Author: marina02

Hematodinium perezi detection in blue crab (Callinectes sapidus) and its seasonal prevalence in northern Adriatic lagoons.

Introduction:The blue crab (Callinectes sapidus) is an allochthonous and invasive species observed in the last decades in the Mediterranean Sea, which has recently spread in the Italian northern Adriatic lagoon, causing significant damage to the local shellfish farming. Evaluation of the presence of dinoflagellate parasites of the genus Hematodinium, which can cause mortality and influence population dynamics in the blue crab native range, has not been investigated in northern Adriatic Sea and data on its seasonal prevalence in commercial size specimens are lacking. Methodology:An average of thirty blue crab specimens (>120 mm in carapace width) were collected with crab pots from professional fishermen from 7 lagoons in the north-western Adriatic Sea (Friuli, Veneto and Emilia Romagna Regions) between April and May 2024. The specimens were screened for Hematodinium infection using haemolymph analysis (real-time PCR, cytology) and histopathology. In each lagoon, the presence of the dinoflagellate was confirmed in specimens that tested positive by real-time PCR, using end-point PCR and Sanger sequencing of the ITS1 region. Additionally, monthly sampling (from April 2024 to May 2025) has been performed in one of these lagoons (Scardovari, Veneto) to assess the seasonal prevalence of Hematodinium. Histological examination of gills, heart, hepatopancreas and muscle tissue was performed and the severity of Hematodinium infection was assessed from heart tissue. The pathogen was additionally isolated in vitro for further characterization. Results:Circulation of Hematodinium perezi in C. sapidus has been confirmed in 4 lagoons (Venice, Scardovari, Goro and Marina di Ravenna) by real time PCR, sequencing and histology. Prevalence in spring 2024 varied between sites (20-97%). Monthly sampling in Scardovari lagoon revealed fluctuation in prevalence between late winter and early summer with Hematodinium not detectable between August and November. Histological evaluation showed different life stages (filamentous and ameboid trophonts, clump colonies) and variable infection intensity of Hematodinium. Furthermore, the sequence analysis not only confirmed the presence of H. perezi but also revealed specific indels in the ITS2 region that differ from those observed in other investigated areas.Conclusions:This study demonstrates that Hematodinium perezi is present in blue crab populations in north-western Adriatic lagoons with seasonal prevalence in adult specimens that differs from native population of the north-western Atlantic coast. These preliminary results show a genetic variability in Hematodinium and underscore the need to investigate its circulation also in autochthonous crab populations.  Funded by the Italian Ministry of Agriculture MASAF CUP J38H23001430001.

1. Pretto, Tobia, Istituto Zooprofilattico Sperimentale delle Venezie, Legnaro, Italy, Presenter
2. Lago, Nicola, Istituto Zooprofilattico Sperimentale delle Venezie, Legnaro, Italy, Author
3. Paolini, Valentina, Istituto Zooprofilattico Sperimentale delle Venezie, Legnaro, Italy, Author
4. Basso, Andrea, Istituto Zooprofilattico Sperimentale delle Venezie, Legnaro, Italy, Author

Salmonid alphaviruses undergo genomic recombination at high frequencies during infection

Introduction

Pancreas disease (PD), caused by salmonid alphavirus (SAV) is a major challenge in salmonid aquaculture. Norwegian outbreaks are caused by two genotypes, SAV2 and SAV3, and although there is a general geographical separation between the two, co-infections have been documented. This has raised concerns that genomic recombination between the two genotypes may result in new variants with altered virulence. In previous studies, we have shown experimentally that SAV genomes can recombine during infection, and that imprecise recombination may cause deletions, producing defective viral genomes (DVGs).

Methodology

We have constructed plasmid-based infectious clones of SAV2 and SAV3. Analyses of DVGs following transfection by electroporation and passaging of SAV3 in salmon CHH-1 cells were performed, combining RNAseq and a computational approach developed to detect DVGs. RNA secondary structure predictions were performed. SAV3 clones containing different deletions in the genome (“defective” SAV) have also been constructed. These clones are not able to produce viable viruses on their own. Different combinations and amounts of the infectious/non-infectious clones were transfected by electroporation into CHH-1 cells and/or combined with live virus at various timepoints. Quantitative assays for viral replication, sequencing and microscopy of cell cultures evaluated potential recombination events or the level of superinfection exclusion.

