Ammonia nitrogen is a ubiquitous environmental stressor in aquaculture systems, posing severe toxicity to aquatic organisms. This study investigated the histopathological and physiological responses of Tachysurus fulvidraco gills under acute ammonia stress. We exposed fish to gradient concentrations of ammonia nitrogen and analyzed gill tissue histology, serum ion concentrations, blood ammonia levels, and inflammatory markers. Results showed a 96h LC50 of 28.12 mg/L. Histopathological analysis revealed severe gill damage, including lamellar fusion, epithelial necrosis, and inflammatory cell infiltration, linked to NF-kappa B-mediated upregulation of inflammatory factors and altered expression of tight junction proteins (occludin, ZO-2). Concurrently, serum Na+ and K+ levels significantly decreased, while blood ammonia rose dose-dependently. These findings demonstrate that acute ammonia stress disrupts gill structural integrity and osmoregulatory function through inflammation and barrier dysfunction, highlighting its role in ammonia toxicity mechanisms and providing insights for aquaculture health management.

Interleukin-1β (IL-1β), interleukin-6 (IL-6), and serum amyloid A (SAA) are key pro-inflammatory mediators in the regulation of immune responses. The hypothesis posits that their expression varies with the progression of Ichthyophthirius multifiliis (Ich) infection and may serve as predictors of disease outcome. To elucidate their spatiotemporal dynamics, the full-length CDS of IL-1β, IL-6, and SAA in Pelteobagrus vachelli were cloned, and then their mRNA levels were tracked from infection onset (day 0) to resolution (day 40) or mortality in seven tissues. Key findings revealed a surge in IL-1β expression in the kidney and SAA expression in the spleen at 5 days post-infection (dpi), coinciding with no visible symptoms. Significant SAA elevation in the head kidney was observed at 10 dpi, preceding the emergence of white spots on the skin. This was followed by gill-specific SAA downregulation at 20 dpi, when 40% of fish presented with white spots. Complete clinical resolution by 40 dpi correlated with reduced hepatic SAA and branchial IL-1β levels. Notably, the concurrent upregulation of all three mediators occurred exclusively in the skin of moribund individuals. These findings identify potential biomarkers for tracking host inflammatory responses in ichthyophthiriasis.

With the growing scale of largemouth bass breeding, the demand for seedlings is increasing. As global temperatures rise, it is crucial to study the effects of high temperature their regulatory mechanisms in largemouth bass. In this study, we simulated a high water temperature (28 °C) in the non-breeding season in aquaculture ponds for 28 days to examine the growth, reproduction, metabolism, apoptosis, and methylation markers in largemouth bass; transcriptome analysis was also performed. The results showed no significant difference in body weight between male and female largemouth bass. However, the high-temperature exposed females had reduced growth hormone (GH) and estradiol (E2) levels and elevated cortisol levels. They also showed upregulated expression of AR, cyp19a, igf, fshβ, and lhβ in ovarian tissue. Transcriptomic comparisons between temperature treatments revealed 963 differentially expressed genes in females and 700 in males. Both the ECM receptor interaction and PPAR signaling pathways were significantly enriched. High-temperature enhanced the lipid metabolism process through the PPAR signaling pathway. High temperatures increased oxidative stress in females, which corresponded with increases in SOD, CAT, and GSH-Px, likely to counteract the excess reactive oxygen species. Moreover, endoplasmic reticulum stress was activated, indicated by increases in IRE1 and ATF6, leading to the upregulation of apoptosis-related genes and ovarian cell apoptosis. At high temperature, 5-MC%, demethylase, and methyltransferase were not different in females, while 5-MC% and methyltransferase were higher and demethylase was lower in males. In summary, sustained high temperature affected ovarian development by altering the expression of hormone and gonad related genes and inducing endoplasmic reticulum stress leading to ovarian cell apoptosis. However, low demethylase activity and high genome-wide methylation in the test is suggested that high temperatures may affect testis development via methylation, potentially impacting offspring production.

