The Carpione rhabdovirus strain 2023 (CAPRV2023) is an emerging viral pathogen that has caused significant morbidity and mortality in cultured golden pompano (Trachinotus ovatus) in China over recent years. There is an urgent need for a rapid and accurate method for the quantitative detection of CAPRV2023. In this study, we developed a TaqMan probe-based quantitative PCR assay targeting the N gene of CAPRV2023 and systematically evaluated its specificity, sensitivity, repeatability, and reproducibility of the assay. Both plasmid DNA, in vitro-transcribed RNA standards, and in vitro-transcribed RNA mixed with RNA extracted from CAPRV2023-negative golden pompano tissues were used as templates to evaluate assay performance under both optimal and biologically relevant conditions. Using plasmid DNA standards, the assay exhibited excellent linearity over a broad range of 2 × 101 to 5 × 109 copies/μL, with a standard curve of Y = -3.3132X + 39.142, a correlation coefficient of R2 = 0.9993, an amplification efficiency of 100.37%, and a detection limit of 20 copies per reaction. In vitro-transcribed RNA standards demonstrated robust linearity over the range of 2 × 102 to 2 × 109 copies/μL, with a standard curve of Y = -3.2327X + 45.502, a correlation coefficient of R2 = 0.9968, and a detection limit of 200 copies per reaction. Notably, when the in vitro-transcribed RNA standards were combined with RNA extracted from CAPRV2023-negative golden pompano tissues, the assay maintained similar performance, yielding a standard curve of Y = -3.2182X + 45.445, a correlation coefficient of R2 = 0.9967, and the same detection limit of 200 copies per reaction. These results indicate that the presence of background tissue RNA does not significantly interfere with assay accuracy or sensitivity. Specificity test revealed that the assay exhibits no cross-reactivity with common bacterial or viral agents present in various aquatic organisms. The assay demonstrated high reproducibility and repeatability, with intra-assay and inter-assay coefficients of variation (CVs) below 2.5%. Field sample detection yielded a significantly higher detection rate compared to the conventional PCR assay. The newly developed TaqMan qPCR assay provides a robust diagnostic tool for the efficient and accurate quantitative detection of CAPRV2023 in field samples and surveillance programs.
Judicious use of antimicrobials in aquaculture requires reliable antimicrobial susceptibility testing (AST) of bacterial pathogens for resistance surveillance and for advising therapy decisions. To improve AST of aquatic bacterial pathogens such as Vibrio harveyi, the Clinical and Laboratory Standards Institute (CLSI) has standardized methods specific to testing isolates collected from fish and other aquatic animals. However, no criteria, called epidemiological cutoff values (ECVs), exist yet to interpret results when testing V. harveyi with these standard methods. Microbiologists use ECVs to determine whether an isolate has decreased susceptibility to an antimicrobial relative to other isolates of the same bacterium. In this study, we generated minimal inhibitory concentration (MIC) data using 3 independent laboratories that tested 76 isolates with the CLSI standard broth microdilution method at 28°C for 24-28 h against 9 antimicrobials. The resulting MIC data for 6 of the antimicrobials listed below was combined with previously published data (Smith et al. 2023; Dis Aquat Org 155:35-42) and analyzed with the programs Normalized Resistance Interpretation (NRI) and ECOFFinder to calculate potential ECVs. In collaboration with CLSI's Working Group on Aquatic Animals, the potential ECVs were proposed to CLSI's Subcommittee on Veterinary Antimicrobial Susceptibility Testing, which voted to accept the values. These new ECVs will be included in the next edition of the VET04 supplement. The approved ECVs for enrofloxacin, florfenicol, gentamicin, oxolinic acid, oxytetracycline, and trimethoprim/sulfamethoxazole are ≤1, ≤2, ≤4, ≤1, ≤1, and ≤0.5/9.5 µg ml-1, respectively. These new interpretive criteria will improve international harmonization regarding monitoring efforts on antimicrobial susceptibility of V. harveyi.
