepsis and tail-rot disease are all caused by bacteria as general in China. Most of the pathogenic bacteria are Gram-negative bacteria. Liver transcriptome analysis of the co-injection of cortisol and lipopolysaccharide (LPS) was performed in this study. Preliminary evidence from the results suggest that after the emergence of immune stress, cortisol will up-regulate the complement cascade pathway, down-regulate the coagulation cascade pathway, down-regulate the platelet activation pathway, down-regulate antigen presentation pathway, and show complex regulation relationship to inflammatory factors. At 12 h, the number of differential genes regulated by cortisol was about half less than the number of differential genes regulated by LPS. At 24 h, there was no significant difference between the number of differential genes regulated by cortisol and LPS, but the types of differential genes vary widely. KEGG enrichment analysis found that cortisol regulated LPS-stimulated immune responses mainly focus on cytokines, complement and coagulation cascades pathways, antigen presentation pathways, haematopoiesis, and inflammation. It is suggested that there may be some strategic choice in the regulation of immune response by cortisol. These results will help understand the pathogenesis and host defence system in bacterial disease caused by Gram-negative bacteria. • Liver of channel catfish (Ictalurus punctatus) transcriptome test was used to study the regulation of LPS-induced immune response by cortisol. • Cortisol regulates immune responses of LPS-stimulated mainly focus on cytokines, complement and coagulation cascades pathway, antigen presentation pathways, haematopoiesis, and inflammation. • Cortisol upregulates the complement alternative pathway at 12 h and negatively regulates it at 24 h. • After the immune stress, the regulation of cortisol on immune response maybe choose different regulation strategies over time. [ABSTRACT FROM AUTHOR]

To determine the role of piscine anti-viral cytotoxic cells, we analyzed the response of channel catfish to Ictalurid herpesvirus 1 , commonly designated channel catfish virus (CCV). Peripheral blood leukocytes (PBL) from catfish immunized with MHC-matched, CCV-infected G14D cells (G14D-CCV) showed marked lysis of G14D-CCV but little to no lysis of uninfected allogenic (3B11) or syngeneic (G14D) cells. Expansion of effectors by in vitro culture in the presence of irradiated G14D-CCV cells generated cultures with enhanced cytotoxicity and often broader target range. Cytotoxic effectors expressed rearranged TCR genes, perforin, granzyme, and IFN-γ. Four clonal cytotoxic lines were developed and unique TCR gene rearrangements including γδ were detected. Furthermore, catfish CTL clones were either CD4+/CD8- or CD4-/CD8-. Two CTL lines showed markedly enhanced killing of G14D-CCV targets, while the other two lines displayed a broader target range. Collectively, catfish virus-specific CTL display unique features that illustrate the diversity of the ectothermic vertebrate immune response. • Teleost anti-viral cytotoxic T cells are heterogeneous. • Four catfish anti-viral clonal cytotoxic T cell lines were established. • Two cell lines preferentially lysed channel catfish virus-infected syngeneic targets. • One clonal γδ T cell line exhibits broad target cell recognition. • None of these T cell lines expressed CD8, however three expressed CD4-like molecules. [ABSTRACT FROM AUTHOR]

In this study, we identified a fish-specific Toll-like receptor (TLR) in Pelteobagrus fulvidraco , an economically important freshwater fish in China. This TLR, Pf TLR26, was shown to be encoded by a 3084 bp open reading frame (ORF), producing a polypeptide 1027 amino acids in length. The Pf TLR26 protein contains a signal peptide, eight leucine-rich repeat (LRR) domains, two LRR_TYP domains in the extracellular region, and a Toll/interleukin (IL)-1 receptor (TIR) domain in the cytoplasmic region, consistent with the characteristic TLR domain architecture. This predicted 117.1 kDa protein was highly homologous to those of other fish, with phylogenetic analysis revealing the closest relation to TLR26 of Ictalurus punctatus. Real-time quantitative reverse transcription-PCR (qRT-PCR) analysis showed that the Pf TLR26 gene was expressed in all tissues tested, with the highest expression levels seen in the head kidney and blood, and the lowest seen in muscle. Pf TLR26 exhibited significant upregulation in liver, spleen, head kidney, and blood at different time points following challenge with the common TLR agonists lipopolysaccharide (LPS) and polyriboinosinic polyribocytidylic acid (Poly I:C). Taken together, these results suggest that Pf TLR26 may be an important component of the P. fulvidraco innate immune system, participating in the transduction of TLR signaling under pathogen stimulation. • A TLR26 gene was cloned from yellow catfish Pelteobagrus fulvidraco. • TLR26 mRNA levels were detected in a wide range of P. fulvidraco tissues. • The mRNA expression levels of PfTLR26 were up-regulated in response to Poly I:C or LPS challenge. [ABSTRACT FROM AUTHOR]

The channel catfish (Ictalurus punctatus) immune response against Ichthyophthirius multifiliis (Ich) after vaccination using plasmid DNA vaccines pcDNA3.1-IAg52a and pcDNA3.1-IAg52b, encoding Ich immobilization antigen genes was studied. Parasite infection level, serum anti-Ich antibodies level, fish mortality after theront challenge, and immune-related gene expression were measured. After in vitro transfection of walking catfish gill cells (G1b) with both pcDNA3.1-IAg52a and pcDNA3.1-IAg52b, antigens IAG52A and IAG52B were detected. During the vaccination trial, 76-fold increase in the Iag52b gene expression was observed in the vaccinated fish group h4 post vaccination. Administration of DNA vaccines by IM injection induced significant gene up-regulation in the head kidney, including immunoglobulin M (IgM), cluster of differentiation 4 (CD4), major histocompatibility I (MHC I), and T cell receptor α (TcR-α) from h4 to d5 post immunization. Fish vaccinated with DNA vaccines or theronts showed increased gene expression of the cytokine interferon (IFN-γ), complement component 3 (C3), and toll-like receptor-1 (TLR-1). Anti-Ich antibodies were detected in fish received pcDNA3.1-IAg52a, pcDNA3.1-IAg52b and the combination of both vaccines d10 post vaccination. Fish vaccinated with pcDNA3.1-IAg52b showed mild parasite infection level, partial survival (20%) and longer mean day to death (MDD) after theront challenge. By contrast, a heavy parasite load, 0% survival and short MDD were observed in the sham vaccinated control fish that received pcDNA3.1 (plasmid without genes encoding Ich immobilization antigen). Further research is needed to improve DNA vaccines for Ich that can induce strong protective immunity in fish. Suggested studies include improved transfection efficiency, use of appropriate adjuvants and including additional parasite antigen genes in the plasmid. [ABSTRACT FROM AUTHOR]

