Journal of fish diseases最新文献

Gyrodactylus spp. pose significant threats to farmed fish due to their high pathogenicity, resulting in substantial economic losses in aquaculture. Currently, treatments for gyrodactylosis primarily rely on chemical agents, the efficacy and safety of which are not always satisfactory, underscoring the urgent need for novel anthelmintic agents. In the pursuit of novel therapeutic agents, we assessed the in vivo anthelmintic efficacy of 20 natural compounds using a goldfish (Carassius auratus)–Gyrodactylus kobayashii infection model. Among these compounds, naringenin (NAR) exhibited the highest efficacy and was selected for further investigation. In vitro results demonstrated NAR's significant anti-parasitic activity, achieving 100% mortality at 4.0 mg/L after 60 min of exposure. Subsequent in vivo investigations revealed that the median effective concentration (EC₅₀) of NAR was 0.859 mg/L at 24 h and 0.704 mg/L at 48 h post-treatment, with EC₁₀₀ at 2 mg/L. Additionally, NAR significantly impaired the mobility of G. kobayashii. Confocal microscopy revealed that NAR-induced structural damage in worm tissues, including epidermal disruption and muscle dissolution. Moreover, both in vitro and in vivo exposure to NAR caused a decline in ATP levels, indicating potential impairment of energy production in G. kobayashii. Collectively, these findings establish NAR as a promising therapeutic agent for protecting farmed fish against Gyrodactylus infections.

Dermocystidium is a pathogenic fungus-like protist that infects many fish species, causing lesions on the skin, gills and other tissues, which may result in systemic disease. In the present study, a new Dermocystidium anguillae infection in the skin and eyes of the koi carp (Cyprinus carpio) from Iran was described using a comprehensive analysis of morphological, histological and molecular data. Filiform hyphal-like cysts were visible on wet mounts. The cysts were filled with spherical to round spores. Wet mount preparations of fresh cyst contents of Dermocystidium anguillae revealed a massive number of spherical to oval spores with refractile bodies. The spores were approximately 5–13 μm in diameter. In histopathological examination, the skin and eye masses were infiltrated by numerous elongated cystic structures. The eosinophilic and hyalinised wall of the cysts was 4–6 μm thick and filled with numerous spherical spores with eccentrically situated nuclei and a large refractile body. In the dermal layer, around the cystic structures, there was edema and granulomatous dermatitis (infiltration of moderate numbers of plasma cells, small lymphocytes and epithelioid cells). Oedema, hyperaemia and multifocal haemorrhages were evident in the ocular masses. The nucleotide sequencing results obtained from the GenBank BLASTN database indicated a 100% sequence similarity with the registered Dermocystidium anguillae.

Shrimp aquaculture plays a crucial role in global food production but is increasingly threatened by viral and microsporidian pathogens such as White Spot Syndrome Virus (WSSV), Enterocytozoon hepatopenaei (EHP) and Infectious Hypodermal and Haematopoietic Necrosis Virus (IHHNV). Conventional reliance on antibiotics to combat these infections has raised serious concerns regarding antimicrobial resistance, environmental contamination and food safety. Additionally, environmental stressors such as salinity shifts and poor water quality exacerbate disease outbreaks, leading to severe production losses across Asia and Latin America. To explore eco-friendly therapeutic alternatives, this study assessed the antiviral potential of cannabidiol (CBD), a bioactive compound extracted from Cannabis sativa seed oil, identified through GC–MS analysis. Using molecular docking techniques, we evaluated CBD's interactions with key viral proteins: VP28 of WSSV, the tubulin β-chain of EHP and the capsid protein of IHHNV. The docking results revealed strong binding affinities of −6.61 kcal/mol (EHP), −6.72 kcal/mol (IHHNV) and −5.38 kcal/mol (WSSV), indicating stable and potentially inhibitory interactions. Structural models were retrieved from RCSB PDB and SwissModel, while ligand preparation and docking were performed using AutoDock 4.2. CBD also demonstrated favourable pharmacokinetic and safety profiles, with predictions indicating no mutagenicity, hepatotoxicity or cardiotoxicity, and acceptable drug-likeness characteristics. Compared to other plant-derived compounds previously tested in shrimp disease models, CBD exhibited superior binding stability, more interaction residues and better bioavailability scores. These findings highlight CBD as a promising dual-function agent, capable of both modulating shrimp immunity and directly inhibiting key viral pathogens. These findings highlight cannabidiol (CBD) as a promising dual-action compound, with the potential to both enhance shrimp immune responses and exert direct antiviral effects against key pathogens. This study lays a robust groundwork for future in vivo validations, formulation strategies and regulatory frameworks, ultimately supporting the development of sustainable, precision-based aquaculture health management.