Vertebrates have undergone two rounds of whole-genome duplication (WGD), termed 1R and 2R, with a third, teleost-specific duplication (TSGD or 3R) occurring in ray-finned fishes. In the order Cypriniformes, additional lineage-specific WGDs have further contributed to species diversification. While polyploidy is well characterized in species like common carp and goldfish, other polyploid taxa-particularly loaches-remain understudied. Here, high-quality, chromosome-level genome assemblies are presented for two loach species: Sinibotia superciliaris (Golden Chinese Loach) and Parabotia fasciatus (Yichang Sand Loach). By integrating these genomes into a comparative framework with 20 other cypriniform species, key phylogenetic relationships are reconstructed, and introduce a novel subgenome partitioning method (M3). Unlike previous approaches, M3 uses differential sequence divergence to accurately and rapidly assign subgenomes, completing partitioning within minutes and outperforming existing tools. Applying M3, a markedly reduced subgenome is uncovered in the Golden Chinese Loach, with lineage-specific molecular changes in several candidate genes, suggesting potential adaptive significance. This study offers a comprehensive view of polyploidy and subgenome evolution in loaches, highlighting the genomic complexity shaped by repeated WGDs in Cypriniformes and providing valuable resources for future research on vertebrate genome evolution and adaptation.

The caspase family, conserved cysteine proteases, play pivotal roles in host anti-infectious immunity and apoptotic regulation. However, systematic investigations into this family in Siluriformes are scarce. Here, we systematically identified 9 apoptosis-related caspase genes in the genome of yellow catfish (Tachysurus fulvidraco) and analyzed their molecular characteristics, evolutionary relationships, and expression dynamics during pathogen infections. Results showed that T. fulvidraco encodes caspase2, 3, 3a, 3b, 6, 7, 8, 9, and 10, but lacks the canonical caspase1. Apoptosis-related caspases were classified into initiators (2/8/9/10) and effectors (3/6/7), with caspase3 existing in three isoforms (3, 3a, 3b). Phylogenetic and synteny analyses indicated strong evolutionary conservation, with close correlations between their conservation and species phylogeny. Tissue-specific expression profiles showed that all caspase genes were ubiquitously expressed across tested tissues, with relatively high levels in the hindgut, gill, and liver. Pathogen challenge assays showed: (1) During Vibrio mimicus infection, most caspase genes were upregulated in the head kidney, skin, and gill at the early phase, whereas in the spleen, their expression was predominantly elevated during the middle to late stages; (2) Following long-term Ichthyophthirius multifiliis infection (20 days post-infection, dpi), all caspase genes in the head kidney were activated, while most in the skin were activated during the dying state, with differential activation patterns between the gill and skin; (3) After yellow catfish calicivirus (YCCV) infection, the majority of caspases were activated in the skin, gill, and head kidney, with caspase3b exhibiting relatively high fold changes (63.81-104.81) across four tissues. In conclusion, the caspase family in T. fulvidraco exhibits differential expression during bacterial, viral, and parasitic infections through evolutionary conservation and specific divergence. These findings provide a foundation for deciphering apoptotic regulation and disease resistance mechanisms in Siluriformes fish.

Rapid development in China over the past decades has been accompanied by an ongoing influx of non-native species. Many non-native mollusc species have been introduced both intentionally and unintentionally, leading to the establishment of feral populations through escapees. However, there is limited information regarding the status, threats to native biodiversity, and the contributions of these non-native molluscs to commercial breeding, the aquarium trade, and other sectors. In this study, we reviewed the impacts of introduced non-native molluscs to address these gaps. Additionally, we identified areas for future research and management recommendations. Our findings show that a total of 61 non-native mollusc species, spanning 15 orders, 23 families, and 41 genera, have been introduced into China. The primary pathway of introduction is through commercial breeding (34 species), followed by unintentional imports (20 species) and the aquarium trade (seven species). While many of these non-native molluscs are valuable as commercial breeding products and provide high nutritional value, some have caused significant negative impacts on environmental health, economic development, human health, and various aspects of aquatic and terrestrial ecosystems. Increased research on the monitoring, control, and management of non-native molluscs in China is urgently needed.