Channel catfish farming is the most important warm water aquaculture in the United States and is very important to the rural economy. This study's objective was to investigate the kinetics of the enzymatic hydrolysis of catfish by-product. Channel catfish (Ictalurus punctatus) by-products (heads and frames) were collected from local catfish processing plant. Papain, ficin, bromelain, neutrase, alcalase, protamex, novo-proD and thermolysin were used for hydrolysis. Proteolytic activities of those proteases were examined at different hydrolysis temperature, proteases cost for reaching certain degree of hydrolysis was predicted. Degree of hydrolysis (DH) of the hydrolysates and hydrolysis kinetics were studied. Emulsifying and foaming property and stability of selected hydrolysates were evaluated. Results indicated that thermolysin had the highest activity (8.2 × 108 Azocoll U/g and 5.6 × 106 Azocasein U/g) at 70 °C. The highest DH of the hydrolysates were observed in 120 min with the concentration of 80 AzU/g for all enzymes. Ficin (80 AzU/g) was the most efficient in hydrolyzing the by-product (DH reaching 71%) in 120 min at 30 °C. The hydrolysis curves fit the Peleg model well with R2 higher than 0.91. This study provides important engineering information for choosing proteases and processing conditions for optimization of efficiency, yield and economy. • Channel catfish processing by-product was hydrolyzed by 8 proteases. • Protease reaction kinetics showed ficin was the most efficient to hydrolyze catfish proteins. • Proteins and peptide pattern changes upon hydrolysis were quantitated by electrophoresis. • Thermolysin showed the least costly to reach a certain DH level as predicted according to the kinetic models. [ABSTRACT FROM AUTHOR]

Columnaris disease has long been recognized as a serious problem worldwide which affects both wild and cultured freshwater fish including the commercially important channel catfish (Ictalurus punctatus). The fundamental molecular mechanisms of the host immune response to the causative agent Flavobacterium columnare remain unclear, though gene expression analysis after the bacterial infection has been conducted. Alternative splicing, a post-transcriptional regulation process to modulate gene expression and increase the proteomic diversity, has not yet been studied in channel catfish following infection with F. columnare. In this study, genomic information and RNA-Seq datasets of channel catfish were used to characterize the changes of alternative splicing after the infection. Alternative splicing was shown to be induced by F. columnare infection, with 8.0% increase in alternative splicing event at early infection stage. Intriguingly, genes involved in RNA binding and RNA splicing themselves were significantly enriched in differentially alternatively spliced (DAS) gene sets after infection. This finding was consistent with our previous study in channel catfish following infection with Edwardsiella ictaluri. It was suggested to be a universal mechanism that genes involved in RNA binding and splicing were regulated to undergo differential alternative splicing after stresses in channel catfish. Moreover, many immune genes were observed to be differentially alternatively spliced after infection. Further studies need to be performed to get a deeper view of molecular regulation on alternative splicing after stresses, setting a foundation for developing catfish broodstocks with enhanced disease resistance. • Infected with F. columnare in channel catfish, alternative splicing events increased quickly then declined to normal level. • Shared DAS genes were observed at different stages by comparing each post-infection group with the control. • Genes involved in RNA binding and RNA splicing were significantly enriched in DAS gene sets after infection. • Many immune genes were shown to be differentially alternatively spliced after infection. [ABSTRACT FROM AUTHOR]

• The channel catfish MC3R cDNA encoded a functional MC3R homologous to several teleost MC3Rs. • Channel catfish MC3R could bind agonists and initiate both cAMP and ERK1/2 signaling. • Channel catfish MC3R had high constitutive activities at both cAMP and ERK1/2 pathways. • AgRP was an inverse agonist decreasing the high basal cAMP level. • MRAP2 preferentially inhibited MC3R-mediated cAMP production rather than ERK1/2 activation. The melanocortin-3 receptor (MC3R) is known to be involved in regulation of energy homeostasis, regulating feed efficiency and nutrient partitioning in mammals. Its physiological roles in non-mammalian vertebrates, especially economically important aquaculture species, are not well understood. Channel catfish (Ictalurus punctatus) is the main freshwater aquaculture species in North America. In this study, we characterized the channel catfish MC3R. The mc3r of channel catfish encoded a putative protein (ipMC3R) of 367 amino acids. We transfected HEK293T cells with ipMC3R plasmid for functional studies. Five agonists, including adrenocorticotropin, α-melanocyte stimulating hormone (α-MSH), β-MSH, [Nle4, D-Phe7]-α-MSH, and D-Trp8-γ-MSH, were used in the pharmacological studies. Our results showed that ipMC3R bound β-MSH with higher affinity and D-Trp8-γ-MSH with lower affinity compared with human MC3R. All agonists could stimulate ipMC3R and increase intracellular cAMP production with sub-nanomolar potencies. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation could also be triggered by ipMC3R. The ipMC3R exhibited constitutive activities in both cAMP and ERK1/2 pathways, and Agouti-related protein served as an inverse agonist at ipMC3R, potently inhibiting the high basal cAMP level. Moreover, we showed that melanocortin receptor accessory protein 2 (MRAP2) preferentially modulated ipMC3R in cAMP production rather than ERK1/2 activation. Our study will assist further investigation of the physiological roles of the ipMC3R, especially in energy homeostasis, in channel catfish. [ABSTRACT FROM AUTHOR]

Abstract Channel catfish is one of the most extensively cultured species worldwide, which is widely used as a classical model for comparative immunology. Interleukin-1β (IL1β) is an immunoregulatory cytokine with the potential to enhance the immune response induced by vaccines in many animals. To characterize the molecular characterization and identify the immunoadjuvant role of channel catfish IL1β, molecular cloning, phylogenetic analysis, and expression of two IL1β genes were performed, the bioactivity of their recombinant proteins (rIL1β1 and rIL1β2) were detected in vitro and their adjuvant effects on a subunit vaccine encoding C5a peptidase (pSCPI) of Streptococcus iniae were evaluated. The results indicated that two IL1βs remained highly conserved possessing five conserved motifs compared with other fish IL1βs, although there were 28 nucleotide differences and 16 amino acid differences between channel catfish IL1β1 and IL1β2. Analysis of the ratios of nonsynonymous (dN) and synonymous (dS) substitutions revealed that fish IL1β genes were subjected to negative/purifying selection with global dN/dS ratios value 0.425. The results of adjuvant effect showed that compared with injection of pSCPI alone, co-injecting pSCPI with both rIL1β1 and rIL1β2 significantly enhanced antibody levels, serum bactericidal activity, lysozyme activity, alternative complement hemolytic activity, and the expression of endogenous IL1β and TNF-α in head kidney and spleen. Although vaccination with rIL1β1 or rIL1β2 failed to offer immunoprotection against S. iniae infection, the RPS (relative percent survival) of pSCPI+rIL1β1 and pSCPI+rIL1β2 groups were both higher than pSCPI alone (RPS, 50%), with 64.26% and 60.71%, respectively. Moreover, pSCPI+rIL1β1+rIL1β2 offered significantly higher (P < 0.05) immunoprotection (RPS, 75%) against S. iniae infection than pSCPI alone. Our present results not only enrich the molecular structure study of fish IL1βs but also signify that two recombinant channel catfish IL1βs can be used as potential adjuvants in a subunit vaccine model against bacterial infection, which are of profound importance to prevent and control bacterial disease in channel catfish. Highlights • Fish IL1βs were subjected to negative/purifying selection throughout the evolution. • Channel catfish IL1βs were highly conserved with five conserved motifs. • Channel catfish IL1βs can be used as molecular adjuvants in subunit vaccine model. • rIL1β1 as adjuvant was slightly better than rIL1β2 to enhance the immune response. • Co-injection of rIL1β1+rIL1β2 induced higher immune response and immunoprotection. [ABSTRACT FROM AUTHOR]

