Journal of fish diseases最新文献

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.

Kudoa thyrsites is a myxosporean endoparasite that infects fish, frequently resulting in myoliquefaction, impacting the texture and eating quality of fish muscle. The aim of this study was to investigate the effects of K. thyrsites infection on the proximate composition and texture parameters of raw fillets from two South African economically important species: Cape hake (Merluccius capensis) and Cape dory (Zues capensis). Infection status was determined using real-time quantitative polymerase chain reaction. Association of Official Agricultural Chemists (AOAC) methods were used to determine moisture, protein, fat and ash of raw fillets. Texture Profile Analysis measured springiness and gumminess, using an Instron. The study revealed host species-specific impacts. For Cape hake, K. thyrsites infection showed no statistically significant effect on proximate composition or texture (springiness, gumminess). In contrast, Cape dory demonstrated a significant increase in moisture content in infected (76.48%) compared to uninfected samples (75.22%). Furthermore, infected Cape dory exhibited significantly lower springiness (5.98%) compared to uninfected samples (6.30%), correlating with a softer texture. These findings are the first for Cape dory and of interest to the fishing industry for developing quality assessment tools.

The Megalocytivirus pagrus1 causes serious disease in aquaculture and is classified into three clades: infectious spleen and kidney necrosis virus (ISKNV), turbot reddish body iridovirus (TRBIV), and red sea bream iridovirus (RSIV), further classified as genotype I or II. Several recent studies have reported RSIV strains designated as mixed genotype I/II because they were assigned to different subtypes depending on the gene used for phylogenetic analysis. In 2024, three RSIV samples were collected in Japan, one of which (GT1-Oita2024) was PCR-positive but tested negative using an immune fluorescent antibody test (IFAT) with M10 antibodies. Thus, we performed whole genome sequencing and phylogenetic analysis of the IFAT-negative sample and the two other RSIV samples (GT2-Oita2024 and Ehime2024). In GT1-Oita2024, LEGFD, a known antigen of the M10 antibody, was found to harbour several mutations. Based on average nucleotide identity, GT2-Oita2024 and Ehime2024 were classified as genotype II, showing high homology with KagYT-96 and RIE12-1. GT1-Oita2024 was classified as the intermediate type, showing high homology with SBIV-VP13 and 17SbTy. GT1-Oita2024 also contained regions showing homology with genotype I, genotype II and TRBIV. This is the first detection of this genotype in Japan. Further monitoring is warranted to determine the extent of its spread.

Host-parasite interactions are influenced by both abiotic and biotic factors. While abiotic drivers, particularly temperature, have received considerable attention in recent years due to global climate change, the role of biotic factors remains comparatively underexplored. The malacosporean parasite Tetracapsuloides bryosalmonae (Tb), which causes proliferative kidney disease in salmonids, is a well-documented example, where elevated temperature and eutrophication have been shown to intensify disease prevalence and severity. In this study, we investigated whether freshwater sponges, known for their particle-filtering capabilities, can graze on malacosporean spores in the aquatic environment, potentially acting as biotic filters that may influence parasite transmission dynamics. Using an experimental setup, we employed environmental DNA sampling to (1) characterise the short-term release of Tb spores from infected 1+ brown trout (Salmo trutta) and (2) assess the ability of freshwater sponge (Ephydatia muelleri) to remove Tb spores from water and function as a bio-sampler. Our results show that sponges significantly reduced Tb DNA concentrations in water. However, their effectiveness as bio-samplers and concentrators of Tb was limited, likely due to the rapid degradation of ingested Tb DNA. These results suggest that freshwater sponges may function as natural biological controllers of Tb by filter feeding on its infectious planktonic stages in natural environments.

Histopathological studies of infections with the nematode Procamallanus (Procamallanus) pseudolaeviconchus Moravec and Van As, 2015, an intestinal parasite of Clarias gariepinus (Burchell, 1822), are scarce. The current study describes histopathological changes in the stomach of C. gariepinus infected with P. (P.) pseudolaeviconchus and links it to the parasite's wound-inflicting and feeding structures using light microscopy (LM) and scanning electron microscopy (SEM). A total of 20 fish were collected from the Vaal River below the Vaal Dam and Lake Heritage in the Crocodile River, Gauteng, South Africa. In Lake Heritage, the prevalence of the infection was 80%, with mean intensity and mean abundance of 2.5 and 2, respectively. Perforation and alteration of the columnar epithelial cells lining the secondary folds of the stomach mucosa, trauma to the loose connective tissue, and gastric glands were observed. Mast cell numbers did not vary in the infected and uninfected samples, indicating the absence of an initiated cellular immune response. No haemorrhage, cellular infiltration, inflammation, necrosis or granuloma formation was observed in the infected sample. The peribuccal flanges, the solid buccal capsule and the muscular oesophagus are the wound-inflicting and feeding structures.