Aeromonas veronii is a major pathogen threatening freshwater aquaculture, yet the molecular mechanisms of Pelteobagrus vachellii’s immune response to this infection remain unclear. This study integrated histopathology, mRNA-seq and small RNA-seq to investigate P. vachellii’s response to A. veronii at 48 h post-challenge. Histopathologically, infection induced gill epithelial detachment, hepatocyte swelling with cytoplasmic vacuolation, and melanomacrophage centers (MMCs) in the mid-kidney (histological assessment of the head kidney was not feasible due to sampling limitations associated with its small size). Transcriptomic analysis identified 1,210 differentially expressed genes (DEGs) in the head kidney (819 downregulated, 391 upregulated), significantly enriched in 11 immune pathways (e.g., NF-κB, Th17 cell differentiation, Complement and coagulation cascades), with key immune genes (e.g., IL-1β, TCRα, CCL4) upregulated. Gene Set Enrichment Analysis (GSEA) revealed activation of the proteasome, ribosome and oxidative phosphorylation pathways, and suppression of the autophagy-animal, FoxO and AMPK pathways. Small RNA-seq identified 544 known and 958 novel miRNAs in the head kidney, with 42 downregulated and 36 upregulated differentially expressed miRNAs (DE miRNAs). The miRNA-mRNA network showed that DE miRNAs (e.g., miR-101-y/z, miR-132-z, miR-3167-y) negatively regulated immune-related target genes (IL-1R1, IRF4, IκBα) in core immune pathways. Collectively, this study clarifies the pathological and miRNA-mRNA regulatory modules of P. vachellii head kidney against A. veronii infection, providing valuable information that enables the further analyses of the defense mechanisms of P. vachellii against A. veronii infection.

Aquaculture, as a rapidly growing industry, plays a significant role in global food production and economic development. However, various infectious diseases, particularly those caused by the gram-negative bacterium Aeromonas hydrophila, pose a critical threat to the sustainability and productivity of world-wide aquaculture operations. Investigating the molecular mechanisms of A. hydrophila infection can help to identify key targets for therapeutic interventions and vaccines, thereby reducing economic losses associated with disease outbreaks. Our present study focuses on wide-bodied sand loach (WBSL, Sinibotia reevesae), a captive-bred commercial fish, to explore detailed molecular effects of exogenous A. hydrophila infection. Firstly, a high-quality chromosome-level haplotype genome with a total length of 774 Mb and 49 chromosomes was assembled, providing valuable insights into its genetic components. Secondly, we isolated and characterized a newfound A. hydrophila F4S strain, examined pathological symptoms of WBSL after infection, and then investigated dynamic gene expressions. Our results revealed that the bacterial infection decreased metabolic activity, causing disruptions in cardiac function, cellular homeostasis, tissue damages, and impaired energy utilization. The immune system responds multifaceted, potentially impacting overall health and survival. In summary, our findings contribute to the understanding of the complicated interactions between WBSL and exogenous A. hydrophila, especially shed lights on the genetic complexity, immune responses, and potential impacts on fish health and survival. Furthermore, this study provides new insights into the mechanisms underlying A. hydrophila infection, and offers potential strategies to offload corresponding pathological effects, not only in WBSL but also in other aquaculture species.