Abstract Motile Aeromonas septicemia (MAS), caused by new virulent Aeromonas hydrophila (vAh) strains, has been one of the major diseases in channel catfish in recent years. Previous studies showed that channel catfish developed immunity against vAh infection after immunization with the pathogen's extracellular proteins (ECP). To understand the mechanisms associated with the immunity, anti-ECP fish serum (antiserum) was analyzed in this study. Our results revealed that the antiserum elicited agglutination of both ECP and cells of vAh. Five fish proteins were identified in ECP agglutinants, including two innate immunity associated proteins (serotransferrin and rhamnose-binding lectin), two immunoglobulin M (IgM) molecules (IgM heavy chain and light chain) and a constitutively-produced protein (warm temperature acclimation protein). More than 68 vAh proteins in ECP were recognized and caused to aggregate by IgM in the antiserum. IgM was isolated from vAh cell agglutinants and the native IgM was shown to form a tetramer that was responsible for bacterial agglutination. Immunoblotting analysis indicated that the isolated native IgM was able to recognize some proteins in ECP, such as aerolysin and hemolysin (in the form of a high molecular weight heterologous polymer). Gene expression analysis by quantitative PCR showed that fish immunized with vAh ECP had more transcripts of genes coding for IgM, serotransferrin and rhamnose binding lectin than mock-immunized fish. Both innate and antibody-mediated immune responses in serum and expressed genes contributed to fish immunity upon immunization with ECP. Results of this study shed light on the versatility of vAh antigens and catfish IgM, which would help identify specific antigens for vaccine development and antigen specific antibodies in catfish. Highlights • Immunization with extracellular proteins (ECP) of virulent Aeromonas hydrophila (vAh) provides channel catfish with immunity • Anti-ECP serum elicited agglutination of both ECP and cells of vAh. • Analysis of agglutinants revealed the diversity and versatility of IgM in the anti-ECP serum. • Both innate and antibody-mediated immune responses in serum and expressed genes contributed to fish immunity. [ABSTRACT FROM AUTHOR]

Columnaris disease continues to inflict substantial losses among freshwater cultured species since its first description one hundred years ago. The experimental and anecdotal evidence suggests an expanded range and rising virulence of columnaris worldwide due to the warming global climate. The channel catfish (Ictalurus punctatus) are particularly vulnerable to columnaris. A recently developed live attenuated vaccine (17–23) for Flavobacterium columnare (now Flavobacterium covae sp. nov.) demonstrated superior protection for vaccinated catfish against genetically diverse columnaris isolates. In this study, we aimed to elucidate the molecular mechanisms and patterns of immune evasion and host manipulation linked to virulence by comparing gene expression changes in the host after the challenge with a virulent (BGSF-27) or live attenuated F. covae sp. nov. vaccine (17–23). Thirty-day-old fry were accordingly challenged with either virulent or vaccine isolates. Gill tissues were collected at 0 h (control), 1 h, and 2 h post-infection, which are two critical time points in early host-pathogen interactions. Transcriptome profiling of the gill tissues revealed a larger number (518) of differentially expressed genes (DEGs) in vaccine-exposed fish than those exposed to the virulent pathogen (321). Pathway analyses suggested potent suppression of early host immune responses by the virulent isolate through a higher expression of nuclear receptor corepressors (NCoR) responsible for antagonizing macrophage and T-cell signaling. Conversely, in vaccinated fry, we observed induction of Ca2+/calmodulin-dependent protein kinase II (CAMKII), responsible for clearing NCoR, and commensurate up-regulation of transcription factor AP-1 subunits, c-Fos, and c-Jun. As in mammalian systems, AP-1 expression was connected with a broad immune activation in vaccinated fry, including induction of CC chemokines, proteinases, iNOS, and IL-12b. Relatedly, divergent expression patterns of Src tyrosine kinase Lck, CD44, and CD28 indicated a delay or suppression of T-cell adhesion and activation in fry exposed to the virulent isolate. Broader implications of these findings will be discussed. The transcriptomic differences between virulent and attenuated bacteria may offer insights into how the host responds to the vaccination or infection and provide valuable knowledge to understand the early immune mechanisms of columnaris disease in aquaculture. • Gene expression divergence in catfish to virulent and vaccine isolates of columnaris. • NCoR gene upregulation induces host immune suppression by virulent isolate. • CAMKII and AP-1 gene induction associated with immune activation in vaccinated fish. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework-8 (ZIF-8) nanoparticles loaded with polysaccharides are excellent drug-delivery carriers with high loading capacity and pH sensitivity. This study describes the one-step encapsulation of Dendrobium huoshanense polysaccharides (DHP) in ZIF-8. The resultant PEG6000/ZIF-8@DHP complex exhibited drug release properties in acidic microenvironments, possessed water solubility, demonstrated high drug loading capacity, and displayed effective encapsulation. The effects of PEG6000/ZIF-8@ DHP administration on immunoregulation, antioxidant activities, and resistance against Aeromonas veronii in channel catfish were assessed. The study revealed that the PEG6000/ZIF-8@DHP complex stimulated cellular proliferation and phagocytosis, while also inducing the production of cytokines and nitric oxide. Additionally, the complex exhibited improved antioxidant properties and increased serum lysozyme and alkaline phosphatase activities. PEG6000/ZIF-8@DHP exhibited efficacy in vivo against Aeromonas veronii infection. These results indicate that PEG6000/ZIF-8@DHP is an efficient immunostimulant and vaccine adjuvant for enhancing immunity in channel catfish. • Isolation, purification and identification of novel polysaccharides from Dendrobium. • PEG6000/ZIF-8@DHP significantly enhanced macrophage activity .... • PEG6000/ZIF-8@DHP induced the secretion of IgG and Th-associated cytokines. • PEG6000/ZIF-8@DHP could as a vaccine applicated in clinical practice. [ABSTRACT FROM AUTHOR]

Abstract IgM transcripts from different mucosal and systemic tissues from a single adult channel catfish have been evaluated. Arrayed heavy chain cDNA libraries from each of these different mucosal and systemic tissues were separately constructed, hybridized with VH family specific probes and a variety of approaches were used to define their structural relationships. Baseline hybridization studies indicated that the tissue libraries had different VH expression patterns, and sequencing studies indicated this was not simply due to varying proportions of the same B cell population. In the systemic tissues of PBL, spleen, and anterior kidney >95% of the sequenced clones in the arrayed libraries represented different heavy chain rearrangements. Diversity was also found in the mucosal libraries of skin, gill lamellae, and two non-adjoining regions of the intestine, but additional populations were identified which indicated localized clonal expansion. Various clonal sets were characterized in detail, and their genealogies indicated somatic mutation accompanied localized clonal expansion with some members undergoing additional mutations and expansion after migration to different mucosal sites. PCR analyses indicated these mucosal clonal sets were more abundant within different mucosal tissues rather than in the systemic tissues. These studies indicate that the mucosal immune system in fish can express B cell transcripts differently from those found systemically. These studies further indicate that the mucosal immune system is interconnected with clonal B cells migrating between different mucosal tissues, results which yield new insight into immune diversity in early vertebrate phylogeny. Highlights • IgM transcripts from catfish show different B cell populations in tissues. • Clonal B cells reveal that somatic mutation accompanied localized clonal expansion. • Mucosal B cell transcripts can be expressed differently from that found systemically. [ABSTRACT FROM AUTHOR]