Results

Analyses of the sequence data from RNAseq show that the overall number of DVGs, the characteristics and frequency of different deletions produced by recombination all increase during passaging in CHH-1. The DVGs are characterized by a wide variety in the size of the deletions, and DVGs with specific deletions were found to accumulate at higher passages. Detailed analysis of the positions of deletions in the genome confirms that the deletions can be linked to predicted RNA secondary structure properties. Preliminary results from co-transfection/co-infection experiments involving SAV3, SAV2, and the “defective” SAV constructs will also be presented.

Conclusions

We show that SAV, like other alphaviruses, recombine at high rates, generating a diverse pool of DVGs, some at comparatively high frequencies. DVGs produced during infection may influence the host immune response and disease severity, as has been shown for other alphaviruses. These observations also suggest molecular mechanisms for putative recombination between SAV2 and SAV3 in the field are present.

1. MARKUSSEN, TURHAN, Norwegian University of Life Sciences, Presenter
2. Kropp, Fabian, Norwegian University of Life Sciences, Author
3. Vallet, Thomas, A*STAR ID Labs, Author
4. Vignuzzi, Marco, A*STAR ID Labs, Author
5. Evensen, Øystein, Norwegian University of Life Sciences, Author
6. Mikalsen, Aase B., Norwegian University of Life Sciences, Author

Vaccination modality and injection site influence the immune response and protection against sea lice Lepeophtheirus salmonis infestation in Atlantic salmon (Salmo salar)

Infestation with the salmon louse has a huge impact on the welfare of the Atlantic salmon. Currently, the aquaculture industry faces substantial economic losses caused by lice infestation and there is a critical need for alternative treatment methods, such as vaccination. The success of the vaccination strategy is dependent on eliciting an immune response, preferably antibody response that confer a long-term protection. There are currently three antibody isotypes detected in Atlantic salmon, IgM, IgT and IgD. The roles of these different isotypes in protection against lice infestation has not been studied in detail. In the present study we investigated the production and protective ability of specific antibodies in different compartments, systemically in the serum and locally in the mucus, using the different vaccines. Three groups of fish were either vaccinated with recombinant previously identified peroxinectins LsPxtl-1 and LsPxtl-2 protein vaccines (LsPxtl-1, LsPxtl-2 groups) or mixture of the two in 1:1 ratio (LsPxtl-1+2 group). The fourth group (IP group) was vaccinated with whole lice antigen preparation (WSL). All the vaccines were given intraperitoneally (IP). A fifth group, named IP+F, was injected with the WSL both IP and subcutaneously at the base of the dorsal fin. Two additional control groups injected with IP (PBS) and IP in addition to the base of fin (PBS+F) were also included. Following a vaccination and challenge trial, the lice numbers were counted and the ability of the vaccines to elicit antibody response, Ig (IgM/IgT) and IgT were measured by ELISA both systemically in the serum and locally in the mucus. The results showed that two of the vaccinated groups, the LsPxtl-1 and IP+F, had significant reduction in lice numbers. All the vaccines induced systemic antibody responses while the number of responders with local antibody responses varied between the groups. There was in general a poor correlation between antibody responses and lice numbers, although the levels of mucus IgT seem to positively correlate with lice counts in the PBS group. This suggests that the fish mount local IgT responses in response to lice infestation. Interestingly a tendence toward negative correlation between mucus IgM/IgT and IgT levels was observed for the most protected groups LsPxtl-1 and IP+F, respectively. Overall, our data suggest that vaccine modality and administration route influence antibody responses and protection. Further, the correlation between reduction in lice numbers and mucosal IgT responses is an interesting trend that warrant further investigation.

1. GISLEFOSS, ELISABETH, NMBU, Presenter
2. GAMIL, AMR, NMBU, Author
3. EVENSEN, ØYSTEIN, NMBU, Author

Genomic and morphological characterisation of a novel iridovirus associated with cockle mortalities

Background: High rates of mortality of the common cockle, Cerastoderma edule, have occurred in the Wash Estuary since 2008. A previous study linked the mortalities to an emerging genotype of Marteilia cocosarum, with a strong correlation between cockle moribundity and the presence of M. cocosarum. In this study, we characterised a novel iridovirus, identified by chance during metagenomic sequencing of a gradient purification of Marteilia cells. Further targeted investigation has shown this pathogen also to be correlated with cockle moribundity in the Wash.

