Journal of fish diseases最新文献

Edwardsiella anguillarum is a gram-negative bacterium, synonymous with previously described atypical, fish-pathogenic Edwardsiella tarda. Originally described from eels in 2015, E. anguillarum is an important global fish pathogen, particularly in tilapia. This study describes intraspecific phenotypic and genotypic variability among 17 E. anguillarum isolates from non-anguillid fish hosts and varied geographic origins. Isolates demonstrated similar biochemical characteristics, with slight variation in motility and hydrogen sulfide production. Genomic relatedness among isolates was analysed with repetitive extragenic palindromic sequence-based PCR (rep-PCR) and multilocus sequence analysis (MLSA). Rep-PCR with the ERIC II primer set revealed two distinct genetic clusters, while amplification strategies utilising the GTG₅, BOX or ERIC I&II primer sets yielded more uniform profiles. While rep-PCR deemed the isolates largely clonal, MLSA schemes using reference genes from published Edwardsiella MLSA studies revealed E. anguillarum isolates formed five discrete phylogroups. A unique, ~91.5 kB plasmid was identified in Costa Rican and Colombian isolates, associated with conjugative and transposable elements, plasmid mobilisation, and adhesion; however, no plasmid mediated antibiotic resistance genes were identified. This study provides insight into genetic diversity among E. anguillarum isolates from different hosts and geographic regions, identifying an optimal MLSA scheme from previous reports applicable to E. anguillarum isolates.

Water temperature is a critical environmental factor influencing the severity, replication and transmission of infectious diseases in aquaculture. However, its role in the pathogenesis and shedding dynamics of tilapia lake virus (TiLV), which is an emerging viral pathogen threatening global tilapia production, remains to be fully characterised. We therefore evaluated the temperature-dependent effects of TiLV infection in Nile tilapia (Oreochromis niloticus) by simulating direct and indirect cohabitation models. The fish were challenged with TiLV and maintained at 24°C, 28°C or 32°C. The highest mortality and viral loads in water and mucus occurred at 28°C, while outcomes at 32°C showed lower mortality, indicating a non-monotonic temperature response. In contrast, infection at 24°C resulted in delayed infection onset, lower viral shedding and minimal mortality among the cohabitant fish. Notably, the indirect cohabitation system consistently showed reduced transmission and lower mortality among the cohabitant fish. The TiLV concentrations in the water and mucus peaked prior to the highest mortality events in both cohabitation experiments, which supports their applicability as noninvasive early warning indicators before outbreaks occur. Our findings demonstrate that tilapia mortality and shedding dynamics of TiLV are significantly influenced by fixed water temperature. These results provide a baseline for understanding how fixed thermal regimes impact TiLV outbreaks and highlight the importance of environmental monitoring in control strategies.

Chemokines are essential for vertebrate immune regulation, and teleosts possess diverse CXCL8 lineages. However, studies on CXCL8 in C. auratus remain limited. In the present study, four CXCL8 homologues (CaCXCL8-1 to -4) were successfully cloned and identified from C. auratus, and their expression patterns were analysed in the tissues of healthy and those naturally infected with H. doneci. Bioinformatic analyses revealed that all homologues possess the conserved structural features of CXC chemokines. However, the divergence was observed in the N-terminal ELR motif: CaCXCL8-1 and CaCXCL8-2 harboured a QLR motif, whereas CaCXCL8-3 and CaCXCL8-4 possessed a DPR motif. Phylogenetic analysis classified CaCXCL8-1 and CaCXCL8-2 into the CXCL8_L2 lineage, and CaCXCL8-3 and CaCXCL8-4 into the teleost-specific CXCL8_L1b lineage. Tertiary structure predictions indicated that CaCXCL8-1, -3, and -4 conserve key receptor-binding sites, whereas CaCXCL8-2 retained only GAG-binding sites, suggesting potential functional divergence. Under healthy conditions, the four homologues were all constitutively expressed but displayed divergent basal profiles. Following H. doneci infection, they exhibited distinct tissue-specific expression patterns: CaCXCL8-1 was significantly upregulated in the gills; CaCXCL8-2 was specifically induced in the spleen; CaCXCL8-3 was markedly upregulated in both the gills and head kidney; and CaCXCL8-4 was upregulated in the liver and head kidney but downregulated in the spleen. These divergent expression patterns suggest functional specialisation among the CaCXCL8 homologues, with different paralogs potentially coordinating localised versus systemic immune responses. Our findings provide evidence for the functional diversification of the CXCL8 chemokine in teleosts and contribute to understanding the evolution of complex immune systems in vertebrates.