cAMP response element binding (CREB) protein 2 (CRTC2) is a transcriptional coactivator of CREB and plays an important role in the immune system. Thus far, the physiological roles of Crtc2 in teleost are still poorly understood. In this study, the crtc2 gene was identified and characterized from yellow catfish (Pelteobagrus fulvidraco; therefore, the gene is termed as pfcrtc2), and its evolutionary and molecular characteristics as well as potential immunity-related roles were investigated. Our results showed that the open reading frame of pfcrtc2 was 2,346 bp in length, encoding a protein with 781 amino acids. Gene structure analysis revealed its existence of 14 exons and 13 introns. A phylogenetic analysis proved that the tree of crtc2 was clustered into five groups, exhibiting a similar evolutionary topology with species evolution. Multiple protein sequence alignment demonstrated high conservation of the crtc2 in various vertebrates with similar structure. Syntenic and gene structural comparisons further established that crtc2 was highly conserved, implying its similar roles in diverse vertebrates. Tissue distribution pattern detected by quantitative real-time PCR showed that the pfcrtc2 gene was almost expressed in all detected tissues except for eyes, with the highest expression levels in the gonad, indicating that Crtc2 may play important roles in various tissues. In addition, pfcrtc2 was transcribed at all developmental stages in yellow catfish, showing the highest expression levels at 12 h after fertilization. Finally, the transcriptional profiles of crtc2 were significantly increased in yellow catfishes injected with Aeromonas hydrophila or Poly I:C, which shared a consistent change pattern with four immune-related genes including IL-17A, IL-10, MAPKp38, and NF-κBp65, suggesting pfCrtc2 may play critical roles in preventing both exogenous bacteria and virus invasion. Anyway, our findings lay a solid foundation for further studies on the functions of pfcrtc2, and provide novel genetic loci for developing new strategies to control disease outbreak in teleost.

Granulomatous chronic inflammation is a typical pathological characteristic of largemouth bass (Micropterus salmoides) infected by Nocardia seriolae, and it is also an important breakthrough to solve the problem of pathogen prevention and treatment. Spleen, the target organ of N. seriolae infection, is significant for studying pathogenic mechanism. However, histopathological characteristics and immunological molecular mechanisms of the development of splenic granulomas in fish have not been extensively studied. In the initial process of exploring the molecular mechanism of N. seriolae infectious splenic granuloma formation, we accidentally found positive signals of necroptosis-related gene by immunohistochemical staining, suggesting that necroptosis may be involved in the formation of granulomas. Nevertheless, the role of necroptosis in the formation of splenic granuloma is still unclear. In this study, we established a granuloma model in the spleen of largemouth bass infected by N. seriolae. Through multiple tissue staining, we compared splenic granulomas with hepatic and renal granulomas, and preliminarily clarified the histopathological characteristics of splenic granulomas and the formation pattern of fibrosis, calcium salt deposition and other lesions. Notably, we found that the expression of inflammatory factors and necroptosis-related molecules in spleen were significantly upregulated during N. seriolae infection. Further immunohistochemical staining showed that the splenic granulomas were accompanied by extensive and intense p-MLKL-positive signals in the peripheral tissue. In addition, western blot and immunofluorescence results showed that N. seriolae could induce necroptosis in primary spleen cells of largemouth bass in vitro. Our data indicated that necroptosis is closely related to the formation of splenic granulomas in largemouth bass, and provide some ideas for the study of the formation mechanism of fish granuloma.

Sturgeons display a slow growth rate and delayed initial sexual maturity, which extends the captive breeding and conservation processes. To date, few studies have revealed the molecular mechanism underlying the growth difference of sturgeons. In the present study, juvenile Yangtze sturgeons (Acipenser dabryanus) with different growth rates were selected from the same cultured pool for muscle structure, enzyme activity and comparative transcriptome analysis. Histological assays showed that the fiber diameter of the fast-growing group was significantly larger than that of the slow-growing group. The activities of four glycometabolism related enzymes, including two key rate-limiting enzymes hexokinase and pyruvate kinase, were significantly higher in fastgrowing group. RNA-Seq of muscle tissues identified 7408 differentially expressed genes (DEGs), which consisted of 3637 upregulated genes and 3771 downregulated genes, in the fast-growing group vs. the slow-growing group. In the brain, a total of 12,213 unigenes were differentially expressed (6050 upregulated unigenes and 6163 downregulated unigenes) between the two groups. The expression levels of IGF1 and IGF1-binding proteins (IGFBPs) in muscle were significantly higher in the fast-growing group and might be promising candidate biomarkers for measuring growth performance in Yangtze sturgeon. Two myogenic regulatory factors (myog and myf6) were significantly upregulated, which indicated that the growth variation in juvenile Yangtze sturgeon might be partly due to the difference in the differentiation of muscle cells. In addition, pathway enrichment analysis revealed that the glycolysis and cell cycle pathways were significantly enhanced in the fast-growing groups, suggesting that they might also play important roles in the improved growth performance of A. dabryanus. Furthermore, the WGCNA as well as hub gene network analyses supported that cell cycle and gluconeogenesis might be involved in the differential growth performance of A. dabryanus. The results of this study may contribute to our understanding of the underlying molecular mechanism of growth variation in fish.