The parasitic dinoflagellate Hematodinium perezi is known to harm and kill marine crustaceans worldwide. It is unclear, however, how the phenology of host infections differs from that of in-water life stages of H. perezi, and how these cycles may vary regionally. Across the US East Coast, including in South Carolina (SC), H. perezi is a parasite of the economically important Atlantic blue crab Callinectes sapidus. The aim of this study was to determine and compare the seasonal presence of H. perezi in C. sapidus and benthic water of the Charleston Harbor estuary, SC, USA, using real-time PCR (RT-PCR). Hemolymph of 322 blue crabs was sampled over 21 mo beginning in September 2022, with concurrent benthic water eDNA sampling beginning in April 2023. DNA from H. perezi was detected in a total of 11 blue crab samples collected in the spring, fall, and winter of 2023. Positive environmental detections of DNA occurred every sampling season, including when H. perezi was reported absent in C. sapidus. Although other unknown factors likely contributed to the observed prevalence, our results suggest a seasonal pattern of the presence of H. perezi in the estuary largely driven by both water temperature and salinity. Altogether, our findings provide foundational information on the phenology of this parasite, critical for understanding disease dynamics in blue crabs in the southeast USA.
Cyprinid herpesvirus 3 (CyHV-3) is a highly contagious virus that causes high mortalities in common and koi carp worldwide. The molecular detection of this double-stranded DNA virus has been extensively researched. Nonetheless, there are currently no real-time PCR assays available for detecting CyHV-3 mRNA, which could serve as an indicator of active virus replication, aiding in the evaluation of the susceptibility of non-target species. This study describes a probe-based reverse transcription, real-time PCR (RT-qPCR) assay that was designed to detect CyHV-3 mRNA for efficient, high-throughput detection. The assay is highly specific for CyHV-3 mRNA, with no detection in samples from non-infected fish, closely related viruses or CyHV-3 DNA. The analytical sensitivity of the assay was examined using dilutions of a plasmid control and nucleic acid from a CyHV-3-infected cell line, where the CyHV-3 mRNA limit of detection was approximately 1 copy per reaction. Testing of diluted CyHV-3 mRNA demonstrated comparable sensitivity of the RT-qPCR with an existing reverse transcription PCR assay. Progressive monitoring of positive control samples revealed that the assay had a high level of repeatability. The assay was used to provide further evidence that non-target species silver perch and Murray cod were not susceptible to developing disease when experimentally exposed to CyHV-3. The novel RT-qPCR assay is an invaluable tool for detection of the replication phase of CyHV-3.
Infectious diseases, particularly those caused by members of the genus Ranavirus (Iridoviridae), have caused mass mortality events in amphibian populations worldwide. Frog virus 3 (FV3) infects a wide range of amphibian hosts and results in high mortality. Despite the global prevalence of FV3, its origin and routes of spread remain unclear, largely because of limited genetic data from limited geographic regions. This study aimed to classify the ranaviruses isolated in the Republic of Korea through whole-genome sequencing. We collected amphibian carcasses and both symptomatic and asymptomatic live amphibians. The asymptomatic amphibians were collected from locations with previous infections. Among the 278 amphibian samples collected from 24 locations, 44 were positive for ranavirus according to quantitative PCR (qPCR) analysis. We obtained whole-genome sequences from 5 isolates, all of which were identified as FV3-like ranaviruses and belonged to the Asian FV3 clade in the maximum likelihood phylogenetic tree. By comparative analysis of open reading frames (ORFs) and phylogenomic trees, the Korean isolates were further divided into 2 strains: FV3-Kor_MT (mountain lineage) and FV3-Kor_LL (lowland lineage). Our findings highlight the importance of surveillance of a wide range of amphibian species and facilitate phylogenetic analyses of global FV3-like strains, including newly verified Korean strains.
