Journal of fish diseases最新文献

A captive-reared cohort of Laurel Dace, Chrosomus saylori (Skelton 2001) (Cypriniformes: Leuciscidae), a federally-endangered species endemic to several streams in eastern Tennessee's Cumberland Plateau, exhibited signs of morbidity and trickling mortalities in a recirculating aquaculture system. Ziehl-Neelsen (ZN) staining revealed acid-fast rod-shaped bacteria within necrotic and intracellular lesions affecting the eye, swim bladder, spleen, and ovary. Histopathology showed granulomatous inflammation characterised by macrophages, multinucleated giant cells, and eosinophilic exudates. The eye, swim bladder, and ovary were particularly impacted: the choroid plexus of the eye displayed haemorrhages and dense cellular infiltrates; the swim bladder exhibited granulomatous inflammation with extensive fibrosis; the ovary contained caseous granulomas; and the choroid plexus of the eye displayed haemorrhages and dense cellular infiltrates. PCR amplification of the hsp65 gene (316 bp) from formalin-fixed and paraffin-embedded lesioned tissues was identical (100% similar; 424 bp fragment) to that of the type strain of Mycobacterium gordonae Bojalil et al. 1962 (AF547840). This is the first report of an infection by M. gordonae in Laurel Dace; the first record of this bacterium causing a lesion in the swim bladder, eye, or ovary; and the first record of M. gordonae from a freshwater fish in North America.

Vibrio species are the main causative agents of vibriosis, the most prevalent bacterial disease affecting the aquaculture industry. Since 2009, Vibrio parahaemolyticus has been identified as the key pathogen responsible for Acute Hepatopancreatic Necrosis Disease (AHPND), leading to widespread outbreaks across several Southeast Asian countries. Although V. parahaemolyticus is the primary causative agent of AHPND, recent studies have shown that other Vibrio species, such as V. campbellii and V. harveyi, can also cause AHPND when they acquire the PirAB toxin-encoding plasmid. This study aimed to develop DNA aptamers that specifically target the LuxP receptor protein, a key component of the quorum sensing system. QS regulates the expression of multiple virulence factors, including novel toxins involved in Vibrio infection. Using Ni-NTA Systematic Evolution of Ligand by Exponential Enrichment, the DNA aptamer, VPQ1, was developed, which binds to the LuxP receptor. From the SELEX cycles, a total of 1114 aptamer candidates were isolated and sequenced. Thermodynamic analyses demonstrated that the interactions between recombinant LuxP and the selected aptamers VPQ1 and VPQ2 were exothermic, with a dissociation constant of 23.3 nanomolar and 24.2 nanomolar, respectively. Functional assays showed that the treatment with VPQ1 led to downregulation of genes associated with bacterial metabolism, quorum sensing, flagellar assembly and biofilm formation. These findings suggest that aptamer VPQ1 may serve as a promising anti-virulence agent to disrupt QS and mitigate Vibrio infection in aquaculture systems.

The composition and structure of the helminth fauna in the intestine of the anostomid fish Rhytiodus microlepis was studied during two distinct periods in a floodplain lake in Central Amazonia. Additionally, the tissue damage in the infected intestine caused by the endoparasites was observed. Of the 38 fish analysed, a high prevalence of infection by Digenea (metacercariae) and Acanthocephala (> 90%) was observed; the metacercariae preferred the initial portions of the intestine, with a high frequency of occurrence in the lamina propria of the mucosa (75.9%), while the acanthocephalans occurred in the intermediate portions of intestine, often free in the lumen (99.5%). The histological alterations caused by the presence of the acanthocephalans were slight compression of the villi, desquamation/abrasion of the mucosal epithelium and hemorrhagic foci. Villi hypertrophy, intense leukocyte infiltration, formation of fibrous capsules and necrosis were the main responses associated with metacercariae. The composition and structure of infracommunities of intestinal helminths in R. microlepis showed seasonal variations, indicating that the hosts are susceptible to infections in the low and in the high-water seasons, with high values of intensity, abundance and pathogenicity (IAH value: 358.8 ± 99.22) of metacercariae during the low waters, suggesting that fish are more vulnerable to infections by these parasites in this period.

Abalone asfa-like virus (AbALV) is a pathogen responsible for the mass mortality of juvenile abalones in hatcheries in Japan. However, the susceptibility of the Ezo abalone, H. discus hannai, to the virus has not been investigated, unlike the other commercially important Haliotis species in Japan. In this study, H. discus hannai at 6 months of age were exposed to effluent from an aquarium containing AbALV-infected H. discus discus and monitored for 49 days. The mortality rate began to increase at approximately 40 days post-infection (dpi). The cumulative mortality was significantly higher in the infected group (45% - 55%) than in the uninfected control group (14% - 15%) at the end of the experiment. The mean viral load peaked at 10^{5.4 ± 0.4} copies/μg total DNA at 29 dpi. Histological analysis detected many degenerated cells in the gills at 29 dpi, and these cells were immunohistochemically positive for AbALV. Although the number of degenerated cells decreased thereafter, oedema became remarkable in the gills at 42 and 49 dpi, which may have contributed to high mortality in juveniles. Our study suggests that infection control against AbALV is essential for stable juvenile production of H. discus hannai, similar to that of other susceptible Haliotis species/subspecies.