The cage aquaculture industry in Lake Victoria, Kenya is growing explosively to meet increasing demand for fish, yet large-scale fish mortalities are prevalent and pose economic shocks with catastrophic livelihood impacts. To gain a more comprehensive understanding of fish health in Lake Victoria, our study applied: (1) survey of cage farmer accounts, perceptions and responses to fish kill events; (2) rapid-response investigation to a significant tilapia mortality event; (3) active disease surveillance; and (4) antimicrobial resistance (AMR) testing of bacterial pathogens via disk diffusion. There were 82 fish kills recalled from 2020 to 2023 with total mortalities exceeding 1.8 million tilapia; yet, only 39% of farmers reported to Kenyan institutions and 17% of farmers attempted medical treatment. Low dissolved oxygen (DO) levels and the isolation of Aeromonas jandaei, Enterobacter hormaechei and Staphylococcus epidermidis were implicated as suspected causes for a recent tilapia mortality event. Active disease surveillance detected trichodinids and monogeneans as common external parasites and identified an additional six bacterial species in tilapia (Acinetobacter soli, Bacillus cereus, Kocuria rhizophila, Micrococcus luteus, Plesiomonas shigelloides, Staphylococcus sciuri) previously published as fish pathogens. Furthermore, we identify AMR patterns that will support the development of host- and pathogen-specific thresholds.

This study examines the effects of iodophor disinfection on the prevalence of Carnobacterium maltaromaticum and Vagococcus salmoninarum during several years of spawning brook trout (Salvelinus fontinalis). The first year of the study, individual eggs were collected from females and separated into four treatment groups: unfertilised, unfertilised and disinfected, fertilised and fertilised and disinfected. Disinfection consisted of iodophor treatment at 100 ppm for 60 min. All eggs were incubated in TSB and monitored for bacterial growth. No growth was observed from disinfected eggs. However, from non-disinfected eggs, C. maltaromaticum was isolated from the surface of 25% of individual unfertilised and 53% of fertilised eggs. V. salmoninarum was only isolated from non-disinfected fertilised eggs. In year two, the process was repeated, though all eggs were fertilised and iodophor disinfected at 100 ppm for 30 min. Again, the pathogens were present on only a small number of disinfected eggs—V. salmoninarum and C. maltaromaticum were detected from the surface of one and five eggs respectively. Throughout the study we found no evidence of intra-ova transmission from disinfected eggs. The study also demonstrates that iodophor is highly efficacious in reducing the prevalence and transmission risk of these pathogens.

Crucian carp (Carassius auratus gibelio) is sensitive to the infection of Cyprinid herpesvirus 2 (CyHV-2), displaying severe inflammatory reactions characterised by systemic congestion and gill bleeding. This study aimed to elucidate the mechanism by which CyHV-2 infection induces interferon gamma (IFNγ) expression in caudal fin cells (GiCF) of Carassius auratus gibelio, specifically investigating the role of the IL-17C/NF-κB signalling axis. In mammalian systems, virus-induced IL-17 has been demonstrated to activate NF-κB, a master regulator of inflammatory responses that controls multiple antiviral immune genes including interferons. Therefore, the induction mechanism of IFNγ gene expression following CyHV-2 infection was elucidated by revealing the interplay among IL-17C, NF-κB and IFNγ in this study. We demonstrated that CyHV-2 infection significantly upregulated the expression of IL-17C, NF-κB and IFNγ at both transcriptional and translational levels in GiCF. Furthermore, overexpression of IL-17C upregulated NF-κB and IFNγ expressions, while pharmacological inhibition of NF-κB (BAY 11-7082) suppressed this upregulation. This study provides the first evidence for the activation of IL-17C/NF-κB/IFNγ antiviral signalling axis in teleost fish in response to herpesvirus infection. Our findings highlight the dual role of virus-induced NF-κB activity, which not only orchestrates host defence (via IFNγ) but may also be exploited by the virus to potentially regulate its own gene transcription.