Background The benefits of combining benzoic acid and essential oils (BAO) to mitigate intestinal impairment during the weaning process have been well established, while the detailed underlying mechanism has not been fully elucidated. Previous research has primarily focused on the reparative effects of BAO on intestinal injury, while neglecting its potential in enhancing intestinal stress resistance. Methods In this study, we investigated the pre-protective effect of BAO against LPS-induced stress using a modified experimental procedure. Piglets were pre-supplemented with BAO for 14 d, followed by a challenge with LPS or saline to collect blood and intestinal samples. Results Our findings demonstrated that BAO supplementation led to significant improvements in piglets' final weight, average daily gain, and feed intake/body gain ratio. Additionally, BAO supplementation positively influenced the composition of intestinal microbiota, increasing beneficial Actinobacteriota and Alloprevotella while reducing harmful Desulfobacterota, Prevotella and Oscillospira . Furthermore, BAO supplementation effectively mitigated oxidative disturbances and inflammatory responses induced by acute LPS challenge. This was evidenced by elevated levels of T-AOC, SOD, and GSH, as well as decreased levels of MDA, TNF-α, and IL-6 in the plasma. Moreover, piglets subjected to LPS challenge and pre-supplemented with BAO exhibited significant improvements in intestinal morphological structure and enhanced integrity, as indicated by restored expression levels of Occludin and Claudin-1 compared to the non-supplemented counterparts. Further analysis revealed that BAO supplementation enhanced the jejunal antioxidative capacity by increasing GSH-Px levels and decreasing MDA levels under the LPS challenge and stimulated the activation of the Nrf2 signaling pathway. Additionally, the reduction of TLR4/NF-κB/MAPK signaling pathways activation and proinflammatory factor were also observed in the jejunal of those piglets fed with BAO. Conclusions In summary, our study demonstrates that pre-supplementation of BAO enhances the anti-stress capacity of weaned piglets by improving intestinal microbiota composition, reinforcing the intestinal barrier, and enhancing antioxidative and anti-inflammatory capabilities. These effects are closely associated with the activation of Nrf2 and TLR4/NF-κB/MAPK signaling pathways.

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

Leucism, a widespread occurrence observed in Northern snakehead (Channa argus), bestows a striking white jade-like body coloration upon affected individuals and has gained substantial popularity in commercial breeding. While the visible manifestation of leucism in snakeheads is primarily limited to body coloration, it is crucial to explore the potential influence of leucism on organ development and elucidate the underlying molecular mechanisms. Through a comparative analysis of growth differences, our study revealed that at 150 days post-fertilization, the white variety exhibited an 8.5% higher liver index and intestinal index, but experienced a 20% and 38% decreased in spleen index and renal interstitial index, respectively, suggesting an enlarged digestive area but relatively smaller immune tissues. Nonetheless, no significant differences were observed in the intestinal flora between the two varieties, suggesting the exclusion of any exogenous impacts from symbiotic flora on the growth and development of the white variety. Importantly, transcriptome analysis demonstrated that the white variety exhibited higher expression levels of innate immune genes. Furthermore, annotation of the gene sets expressed in the liver and spleen revealed 76 and 35 genes respectively, with the white variety displaying lower expression in genes associated with "Viral protein interaction with cytokine and cytokine receptor", "Protein processing in endoplasmic reticulum", and "TNF signaling pathway", while exhibiting higher expression in "Estrogen signaling pathway". Notably, three genes, namely pcdhf 4, nlrc3 card 15-like, and a pol-like were identified in both the liver and spleen, indicating their potential involvement in altering the development and innate immunity of the white variety. This study reveals the systemic impact of leucism that extends beyond mere pigmentation alterations, highlighting the prominent characteristics of this phenotype and providing a foundation for future molecular breeding programs aimed at enhancing this variety.