Quasispecies represent a general evolutionary model for most RNA viruses and other viruses with high mutation rates. However, quasispecies have not been previously reported in the grass carp reovirus (GCRV), which has caused severe hemorrhagic disease in grass carp in China for several decades. This study revealed the presence of multiple co-existing mutant sequences within individual viral strains, indicative of a quasispecies distribution in GCRV strains through Sanger sequencing of viral genomic segments. Different viral strains exhibited varying degrees of quasispecies diversity and heterogeneity, potentially establishing a basis for viral evolution in response to environmental changes and host adaptation. This study provides novel insights into the genetic variation and evolution of GCRV, which will not only enhance the understanding of GCRV transmission and prevalence but also facilitate the development of vaccines against grass carp hemorrhagic disease.

Erythromycin (EM) resistance in the emerging and prevalent fish pathogen Lactococcus formosensis is mediated by the erythromycin ribosomal methylase B gene [erm(B)], which is located on a transferable R-plasmid. The R-plasmid structure in EM-resistant L. formosensis was highly homologous to that of the drug resistance plasmid pAMβ1 found in Enterococcus faecalis. Thus, we speculate that the source of the erm(B) gene in fish-pathogenic L. formosensis may have been environmental bacteria in aquaculture areas, particularly enterococci, such as E. faecalis and Enterococcus faecium. However, no direct evidence has been obtained for the genetic exchange of the EM-resistant trait between EM-resistant enterococci and fish-pathogenic lactococci in aquaculture environments. This study aimed to isolate enterococci resistant to EM carrying the erm(B) gene from seawater in aquaculture areas. The detection levels of EM-resistant enterococci ranged from below the detection limit to 130/100 mL as determined using the most probable number method. Among the 17 erm(B)-positive isolates, five EM-resistant enterococcal strains transferred EM resistance to the recipient fish pathogens (L. formosensis or L. garvieae serotype III). These erm(B)- carrying EM-resistant enterococci (n = 5) exhibited high minimal inhibitory concentrations (MIC) for EM, lincomycin (LCM), and oxytetracycline (OTC). Recipient strains that acquired erm(B) displayed elevated MIC values against EM and LCM, but not against OTC. These results suggest that EM-resistant enterococci carrying erm(B) are present in aquaculture environments, and that the erm(B) gene can potentially be transferred to fish pathogens.

Baicalin, a bioactive flavonoid from Scutellaria baicalensis, shows significant therapeutic efficacy on tilapia (Oreochromis niloticus) bacterial infections, but its application remains limited due to the lack of pharmacokinetic data. In this study, single oral administration of baicalin at 12 mg/kg was carried out in O. niloticus under 32°C. Then, samples of plasma, kidney, bile, muscle, liver and brain were collected at various time intervals up to 96 h. A high-performance liquid chromatography (HPLC) method was developed and validated for baicalin quantification assay in each sample and subjected to non-compartmental analysis. Results showed that baicalin was rapidly absorbed following oral administration. A double-peak phenomenon was observed in tilapia plasma. The first (C_max1) and the second (C_max2) peaks were 46.828 μg/mL at 1 h and 17.069 μg/mL at 4 h, respectively. The elimination half-life (t_1/2) and the volume of distribution (V_d) were 26.654 h and 0.462 L/kg, respectively. A double-peak phenomenon was also observed in kidney and liver. The C_max1 and C_max2 in kidney were 66.981 μg/g at 2 h and 85.577 μg/g at 8 h, respectively, and in liver were 34.147 μg/g at 2 h and 39.971 μg/g at 8 h. While a single peak was observed in brain and bile, their C_maxs were 29.787 μg/g at 8 h and 63.038 μg/g at 12 h, respectively. Notably, the triple-peak phenomenon was observed in muscle and the C_max1, C_max2 and C_max3 were 55.771 μg/g at 1 h, 23.603 μg/g at 4 h, 25.488 μg/g at 12 h and 30.192 μg/g at 48 h. The t_1/2 of baicalin in kidney, liver, brain and bile were 57.273, 38.169, 38.169, 8.315 and 72.705 h, respectively. In plasma, liver, kidney, brain, muscle and bile, the area under the concentration-time curve from 0 to 96 h relative to the half maximal inhibitory concentration against Streptococcus agalactiae β-hemolysin/cytolysin (AUC_0-96 h/IC₅₀) of baicalin were 132.755, 443.169, 731.920, 66.283, 452.864 and 540.540 h, respectively; the peak concentration to IC₅₀ ratio (C_max/IC₅₀) in plasma, liver, kidney, brain, muscle and bile were 8.688, 7.416, 15.877, 5.526, 10.347 and 11.695, respectively; the concentration remained above the IC₅₀ (T > IC₅₀)for over 96 h in all tissues examined, with the exception of the brain (27.205 h). These results provide a scientific basis for the application of baicalin in the prevention and control of tilapia bacterial diseases, especially tilapia streptococcosis.