A novel dinoflagellate is described from bluegill Lepomis macrochirus, rock bass Ambloplites rupestris, largemouth bass Micropterus nigricans, and yellow perch Perca flavescens collected from Lundgren Lake and Townsend Flowage, Wisconsin, USA. A new genus, Dermisichthinium gen. nov., is established for this species, D. pseudosporum sp. nov., which produces white spots grossly similar to those caused by Ichthyophthirius multifiliis. Microscopically, however, the vegetative cysts of D. pseudosporum closely resemble Haidadinium ichthyophilum, a parasite of threespine stickleback Gasterosteus aculeatus. Haidadinium ichthyophilum was collected from Haida Gwaii, British Columbia, Canada, for morphological and molecular comparison. Molecular analysis of the small subunit (18S), large subunit (28S), and internal transcribed spacer rDNA regions supports the novel species description and erection of a new genus. Pairwise comparisons of partial 18S and 28S sequences revealed divergence levels approximately 3 times greater than those among congeneric suessiacean dinoflagellates. Dermisichthinium pseudosporum sp. nov. lacks a 25 bp insertion in 28S unique to H. ichthyophilum, providing a molecular character for distinguishing the 2 species and supporting their placement in separate genera. Phylogenetic analyses consistently place D. pseudosporum sp. nov. and H. ichthyophilum in distinct clades. This study enhances our understanding of parasitic dinoflagellate diversity, underscores the importance of integrating morphological, molecular, and other diagnostic characteristics in their taxonomic classification, and offers valuable diagnostic insight for fish health professionals and parasitologists encountering this unusual group of cyst-forming dinoflagellates.
This study analysed published data on the distributions of minimum inhibitory concentrations of a group of freshwater isolates classified as Aeromonas spp. with the aim of establishing whether they provided any evidence that epidemiological cut-off values set from these data would be unreliable. This group contained 233 isolates and included members of at least 11 species. The standard deviations (SDs) of the wild-type distributions for 10 antimicrobial agents were calculated for this multi-species group using the ECOFFinder and normalised resistance interpretation (NRI) algorithms. These were compared to the SDs of 110 distributions established for individual species published by the European Committee on Antimicrobial Susceptibility Testing. Fifty-one of these distributions had been generated by multiple laboratories and 59 by single laboratories. When the ECOFFinder algorithm was used to calculate the SDs, the mean for the multi-species group was 0.63 log2 µg ml-1, and the 51 individual species and multiple-laboratory groups were 0.68 and 0.65 log2 µg ml-1, respectively. When the NRI algorithm was used, the mean for the multi-species group was 0.79 log2 µg ml-1, and the 51 individual species and multiple-laboratory groups were 0.79 and 0.76 log2 µg ml-1, respectively. These comparisons indicate that the heterogeneity in the susceptibility to antimicrobial agents within the multi-species group of Aeromonas is not significantly different from that recorded for individual species. This analysis, therefore, suggests that epidemiological cut-off values designed to be applied to all members of the genus Aeromonas would not be inherently unreliable.
Ostreid herpesvirus-1 (OsHV-1) is a threat to the global production of Pacific oysters Crassostrea gigas, often resulting in nearly complete mortality in affected stocks. A sentinel monitoring program was conducted between June and October 2020, to characterize OsHV-1 outbreaks in Pacific oysters along the west coast of the USA. Deployment of sentinel oysters at 5 commercial growing locations, coupled with frequent sampling, allowed measurement of the spatial and temporal occurrence of OsHV-1 outbreaks as well as the viral load and pathogenesis of OsHV-1 during C. gigas mortality events. In addition, 2 divergent oyster families were deployed at sites that have historically tested positive for OsHV-1 to measure the effect of oyster genotype on the severity of OsHV-1-induced mortality in the field. Mortality events at California test sites were associated with elevated levels of OsHV-1 in oyster tissue. OsHV-1 was not detected in oysters at Oregon and Washington test sites. In Tomales Bay, California, high variation among replicate culture units was observed in cumulative field survival and peak viral load. A negative relationship was observed between peak OsHV-1 load in oyster tissues and shell height at the time of peak viral load, suggesting larger seed may be less vulnerable during periods of OsHV-1 infection risk. Cumulative survival over the duration of the growing season in Tomales Bay was related to peak viral load and differed by family. These results corroborate previous findings suggesting selective breeding may effectively increase survival of oyster families during OsHV-1 outbreaks along the US west coast.