This study explores the integration of black soldier fly larvae (BSFL) as a complementary functional ingredient to increase the soybean meal (SBM) inclusion in rainbow trout (Oncorhynchus mykiss) diets. Six experimental diets were formulated including a control diet as fishmeal (FM), an SBM-based diet, and 2.5% and 5% whole-body (WB) or defatted (DB) BSFL-supplemented SBM-based diets. Results revealed that BSFL inclusion positively influences gut health, immune response and survival rates following challenge with Flavobacterium psychrophilum. Dietary lauric acid content significantly impacted whole-body lauric acid levels in a dose-dependent manner, with BSFL diets showing higher levels than FM and SBM diets. Fish fed diets with BSFL exhibited enhanced survivability against F. psychrophilum infection compared to SBM-fed fish, with the highest survival rates observed in the WB5 (5% whole-body BSFL) group. Histological analysis demonstrated improved intestinal morphology in BSFL-fed fish, particularly evident in the absence of pathogenic enteritis. Gene expression analysis revealed upregulated proinflammatory markers (IL-8, TNF-α, C5) in BSFL-fed fish post-challenge, indicating an enhanced immune response. These findings indicate the potential of BSFL as a functional feed ingredient to complement high SBM inclusion in rainbow trout with improved health and performance. By strategically reducing inclusion levels and repositioning BSFL as a functional feed ingredient instead of fishmeal replacer in aquafeed formulations, one can mitigate economic concerns while maximising the benefits of this sustainable alternative.

Streptococcus agalactiae (Group B Streptococcus, GBS) poses a significant threat to Nile tilapia (Oreochromis niloticus) aquaculture, causing severe streptococcosis characterised by high mortality and economic losses. This study elucidates the pathogenesis of S. agalactiae through an integrated diagnostic approach and evaluates bacteriophage therapy as a sustainable alternative to antibiotic treatments. Clinical signs in infected tilapia, including erratic swimming, exophthalmia, and haemorrhagic lesions, were accompanied by systemic postmortem findings such as hepatosplenomegaly and ascitic fluid accumulation. Comprehensive identification of S. agalactiae isolates from pond water and diseased fish was achieved using morphological, biochemical, serological, and molecular techniques, confirming its role as the causative agent. Concurrently, three bacteriophages (STRA1, STRA2, STRA3) were isolated from aquaculture ponds and characterised by their lytic efficacy, host specificity, and environmental stability. These phages exhibited tailed morphologies, high lytic activity (up to 83.3% against S. agalactiae), and resilience under pond-like conditions (pH 4.0–10.0, 28°C–50°C), with STRA1 demonstrating efficacy against multidrug-resistant strains. In vitro assays revealed significant bacterial load reductions (e.g., STRA3: 1.03 × 10⁶ CFU/mL vs. control: 6.13 × 10⁶ CFU/mL at 72 h), though resistant mutants emerged at low frequencies (8.11–8.40 × 10⁻⁴). Suboptimal water quality parameters, including low dissolved oxygen (3.6 mg/L) and elevated iron (1321 μg/L), likely exacerbated infection severity. These findings underscore S. agalactiae's pathogenicity and position bacteriophage therapy as a promising, eco-friendly biocontrol strategy, warranting further in vivo validation to optimise its application in tilapia aquaculture.

Tenacibaculosis, caused by T. dicentrarchi, results in skin lesions, ulceration, yellow plaques on teeth, and haemorrhaging in the operculum, peduncle and pectoral fins. It is the second leading cause of mortality in farmed Atlantic salmon (Salmo salar) in Chile. Currently, no vaccine is available to prevent the disease. In silico and in vivo studies have shown that iron plays a key role in T. dicentrarchi infection. We hypothesised that culturing the TdCh05 vaccine strain under iron-limiting conditions (i.e., with non-assimilable iron chelator 2.2′-dipyridyl [DIP]) would enhance Atlantic salmon protection against tenacibaculosis. Fish were vaccinated intraperitoneally with prototypes (A) TdCh05, (B) TdCh05 + DIP or (C) A + B (a 1:1 mixture of inactivated cultures), and a control group was challenged by bath immersion with a heterologous T. dicentrarchi strain. Each prototype was emulsified with a commercial adjuvant. At 14 days post-challenge, Atlantic salmon injected with FMM broth had a cumulative mortality of 73.3%, followed by the TdCh05 + DIP (66.7%) and A + B (54.8%) prototypes. The lowest cumulative mortality value (50%) was observed for the prototype containing T. dicentrarchi TdCh05 grown only in FMM. Moreover, a high proportion of the vaccinated fish that survived the challenge, regardless of the vaccine prototype, carried T. dicentrarchi in various internal organs, particularly in the spleen. Future studies should focus on identifying the most suitable antigens to develop an effective vaccine for the prevention of T. dicentrarchi-induced tenacibaculosis.