Pelteobagrus fulvidraco, which is popular with consumers because of its fine meat and appreciated taste, occupies an important position in freshwater fish in China. In recent years, P. fulvidraco has been seriously infected by Aeromonas veronii, Aeromonas sobria and Edwardsiella ictaluri, which has caused great economic losses. However, the current detection methods for these three pathogens are difficult to meet the needs of disease prevention and control. To address this challenge, this study established a TaqMan multiplex real-time fluorescence quantitative PCR method capable of simultaneously detecting three pathogens based on the conserved genes gyrB of A. veronii, A. sobria and E. ictaluri. This method has strong specificity and no cross reactivity between different pathogens. In addition, this method has high sensitivity, with detection limits of 10¹, 10⁰ and 10⁰ copies/μL for A. veronii, A. sobria and E. ictaluri, respectively. Using this method to detect 100 clinical specimens collected in 2023-2024, the detection rates of A. veronii, A. sobria and E. ictaluri were higher than those of conventional PCR. In conclusion, the TaqMan multiplex qPCR method developed in this study provides a new and powerful tool for early diagnosis, prevention, control and purification of A. veronii, A. sobria and E. ictaluri. This study is of great significance in improving the efficiency of P. fulvidraco culture and ensuring the healthy development of the aquaculture.

Intensification of fish aquaculture worldwide has led to severe problems of diseases caused by parasitic dactylogyrideans. In this study, the anti-dactylogyridean efficacy of treating Colossoma macropomum with baths of emamectin benzoate (EMB) was investigated for the first time, along with the effects of this treatment on the haematology and histology of its gills. Thirty-nine fish (three replicates of 13 each) received four consecutive daily baths with EMB at a concentration of 0.5 g L^-1 and one control group of 39 fish (three replicates of 13 each) only received water from the cultivation tank. The EMB treatments showed effectiveness of 50.2% against Anacanthorus spathulatus, Notozothecium janauachensis and Mymarothecium boegeri infecting the gills of C. macropomum. Fish treated with EMB only caused decreases in the total red blood cell, total thrombocytes, leukocytes, monocytes and neutrophils numbers, while the mean corpuscular haemoglobin concentration (MCHC) increased. Aneurysm was the gill structural alteration caused by EMB treatment, and mean assessment values (MAV) indicated moderate to severe damage due to this irreversible gill alteration. Our results lay a safe foundation for the application of EMB as a potential chemotherapeutic agent for dactylogyridean control in C. macropomum aquaculture, because this drug should be used cautiously for anthelminthic treatment in fish.

White Spot Syndrome Virus (WSSV) is known to cause significant mortality in farmed shrimp, including black tiger shrimp (Penaeus monodon) and white leg shrimp (Litopenaeus vannamei) across several countries. Prolonged infections with WSSV are difficult to eliminate with traditional methods like vaccinations, probiotics, and immunostimulants. Herein, we assessed the antiviral effectiveness of two medicinal plants, Cydonia oblonga and Juglans regia, against WSSV. The crude ethanolic leaf extract of J. regia and the acetone fruit extract of C. oblonga were evaluated through phytochemical analysis, GC-MS profiling, in silico studies, in vivo toxicity assessment, and antiviral validation. The presence of bioactive substances, such as phenolics, flavonoids, and antioxidants known for their strong antiviral and immunomodulatory properties, was verified by phytochemical analysis. In particular, the important bioactive constituents with known antiviral potential, including naringenin, juglone, kaempferol, beta-sitosterol, quercetin, and epicatechin, were confirmed in these plant extracts by GC-MS analysis. Strong binding affinities of these medicines to the VP28 envelope protein of WSSV were shown in silico molecular docking studies, with the binding energies ranging from -6.0 to -8.9 kcal/mol. Significant protection against WSSV challenge was demonstrated by in vivo neutralisation tests. Pairwise comparisons confirmed extremely significant differences between the treated and untreated infected groups, and these results were statistically significant (p ≤ 0.05). Molecular diagnostics by PCR provided additional confirmation of the antiviral activity of the medicinal plants, coupled with a Western blot assay and an indirect ELISA. Taken together, the findings suggest that the studied medicinal plants can offer a safe, affordable, and environmentally beneficial substitute for synthetic antiviral drugs in aquaculture.