Methods: Moribund (weak and unable to bury) cockles were collected from the Wash Estuary in 2022. Tissues were processed for the purification of M. cocosarum, and DNA from resulting suspension was sequenced for metagenomics using Illumina technology. During bioinformatic assembly of the metagenomic reads, it became apparent that an iridovirus had been co-purified with M. cocosarum. The complete genome of a novel iridovirus was assembled and annotated, and the virus was characterised by histopathology and transmission electron microscopy. A nested PCR assay was designed to amplify the ATPase gene of the novel virus and used to screen healthy and moribund cockles from the Wash in 2021 and 2023.

Results: The novel 179,695 bp iridovirus, bivalve iridovirus 1 (BiIV1), encodes 193 predicted open reading frames and has a 41% G+C content. BiIV1 clusters with other aquatic invertebrate iridoviruses in phylogenetic analyses and has a similar genome size to other invertebrate iridoviruses. Electron microscopy showed 158 nm icosahedral virions present in the haemocytes of cockles, typical of those observed in host tissues infected with viruses of the family Iridoviridae. Prevalence of BiIV1 in moribund cockles was higher than that in apparently healthy cockles at most sites in the Wash Estuary, with up to 100% PCR prevalence in moribund cockles.

Conclusions: Our findings produce the first genome for a bivalve-infecting iridovirus, adding to the knowledge of invertebrate iridovirus genomics and diversity. The discovery of this additional potential disease agent, associated with moribund cockles in the Wash, demonstrates the need for holistic approaches to understanding mortality events.

1. Hooper, Chantelle, The Centre for Environment, Fisheries and Aquaculture Science, Presenter
2. Tidy, Anna, The Centre for Environment, Fisheries and Aquaculture Science, Author
3. Jessop, Ron, 5Eastern Inshore Fisheries & Conservation Authority (EIFCA), Author
4. Bateman, Kelly S., The Centre for Environment, Fisheries and Aquaculture Science, Author
5. Green, Matthew, The Centre for Environment, Fisheries and Aquaculture Science, Author
6. Ross, Stuart H., The Centre for Environment, Fisheries and Aquaculture Science, Author
7. Ward, Georgia M., The Centre for Environment, Fisheries and Aquaculture Science, Author
8. Hazelgrove, Richard, The Centre for Environment, Fisheries and Aquaculture Science, Author
9. Hunt, Jasmine E., The Centre for Environment, Fisheries and Aquaculture Science, Author
10. Parker, Megan, The Centre for Environment, Fisheries and Aquaculture Science, Author
11. Bass, David, The Centre for Environment, Fisheries and Aquaculture Science, Author

Quantification of myocardial inflammation in salmon hearts using a machine learning model

Heart and skeletal muscle inflammation (HSMI) and cardiomyopathy syndrome (CMS) are among the most important disease problems in the Norwegian salmon industry, causing significant welfare problems and economic losses. In both conditions, myocardial inflammation is a prominent feature and is considered the reason for the morbidity and mortality that is often observed.

Semiquantitative scoring of the myocarditis severity is commonly done by veterinary pathologists as part of experimental research focusing on CMS and HSMI. Several published scoring protocols with well-defined grading criteria exist for both diseases. In addition, there is a need for myocarditis scoring in field situations where a less specific protocol is often used, as heart morphology can be influenced by multiple diseases simultaneously. Many pathologists have long experience using these methods, and in small and medium sized studies the results can be obtained quickly in a fairly reproducible way.

However, in larger studies, the demand for veterinary pathology resources may become disproportionately high. Since it is preferable to involve only one or as few pathologists as possible, the turnaround time for such projects can become quite lengthy. Inherently, most methods for scoring histopathology slides can suffer from limitations such as inter- and intraobserver variability (diagnostic drift).

To reduce turnaround times for larger studies and to make the measurement of cardiac inflammation consistent we developed a machine learning (ML) model capable of quantifying inflammatory lesions in salmon hearts. This model was generated using datasets of annotated images obtained from digital slides of salmon tissues. The ML model performance was evaluated by comparing its output with the ordinal scores of the same slides provided by a histopathologist. Statistical methods were employed to assess the correlation between ML-estimated extent of inflammation and the semiquantitative manual scores.