Granulomatous diseases caused by Nocardia seriously endanger the health of cultured fish. These bacteria are widely distributed, but prevention and treatment methods are very limited. Chronic granulomatous inflammation is an important pathological feature of Nocardia infection. However, the molecular mechanisms of granuloma formation and chronic inflammation are still unclear. Constructing a granuloma infection model of Nocardia is the key to exploring the pathogenesis of the disease. In this study, we established a granuloma model in the liver of largemouth bass (Micropterus salmoides) and assessed the infection process of Nocardia seriolae at different concentrations by analysing relevant pathological features. By measuring the expression of pro-inflammatory cytokines, transcription factors and a pyroptosis-related protein, we revealed the close relationship between pyroptosis and chronic inflammation of granulomas. We further analysed the immunofluorescence results and the expression of pyroptosis-related protein of macrophage infected by N. seriolae and found that N. seriolae infection induced macrophage pyroptosis in vitro. These results were proved by flow cytometry analysis of infection experiment in vivo. Our results indicated that the pyroptosis effect may be the key to inducing chronic inflammation in the fish liver and further mediating granuloma formation. In this study, we explored the molecular mechanism underlying chronic inflammation of granulomas and developed research ideas for understanding the occurrence and development of granulomatous diseases in fish.

The use of plant polysaccharides in aquaculture is recognized as a healthy strategy to enhance disease resistance and reduce medication use. Salvia miltiorrhiza polysaccharide (SMP) can regulate the immune function of higher vertebrates. However, the effects of SMP on fish have not been fully investigated. In this study, the ability of SMP to activate the macrophages of Siberian sturgeon (Acipenser bareii) was analyzed in vitro. The effects of SMP on immune cell activity of hybrid sturgeon (A. baerii ♀ × Acipenser schrenckii ♂) and resistance to Aeromonas hydrophila were further detected in vivo. The in vitro results showed that SMP up-regulated phagocytosis, respiratory burst, inducible nitric oxide synthase activity, nitric oxide (NO) concentration, and cytokine mRNA expression of macrophages. The in vivo results showed that dietary supplementation with SMP enhanced the respiratory burst of macrophages and proliferative activity of lymphocytes. Dietary supplementation with SMP increased serum concentrations of lysozyme and NO, and improved the survival rate of hybrid sturgeon challenged with A. hydrophila. Collectively, these results suggest that SMP can improve the immune function and disease resistance of sturgeon. This study provides a theoretical basis for the application of SMP for healthy farming of sturgeon.

Aeromonas allosaccharophila belongs one of the causative agent of Aeromonas disease in teleosts. Here, we reported on multiple outbreaks of A. allosaccharophila with mortality up to 80% in farmed hybrid sturgeon in Sichuan, China, from 2019 to 2021. This was the first study to A. allosaccharophila from diseased hybrid sturgeons by phenotypic characterization and 16S rRNA analysis. The typical clinical signs of these fish were intestinal segments empty and often with yellow mucus or swelling. Histopathological observation of diseased fish infected with A. allosaccharophila showed the intestinal villus structure disappeared and the intestinal mucosa epithelium was necrotic and shed. Experimental infection indicated that A. allosaccharophila was the pathogen responsible for the mortalities. Antibiotic sensitivity test results showed that A. allosaccharophila was resistant to ampicillin, neomycin, tetracycline, and penicillin, while sensitive to sulfamethoxazole, streptomycin, florfenicol, enrofloxacin, and cefoxitin. Our findings provide references for the disease diagnosis and treatment.