Edwardsiella ictaluri and E. piscicida are bacterial pathogens that infect a variety of commercially important wild and cultured fish and cause significant economic losses among various farmed fish sectors, especially the catfish industries in the USA and Vietnam. The Clinical and Laboratory Standards Institute (CLSI) offers standard antimicrobial susceptibility testing (AST) methods for these pathogens and others, but internationally harmonized criteria, called epidemiological cutoff values (ECVs), are still needed to identify isolates with decreased antimicrobial susceptibility. To address this need, minimal inhibitory concentration (MIC) data for 9 antimicrobials were generated using the standard broth microdilution AST method at 28 ± 2°C for 44-48 h. The data sets comprise MICs from 101 E. ictaluri isolates from 4 independent laboratories and 115 E. piscicida isolates from 3 laboratories. Aggregated MIC distributions were used to calculate wild-type (WT) cutoff values for the 18 bacteria/antimicrobial combinations. WT cutoff values for E. ictaluri against ampicillin, enrofloxacin, erythromycin, florfenicol, gentamicin, oxolinic acid, oxytetracycline, ormetoprim/sulfadimethoxine, and trimethoprim/sulfamethoxazole were ≤1, ≤0.12, ≤128, ≤2, ≤2, ≤0.5, ≤2, ≤0.5/9.5, and ≤0.25/4.8 µg ml-1, respectively. WT cutoff values for E. piscicida were ≤8, ≤0.12, n/a, ≤2, ≤2, ≤0.25, ≤2, ≤0.12/2.4, and ≤0.12/2.4 µg ml-1, respectively. No E. piscicida WT cutoff value could be calculated for erythromycin. These WT cutoff values provided the CLSI with data needed to approve ECVs which will be included in the next edition of the VET04 supplement. CLSI-approved ECVs resulting from this work will greatly improve antimicrobial resistance surveillance of these bacterial pathogens impacting global aquaculture.
Fan mussels Pinna nobilis across the Mediterranean Sea have been severely impacted by a widespread mass mortality event, largely attributed to Haplosporidium pinnae. While the Sea of Marmara (SoM) has historically served as a refuge for this Critically Endangered species, recent findings suggest the emergence of various pathogens, including haplosporidian parasites, in SoM populations. This study presents the first confirmed case of H. pinnae infection in fan mussels from the southern SoM, with a focus on species-level identification, and contributes to growing concerns about the potential spread of this pathogen into previously unaffected regions. On 23 November 2024, 5 live fan mussels were collected from depths of 2.3-6.5 m in the southern SoM. Histopathological examination revealed structural alterations in the mantle tissue and the presence of plasmodial stages of H. pinnae. Molecular analyses further confirmed the presence of H. pinnae in several samples, exhibiting 100% sequence similarity with isolates from other Mediterranean regions. This study provides essential evidence of infection in the SoM and underscores the need for continued monitoring and conservation efforts for fan mussel populations in the region, especially as pathogens continue to spread across the Mediterranean Sea. The results represent a significant conservation alarm and highlight the urgent need for continued pathogen surveillance, early warning strategies, and robust management interventions in one of the last strongholds of this keystone species.
The American eel Anguilla rostrata is a catadromous fish with a unique life history; however, parasite surveys of these eels in the southeastern USA are limited. In this study, we surveyed the parasite fauna of 98 American eels collected from the Altamaha and Ocmulgee rivers in Georgia between January 2024 and August 2025. Eels were examined for external and internal parasites. The invasive, pathogenic swim bladder nematode Anguillicoloides crassus was detected in 62 of 98 eels (63.2% prevalence), with all infections occurring in the Altamaha River population. Infected eels harbored up to 21 nematodes, although most infections consisted of fewer than 5 individuals. No clear seasonal trends of infection were observed. The prevalence and mean intensity of A. crassus infections observed in Georgia were higher than those reported for most other regions along the US east coast. This study provides the first published record of A. crassus from Georgia and expands the known parasite diversity of American eels within the state. Our data also demonstrates the presence of 2 trematode genera, 3 cestode genera, 6 nematode genera, 3 acanthocephalan genera, and 1 arthropod genus. Many of these represent the first reports from eels in the state of Georgia.