Our ML model demonstrated a positive correlation with the histopathologists’ semiquantitative scoring, achieving a Spearman correlation coefficient of up to 0.89 (p < 0.001). This indicates its usability for quantifying inflammatory lesions in salmon hearts affected by CMS and HSMI. The integration of this method will enable significantly shorter turnaround for large projects and highly reproducible measurements. The model’s output is a continuous numerical value representing the fraction of detected myocardium with inflammation. Continuous numerical variables offer clear advantages over semiquantitative ordinal scores.

1. Lie, Kai-Inge, PHARMAQ ANALYTIQ AS, Presenter
2. Kraugerud, Marianne, PHARMAQ ANALYTIQ AS, Author

Effects of glucocorticoid receptor activation on gene expression and antiviral responses in Atlantic salmon red blood cells

Intensified aquaculture strategies increase stress and infection pressure, leading to higher disease susceptibility among farmed populations. Farmed Atlantic salmon (Salmo salar) are prone to viral outbreaks, with stress often acting as a trigger for disease development. Fish red blood cells (RBCs) are nucleated and metabolically active with both physiological and immunological properties. In this study, we treated A. salmon RBCs with dexamethasone, a synthetic glucocorticoid, and hydrocortisone ex vivo to investigate whether RBCs modulate stress responses through activation of glucocorticoid receptor (GR)-signaling. Then, we examined whether similar transcriptional responses could be observed in RBCs from A. salmon injected with cortisol in vivo. Transcriptional analysis showed that A. salmon RBCs express GR genes. A four-day exposure to dexamethasone led to over 200-fold upregulation of FKBP propyl isomerase 5 (FKBP5) and Krueppel like factor 9 (KLF9) genes, both key regulators of GR signaling in fish and mammals. The mRNA levels of FKBP remained significantly elevated up to 14 days post glucocorticoid stimulation ex vivo, compared to unstimulated controls, suggesting that secondary stress responses in RBCs may persist even after plasma cortisol levels return to baseline. The effects of cortisol on gene expression in A. salmon blood cells in vivo were limited and did not resemble the patterns found in the dexamethasone-treated RBCs ex vivo. Only DDIT4 gene was significantly induced both ex vivo and in vivo.

We also explored the effects of GR activation on double-stranded (ds) RNA-mediated antiviral responses in A. salmon RBCs. The cells were pre-treated with glucocorticoids and subsequently exposed to poly(I:C), a synthetic dsRNA analogue, ex vivo. Dexamethasone and cortisol suppressed poly(I:C)-induced antiviral responses, including genes associated with dsRNA recognition, interferon (IFN) signaling and IFN-mediated immunity. In addition, genes involved in ubiquitin-dependent proteolysis via proteasomes and major histocompatibility complex (MHC) class I antigen presentation were significantly inhibited. Altogether, these findings demonstrate that A. salmon RBCs respond to glucocorticoids with pronounced effects on antiviral innate immunity and protein degradation pathways.

1. TSOULIA, THOMAIS, NORWEGIAN VETERINARY INSTITUTE; UIT THE ARCTIC UNIVERSITY OF NORWAY, Presenter
2. TSOULIA, THOMAIS, NORWEGIAN VETERINARY INSTITUTE; UIT THE ARCTIC UNIVERSITY OF NORWAY, Author
3. SUNDARAM, ARVIND Y.M., NORWEGIAN VETERINARY INSTITUTE; OSLO UNIVERSITY HOSPITAL, Author
4. AMUNDSEN, MARIT M., NORWEGIAN VETERINARY INSTITUTE, Author
5. AARDAL, MARTINE J., NORWEGIAN VETERINARY INSTITUTE; UIT THE ARCTIC UNIVERSITY OF NORWAY, Author
6. SALVADOR MIRA, MARIA, INSTITUTE OF RESEARCH, DEVELOPMENT AND INNOVATION IN HEALTHCARE BIOTECHNOLOGY OF ELCHE, Author
7. PLOSS, FRIEDA B., NORWEGIAN VETERINARY INSTITUTE, Author
8. FALLER, RANDI, NORWEGIAN VETERINARY INSTITUTE, Author
9. JENSEN, INGVILL, UIT THE ARCTIC UNIVERSITY OF NORWAY, Author
10. GJESSING, MONA C., NORWEGIAN VETERINARY INSTITUTE, Author
11. BRAUNER, COLIN J., UNIVERSITY OF BRITISH COLUMBIA, Author
12. DAHLE, MARIA K., NORWEGIAN VETERINARY INSTITUTE; UIT THE ARCTIC UNIVERSITY OF NORWAY, Author

