Journal of fish diseases最新文献

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.

Quantifying intestinal parasite load in freshwater fish requires the development of reliable, minimally invasive methods. We evaluated the use of a very thin and flexible endoscope to detect and quantify acanthocephalan parasites in 25 European chubs (Squalius cephalus). The presence and number of parasites, as estimated using the endoscope, were correlated with dissection-based counts, especially in the anterior part of the intestine accessible via the insertion tube. Accuracy declined in highly infected fish due to overlapping parasites, but endoscopy still provides an accurate evaluation of infection probability and intensity. Thus, this study validates the use of endoscopy as a reliable method for intestinal parasite monitoring in freshwater fish. The deployment of this tool for field-based studies offers promising perspectives for parasitology research.

Yellowfin tuna (Thunnus albacares) is a valuable recreational and commercial species in Grenada and the Caribbean region. Myxozoans, specifically the monotypic Kudoidae family within the Order Multivalvulida, are marine parasitic organisms that can negatively impact fish health and marketability. On 8 September 2023, muscle fillets from a yellowfin tuna caught off the coast of Grenada and containing numerous white nodules were submitted for diagnostic evaluation. Gross examination of the muscle showed firm, spherical to ovoid, white polysporous cysts approx. 0.8-1.3 mm in diameter and approx. 10-20 cysts per 2 × 2 cm section of muscle. Cysts were sharply excised and assessed by wet mount cytology revealing a myriad of quadrate myxosporean parasites consistent with the genus Kudoa. Histopathologic examination demonstrated numerous, intracytoplasmic plasmodia with thick hyaline walls containing intact and necrotic myxospores. Parasites present outside of plasmodia were associated with myoliquifaction of the tissue. The case isolate was morphologically consistent with K. thunni and the partial 18S small subunit rDNA (SSU) and 28S large subunit rDNA (LSU) demonstrated high homology (SSU: 99.8%-100%; LSU: 99.5%-100%) to several K. thunni isolates, including those isolated from blackfin tuna (T. atlanticus) harvested near the Caribbean islands of St. Kitts and Nevis. This is the first report of K. thunni infecting yellowfin tuna in the Caribbean region and expands the epidemiologic, pathologic, and molecular record for this parasite.

Thirty lactic acid bacteria (LAB) isolates were obtained from the digestive tracts of whiteleg shrimp (Penaeus vannamei) and screened for antagonistic activity against Vibrio parahaemolyticus, the causative agent of Acute Hepatopancreatic Necrosis Disease (AHPND). Among these, four isolates demonstrated strong inhibitory effects, producing inhibition zones of 16-20 mm in agar well diffusion assays. These four LAB isolates were reported to cause no shrimp mortality during the feeding trials. Notably, shrimp fed with the isolate CG02 for 4 weeks showed a significantly improved survival (p < 0.05) after the immersion challenge with V. parahaemolyticus strain pVPA3-1. Based on 16S rDNA sequencing, the isolate CG02 was identified as Lactobacillus plantarum. To improve its viability, the isolate CG02 was encapsulated into spray-dried microcapsules. The resulting probiotic powder exhibited high cell viability, with counts of 9 ± 1.45 × 10⁸ CFU g^-1 after 4 months at room temperature, and 4.11 ± 0.38 × 10⁸ CFU g^-1 after 8 months at 4°C. When incorporated into shrimp feed, the CG02 powder did not cause any shrimp mortality. Moreover, it provided a relative percent survival (RPS) of 34.78% compared to the control group following the immersion challenge with V. parahaemolyticus. These results highlight the potential of spray-dried L. plantarum CG02 as a probiotic feed additive for enhancing shrimp health and supporting sustainable aquaculture practices.

Red-spotted masu trout (Oncorhynchus masou ishikawae; hereinafter, referred as amago trout), is a freshwater salmonid fish species endemic to Japan. From September to October 2023, chronic mortality was observed on an amago trout farm in eastern Japan. To identify the cause of death, bacterial isolation, predominant bacterial species identification, histopathology and experimental challenge test were performed. As a result, bacterial colonies with characteristic features were isolated from all moribund fish. The 16S rRNA and rpoB gene sequences of the isolates showed high similarity with those of Bacillus sp. Identical 16S rRNA and rpoB gene sequences were also detected in moribund fish tissues. The histopathology revealed bacteria in multiple organs, including the spleen, in five of six fish examined. In the experimental challenge test, the fish that were infected with a high dose of bacteria (1.26E+07 cfu per fish) started to die at 3 days post-infection (dpi) and all fish died by 7 dpi. The cumulative mortality rate was lower in the group infected with a lower number of bacteria (1.26E+06 cfu per fish). Our findings identify Bacillus sp. as the disease agent. This is the first report of Bacillus infection in salmonids.

Largemouth bass ranavirus (LMBV) poses a significant threat to the aquaculture industry by causing severe systemic disease and substantial economic losses. This study investigates the tissue distribution, pathological damage, and host response following LMBV-GD1909 infection using two infection models: experimental injection and simulated natural immersion. In the injection model, infected fish exhibited clinical signs, including skin ulcers, haemorrhaging at fin bases, body darkening and organ swelling. Histopathological analysis revealed extensive multi-organ damage, particularly in the liver, spleen, and kidney, characterised by necrosis, haemorrhage, vacuolar degeneration and inflammatory infiltration. Haematological and serum biochemical analyses indicated significant alterations in key parameters, including elevated WBC, RBC and GLU levels, and reduced PLT, TP and LDH levels, reflecting systemic physiological disruption. Viral dynamics analysis demonstrated the pantropic nature of LMBV, with rapid dissemination to multiple tissues post-injection. The liver and spleen were identified as primary target organs, showing the highest viral loads and most severe pathology, indicating a direct correlation between viral load and organ dysfunction. In the immersion model, simulating natural infection, the gills and skin displayed the highest viral loads initially, identifying them as the major entry portals. The gills also served as a key site for viral replication, with a clear gradient of viral spread from external to internal tissues observed over time. This study comprehensively elucidates the tissue tropism, dissemination pathways, and pathological impact of LMBV, providing critical insights for developing targeted prevention and control strategies against LMBV.

While nephrocalcinosis has received considerable attention in Atlantic salmon aquaculture, mineralisation of the urinary bladder remains largely overlooked. Obstruction of the urinary bladder, well recognised in terrestrials as a potentially fatal condition, is often missed in fish due to its exclusion from routine histological assessments. An increasing number of field cases, colloquially referred to as 'urinary plugs', are now being observed, frequently occurring without or with only slight, nephron mineralisation. This study describes histopathological changes associated with bladder mineral deposits, urocystolithiasis, in farmed Atlantic salmon, including obstruction, urothelial degeneration and intra-renal lesions. The findings highlight urocystolithiasis as an underdiagnosed condition with potential fish health and welfare implications. Functional and histopathological studies targeting the entire urinary system are warranted to elucidate its pathophysiological nature and to support the development of preventative and therapeutic approaches.