Abstract Affinity maturation of the antibody response, a process of antibody affinity increasing over response, is one of the key features of the mammalian immune system. However, the process is incompletely understood in teleost, including channel catfish (Ictalurus punctaus). In this study, IgM affinity maturation in channel catfish was investigated by estimating the kinetics of antibody affinity using ELISA and ELISPOT assays. Fish were immunized with a T-cell dependent antigen (TNP-KLH), and individual serum IgM antibody titers and affinities, and IgM+ antibody-secreting cells (ASCs) in peripheral blood were analyzed over a period of 14 weeks. A detectable serum anti-TNP response developed by 2-weeks post-immunization, and the maximal antibody production was observed by 6-weeks post-immunization. The average affinity of anti-TNP serum antibody increased consistently and reached the maximum by 10-weeks post-immunization. The increase of antibody affinity beyond the point of optimal antibody titer revealed that the affinity maturation of IgM antibody response occurred in channel catfish. Dissection of dynamics of individual affinity subpopulations indicated that a significant proportion of low affinity subpopulations appeared at early response, and high affinity subpopulations appeared predominantly at later, resulting in a 100-fold increase in affinity over response. Additional, TNP+ IgM+ ASCs was detected by 2-weeks post-immunization and achieved the maximal number by 6-weeks post-immunization. Using an inhibition ELISPOT assay, the findings of a consistent increase in the average affinity of secreted IgM antibody by peripheral blood ASCs, as the immune response progressed, confirmed the occurrence of the affinity maturation. Taken together, the results of this study indicated that affinity maturation occurred in channel catfish following immunization with a TD antigen TNP-KLH. Highlights • Anti-TNP specific IgM antibody titer and antibody-secreting cells reached the peak at week 6 post-immunization. • TNP-specific IgM antibody affinity achieved the maximum at week 10 post-immunization. • Affinity maturation of IgM response occurred in channel catfish following immunization with TNP-KLH. [ABSTRACT FROM AUTHOR]

Herein, the effects of Agaricus bisporus Polysaccharides (ABPs) on anti-channel catfish virus (CCV) infections to promote their application in channel catfish culture were explored. Transcriptome and metabolome analyses were conducted on the spleen of a CCV-infected channel catfish model fed with or without ABPs. CCV infections upregulated many immune and apoptosis-related genes, such as IL-6 , IFN-α3 , IFN-γ1 , IL-26 , Casp3 , Casp8 , and IL-10 , and activated specific immunity mediated by B cells. However, after adding ABPs, the expression of inflammation-related genes decreased in CCV-infected channel catfish, and the inflammatory inhibitors NLRC3 were upregulated. Meanwhile, the expression of apoptosis-related genes was reduced, indicating that ABPs can more rapidly and strongly enhance the immunity of channel catfish to resist viral infection. Moreover, the metabonomic analysis showed that channel catfish had a high energy requirement during CCV infection, and ABPs could enhance the immune function of channel catfish. In conclusion, ABPs can enhance the antiviral ability of channel catfish by enhancing immune response and regulating inflammation. Thus, these findings provided new insights into the antiviral response effects of ABPs, which might support their application in aquaculture. • ABPs enhance immune responses in ictalurus punctatus. • ABPs can inhibit the harmful inflammatory reaction in CCV infection. • ABPs improve the anti-CCV ability of channel catfish. [ABSTRACT FROM AUTHOR]

To promote the application of Agaricus bisporus polysaccharides (ABPs) in channel catfish (Ictalurus punctatus) culture, we evaluated the effects of ABPs on the growth, immunity, antioxidant, and antibacterial activity of channel catfish. When the amount of ABPs was 250 mg/kg, channel catfish's weight gain and specific growth rates increased significantly while the feed coefficient decreased. We also found that adding ABPs in the feed effectively increased the activities of ACP, MDA, T-SOD, AKP, T-AOC, GSH, and CAT enzymes and immune-related genes such as IL-1β, Hsp70, and IgM in the head kidney of channel catfish. Besides, long-term addition will not cause pathological damage to the head kidney. When the amount of ABPs was over 125 mg/kg, the protection rate of channel catfish was more than 60%. According to the intestinal transcriptome analysis, the addition of ABPs promoted the expression of intestinal immunity genes and growth metabolism-related genes and enriched multiple related KEEG pathways. When challenged by Yersinia ruckeri infection, the immune response of channel catfish fed with ABPs was intenser and quicker. Additionally, the 16S rRNA gene sequencing analysis showed that the composition of the intestinal microbial community of channel catfish treated with ABPs significantly changed, and the abundance of microorganisms beneficial to channel catfish growth, such as Firmicutes and Bacteroidota increased. In conclusion, feeding channel catfish with ABPs promoted growth, enhanced immunity and antioxidant, and improved resistance to bacterial infections. Our current results might promote the use of ABPs in channel catfish and even other aquacultured fish species. • ABPs can increase the weight gain rate and specific growth rate of channel catfish, and reduce its feed coefficient. • ABPs can enhance the ability of channel catfish to resist bacterial infection. • Long term use of ABPs will not cause pathological loss to channel catfish. [ABSTRACT FROM AUTHOR]

A recently developed attenuated vaccine for Flavobacterium columnare has been demonstrated to provide superior protection for channel catfish, Ictalurus punctatus , against genetically diverse columnaris isolates. We were interested in examining the mechanisms of this protection by comparing transcriptional responses to F. columnare challenge in vaccinated and unvaccinated juvenile catfish. Accordingly, 58 day old fingerling catfish (28 days post-vaccination or unvaccinated control) were challenged with a highly virulent F. columnare isolate (BGSF-27) and gill tissues collected pre-challenge (0 h), and 1 h and 2 h post infection, time points previously demonstrated to be critical in early host-pathogen interactions. Following RNA-sequencing and transcriptome assembly, differential expression (DE) analysis within and between treatments revealed several patterns and pathways potentially underlying improved survival of vaccinated fish. Most striking was a pattern of dramatically higher basal expression of an array of neuropeptides (e.g. somatostatin), hormones, complement factors, and proteases at 0 h in vaccinated fish. Previous studies indicate these are likely the preformed mediators of neuroendocrine cells and/or eosinophilic granular (mast-like) cells within the fish gill. Following challenge, these elements fell to almost undetectable levels (>100-fold downregulated) by 1 h in vaccinated fish, suggesting their rapid release and/or cessation of synthesis following degranulation. Concomitantly, levels of pro-inflammatory cytokines (IL-1b, IL-8, IL-17) were induced in unvaccinated fish. In contrast, in vaccinated catfish, we observed widespread induction of genes needed for collagen deposition and tissue remodeling. Taken together, our results indicate an important component of vaccine protection in fish mucosal tissues may be the sensitization, proliferation and arming of resident secretory cells in the period between primary and secondary challenge. [ABSTRACT FROM AUTHOR]

