Diseases of aquatic organisms最新文献

The host specificity of Marteilia pararefringens is under discussion after its suggested reseparation from the flat oyster pathogen M. refringens in 2018. In Norway, M. pararefringens has been detected in mussels Mytilus spp. sampled from several isolated, small heliothermic ponds (polls) that, at least on the western coast, inhabit some of the last reproducing flat oyster populations. M. refringens has never been detected in Norway. The polls have a limited water exchange, and their uniquely warm temperature can result in high M. pararefringens prevalence and infection intensities, representing unique sites to study the susceptibility of flat oysters to this parasite. We have sampled flat oysters and mussels from all known M. pararefringens sites along the Norwegian coast. All flat oysters and mussels were screened by histology and PCR. Furthermore, to study the potential effect of natural resistance breeding of local flat oysters subjected to repetetive M. pararefringens cycles, we deployed naïve flat oysters from a known Marteilia-free poll to Agapollen, where the parasite has had consistent infection cycles since its discovery in 2016. Naïve mussels were deployed simultaneously in 2 separate years to verify that the flat oysters were subjected to at least 2 transmission cycles. M. pararefringens was not detected in any flat oysters in any poll, local or naïve, despite presence in the mussel populations. Our results show that the European flat oyster Ostrea edulis is not a susceptible host for M. pararefringens.

Viral hemorrhagic septicemia virus (VHSV) was detected and identified in healthy bastard halibut Paralichthys olivaceus on the east coast of China through a combination of virus isolation, real-time reverse transcription polymerase chain reaction (RT-PCR) and conventional RT-PCR followed by sequencing. Analysis using MEGA11 software revealed that the isolated VHSV belongs to genotype IVa. Bastard halibut fry were experimentally infected by immersion and gill inoculation with infected cell culture medium and exhibited clinical signs. Cytopathic effects (CPE) were observed again when the epithelioma papulosum cyprini (EPC) cells were inoculated with homogenized tissue samples from the diseased fish. Real-time RT-PCR confirmed the existence of the virus in the infected fish tissues. Transmission electron microscopy (TEM) revealed the presence of numerous virus particles in the infected EPC cells, both extracellularly and intracellularly. The combination of clinical signs, typical CPE, and genetic analysis identified the isolated virus as VHSV.

Bonamia (Haplosporida) are oyster parasites capable of devastating oyster populations. The near-circumglobal distribution of the host generalist B. exitiosa has previously been associated with the natural and anthropogenic dispersal of broadly distributed non-commercial oysters in the Ostrea stentina species complex. Here, we took a global snapshot approach to explore the role of the widely introduced Pacific oyster Magallana gigas, a commercially important species that can be found on every continent except Antarctica, in transporting Bonamia. We screened 938 M. gigas individuals from 41 populations in this oyster's native and non-native geographic range for presence of Bonamia DNA using PCR. B. exitiosa was the only species detected and only within 2 of 5 populations from southern California, USA (10 and 42% PCR prevalence). Therefore, M. gigas could have played a role in transporting B. exitiosa to California (if introduced) and/or maintaining B. exitiosa populations within California, but morphological confirmation of infection needs to be done to better understand the host-parasite dynamics within this system. We detected no Bonamia DNA within any other non-native M. gigas populations (n = 302) nor within native M. gigas populations in Japan and Korea (n = 582) and thus found no evidence to support the co-dispersal of M. gigas and other Bonamia species. Lower sample sizes within some populations and the non-systematic nature of our sampling design may have led to false negatives, especially in areas where Bonamia are known to occur. Nevertheless, this global snapshot provides preliminary guidance for managing both natural and farmed oyster populations.