Ecological, genomic and virulence insights into Vibrio aestuarianus cardii: A pathogen of cockles

Introduction: Understanding the genomic diversity and population structure of pathogenic bacteria is crucial for elucidating their evolutionary trajectories, ecological niches and virulent potential. Vibrio aestuarianus cardii, a recently described subspecies, has caused recurring mortality events in cockle (Cerastoderma edule) populations along the French Channel coast since 2012. However, its ecological dynamics, genetic diversity, and virulence mechanisms remain poorly characterized.

Methodology: We conducted a two-year ecological and genomic study at two sites in France (Bay of Somme and Bay of Authie) monitoring natural cockle beds to assess environmental conditions favoring disease emergence. 383 strains of V. aestuarianus cardii were isolated from cockle spat, adult cockles, mussels, and sediments. 40 of these strains were subjected to whole-genome sequencing and comparative genomic analyses to investigate population structure, recombination patterns, and potential virulence factors. Virulence assays were performed to evaluate strain pathogenicity in vivo, and three distinct genogroups were described based on genetic clustering and virulence profiles. We selected three representative strains per genogroup to conduct in vitro assays aimed at elucidating mechanisms underlying their differential virulence. These assays assessed bacterial multiplication in the presence of cockle hemocytes, bacterial cytotoxicity towards hemocytes, and bacterial gene expression (focusing on toxin-encoding genes) in the presence and absence of hemocytes.

Results: Environmental monitoring identified specific thermal windows permissive to V. aestuarianus cardii proliferation in cockle populations, with cockle spat emerging as a probable reservoir. Comparative genomics revealed three genogroups associated with cockles, two exhibiting high virulence and one exhibiting low virulence in vivo. Frequent genetic exchanges within genogroups contributed to differentiation and acquisition of virulence factors, notably Type I and Type VI Secretion Systems. In vitro assays demonstrated that high-virulence strains exhibited enhanced multiplication and cytotoxicity in the presence of cockle hemocytes compared to low-virulence strains. Gene expression analyses revealed differential regulation of toxin-related genes, which showed distinct genomic profiles, during interaction with hemocytes.

Conclusions: Our study advances understanding of the ecological niche, population structure, and virulence mechanisms of V. aestuarianus cardii. The identification of three genogroups with distinct virulence profiles, coupled with mechanistic insights from in vitro assays, highlights the complex interplay between bacterial genetic makeup and host interactions. Our findings underscore the role of temperature and cockle spat reservoirs in disease dynamics and suggest that horizontal gene transfer facilitates virulence evolution. This work provides a foundation for improved risk assessment and management strategies for mitigating V. aestuarianus cardii-associated disease outbreaks in cockle fisheries.

1. Hernández-Cabanyero, Carla, Université de Montpellier, CNRS, Ifremer, UPVD, Presenter
2. Mesnil, Aurélie, Ifremer, Author
3. Tourbiez, Delphine, Ifremer, Author
4. Jacquot, Maude, Ifremer, Author
5. Hocquet, Juliette, Ifremer, Author
6. Dégremont, Lionel, Ifremer, Author
7. Girardin, Frédéric, Ifremer, Author
8. Ricard, Morgane, CRPMEM Hauts de France, Author
9. Rocroy, Mélanie, GEMEL, Author
10. Meirland, Antoine, CRPMEM Hauts de France, Author
11. Charrière, Guillaume, Université de Montpellier, CNRS, Ifremer, UPVD, Author
12. Destoumieux-Garzon, Delphine, Université de Montpellier, CNRS, Ifremer, UPVD, Author
13. Travers, Marie-Agnès, Université de Montpellier, CNRS, Ifremer, UPVD, Author
14. Garcia, Céline, Ifremer, Author