Flavobacterium columnare is the etiological agent of columnaris disease in rainbow trout Oncorhynchus mykiss. F. columnare has recently been speciated into 4 independent columnaris disease-causing Flavobacterium species. Several F. columnare isolates from different geographic origins have been tested for variations in virulence and genetic diversity via multilocus sequence analysis of housekeeping genes. These studies have been limited in their ability to differentiate between highly variable and evolving regions of genetic diversity or to reliably predict differences in virulence between strains. To initiate a serotyping scheme, polyclonal antibodies were generated to F. columnare strains CSF-298-10, MS-FC-4 and PSFC-081215-1, and 7 serotypes were identified based on Western blot analysis of 54 F. columnare strains. Genome sequencing identified a 35-40 kb region encoding 32-36 putative lipopolysaccharide (LPS)-related genes that support 7 serotypes. Genes within this region encode molecules associated with the Lipid A, core region and O-antigen. All isolates were derived from columnaris outbreaks in the Columbia River of Washington State and the Snake River region of Idaho (USA). Serotyping and regional genome analyses allow for rapid and focused determination of isolate comparisons for population heterogeneity, LPS evolution and strain tracking. This is of the utmost importance when considering that all of these isolates were derived from columnaris outbreaks within the main US rainbow trout-producing regions. Knowledge of genetic and serotype diversity will help inform development of therapeutic strategies and vaccines.
Following a previous description from the Campania region (southern Italy), a survey for perkinsosis was performed at 12 mussel farms along the Italian coast during the period October 2022 to July 2023. The prevalence of Perkinsus parasites was estimated by PCR using genus-specific primers. Seven farms tested positive and sequencing was performed to identify the Perkinsus species. The parasite Perkinsus olsenii was detected in the farm samples with a BLAST identity of 97-100%. One of the affected farms was also monitored for the period of July 2022-June 2023 using histopathology, Ray's fluid thioglycollate culture method, and quantitative PCR. The sensitivity of each of the techniques was also determined. Trophozoite stages were observed mostly aggregated in the connective tissue of the digestive tract and gonad/mantle, and to a lesser extent in the foot and kidney, producing an encapsulated inflammatory response that occupied most of the tissues in some samples. The condition index of affected individuals was lower than in healthy ones (p < 0.05) and larger animals (5.8-6 cm) were more often infected (p < 0.05). This study provides information regarding P. olsenii pathogen infections in M. galloprovincialis in the Campania region, its seasonal variations, and host-parasite interactions over a 1 year period.
Melanoma is a highly aggressive neoplasm of melanocytes, commonly studied in mammals but rarely documented in wild fish populations. This study reports the first confirmed case of malignant melanoma in Terapon jarbua (Forsskål, 1775) from the Parangipettai landing center on the southeastern coast of India. Gross examination revealed superficial raised, hyperpigmented lesions primarily distributed along the dorsal and lateral body surfaces. Wet mount analysis showed extensive melanization within the dermal layers of the affected tissue. Histological examination identified pleomorphic melanocytes with dense melanin deposition, architectural disruption of the skin, and features consistent with superficially spreading melanoma. Scanning electron microscopy of melanotic lesions revealed significant alterations to the epidermal surface, with rounded or angular projections and sharply defined crevices. Transmission electron microscopy showed classical ultrastructural abnormalities such as pleomorphism, irregular melanosome aggregation, binucleation, cytoplasmic vacuolation, and necrotic cells with compromised plasma membranes. The presence of melanosomes at various maturation stages indicated hyperactive melanogenic activity. This novel discovery points to the importance of regular tumour surveillance and research into environmental stressors as possible causative agents, adding to the small but increasing body of evidence of neoplastic disease in Indian marine ecosystems.