The channel catfish virus (CCV) can cause lethal hemorrhagic infection in juvenile channel catfish, thereby resulting in a huge economic loss to the fish industry. The genome of the CCV has been fully sequenced, and its prevalence is well documented. However, less is known about the molecular mechanisms and pathogenesis of the CCV. Herein, the channel catfish ovary cells (CCO) were infected with CCV and their transcriptomic sketches were analyzed using an RNA sequencing technique. In total, 72,686,438 clean reads were obtained from 73,231,128 sequence reads, which were further grouped into 747,168 contigs. These contigs were assembled into 49,119 unigenes, of which 20,912 and 18,333 unigenes were found in Nr and SwissProt databases and matched 15,911 and 14,625 distinctive proteins, respectively. From these, 3641 differentially expressed genes (DEGs), comprising 260 up-regulated and 3381 down-regulated genes, were found compared with the control (non-infected) cells. For verification, 16 DEGs were analyzed using qRT-PCR. The analysis of the DEGs and their related cellular signaling pathways revealed a substantial number of DEGs that were involved in the apoptosis pathway induced by CCV infection. The apoptosis pathways were further elucidated using standard apoptosis assays. The results showed that CCV could induce extrinsic apoptosis pathway (instead of a mitochondrial intrinsic apoptosis pathway) in CCO cells. This study helps our understanding of the pathogenesis of CCV and contributes to the prevention of CCV infection in channel catfish. [ABSTRACT FROM AUTHOR]

Bath immersion remains a practical route for immunizing against disease in channel catfish; however research efforts in this area have revealed variable results when activating mucosal Ab responses with different antigens. This is likely due to a number of factors including the individual species, age of the fish, preparation of the immunogens, and differences in the overall dosage and the duration of exposure to vaccines. The current study sought to evaluate the effect of water temperature on the in vivo mucosal adaptive immune response in channel catfish to a protein-hapten antigen, DNP-KLH. Fish were bath immersed at different water temperatures and periodically evaluated over an eighteen week period for the development of serum and mucosal IgM antibodies to DNP-KLH using an indirect enzyme-linked immunosorbent assay. None of the temperature groups produced a serum antibody response; however there were detectable DNP-KLH specific IgM antibodies in the mucus starting at week eight. The extent of the mucosal antibody response and duration differed between the treatments. Our results show that there are intrinsic differences in the capacity to generate in vivo mucosal Ab responses in the skin at different water temperatures and the implications of these findings to channel catfish farming will be discussed. [ABSTRACT FROM AUTHOR]

Ichthyophthiriasis caused by Ichthyophthirius multifiliis (Ich) has a worldwide distribution and affects most freshwater fishes. Fish surviving natural infection and/or immunized with Ich develop strong innate and adaptive immune responses. However, there is a lack of the knowledge regarding immune gene expression patterns in systemic and mucosal immune tissues, and how immune genes interact and lead to innate and adaptive immune protection against Ich infection in fish. The objective of this study was to investigate the expression of innate and adaptive immune-related genes in systemic (liver, spleen) and mucosal (gill, intestine) tissues of channel catfish over time following vaccination with live Ich theronts. The vaccinated fish showed significantly higher antibody titers and survival (95%) than those of mock immunized fish. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 h (h4) to 2 days (d2) post-vaccination in systemic immune tissues. Immune cell receptor genes (CD4, CD8-α, MHC I, MHC II β, TcR-α, and TcR-β) were more highly upregulated and remained upregulated for longer duration in systemic tissues than in mucosal tissues of the vaccinated fish. The cytokine genes IL-1βa and IFN-γ were rapidly upregulated in both systemic and mucosal tissues of vaccinated fish, with peak expression from h4 to d1 post-vaccination. Toll-like receptor genes TLR-1 and TLR-9 showed relatively stable upregulation in the gill of immunized fish following vaccination. Results of this study revealed the molecular immune responses in mucosal and systemic tissues of vaccinated fish and demonstrated that Ich vaccination resulted in innate and adaptive immune responses against Ich infection. [ABSTRACT FROM AUTHOR]

Under oxidative stress condition, the protective effects of dietary chlorogenic acid (CGA) supplementation on liver antioxidant capacity, intestinal inflammation and barrier function, muscle development and skin coloration in channel catfish Ictalurus punctatus were explored in the current study. With that purpose, I. punctatus were fed five experimental diets containing 2% fresh fish oil (FFO, 9.2 meqO 2 /kg) or 2% oxidized fish oil (OFO, 897.4 meqO 2 /kg) without or with CGA supplementation (0.02%, 0.04% and 0.08%) for 8 weeks. Upon comparative analysis, the oxidized fish oil consumption significantly lowered weight gain rate, decreased intestinal villi length and muscular thickness values and the tight junction proteins mRNA abundance, augmented the intestinal proinflammatory factors, attenuated hepatic antioxidant enzymes activities and related genes mRNA expression levels, influenced the myogenic regulatory factors expression profile and impacted the myocyte density, myocyte area values as well as the skin pigments contents compared to the FFO treatment. Collectively, long-term feeding of the oxidized fish oil diet suppressed the growth performance, destroyed intestinal structural integrity, caused intestinal inflammation and hepatic oxidative stress, impacted the skeletal development and skin color of I. punctatus. Whereas CGA supplementation in oxidized fish oil diets partially counteracted the negative effects of the oxidized fish oil on I. punctatus in terms of increasing the growth performance, improving the intestinal mucosal structure, alleviating hepatic oxidative stress and intestinal inflammation, recompiling the myogenic regulatory factors expression and improving skin color. In conclusion, CGA has great potential to be an aquatic feed additive. • Oxidized fish oil suppressed growth, destroyed intestinal structural integrity, attenuated liver antioxidant capacity. • Long-term feeding of the oxidized fish oil diet impacted the skeletal growth and development and skin color of Ictalurus punctatus. • CGA supplementation partially counteracted the negative effects of oxidized fish oil on Ictalurus punctatus. [ABSTRACT FROM AUTHOR]

Interactions between host and pathogen are involving various dynamic changes in transcript expression and critical for understanding host immunity against infections and its associated pathogenesis. Herein, we established a model of channel catfish infected with Aeromonas veronii. The infected fish had prominent body surface bleeding, and the spleen showed hyperemia and swelling. Then, the spleen of channel catfish infected with A. veronii was analyzed by dual RNA sequencing (RNA-seq), and the transcriptome data were compared with uninfected channel catfish spleen or bacteria cultured in vitro. The transcript expression profile of pathogen-host interaction between A. veronii and channel catfish was successfully studied. During infection, the host was enriched for multiple immune-related signaling pathways, such as the Toll-like receptor signaling pathway, Cytokine-cytokine receptor interaction, and T cell receptor signaling pathway; and significantly upregulated for many innate immune-related genes, including IL-8. At the same time, we found that A. veronii mainly harmed the host spleen through hemolysin. Our current findings are of great significance in clarifying the pathogenesis of channel catfish induced by A. veronii and provide gene targets for developing preventive measures. • A. veronii can not only activate the non-specific immunity of channel catfish, but also activate the specific immunity. • A. veronii mainly depends on hemolysin D to cause channel catfish disease. • The interaction between pathogen and host needs a lot of energy. [ABSTRACT FROM AUTHOR]