In the process of continuous combat between pathogens and fish, bacteria have evolved a series of unique strategies to evade the defenses of the natural immune system. The bacterial type IV secretion system (T4SS), as an important multi-protein complex, plays an important role in the process of bacterial infection of the host. However, the T4SS effector protein and its function during bacterial infection remain to be elucidated. A typical T4SS is present in the integrative and conjugative element ICE (r2) of Yersinia ruckeri SC09. In this study, we found that SC09-T4SS mediated the virulence of bacteria and improved the viability of bacteria in eukaryotic cells. SC09-T4SS also mediated the inhibition of pro-inflammatory signals, thereby assisting in the immune escape of bacteria during infection. These effects of SC09-T4SS were due to the secretion of molecules such as STIR-1, STIR-2, and STIR-3. We believe that SC09-T4SS secretion systems are common in bacteria, and our research may provide a general rule of bacterial pathogenicity.

In 1996, kiss was reported to regulate feeding in mammals, but studies are limited in fish. Our study aimed to explore the possible role of kiss in the regulation of feeding in Siberian sturgeon (Acipenser baerii). kiss1 and kiss2 were cloned, and the expression patterns were analyzed in Siberian sturgeon. The complete coding regions of kiss1 and kiss2 genes were 393 and 471 bp. Both kiss1 and kiss2 showed the highest expression level in the hypothalamus. During the periprandial and fasting experiments, the expression of kiss1 and kiss2 highly significantly increased in the hypothalamus after feeding (P < 0.01). Compared with the feeding group, in hypothalamus, kiss1 expression in the fasting group highly significantly decreased (P < 0.01). In contrast, kiss2 expression had no significant difference on days 1 and 7 (P > 0.05) but highly significantly increased on day 14 (P < 0.01). Subsequently, the feeding function was verified by intraperitoneal (i.p.) injection of Kp1(10) and Kp1(10) into fish. The results showed that i.p. injection of 1 µg/g BW Kp1(10) or 0.01 µg/g BW Kp2(10) could significantly reduce 0–1 h food intake (P < 0.05) and affected the expression levels of apelin, ghrelin, leptin, nmu, etc. in the hypothalamus. These results suggested that kiss1 plays an anorexic role in both short- and long-term feeding regulation, while kiss2 plays a short-term anorexic and long-term orexigenic role. This study described kiss as a novel regulator of appetite in fish and laid the groundwork for further studies focused on physiological function. • The kiss1 and kiss2 of Siberian sturgeon were cloned. • The expression levels of kiss1 and kiss2 mRNA were the highest in the hypothalamus. • Postprandial hypothalamic kiss1 and kiss2 expression levels increased in the periprandial experiment. • In the fasting test, the expression of hypothalamic kiss1 decreased after fasting, while the expression of kiss2 increased after fasting on the 14th day. • Siberian sturgeon food intake was reduced, and appetite factors expression levels in the hypothalamus were altered after intraperitoneal injection of Kp1(10) and Kp2(10).

Amylin is a 37-amino acid polypeptide that has been found to be involved in feeding regulation in some mammals, birds, and goldfish. We cloned amylin of Siberian sturgeon and detected its distribution pattern in 15 tissues. The expression levels in the periprandial period (pre-and post-feeding), the changes in the food intake, and the expression levels of related appetite factors after the intraperitoneal injection of amylin were detected. The expression of amylin was found to be the highest in the hypothalamus. Compared with 1 h pre-feeding, the expression levels of amylin in the hypothalamus and duodenum were increased significantly 1 h post-feeding. Compared with the control group (saline), intraperitoneal injection of 50 ng/g, 100 ng/g, and 200 ng/g of amylin significantly inhibited food intake at 1 h post injection, but not at 3 h and 6 h. The injection of 50 ng/g, 100 ng/g, and 200 ng/g amylin significantly inhibited the cumulative feed. After 1 h of 50 ng/g amylin injection, the levels of MC4R and somatostatin in the hypothalamus increased significantly, while the levels of amylin and NPY decreased significantly. The levels of CCK in the valvular intestine were increased significantly. Insulin in the duodenum was also increased significantly, but there was no significant change in ghrelin in the duodenum. These results show that amylin inhibits feeding in Siberian sturgeon by down-regulating the appetite-stimulating factor NPY and up-regulating the appetite-suppressing factors somatostatin, MC4R, CCK, and insulin. This study provides a theoretical basis for studying the feeding function and action mechanisms of amylin in Siberian sturgeon.