Analysis of virus replication and host responses induced following infection with different doses of heart homogenate

Cardiomyopathy syndrome (CMS), caused by piscine myocarditis virus (PMCV), is one of the main infectious challenges facing the salmonid industry. The disease is widespread in different production areas in Norway and the numbers of registered cases has been increasing in recent years. The replication dynamic and host responses induced post PMCV infection are yet to be well understood. Here we have infected Atlantic salmon post-smolt with three different concentrations of heart homogenates obtained from fish during a field outbreak. Fish were then sampled after 2, 4 and 5 weeks of infection and histopathological evaluation was used to monitor the degree of heart inflammation induced in the heart. In addition, real time PCR was employed to measure virus replication in the heart, head kidney, spleen, and blood, as well as MX and IRF3 expression in the heart. The result show differences in virus induced pathogenicity in the heart of fish exposed to different infection dose. Moreover, the level of virus replication differed between the infection doses as well as between the different tissues. The number of fish with positive virus detection in blood suggests that viremia may occur at different time points. There was a negative correlation between Mx expression and virus replication in the heart suggesting that the virus may possess a mechanism to suppress antiviral responses. Metabolomic analysis of serum obtained from infected fish revealed upregulation of EPA derived anti-inflammatory metabolites at 4- and 5-weeks post infection. Our results provide new insights into that can help in understanding the infection biology of PMCV.

1. GAMIL, AMR, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Presenter
2. XU, CHENG, Norwegian university of life sciences, Author
3. RANGEL-HUERTA, OSCAR, Norwegian Veterinary Institute, Author
4. Evensen, Øystein, Norwegian university of life sciences, Author

Testis during viral infections in common carp – not so immune privileged?

Introduction: Koi herpes virus (KHV) and carp edema virus (CEV) are the most common viral infections in common carp. These viruses have distinct tissue tropisms, affecting gills and other organs during infection.  The testes of fish are unique in that they have a partial immune privilege, which allows germ cells to develop in a relatively protected environment despite exposure to potential immune challenges in aquatic settings. However, little is known about the consequences of viral infections in fish testes, particularly their impact on fertility, immune responses, and long-term reproductive success.

Methodology: To better understand the mechanisms involved in the response to viral infection and viral pathogenesis in the reproductive tract of common carp, a data-independent acquisition (DIA) mass spectrometry-based proteomic approach was used to determine how seminal plasma proteins are differentially expressed upon KHV and CEV infection. Additionally, a transcriptomic analysis of the gills and testis was performed using a Fluidigm array. Histology was performed using HE staining. Sperm integrity was evaluated using nigrosine staining. Viral load was evaluated by qPCR.

Results: The highest levels of both viruses were detected in the gills, followed by the gonads and semen. Histological evaluation showed necrotic changes in testicular lobules caused by both viral infections. This resulted in an increased number of damaged sperm with disrupted cellular morphology. Differential protein abundance analysis using DIA LC-MS/MS revealed that 660 proteins were significantly altered between the KHV and control groups and that 1,079 proteins were differentially abundant between the CEV and control groups, based on an adjusted q-value threshold of <0.05. Directly comparing the effects of CEV and KHV infections revealed that 883 proteins were upregulated and 149 were downregulated. We observed an upregulation of cell wall and membrane proteins involved in the stress response. The upregulation of coagulation factors demonstrates that the complement and coagulation cascades play a critical role in defending against viral infections in the testes. IL6 responses seem to be responsible for pathogenesis.

Conclusions: Overall, these findings indicate distinct and overlapping host proteomic responses to KHV and CEV infections, with shared immune and metabolic disruptions and virus-specific regulatory patterns in seminal plasma protein expression. These results suggest that the fish testis, unlike the mammalian testis, is not strictly immune-privileged. This allows for more dynamic interactions between immune responses and reproductive function, which can be detrimental to the latter, especially during highly virulent infections such as KHV and CEV.

