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Aeromonas schubertii is the etiological pathogen of internal organ nodules in snakehead fish. Infections with A. schubertii produce a significant economic loss in aquaculture. Therefore, it is important to examine the immune mechanisms by which snakeheads defend against A. schubertii infection. In this study, we established a hybrid snakehead infection model by intraperitoneal injection of A. schubertii that produced internal organ nodules. The splenic immune response of infected fish was examined at the transcriptome level by Illumina-seq analysis. Results showed 14,796 differentially expressed genes (DEGs) following A. schubertii infection, including 4441 up-regulated unigenes and 10,355 down-regulated unigenes. KEGG analysis showed 2084 DEGs to be involved in 192 pathways, 14 of which were immune-related. Twelve DEGs were used to validate quantitative real-time PCR results with RNA-seq data. Time-course expression analysis of six genes demonstrated modulation of the snakehead immune response by A. schubertii. Furthermore, transcriptome analysis identified a substantial number of DEGs that were involved in the apoptosis signaling pathway. TUNEL analysis of infected spleens confirmed the presence of apoptotic cells. This study provided new information for a further understanding of the pathogenesis of A. schubertii in snakeheads, which can be used to prevent and possibly treat A. schubertii infections.

This research was intended to investigate the kinetics of polymeric immunoglobulin receptor (pIgR) and its ligand immunoglobulins (Ig) in snakehead ( Channa argus ) through different vaccine delivery methods. First, we employed Oxford Nanopore Technologies (ONT) sequencing technology to acquire the snakehead fish’s complete transcriptome, and the full coding sequence (CDS) of pIgR was identified and isolated through transcriptome sequencing named Ch pIgR. The CDS sequence spanned 1251 base pairs, translating into a protein that consists of 416 amino acids and has a molecular weight of around 45.80 kDa. The Ch pIgR had a pair of immunoglobulin-like domains in addition to a transmembrane region and an intracellular region. Furthermore, a polyclonal antibody targeting the snakehead recombinant Ch pIgR was constructed. Ch pIgR and IgM responses were analyzed after immunization with Aeromonas hydrophila . Although Ch pIgR and IgM displayed a comparable transcription level, Ch pIgR exhibited a more rapid increase and reached its peak earlier than IgM . Both vaccinated groups experienced an elevation in ChpIgR mRNA levels in the gill and spleen. On the other hand, the bath immersion group manifested that the skin, gills, and intestines had an elevated IgM mRNA expression, whereas the intraperitoneal vaccination group reported that the spleen and head kidney possessed a greater expression. The ELISA results indicated that the IgM and Ch pIgR levels reached their highest peak more rapidly in the skin and gill mucus in the bathing group, whereas they reached a greater peak in intestinal mucus in the injection group. The outcomes indicated that both bath and intraperitoneal vaccinations increased Ch pIgR and secretory Ig levels in mucus and bile, shedding light on the function of pIgR in immune response and laying the foundation for future studies on pIgR-linked immune defenses in teleosts.