The microsporidium Ecytonucleospora hepatopenaei (EHP) continues to disrupt farmed shrimp production globally by causing growth retardation, chronic mortality, and enhancing susceptibility to other diseases. While the susceptibility of black tiger shrimp Penaeus monodon and Pacific white shrimp P. vannamei to EHP is well known, the susceptibility of Pacific blue shrimp P. stylirostris to EHP has not been demonstrated. To determine the susceptibility of P. stylirostris to EHP, infectious inoculum was directly injected into the hepatopancreas of specific-pathogen-free (SPF) P. stylirostris. At 17 d post-injection, the developmental stages of the parasite were observed in the EHP-injected P. stylirostris, and EHP was detected by real-time PCR. The EHP-injected P. stylirostris were then divided into 2 groups. In the first group, P. stylirostris (n = 9) were cohabitated with SPF P. vannamei (n = 55), and in the second group, the hepatopancreas was excised from EHP-injected P. stylirostris, homogenized, and fed to SPF P. vannamei (n = 12). Both experimental challenge routes led to the horizontal transmission of EHP from P. stylirostris to P. vannamei, but cohabitation resulted in a stronger infection. In a follow-up study, one group of SPF P. stylirostris was fed EHP-infected P. vannamei tissue, and another group cohabitated with EHP-infected P. vannamei. Both groups of P. stylirostris developed EHP infections. These results clearly provide evidence of both P. stylirostris susceptibility to EHP and the transmission potential of EHP between P. stylirostris and P. vannamei via natural routes such as cohabitation and cannibalism.
The amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd) has devastated global amphibian biodiversity. Non-amphibian hosts might facilitate Bd spread across the landscape, but our understanding of their role remains severely limited. Several species of invertebrates have been implicated to varying degrees as potential carriers of Bd, but research is needed to understand the impact these invertebrates have on the spread and maintenance of this pathogen in the wild. Detecting Bd presence in field-collected invertebrates is a necessary first step for identifying potential vectors, but methodological comparisons have not been conducted. Detection thresholds of DNA extraction methods for Bd detection from amphibian skin swabs may not be applicable for invertebrate samples, because they may contain lower Bd loads and higher amounts of PCR-inhibitory substances. This study aimed to identify the most cost-effective and reliable method of DNA extraction for detecting Bd DNA in invertebrate samples using qPCR. We compared the effectiveness of 5 commonly used DNA extraction kits (QIAGEN, Zymo, SPINeasy, PrepMan Ultra, and Chelex resin) for Bd detection in homogenised cricket samples spiked with known concentrations of Bd. We found PrepMan Ultra to be the optimal extraction kit for a broad screening of field-collected invertebrate samples, due to its relatively low cost and the ability to detect Bd presence in homogenised cricket samples containing at least 100 zoospore equivalents. However, researchers need to conduct their own cost-benefit analysis when choosing an extraction method to ensure that the method suits their needs.
Nutrient deficiency can cause increased susceptibility to infectious diseases in fish, thus leading to high rates of morbidity and mortality. Thiamine deficiency complex (TDC) in fish can lead to low reproductive success and high mortality rates. Columnaris disease in salmonids, caused by Flavobacterium columnare, has resulted in devastating losses in aquaculture production and wild populations of Pacific salmon particularly associated with climate change and high water temperatures. There is growing awareness that both TDC and columnaris are emerging diseases of salmonids on the west coast of North America; however, it is unknown whether fish that survive from low/intermediate thiamine level eggs will experience latent mortality due to susceptibility to infectious diseases like columnaris. To investigate the interaction of TDC survivors and columnaris, Chinook salmon Oncorhynchus tshawytscha fry reared from either thiamine-deficient (n = 120) or thiamine-replete (n = 120) eggs were challenged with F. columnare using an immersion challenge model of infection, and morbidity/mortality, immune responses, and bacterial load were evaluated. The cumulative mortalities between the treatment groups were significantly different, with the thiamine-deficient, F. columnare-exposed fry ending the challenge with an 80.3% survival rate and the thiamine-replete, F. columnare-exposed fry ending with a 29.03% survival rate (p < 0.0001). Different transcript abundance was detected in gills and spleen of thiamine-deficient and thiamine-replete fry exposed to F. columnare. This study demonstrated that fry reared from eggs low in thiamine have an altered immune response and warrants further studies to better understand interaction with potential pathogens at different life stages.