Streptococcus agalactiae is a multi-host pathogen and a major threat to aquaculture, particularly tilapia production. This study characterised the serotype distribution and virulence gene profiles of 97 S. agalactiae isolates obtained from non-tilapia freshwater species in Vietnam, including carp species not previously recognised as hosts, namely black carp, grass carp and common carp. Three serotypes were identified among non-tilapia isolates, Ia (44.3%), III (39.2%) and Ib (16.5%). Virulence gene distributions varied substantially within and between serotypes; however, all isolates consistently carried the fbsA and cfb genes. Distinct serotype-associated gene patterns were observed. Serotype Ia isolates possessed fbsA, fbsB, bca, hylB and cfb but lacked lmb and spb1-F, whereas serotype III isolates harboured pavA, cylE, fbsA, lmb, scpB, cfb and cspA but lacked bac. Serotype Ib isolates carried pavA, cylE, fbsA, hylB, cfb and cspA, while spb1-F and bac were absent. Overall, this study identifies additional non-tilapia hosts of S. agalactiae in freshwater aquaculture provides the first evidence of infection in black carp, grass carp and common carp. These findings demonstrate the diversity of circulating serotypes and virulence gene profiles. These findings indicate increasing epidemiological complexity and highlight the need for integrated prevention and disease management strategies targeting this pathogen.

Adult Chinook salmon (Oncorhynchus tshawytscha) trap-and-haul operations exist in rivers across the Pacific Northwest with the objective of re-establishing salmon populations above impoundments. These efforts are complicated by high prespawn mortality (PSM), which can hinder restoration by reducing reproductive success. Recent improvements at trapping facilities in the Willamette River Basin, Oregon, USA, may reduce PSM by streamlining trap-and-haul operations to reduce handling stress. However, studies suggest that PSM is also related to factors associated with haul operations, including fish density and exposure to external stressors such as pathogens. Environmental DNA (eDNA) can help detect pathogens in confined systems with high fish-to-water ratios. In this work, pathogen eDNA samples were collected from anaesthesia and transport tank waters at a trap-and-haul facility in 2017 and 2021 and analysed to assess pathogen presence. Pathogen DNA was detected in both tanks prior to fish addition, including Aeromonas salmonicida, Renibacterium salmoninarum, Salmincola californiensis, and Ceratonova shasta. After fish entered the anaesthesia tank, average pathogen concentrations increased in magnitude for A. salmonicida (73%), S. californiensis (3165%), C. shasta (1619%), and decreased for R. salmoninarum (-57%). Results suggest shedding of horizontally transmitted pathogens, particularly A. salmonicida, during transport.

The myxozoan endoparasite Tetracapsuloides bryosalmonae (Tb), the causative agent of proliferative kidney disease (PKD) in salmonids, has predominantly been reported in temperate regions of continental Europe and North America. Here, we present the first record of Tb in the Faroe Islands, extending the known northern distribution of the parasite. We sampled 161 brown trout (Salmo trutta) and three Atlantic salmon (Salmo salar) from 16 streams across the Faroes. Quantitative PCR (qPCR) analysis of kidney tissue detected Tb in 14 streams, with mean prevalence of 65.6%, reaching 100% in six streams. Parasite load, quantified as Tb 18S rRNA gene copies per qPCR reaction, ranged from 109.5 to 281,219 (mean 16,127) among infected fish. Despite high Tb prevalence and load, no clinical signs of renal hyperplasia, indicative of PKD, were observed. Sanger sequencing of the Tb 18S rRNA gene showed 99.8% to 100% identity with European isolates. These results indicate Tb is well established in Faroese freshwater and is genetically similar to European isolates. Given the known temperature dependence of PKD, climate warming is likely to increase disease risk in northern regions. Continued monitoring is essential to assess the potential long-term ecological impacts of Tb on wild salmonid populations under changing environmental conditions.