Flavobacterium columnare is the causative agent of columnaris disease and causes tremendous morbidity and mortality of farmed fish globally. Previously, we identified a potential lectin-mediator (a rhamnose-binding lectin; RBL1a) of F. columnare adhesion and showed higher RBL1a expression in susceptible channel catfish under basal conditions and following infection. Exposure of challenged fish to the carbohydrate ligand l -rhamnose just prior to a challenge substantially decreased columnaris mortality and pathogen adherence via the down-regulation of RBL1a. While highly effective in protecting fish from columnaris, l -rhamnose is prohibitively expensive, underscoring the need for alternative cost-effective sources of rhamnose for disease control. One such alternative may be microbially produced glycolipid compounds termed rhamnolipids (RLs), which feature abundant l -rhamnose moieties and are readily available from commercial sources. In the present study, we examined whether commercially available RLs (administered either by immersion or via feed) would function similarly to l -rhamnose in affording host protection against F. columnare . A four-week feeding trial with basal and RL top-coated diets (basal diet + RLs) was conducted in channel catfish fingerlings. Surprisingly, columnaris challenges revealed significantly lower survival following the 10 d challenge period in RL diet fed fish when compared with the basal treatment group ( p < 0.001). In fish fed RLs, we observed a rapid and large-scale upregulation of RBL1a immediately after challenge combined with a suppression of mucin and lysozyme transcripts. Similarly, fish that were briefly pre-exposed to RLs by immersion and then challenged exhibited lower survival as compared to unexposed fish during a 4 d trial. In conclusion, RLs do not represent an alternative to rhamnose as an experimental treatment for protecting catfish from columnaris mortality. Further research is needed to find other affordable and efficacious alternative sources of l -rhamnose. [ABSTRACT FROM AUTHOR]

Dendritic cells (DCs) are the most powerful antigen presenting cells (APCs) that have a critical role in bridging innate and adaptive immune responses in vertebrates. Dendritic cells have been characterized morphologically and functionally in the teleost fish models such as rainbow trout, salmonids, medaka, and zebrafish. The presence of DCs with remarkable similarities to human Langerhans cells (LCs) has been described in the spleen and anterior kidney of salmonids and rainbow trout. However, there is no evidence of the presence of DCs and their role in channel catfish immunity. In this study, we assessed DC-like cells in the immunocompetent tissues of channel catfish by immunohistochemistry (IHC), flow cytometry and transmission electron microscopy (TEM). We identified Langerin/CD207 + (L/CD207 + ) cells in the channel catfish anterior kidney, spleen and gill by IHC. Moreover, we described the cells that resembled mammal LC DCs containing Birbeck-like (BL) granules in channel catfish spleen, anterior and posterior kidneys and gill by TEM. Our data suggest that cells with DC-like morphology in the immune related organs of catfish may share morphological and functional properties with previously reported DCs in teleost fish and mammals. More detailed knowledge of the phenotype and the function of catfish DCs will not only help gain insight into the evolution of the vertebrate adaptive immune system but will also provide valuable information for development and optimization of immunotherapies and vaccination protocols for aquaculture use. [ABSTRACT FROM AUTHOR]

Edwardsiella ictaluri is a Gram-negative facultative intracellular pathogen causing enteric septicemia in fish, particularly in channel catfish. Ferric iron is an essential micronutrient for bacterial survival, and some bacterial pathogens use secreted hydroxamate-type siderophores to chelate iron in host tissues. Siderophore-iron complexes are taken up by these bacteria via the ferric hydroxamate uptake (Fhu) system. In E. ictaluri , the Fhu system consists of fhuC , fhuD , fhuB , and fhuA genes. However, the importance of the Fhu system in E. ictaluri virulence has not been investigated completely. Here, we present construction of E. ictaluri fhuD and fhuB mutants ( Ei Δ fhuD and Ei Δ fhuB ) by in-frame gene deletion and evaluation of the mutants' virulence and immunogenicity in channel catfish fingerlings and fry. Immersion challenges showed that Ei Δ fhuD was not significantly attenuated ( p < 0.05) in catfish fingerlings, whereas Ei Δ fhuB was significantly attenuated ( p < 0.01). Catfish fingerlings immunized with Ei Δ fhuD and Ei Δ fhuB showed 100% and 97.62% survival, respectively. Fry immersion challenges indicated Ei Δ fhuB was also significantly attenuated ( p < 0.05) in two-week old fry compared to the wild-type (48.96% vs. 82.14% mortalities). The survival rate in the fry vaccinated with Ei Δ fhuB was significantly higher ( p < 0.05) than that of non-vaccinated fry (96.77% vs. 21.42% survival). Our data indicates that the fhuB gene, but not the fhuD gene, contributes to E. ictaluri virulence. [ABSTRACT FROM AUTHOR]

Channel catfish ( Ictalurus punctatus ) is an important agricultural fish that has been plagued by Stenotrophomonas maltophilia (S. maltophilia ) infections in recent years, some of them severe. The outer membrane proteins (OMPs) of S. maltophilia are one of the most immunogenic and highly conserved candidates for vaccine development in aquaculture. The present study investigated OMPs of S. maltophilia as vaccine on immune response and disease resistance against S. maltophilia of channel catfish and investigated the enhancement effect of natural adjuvants Propolis (Pro), FIG polysaccharide (Fcps), Glycyrrhizine (Gly) to OMPs of S. maltophilia for further study. The results indicated that channel catfish injected intraperitoneally with OMPs showed better immune response including leukocytes phagocytosis activity, serum bactericidal activity, complement C3, IgM level and an increasement of resistance against S. maltophilia compared to the control group. Moreover, Pro, Fcps and Gly could enhance the immune response of OMPs. The relative percent of survival (RPS) was 73.33%, 66.67%, 63.33%, 60%, 0% in fish injected OMPs + Pro, OMPs + Fcps, OMPs + Gly, OMPs and 0.65% normal saline, respectively. These results suggested that OMPs used as vaccine could induce and stimulate immune response and enhance disease resistance in channel catfish, especially for Pro as immunoenhancer. Results revealed that OMPs were an effective vaccine against S. maltophilia in channel catfish. [ABSTRACT FROM AUTHOR]