1. ADAMEK, MIKOLAJ, UNIVERSITY OF VETERINARY MEDICINE HANNOVER, Presenter
2. Rakus, Krzysztof, Department of Evolutionary Immunology, Institute of Zoology and Biomedical Research, Faculty of Biology, Jagiellonian University, Author
3. Zawisza, Maria, Department of Evolutionary Immunology, Institute of Zoology and Biomedical Research, Faculty of Biology, Jagiellonian University, Author
4. Ciereszko, Andrzej, Department of Gamete and Embryo Biology, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Olsztyn, Author
5. Jung-Schroers, Verena, UNIVERSITY OF VETERINARY MEDICINE HANNOVER, Author
6. Dietrich, Mariola, Department of Gamete and Embryo Biology, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Olsztyn, Author

Cockle health in the UK: a case study for the implementation of holistic investigative approaches to explain complex mortalities and long-term population declines

Introduction:

Cerastoderma edule (C.edule) populations of the Wash estuary embayment in eastern-England, UK have suffered long-term declines linked to recurrent annual mortalities. Essential to local fisheries, and wildlife populations, Wash cockle stocks were largely wiped out due to a mass mortality event in 2008, occurring annually ever since. Whilst disease investigations have provided significant insights into key pathologies impacting cockle health, the various mechanisms contributing to cockle mortality, including environmental, ecological and anthropogenic variables, have yet to be fully determined. Contributory factors may be sub-lethal individually, but act in a synergistic manner to drive mortalities. Hence, a more holistic approach is required to understand the complexed nature of cockle population decline.

Methodology:

Wash cockle populations have been sampled over multiple years. In a traditional disease investigation, samples were taken for molecular screens and histopathology for identification of pathogens and pathologies. Additional tissue samples were collected for chemical analysis including metals and pharmaceuticals, as well as environmental samples, including bulk water, incubation water, bulk sediment and sediment cores, taken for eDNA analyses and chemical analyses. A systems mapping exercise was conducted to identify key variables influencing adult cockle population size. The suitability of existing data was assessed, with analysis of trends in data and cockle population dynamics.

Results:

Three key pathologies were identified from C.edule individuals: Marteilia cocosarum (a paramyxid parasite previously linked to similar cockle mortalities in the Burry Inlet), a novel iridovirus Bivalve Iridovirus 1 (BilV1), and disseminated neoplasia (DN) types A and B. However, no one pathology alone or in combination with others can fully explain the observed mortalities. A subset of cockles underwent tissue chemical analyses to explore differences between individuals of varying health status, alongside environmental chemical exposure revealed from sediment samples. Age-depth relationships were obtained from sediment cores and linked to chemical and contaminant levels to identify historical disturbance. A systems map output provided expert consensus on key factors affecting cockles in the Wash, determining potential synergistic drivers controlling adult population size.

Conclusion:

Findings have identified three likely deleterious pathologies previously linked to population declines. On-going analysis will provide an overview of cockle health in relation to the broader ecosystem. Development of stakeholder and cross-agency collaboration will strengthen our understanding of the Wash ecological system and advance current research campaigns to improve existing data. Additional metagenomic and transcriptomic work undertaken on 2024 cockle samples will provide further insight into metabolic and host responses to stressors.

1. Tidy, Anna, Centre for the Environment, Fisheries and Aquaculture Science, Presenter
2. Jessop, Ron, Eastern Inshore Fisheries Conservation Authority, Author
3. Chantelle, Hooper, Centre for the Environment, Fisheries and Aquaculture Science, Author
4. Georgia, Ward, Centre for the Environment, Fisheries and Aquaculture Science, Author
5. Matthew, Green, Centre for the Environment, Fisheries and Aquaculture Science, Author
6. Kelly, Bateman, Centre for the Environment, Fisheries and Aquaculture Science, Author
7. Jasmine, Hunt, School of Biosciences and Medicine, University of Surrey, Author
8. Stuart, Ross, Centre for the Environment, Fisheries and Aquaculture Science, Author
9. Patrick, Keith, Newcastle University, Author
10. Adeel, Yusuf, Centre for the Environment, Fisheries and Aquaculture Science, Author
11. Pip, Mountjoy, Natural England, Author
12. Franck, Dal-Molin, Centre for the Environment, Fisheries and Aquaculture Science, Author
13. Marie, Hanin, Centre for the Environment, Fisheries and Aquaculture Science, Author
14. David, Bass, Centre for the Environment, Fisheries and Aquaculture Science, Author