Newly stocked Danube sturgeons Acipenser gueldenstaedtii developed cutaneous lesions and nearly 100% mortality over the course of 2 mo after introduction into an Austrian fish farm. Necropsy revealed cutaneous plaques and hemorrhages, and histological findings in skin, gills, spleen and kidney tissues showed cell-nucleus alterations consistent with infection by a herpesvirus. The presence of a herpesvirus was demonstrated by the visualization of numerous typical viral particles in different tissues by electron microscopy. A newly developed conventional PCR protocol, targeting a fragment of the viral DNA polymerase gene, further confirmed the presence of a virus related to the species Ictavirus acipenseridallo2 (formerly Acipenserid herpesvirus-2; AciHV-2) in the diseased fish. Amplification products were sequenced and showed 100% identity to the Siberian sturgeon herpesvirus (SbSHV) strain. This is the first report of herpesvirus detection in sturgeon in Austria and of SbSHV, a strain of AciHV-2, in Danube sturgeons.

Infection with the oyster herpesvirus type 1 microvariant (OsHV-1 μVar) has caused mass mortalities of Pacific oyster larvae and spat in multiple countries. Selective breeding to enhance resilience against that virus had been shown as a promising defence strategy. Mass spat mortalities associated with OsHV-1 μVar affected Pacific oyster farms in Ría de Arousa (Galicia, NW Spain), which led us to explore the potential utility of selective breeding to increase cultured oyster survival. Thus, adult oysters that had survived through culture in that area, heavily affected by OsHV-1 μVar, and oysters collected from a naturalised oyster bed that had never been affected, were used as broodstocks in hatchery facilities to produce spat families from each origin. Spat families derived from each stock were transferred into a culture raft in Ría de Arousa; survival and occurrence of OsHV-1 μVar were monitored through cultivation. Spat mortality associated with OsHV-1 μVar was higher in the families deriving from the naïve stock. Adult oyster mortality was detected close to the end of growing-out, which was not associated with OsHV-1 μVar but putatively caused by Vibrio aestuarianus infection. Adult mortality was higher in the families with the highest V. aestuarianus loads; notably, the oyster families with the lowest spat mortality showed the highest adult mortality. Therefore, a potential increase of spat survival in Ría de Arousa through selective breeding to enhance oyster resilience against OsHV-1 μVar could be counteracted by high adult mortality associated with V. aestuarianus infection.

The 2022 Oder River disaster was one of the most significant harmful events in recent European river history, with an estimated 60% reduction in fish biomass in the lower section of the river. While the prevailing hypothesis attributes associated fish kills to toxins from golden algae Prymnesium parvum, our histopathological study on the gills of 2 common cyprinid fish species, namely vimba bream Vimba vimba (L.) and roach Rutilus rutilus (L.), collected from the lower Oder River at 3, 4, and 6 mo after the disaster, suggests another mechanism. Vimba bream showed damage to the epithelial layer of lamellae and increased mucus production. Roach exhibited interlamellar cell mass (ILCM), lamellar damage, including hypertrophy of epithelial cells, lamellar fusion, as well as significant thickening of the water-blood barrier compared to controls. These findings suggest that adverse factors, most likely the increase in toxin concentrations resulting from reduced water levels together with elevated temperatures and low precipitation, triggered the formation of ILCM, increasing the susceptibility of fish to hypoxia. Fish species with a capacity for adaptive interlamellar hyperplasia, such as common bream Abramis brama, roach, and common perch Perca fluviatilis, accounted for the largest number of deaths during the disaster. Vimba bream, which showed no ILCM, were observed only sporadically, with mortality confined to a single area of the Oder. In conclusion, fish capable of adaptive hyperplasia, whereby the gills attempt to protect themselves by developing ILCM, appear to be particularly vulnerable in conditions of aquatic hypoxia.

Cyvirus cyprinidallo 2 (CyHV-2) is the pathogen of herpesviral hematopoietic necrosis (HVHN) that mainly infects goldfish Carassius auratus and crucian carp C. carassius and is characterized by high infectivity and pathogenicity. The availability of rapid and convenient detection methods is essential for early detection of CyHV-2. A colloidal gold immunochromatographic strip using 2 specific anti-CyHV-2 monoclonal antibodies (MAbs) has been developed and validated for rapid detection of CyHV-2. The test results can be viewed within 10min. The detection limit of test strip was 2.08 × 102TCID50 ml-1, and it showed no cross-reactivity with other freshwater fish viral pathogen except KHV (koi herpesvirus). The specificity of the strip was 100% when spleen and kidney tissues of CyHV-2 infected and healthy crucian carp were assayed following an experimental challenge. The colloidal gold immunochromatographic strip will be an effective device for the rapid detection of CyHV-2 in the future.