Mycotoxin contamination of agricultural commodities poses a serious risk to animal health, including aquaculture species. Ochratoxin A (OA) is the most immunotoxic ochratoxin, yet little is known about its effect on immune function in fish. Antimicrobial polypeptides (AMPPs) are one of the most potent, innate, host defense factors, yet very little is known about what types of chronic stressors affect their expression. Among the most prevalent and potent AMPPs in fish are histone-like proteins (HLPs). In this study, fish were fed 2, 4, or 8 mg OA/kg diet. Skin antibacterial activity and HLP-1 levels were measured on Days 0, 28 and 56. Feeding 2, 4 or 8 mg OA/kg diet resulted in significant growth depression, but higher levels (4 or 8 mg OA/kg diet) resulted in lowering feed intake (FI) and impaired feed conversion ratio. In addition, feeding 8 mg OA/kg diet increased susceptibility to experimental water mold ( Saprolegnia ) challenge, suggesting that OA toxicity might contribute to some saprolegnosis outbreaks. However, there were no changes in AMPP expression in any treatment group. Our data suggests that the increased disease susceptibility of channel catfish due to OA is probably due to mechanisms other than a direct effect on antimicrobial polypeptide expression. [ABSTRACT FROM AUTHOR]

The parasite Ichthyophthirius multifiliis (Ich) has been reported in various freshwater fishes worldwide and results in severe losses to both food and aquarium fish production. The fish surviving natural infections or immunized with live theronts develop strong specific and non-specific immune responses. Little is known about how these immune genes are induced or how they interact and lead to specific immunity against Ichthyophthirius multifiliis in channel catfish Ictalurus punctatus . This study evaluated the differential expression of immune-related genes, including immunoglobulin, immune cell receptor, cytokine, complement factor and toll-like receptors in head kidney from channel catfish at different time points after immunization with live theronts of I. multifiliis . The immunized fish showed significantly higher anti-Ich antibody expressed as immobilization titer and ELISA titer than those of control fish. The vast majority of immunized fish (95%) survived theront challenge. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 hour (h4) to 2 days (d2) post immunization. Expression of immune cell receptor genes (CD4, CD8-α, MHC I, MHC II β, TcR-α, and TcR-β) showed up-regulation from h4 to d6 post immunization, indicating that different immune cells were actively involved in cellular immune response. Cytokine gene expression (IL-1βa, IL-1βb, IFN-γ and TNF-α) increased rapidly at h4 post immunization and were at an up-regulated level until d2 compared to the bovine serum albumin control. Expression of complement factor and toll-like receptor genes exhibited a rapid increase from h4 to d2 post immunization. Results of this study demonstrated differential expression of genes involved in the specific or non-specific immune response post immunization and that the vaccination against Ich resulted in protection against infection by I. multifiliis . [ABSTRACT FROM AUTHOR]

Vaccination remains a viable alternative for bacterial disease protection in fish; however additional work is required to understand the mechanisms of adaptive immunity in the channel catfish. To assess the humoral immune response to Flavobacterium columnare ; a group of channel catfish were first immunized with F. columnare LV-359-01 cultured in iron-depleted media, before being challenged with wild type F. columnare LV-359-01. The immunization protocol did not confer increased protection against F. columnare ; however both control and immunized responders generated serum and skin IgM antibodies against F. columnare proteins. Western blot analyses of individuals from both groups showed that IgM antibodies were generated to the same 70 kDa extracellular protein, which was identified to be the bacterial chaperonin protein DNAk. Antibodies generated were cross reactive to DNAk proteins found in other gram negative bacteria. Our data suggests that DNAk is the dominant epitope in the channel catfish B-cell response to F. columnare . [ABSTRACT FROM AUTHOR]

Galectins, a family of β-galactoside-binding lectins with conserved CRDs, which can recognize the glycans on the surface of viruses, bacteria and protozoan parasites, are emerging as key players in many important pathological processes, including acute and chronic inflammatory diseases, autoimmunity and apoptosis. Although galectins have attracted great interest in mammals, they are still poorly-characterized in teleost. Previously, several studies have reported their high expression levels in mucosal tissues before and post infection. Given the important roles for galectins in mucosal immunity, therefore, we characterized the galectin gene family and profiled family member expression after challenge with two different Gram-negative bacterial pathogens. Here, twelve galectins genes were captured in channel catfish ( Ictalurus punctatus ), and phylogenetic analysis showed the strongest relationship to zebrafish and salmon, which is consistent with their phylogenetic relationships. Furthermore, the galectin genes were widely expressed in catfish tissues, while most of the galectin genes were strongly expressed in mucosal tissues (skin, gill and intestine). In addition, the expression profiles of galectins after bacterial infection varied depending on both pathogen and tissue type, suggesting that galectins may exert disparate functions or exhibit distinct tissue-selective roles in the host immune response to bacterial pathogens. Further studies are needed, however, to expand functional characterization and examine whether galectins may also play additional physiological roles in catfish immunity. [ABSTRACT FROM AUTHOR]

Cathepsin S belongs to the papain family of cysteine protease, and is considered to play key roles in immune responses after bacterial challenge. However, despite the recognized importance of Cathepsin S in immunity, no studies have systematically characterized Cathepsin S in catfish. In this regard, here, we characterized the Cathepsin S gene family in channel catfish, and investigated their expression patterns following two different Gram-negative bacterial challenge. In the present study, two Cathepsin S genes ( ctss and ctssa ) were captured in channel catfish. In comparison to other species, the catfish Cathepsin S genes are highly conserved in their structural features. Phylogenetic analysis indicated the strongest phylogenetic relationship with zebrafish, which is consistent with their evolutional relationships. Tissue distribution analysis revealed that Cathepsin S genes were ubiquitously expressed in catfish tissues. Following bacterial infection, the Cathepsin S genes were significantly up-regulated at most time-points in mucosal surfaces, with an acute response post Edwardsiella ictaluri infection. Obviously, the expression profiles were quite distinct between two Cathepsin S genes, across the tissues and between pathogens, suggesting that Cathepsin S genes may exert disparate roles in mucosal immune responses. Our findings here, provide early insight into the immune functions of Cathepsin S in catfish; however, further studies are needed to determine the mechanisms of Cathepsin S for antigen presentation during inflammatory processes and innate host defense. [ABSTRACT FROM AUTHOR]

The mucosal surfaces of fish (skin, gill and intestine) constitute the primary line of defense against pathogen invasion. Although the importance of fish mucosal surfaces as the first barriers against pathogens cannot be overstated, the knowledge of teleost mucosal immunity are still limited. Cathepsin B, a lysosomal cysteine protease, is involved in multiple levels of physiological and biological processes, and playing crucial roles for host immune defense against pathogen infection. In this regard, we identified the cathepsin B ( ctsba ) of channel catfish and investigated the expression patterns of the ctsba in mucosal tissues following Edwardsiella ictaluri and Flavobacterium columnare challenge. Here, catfish ctsba gene was widely expressed in all examined tissues with the lowest expression level in muscle, and the highest expression level in trunk kidney, followed by spleen, gill, head kidney, intestine, liver and skin. In addition, the phylogenetic analysis showed the catfish ctsba had the strongest relationship to zebrafish. Moreover, the ctsba showed a general trend of up-regulated in mucosal tissues following both Gram-negative bacterial challenge. Taken together, the increased expression of ctsba in mucosal surfaces indicated the protective function of ctsba against bacterial infection, and the requirement for effective clearance of invading bacteria. Further studies are needed, indeed, to expand functional characterization and examine whether ctsba may play additional physiological and biological roles in catfish mucosal tissues. [ABSTRACT FROM AUTHOR]