We report significant pathological findings from 272 stranding investigations of 20 cetacean species in the Pacific Islands region between 2006 and 2024. Full or partial necropsies of 209 cases (76.8%) resulted in one or more diagnoses associated with death in 137 cases. Natural disease accounted for 62% of stranded animals; approximately half were in poor body condition due to chronic illness. Morbillivirus and Brucella sp. infections caused mortality in 11 species, including striped dolphins and Longman's beaked whales. Toxoplasmosis, of anthropogenic cause in Hawai'i, led to deaths of 2 spinner dolphins and a bottlenose dolphin. Pygmy and dwarf sperm whales, beaked whales and pilot whales showed heavy parasitism by nematodes, cestodes and trematodes. Approximately 12.4% of stranded individuals were perinates/neonates, with 3 cases of dystocia with maternal mortality. Anthropogenic trauma was observed in 29.2% of strandings, including 6 goose-beaked whales with cranial and/or microvascular hemorrhages. Vertebral and skull fractures were attributed to direct vessel strikes for 2 pygmy sperm whales, 2 humpback whale calves, a goose-beaked whale, a spinner dolphin and a striped dolphin. Blast trauma was observed in 3 Fraser's dolphins in an uncommon stranding event. Significant plastic debris and/or fishery debris were found in stomachs of 6 species, with fatal gastric obstruction in a sperm whale and fatal fishhook penetration in a bottlenose dolphin. This study highlights the value of necropsy examinations in a region inhabited by small island-associated populations where carcass recovery rates are low, and cetaceans face an array of natural and anthropogenic threats.
Globally, Marteilia spp. parasites have been associated with significant mass mortality events in populations of commercially important bivalve molluscs, frequently resulting in large-scale fishery collapses and substantial socio-economic impacts. The Wash Estuary, UK, supports several bivalve fisheries, and among these, common cockles Cerastoderma edule have suffered unusually high mortalities since 2008. We investigate potential causes of these mortalities, and confirm infection with M. cocosarum, strongly associated with cockle moribundity, also confirming its presence in archived samples collected in 2009. Molecular and light microscopy screening of samples collected during mortality events in 2021, including healthy (buried) and moribund (weak, unable to bury) cockles, indicated high prevalence of M. cocosarum in moribund cockles (PCR incidence up to 95%) in contrast to healthy cockles (up to 42%), suggesting an association between cockle moribundity and Marteilia infection. Analysis of the full ribosomal RNA array identified consistently different nucleotides between M. cocosarum infections in the Wash (denoted as genotype WE1) and those in Wales (denoted genotype WA1). A total of 83% of infections in the Wash could be identified as M. cocosarum WE1 and 12% as M. cocosarum WA1, with both genotypes recovered from 5% of infected animals. Histopathologically, M. cocosarum WE1 infects the gill, mantle and connective tissues, identical to observations of M. cocosarum infecting Welsh cockles. Ongoing cockle mortalities in the Wash raise concerns regarding the sustainability of this resource ecologically and economically. Additional measures may be required to reduce the spread of this pathogen, noting that its distribution beyond the Wash and Wales is currently unknown.
Sessilid ciliates are common epibionts of aquatic crustaceans, where mass colonisation of economically important prawns may lead to adverse effects on host health and ecosystem dynamics. The Oriental river prawn Macrobrachium nipponense, which is native to Asia, has recently expanded into European freshwater and brackish systems. As a host species, it may act as a vector for sessilid ciliates into new habitats, posing risks to native biota and aquaculture. We examined M. nipponense populations in brackish water bodies of southwestern Ukraine to assess the prevalence and localization of sessilid ciliates. Live and preserved specimens were microscopically examined. Morphological analysis focused on the distribution and abundance of Zoothamnium colonies on various body parts. Molecular material was also preserved for future species identification. Over 80% of prawns were found to carry large colonies of Zoothamnium sp., with high infestation intensity particularly on pereiopods and uropods. Ciliate aggregations often appeared near articulation points, which may obstruct mobility or respiration. Infestation patterns were consistent across sexes, though some correlations were noted between parasite load and reproductive condition in females. These results suggest that sessilid ciliates may exhibit parasitic characteristics under favourable conditions, undermining host performance. The expansion of M. nipponense may facilitate the introduction and establishment of such organisms across Europe. This study highlights the ecological implications of overlooked epibionts and stresses the importance of monitoring invasive host-epibiont complexes in aquatic environments.