Dietary tryptophan (Trp) has been shown to influence fish feed intake, growth, immunity and inflammatory responses. The purpose of this study was to investigate the effect and mechanism of Trp on immune system of juvenile northern snakehead ( Cantor, 1842). A total of 540 fish (10.21 ± 0.11 g) were fed six experimental diets containing graded levels of Trp at 1.9, 3.0, 3.9, 4.8, 5.9 and 6.8 g/kg diet for 70 days, respectively. The results showed that supplementation of 1.9-4.8 g/kg Trp in diets had no effect on the hepatosomatic index (HSI) and renal index (RI), while dietary 3.9 and 4.8 g/kg Trp significantly increased spleen index (SI) of fish. Dietary 3.9, 4.8, 5.9 and 6.8 g/kg Trp enhanced the total hemocyte count (THC), the activities of total antioxidant capacity (T-AOC) and superoxide dismutase (SOD). Malondinaldehyde (MDA) levels in the blood were significantly decreased by consuming 3.9 and 4.8 g/kg Trp. Fish fed with 3.0 and 3.9 g/kg Trp diets up-regulated interleukin 6 ( ) and interleukin 8 ( ) mRNA levels. The expression of tumor necrosis factor α ( ) was highest in fish fed with 3.0 g/kg Trp diet, and the expression of interleukin 1β ( ) was highest in fish fed with 3.9 g/kg Trp diet. Dietary 4.8, 5.9 and 6.8 g/kg Trp significantly decreased and mRNA levels in the intestine. Moreover, Trp supplementation was also beneficial to the mRNA expression of interleukin 22 ( ). Additionally, the mRNA expression levels of target of rapamycin ( ), toll-like receptor-2 ( ), toll-like receptor-4 ( ), toll-like receptor-5 ( ) and myeloid differentiation primary response 88 ( ) of intestine were significantly up-regulated in fish fed 1.9, 3.0 and 3.9 g/kg Trp diets, and down-regulated in fish fed 4.8, 5.9 and 6.8 g/kg Trp diets. Dietary 4.8 and 5.9 g/kg Trp significantly increased the expression of inhibitor of nuclear factor kappa B kinase beta subunit ( ) and decreased the expression of inhibitor of kappa B ( ), but inhibited nuclear transcription factor kappa B ( ) mRNA level. Collectively, these results indicated that dietary 4.8 g/kg Trp could improve antioxidant capacity and alleviate intestinal inflammation associated with TOR and TLRs/MyD88/NF-κB signaling pathways.

The northern snakehead, is a significant economic fish species in Asia and Africa, with an albino strain from China's Jialing River Basin noted for its aquaculture potential due to high nutritional value and temperature resilience. Despite prior research on partial mitochondrial genes, its complete mitochondrial genome was unpublished. This study sequenced and analyzed the complete mitochondrial genome of this albino variant, revealing a 16,558 bp circular DNA molecule with 13 protein-coding genes, 22 tRNAs, two rRNAs, and a control region. Phylogenetic analysis based on this genome positioned the species within an early-branching percomorph lineage, Anabantaria, closely related to other species. The high sequence identity with other variants suggests that mitochondrial DNA may not be the primary driver of phenotypic variations like albinism. This study provides the first complete mitochondrial genome sequence for the albino , enhancing our understanding of genetics and laying a foundation for future research on its evolutionary biology and phenotypic diversity.

The present study evaluated the impact of dietary multienzyme complex (MEC) supplementation on growth performance, digestive enzyme activity, histomorphology, serum metabolism and hepatopancreas glycometabolism in snakeheads (Channa argus). A total of 600 fish (initial weight, 69.70 ± 0.30 g) were randomly divided into four groups. Four diets were formulated: (1) control (basic diet); (2) E1 (400 U kg−1 amylase, 150 U kg−1 acid protease, 1900 U kg−1 neutral protease and basic diet); (3) E2 (800 U kg−1 amylase, 300 U kg−1 acid protease, 3800 U kg−1 neutral protease and basic diet); and (4) E3 (1200 U kg−1 amylase, 450 U kg−1 acid protease, 5700 U kg−1 neutral protease and basic diet). The results show that the E2 group increased the specific growth rate, weight gain rate and the final body weight, as well as decreasing the blood urea nitrogen, alanine aminotransferase and triglyceride. The mRNA levels and activities of digestive enzymes and key glucose metabolism enzymes in the hepatopancreas were enhanced in snakeheads fed the MEC. Meanwhile, moderate MEC diet (E2 groups) supplementation improved digestive tract morphology, increased the glycogen in the hepatopancreas and the lipids in the dorsal muscle. Moreover, plasma metabolomics revealed differential metabolites mainly involved in amino acid metabolism. These findings suggest that dietary supplementation with the MEC improved growth performance, digestive tract morphology, gene expression and the activity of digestive enzymes, enhanced the glycolysis-gluconeogenesis and amino acid metabolism of snakeheads, and the optimal composition of the MEC was group E2.