The mucosal surfaces of fish are the first line of host defense against various pathogens. The mucosal immune responses are the most critical events to prevent pathogen attachment and invasion. Cathepsins are a group of peptidases that involved in different levels of immune responses, but the knowledge of the roles of Cathepsin in mucosal immune responses against bacterial infection are still lacking. Therefore, in the present study we characterized the Cathepsin L gene family in channel catfish, and profiled their expression levels after challenging with two different Gram-negative bacterial pathogens. Here, two Cathepsin L genes were identified from channel catfish and were designated CTSL1a and CTSL.1 . Comparing to other fish species, the catfish CTSL genes are highly conserved in their structural features. Phylogenetic analysis was conducted to confirm the identification of CTSL genes. Expression analysis revealed that the CTSL genes were ubiquitously expressed in all tested tissues. Following infection, the CTSL genes were significantly induced at most timepoints in mucosal tissues. But the expression patterns varied depending on both pathogen and tissue types, suggesting that CTSL genes may exert disparate functions or exhibit distinct tissue-selective roles in mucosal immune responses. Our findings here, clearly revealed the key roles of CTSL in catfish mucosal immunity; however, further studies are needed to expand functional characterization and examine whether CTSL may also play additional physiological roles in catfish mucosal tissues. [ABSTRACT FROM AUTHOR]

In winter, fish have suppressed immune functions and are susceptible to bacteria or virus which may lead to a high mortality. It is necessary to improve the immune response and disease resistance for overwintering fish. A recent study suggested that repeated handling increased the innate immune mechanisms and disease resistance in Senegalese sole. Therefore, the present study tested the hypothesis that appropriate repeated handling could compromise the immune depression and increase the disease resistance in channel catfish over winter. The experiment was carried out in field cages from Nov. 2012 to April 2013. Before the experiment, 35 fish with an average weight of 188.4 g were randomly assigned to one of six cages (2 m × 2 m × 2 m). Three cages were designed as the control group and did not receive any interfere. Fish in the other three cages received a weekly repeated handling of an air exposure for 5 min. Fish were not fed over winter. At the end of the trial, fish were challenged with Aeromonas hydrophila at a dose of 5.6 × 10 8 CFU ml −1 . The results showed that final body weight was not changed between groups. The spleen somatic index increased while the head kidney somatic index decreased in the unhandled fish after bacterial challenge, but these indices were not significantly changed in the repeated handled fish. Plasma cortisol levels in the control fish were induced at 6 h post challenge and then declined to the normal levels. However, plasma cortisol levels in the repeated handled fish did not show any significant change after bacteria challenge. The reduced inducement of heat shock protein 70 (HSP70) expression by repeated handling was observed in fish post bacterial challenge. After overwintering, repeated handled fish exhibited increased catalase (CAT) activities and reduced malondialdehyde (MDA) contents. Plasma total antioxidant capacity (TAOC), CAT and superoxide dismutase (SOD) activities of channel catfish were enhanced by repeated handling post bacterial challenge. The enhanced up-regulation of Interleukin 8 (IL8), IL1β-a, IL1β-b together with the immune related genes of Toll-like receptor 2 (TLR2), TLR3, nucleotide-binding oligomerization domain 1 (NOD1) and NOD2 by repeated handling was found in catfish after bacterial challenge. The present results indicated that a combination of signaling pathways through TLRs and NODs was involved in the innate immune response of the overwintering repeated handled channel catfish against invading bacteria. [ABSTRACT FROM AUTHOR]

Fish are covered by a watery gel–mucus, mainly secreted by the goblet cells, serving as the physical and biochemical barrier between the external environment and the interior milieu, playing more important roles in fish that without scale. Despite the important roles of mucus in fish immunity, the knowledge of detailed molecular events happened during infection process is still limited. While most studies were focused on characterizing the protein and enzyme activities in the mucus following challenge, no studies have examined the gene expression profiles in fish mucus. In this regard, herein we carried out the first gene profiling analysis in catfish mucus using real-time PCR. Ten important immune-related genes were selected according to our previous studies. Their expression levels were examined in the early timepoints (namely, 1 h, 2 h, 4 h, 8 h, and 24 h) following Flavobacterium columnare challenge. Notably, expression levels of most of the selected genes were rapidly altered by the challenge. Seven genes were down-regulated, while only three genes were up-regulated. In addition, the gene expression patterns in mucus were very different from the mucosal surfaces (skin, gill and intestine) and the classical immune organs (liver, spleen and kidney). The unique expression patterns obtained here may be resulted from the great advantage of the large amount of attached bacteria in the mucus than the internal tissues, and resulted from the bacteria virulent actors to suppress the host immune response. Taken together, our results can expand our knowledge of fish mucosal immunity, and the un-lethal mucus sampling can provide early insight for developing the strategies for selection of disease resistant families and strains in catfish as well as other fish species. [ABSTRACT FROM AUTHOR]

One of the highest priority areas for improvement in aquaculture is the development of dietary additives and formulations which provide for complete mucosal health and protection of fish raised in intensive systems. Far greater attention has been paid to dietary impact on gut health than to protective effects at other mucosal surfaces such as skin and gill. These exterior surfaces, however, are important primary targets for pathogen attachment and invasion. Flavobacterium columnare , the causative agent of columnaris disease, is among the most prevalent of all freshwater disease-causing bacteria, impacting global aquaculture of catfish, salmonids, baitfish and aquaria-trade species among others. This study evaluated whether the feeding of a standard catfish diet supplemented with Alltech dietary additives Actigen ® , a concentrated source of yeast cell wall-derived material and/or Allzyme ® SSF, a fermented strain of Aspergillus niger, could offer protection against F. columnare mortality. A nine-week feeding trial of channel catfish fingerlings with basal diet (B), B + Allzyme ® SSF, B + Actigen ® and B + Actigen ® +Allzyme ® SSF revealed good growth in all conditions (FCR < 1.0), but no statistical differences in growth between the treatments were found. At nine weeks, based on pre-challenge trial results, basal, B + Actigen ® , and B + Allzyme ® SSF groups of fish were selected for further challenges with F. columnare . Replicated challenge with a virulent F. columnare strain, revealed significantly longer median days to death in B + Allzyme ® SSF and B + Actigen ® when compared with the basal diet (P < 0.05) and significantly higher survival following the eight day challenge period in B + Actigen ® when compared with the other two diets (P < 0.05). Given the superior protection provided by the B + Actigen ® diet, we carried out transcriptomic comparison of gene expression of fish fed that diet and the basal diet before and after columnaris challenge using high-throughput RNA-seq. Pathway and enrichment analyses revealed changes in mannose receptor DEC205 and IL4 signaling at 0 h (prior to challenge) which likely explain a dramatic divergence in expression profiles between the two diets soon after pathogen challenge (8 h). Dietary mannose priming resulted in reduced expression of inflammatory cytokines, shifting response patterns instead to favor resolution and repair. Our results indicate that prebiotic dietary additives may provide protection extending beyond the gut to surface mucosa. [ABSTRACT FROM AUTHOR]