The present study evaluated the immunomodulatory and disease resistance-enhancing effects of dietary supplementation of Withania somnifera root powder in Labeo rohita (22.10 ± 3.30 g, 12.35 ± 1.15 cm), a commercially important freshwater fish species, against Aphanomyces invadans infection under the agro-climatic conditions of Tripura, Northeast India. Four isonitrogenous and isocaloric experimental diets were formulated with varying levels of W. somnifera root powder: control (0%), D1 (0.1%), D2 (0.2%), and D3 (0.3%). After a 21-d feeding period, the fish were challenged with A. invadans zoospores (1 × 104 spores ml-1; 0.1 ml fish-1) and observed for mortality and blood parameter assessment according to standard protocols. The survival rate was markedly higher at 83.33% in the 0.2% W. somnifera group compared to 31.11% in the control group 14 d post-infection. Dietary W. somnifera supplementation improved serum protein, enzymatic, and hematological parameters. Immunological parameters, including nitroblue tetrazolium activity, serum lysozyme activity, and bactericidal activity, were also significantly higher in W. somnifera-fed fish. The findings suggest that W. somnifera root powder at 0.1-0.3% inclusion levels, with 0.2% being the optimal dose, can enhance disease resistance against A. invadans in L. rohita by modulating innate immune mechanisms. Given the growing concerns over antimicrobial resistance and the need for sustainable aquaculture practices, the use of natural immunostimulants such as W. somnifera offers a promising alternative for disease management, particularly in regions prone to epizootic ulcerative syndrome outbreaks.

This report documents complications in false pilchard Harengula clupeola and scad Decapterus macarellus associated with a salinomycin (60 mg kg-1) and amprolium (100 mg kg-1) gel feed treatment, along with prolonged temperature increase, for an Enteromyxum leei outbreak in a salt water, mixed species, public aquarium exhibit. Shortly after administration, a mass mortality event ensued where hundreds of false pilchards and a few scad died. Medicated gel feed was noted within the gastrointestinal tracts of all affected fish. Microscopic lesions consistently involved myodegeneration and necrosis of the gastric muscularis layer and myocardium. Salinomycin was detected in multiple tissues while amprolium was largely limited to the stomach. Based upon the clinical, pathological, and toxicologic findings, the mortality event was attributed to salinomycin toxicity. False pilchards and scad were the only species affected, suggesting a species-specific sensitivity.

This work was performed to generate the data needed to set epidemiological cut-off values for minimal inhibitory concentrations (MICs) of 10 antimicrobial agents against Vibrio parahaemolyticus determined using standardised broth microdilution protocols. Eight laboratories performed broth microdilution tests with incubation at 35°C for 16 to 20 h, and 7 also performed tests on the same isolates with incubation at 28°C for 24 to 28 h. Data were analysed by the ECOFFinder and normalised resistance interpretation algorithms. The cut-off values calculated for ceftazidime, florfenicol and trimethoprim/sulfamethoxazole, 1, 1 and 0.25/4.75 µg ml-1, respectively, were the same when calculated from data obtained at both temperatures. The cut-off values calculated from data obtained at 35°C and from data obtained at 28°C were 0.25 and 0.5 µg ml-1 for enrofloxacin, 2 and 4 µg ml-1 for gentamicin, 0.5 and 1 µg ml-1 for oxolinic acid and 2 and 1 µg ml-1 for oxytetracycline, respectively. The influence of incubation temperature on MIC values was investigated by comparing MICs obtained at 35 and 28°C for a specific antimicrobial agent with a particular isolate by an individual laboratory. Results showed that 56% of 1473 of these paired MIC values were identical, while 38% differed from one another by not more than 1 dilution step. The data generated in this work will be submitted to the Clinical and Laboratory Standards Institute for consideration in their setting of internationally agreed epidemiological cut-off values for V. parahaemolyticus that are essential for interpreting antimicrobial susceptibility testing data of this species.