The great albino northern snakehead, Channa argus, is one of the most important economical fish in China. In the present study, cDNA encoding heat shock protein 60 (HSP60) was cloned and characterized. The cDNA was 2462 bp, containing an open reading frame (ORF) encoding a 575-amino-acids polypeptide of 61.10 kDa (theoretical isoelectric point [pI]: 5.66). BLAST analysis showed that AcaHSP60 was highly similar with other HSP60s, and three conserved amino acid blocks and characteristic motifs or domains defined as HSP60 protein family signatures. Genomic DNA analysis showed that AcaHSP60 had ten exons in the coding region (from 94 to 336 bp). Changes in AcaHSP60 gene expression profiles in albino C. argus experimentally exposed to different temperature stress (8.5, 26, and 37 °C) was investigated. Quantitative real-time PCR and western blot analysis revealed that tissue-specific AcaHSP60 expressions were in the spleen, muscle, liver, kidney, heart and brain. Expression was highly significantly stimulated after heat shock (37 °C), but showed no significant differences after cold treatment (8.5 °C) except in the brain. In summary, these results showed that AcaHSP60 was significantly tissue specific and indicate that AcaHSP60 expression might be sensitive to thermal resistance in albino C. argus.

Microbial communities in different gastrointestinal regions (stomach, foregut, midgut, and hindgut) of the northern snakehead Channa argus (Cantor, 1842) were compared by polymerase chain reaction and partial 16S rDNA sequencing. A total of 194, 140, 212, and 122 OTUs were detected in the stomach, foregut, midgut, and hindgut, respectively. Significant differences were found in the Sobs, ACE, Shannon, and Simpson indices among samples ( P <0.05). The gastrointestinal microbial community of C. argus consisted predominantly of Proteobacteria with either Halomonas , Shewanella , Plesiomonas , or Sphingomonas . Fusobacteria, Firmicutes, and Bacteroidetes also existed in the gastrointestinal tracts. However, significant differences were found in the compositions of microbial community among the four regions ( P <0.05). Cyanobacteria and Spirochetes were significantly higher in the midgut and hindgut ( P <0.05). Fusobacteria and Firmicutes were dominant in the hindgut and foregut, respectively ( P <0.05). Proteobacteria was the lowest in the hindgut ( P <0.05). At genus level, Cetobacterium and Plesiomonas were significantly higher in the hindgut than in the other three samples ( P <0.05). Clostridium and Prevotella were the highest in the midgut ( P <0.05). Halomonas , Shewanella , and Sphingomonas were the highest in the foregut ( P <0.05). Paracoccus and Vibrio were the highest in the stomach. Several genera were only detected in certain regions, as follows: stomach, Paracoccus and Vibrio ; foregut, Halomonas , Shewanella , and Sphingomonas ; midgut, Clostridium and Prevotella ; and hindgut , Cetobacterium and Plesiomonas ( P <0.05). At the species level, Acinetobacter rhizosphaerae was only detected in the stomach. Prevotella copri and Clostridium perfring were not detected in the foregut and midgut, respectively, whereas Prevotella copri and Faecalibacterium pra were not detected in the hindgut. These findings provide valuable information on the microbial community in each gastrointestinal region of C. argus . Moreover, this study indicated that microbial community was not only related to rearing environment but also to the physico-chemical characteristics of each gastrointestinal region.