The PSMB8 gene belongs to the immunoproteasome β-subunit (PSMB) family and has been implicated in diverse physiological processes in mammals, including tumorigenesis, autophagy and apoptosis. However, its role in antiviral immunity in groupers remains largely unexplored. In this study, we cloned and characterised EcPSMB8, a homologue of PSMB8, from the orange-spotted grouper (Epinephelus coioides), and investigated its potential involvement in antiviral immune responses. EcPSMB8 encodes a conserved 275-amino-acid protein that is ubiquitously expressed in grouper tissues and predominantly localised in the cytoplasm. Functional analyses showed that EcPSMB8 overexpression was associated with reduced replication of both Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV). This antiviral effect was accompanied by suppression of basal and virus-induced autophagy, as indicated by decreased LC3-II accumulation and reduced expression of autophagy-related genes. Meanwhile, EcPSMB8 overexpression correlated with enhanced major histocompatibility complex class I (MHC I)-associated immune signalling, including increased promoter activities of MHC I-A, ISRE and IFN3, as well as upregulation of related cytokines. Together, these findings suggest that EcPSMB8 may contribute to grouper antiviral defence through coordinated modulation of immune signalling and autophagy. Importantly, a specific polyclonal antibody against EcPSMB8 was generated, providing a useful tool for protein-level analyses and supporting future studies on antiviral immune mechanisms in teleost fish.

Lauric Acid (LA) and Glycerol Monolaurate (GML) are naturally present in several plant-derived oils, particularly coconut and palm kernel oil. These compounds have been widely applied in swine production owing to their proven antiviral activity against Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), Porcine Epidemic Diarrhoea Virus (PEDV), and African Swine Fever Virus (ASFV). In this study, we investigated the potential of LA and GML as antiviral agents against Cyprinid herpesvirus 2 (CyHV-2), the causative agent of Herpesviral haematopoietic necrosis (HVHN), which poses significant challenges to China's freshwater aquaculture industry, particularly in crucian carp farming. Notably, no commercially available drugs or vaccines are currently approved for CyHV-2 infection. Our findings demonstrated that LA and GML significantly inhibit CyHV-2 replication and reduce viral infectivity. Further investigation into the antiviral mechanisms revealed that treatment with LA or GML disrupts the viral envelope structure, alters its physicochemical properties, and compromises virions' stability. Based on these results, we propose that LA and GML are promising natural antiviral agents for the control of CyHV-2 infection.

Bacterial infections are increasingly recognised as a major threat to ornamental freshwater shrimp aquaculture. Diseased Neocaridina spp. displaying abnormal swimming, lethargy, hypoxia, cutaneous abrasions, dark-brown lesions, and occasional moulting were investigated. Pure cultures from moribund shrimp yielded Gram-negative, motile, catalase- and oxidase-positive rods producing hemolysis and resistant to vibriostatic agent O/129. Biochemical profiling (API 20E) identified all isolates (KRW1-KRW5) as Aeromonas hydrophila, clustering with A. hydrophila CECT 839 and A. bestiarum CECT 4227, while MALDI-TOF MS confirmed their highest similarity to A. hydrophila CECT 839T DSM. Virulence gene screening revealed the universal presence of aer, alongside variable combinations of ela, hlyA, act, alt, ast, and lip. Pathogenicity assays fulfilled Koch's postulates, linking isolates to 'black disease', with cumulative mortality reaching 100% by Day 4-5 postinfection for strains KRW1 and KRW2, whereas KRW4 was least virulent. Antimicrobial susceptibility testing revealed multidrug resistance, with MAR indices ranging from 0.130 (KRW4) to 0.478 (KRW5). These findings identify A. hydrophila as the etiological agent of black disease in Neocaridina shrimp, underscore its virulence heterogeneity, and highlight the alarming prevalence of antimicrobial resistance in strains circulating in ornamental aquaculture.

Hyperostosis is a natural phenomenon characterised by bone thickening and remodelling that occurs more frequently in wild marine teleosts than in captive populations. Within the family Carangidae, species of the genus Trachinotus are among the most frequently affected, although expression patterns vary widely among taxa. This study provides a comparative assessment of hyperostosis across four Trachinotus species from the southwestern Atlantic (T. marginatus, T. goodei, T. carolinus and T. falcatus), integrating radiographic analyses of freshly collected specimens with museum material and digital archives from the Smithsonian Institution. The occurrence in T. goodei represents the first documented record of this condition for the species. No signs of hyperostosis were observed in T. carolinus or T. falcatus, likely due to ontogenetic size differences relative to previously reported cases. Additional evaluations of four species (T. rhodopus, T. blochii, T. mookalee and T. kennedyi) revealed hyperostotic manifestations in skeletal regions not previously documented in the literature, underscoring taxonomic and anatomical variability within the genus. Overall, our findings expand the known diversity of hyperostosis in Trachinotus, highlight previously unrecognised anatomical patterns, and reinforce the importance of broad geographic and ontogenetic sampling for understanding the evolutionary, functional and ecological implications of this condition in wild fish populations.