The melanocortin-4 receptor (MC4R) plays an important role in the regulation of food intake and energy expenditure. Melanocortin-2 receptor accessory protein 2 (MRAP2) modulates trafficking, ligand binding, and signaling of MC4R. The Northern snakehead (Channa argus) is an economically important freshwater fish native to East Asia. To explore potential interaction between snakehead MC4R and MRAP2, herein we cloned snakehead mc4r and mrap2. The snakehead mc4r consisted of a 984 bp open reading frame encoding a protein of 327 amino acids, while snakehead mrap2 contained a 693 bp open reading frame encoding a protein of 230 amino acids. Synteny analysis indicated that mc4r was highly conserved with similar gene arrangement, while mrap2 contained two isoforms in teleost with different gene orders. Snakehead mc4r was primarily expressed in the brain, whereas mrap2 was expressed in the brain and intestine. Snakehead mc4r and mrap2 expression was modulated by fasting and refeeding. Further pharmacological experiments showed that the cloned snakehead MC4R was functional, capable of binding to peptide agonists and increasing intracellular cAMP production in a dose-dependent manner. Snakehead MC4R exhibited high constitutive activity. MRAP2 significantly decreased basal and agonist-stimulated cAMP signaling. These findings suggest that snakehead MC4R might be involved in energy balance regulation by interacting with MRAP2. Further studies are needed to elucidate MC4R in regulating diverse physiological processes in snakehead.

Lectins are sugar-binding proteins that mediate pathogen recognition and cell-cell interactions. A rhamnose-binding lectin (RBL) gene and its promoter region have been cloned and characterized from snakehead Channa argus. From the transcription initiation site, snakehead rhamnose-binding lectin (SHL) gene extends 2,382 bp to the end of the 3′ untranslated region (UTR), and contains nine exons and eight introns. The open reading frame (ORF) of the SHL transcript has 675 bp which encodes 224 amino acids. The molecular structure of SHL is composed of two tandem repeat carbohydrate recognition domains (CRD) with 35% internal identity. Analysis of the gene organization of SHL indicates that the ancestral gene of RBL may diverge and evolve by exon shuffling and gene duplication, producing new forms to play their own roles in various organisms. The characteristics of SHL gene 5′ flanking region are the presence of consensus nuclear factor of interleukin 6 (NF-IL6) and IFN-γ activation (GAS) sites. The results provide indirect evidence that up-regulation of SHL expression may be induced in response to inflammatory stimuli, such as lipopolysaccharide (LPS), interleukin 6 (IL-6), and interferon gamma (IFN-γ). The transcript of SHL mRNA was expressed in the head kidney, posterior kidney, spleen, liver, intestine, heart, muscle, and ovary. No tissue-specific expressive pattern is different from reported STLs, WCLs, and PFLs, suggesting that different types of RBLs exist in species-specific fish that have evolved and adapted to their surroundings.

Detecting and documenting the occurrence of invasive species outside their native range requires tools to support their identification. This can be challenging for taxa with diverse life stages and/or problematic or unresolved morphological taxonomies. DNA barcoding provides a potent method for identifying invasive species, as it allows for species identification at all life stages, including fragmentary remains. It also provides an efficient interim taxonomic framework for quantifying cryptic genetic diversity by parsing barcode sequences into discontinuous haplogroup clusters (typical of reproductively isolated species) and labelling them with unique alphanumeric identifiers. Snakehead fishes are a diverse group of opportunistic predators endemic to Asia and Africa that may potentially pose significant threats as aquatic invasive species. At least three snakehead species (Channa argus, C. maculata, and C. marulius) are thought to have entered North America through the aquarium and live-food fish markets, and have established populations, yet their origins remain unclear. The objectives of this study were to assemble a library of DNA barcode sequences derived from expert identified reference specimens in order to determine the identity and aid invasion pathway analysis of the non-indigenous species found in North America using DNA barcodes. Sequences were obtained from 121 tissue samples representing 25 species and combined with public records from GenBank for a total of 36 putative species, which then partitioned into 49 discrete haplogroups. Multiple divergent clusters were observed within C. gachua, C. marulius, C. punctata and C. striata suggesting the potential presence of cryptic species diversity within these lineages. Our findings demonstrate that DNA barcoding is a valuable tool for species identification in challenging and under-studied taxonomic groups such as snakeheads, and provides a useful framework for inferring invasion pathway analysis.