Author: marina02

Structured risk source analysis: events and consequences involved in pathogen transmission – with examples from Atlantic cod farming

Introduction:

Fish farming world-wide, provides healthy protein rich food that makes up half of the global seafood consumption today. Securing sustainable aquaculture production is thus imperative. Risk assessment play an important role in this process by elucidating the main challenges and associated risk factors. A useful aquaculture risk assessment should provide a sound and starting point for discussions on risk, and contribute to mutual risk understanding and risk acknowledgement among stakeholders.

Methodology:

An approach to environmental risk assessment in aquaculture anchored in the latest thinking in risk science has been developed and thoroughly tested since 2018 (Andersen et al. 2022, Grefsrud et al. 2025).

Results and conclusions:

Analyzing risk to the marine environment from aquaculture activity is often characterized by high complexity, scares data and frequent knowledge gaps. The application of frequency based on probabilities based on hard data as a sole measurement of risk to the marine environment is thus, both problematic and insufficient. In our presentation we argue for a broader and more comprehensive approach to risk that includes experts justified believes, the knowledge perspective, and surprises. Weak knowledge creates uncertainty and with respect to future outcome of events and consequences, and risk increases.

We present an overview of this risk methodology with examples of applications related to disease transmission from Atlantic cod (Gadus morhua) farming.

References:

Andersen LB, Grefsrud ES, Svåsand T, Sandlund N (2022) Risk understanding and risk acknowledgement. A new approach to environmental risk assessment in marine aquaculture. ICES J Mar Sci, doi:10.1093/icesjms/fsac028

Grefsrud ES et al. (2025) Risikorapport norsk fiskeoppdrett – Produksjonsdødelighet hos oppdrettsfisk og miljøeffekter av norsk fiskeoppdrett. rapportserie: Rapport fra Havforskningen 2025-14 ISSN: 1893-4536

1. SANDLUND, NINA, INSTITUTE OF MARINE RESEARCH, Presenter
2. Qviller, Lars, Norwegian Veterinary Institute, Author
3. Patel, Sonal, Norwegian Veterinary Institute, Author
4. Weli, Simon, Norwegian Veterinary Institute, Author
5. Skår, Cecilie, INSTITUTE OF MARINE RESEARCH, Author
6. Grefsrud, Elen Sofie, INSTITUTE OF MARINE RESEARCH, Author
7. Andersen, Lasse Berg, INSTITUTE OF MARINE RESEARCH, Author

First case of Exophiala aquamarina infection in gilthead seabream (Sparus aurata), under intensive marine farming conditions in Greece

Introduction

In recent years, infections caused by fungi of the Exophiala genus have been reported in a wide range of aquatic organisms, including farmed fish. In hatcheries and sea cages, fungal infections are often associated with poor water quality and stress. Systemic mycosis caused by the fungus Exophiala aquamarina has been observed in farmed marine or brackish water fish, leading to severe symptoms and mortality. This study investigates a clinical case of systemic mycosis in juvenile gilthead seabream (Sparus aurata) that resulted in moderate mortality after the fry were introduced into sea cages in Eastern Greece. Laboratory analysis confirmed E. aquamarina as the primary etiological agent.

Methology

The clinical outbreak occurred in spring 2024, at a water temperature of 19.6°C, affecting four seabream cages. A total mortality rate of 7.3% was observed. Affected juveniles (5–20g) exhibited lethargy, erratic swimming, size variation, anorexia, abdominal distension, ulcerative skin lesions and caudal fin erosion. Internally, spleen discoloration, spleno-renal hypertrophy, and whitish nodules in the spleen, kidney and liver were observed. Sampling was conducted over a two-month period and involved macroscopic and microscopic examination of the fish, along with Gram, PAS and Giemsa staining of organ smears. Microbial cultures were performed on Blood Agar 2% NaCl, Sabouraud Dextrose Agar, Brain Heart Infusion Agar and Tryptic Soy Agar (incubated at 23°C for 24–72 hours), complemented by histological examination and molecular identification.

Results and Conclusions

Clinical signs were consistent with fungal infection. Microscopic examination of smears revealed fungal hyphae and spores. Cultures on BA and BHIA developed characteristic, black-pigmented colonies. Histopathology (PAS staining) showed fungal hyphae in the dermis and epidermis, along with localized granulomas in the kidney and spleen. Molecular analysis confirmed E. aquamarina as the causative agent. This is the first recorded case of systemic mycosis caused by E. aquamarina in juvenile gilthead seabream under intensive aquaculture conditions in Greece. This outbreak and its immediate appearance post-stocking suggest vertical transmission from hatchery rather than horizontal infection from the marine environment. It is likely that fry were asymptomatic carriers and immunosuppression due to transport and environmental stress triggered disease onset. The fungus did not appear to spread to adjacent cages, supporting the limited environmental transmissibility. These findings highlight the need for further investigation into the seasonality and pathogenicity of E. aquamarina in gilthead seabream, as well as in other farmed marine fish species in Greece.

1. GOURZIOTI, EVGENIA, IRIDA S.A., Presenter
2. PAGONIS, CHARALAMPOS, IRIDA S.A., Author
3. VASILAKI, PHELLY, IRIDA S.A., Author
4. KLAOUDATOS, DIMITRIS, UNIVERSITY OF THESSALY, Author

Assessing the Current State of Farmed Fish Welfare in Finland: Insights from Stakeholder and Veterinary Surveys

Introduction
The welfare of farmed fish is a growing concern in aquaculture, impacting both ethical considerations and production efficiency. In Finland, the welfare of farmed fish has not previously been systematically assessed. Understanding current welfare conditions and evaluation practices are essential for developing effective monitoring and improvement strategies. To address this gap, two parallel surveys were conducted in spring 2023: one targeting fish farmers and the other veterinarians responsible for fish health and farm oversight. The surveys explored the welfare indicators currently in use, perceptions of their effectiveness, and areas requiring further development.

Methodology
Structured Webropol questionnaires, consisting of multiple-choice questions and open comment fields, were distributed by email to respondents. The survey received anonymous responses from 26 fish farmers and 16 veterinarians, providing a solid representation of professional perspectives from both industry and regulatory viewpoints in Finland.

Results
The survey findings revealed both shared perspectives and notable differences in welfare assessment approaches between fish farmers and veterinarians. Fish farmers predominantly emphasized production-related welfare indicators, such as mortality rates, disease occurrence, and medication use. Veterinarians, in contrast, focused more on the fulfilment of species-specific welfare needs and raised concerns about the narrow scope of current assessment practices. Routine farm inspections primarily monitor clear and overt signs of compromised welfare, while early or subtle indicators are often under-recognized. One important limiting factor recognised by many veterinarians was the strong dependence on standardized inspection forms, which constrains the ability to perform comprehensive welfare evaluations. Both groups highlighted fish health as central to welfare and emphasized the mutual relationship between good welfare and disease resistance. Key development needs included finding practical welfare indicators, effective solutions for environmental enrichment, assuring the welfare of fish during slaughter and more effective treatment strategies especially for water mould infections. Other priorities included water quality challenges in recirculating aquaculture systems, improving fish resilience to temperature extremes, mitigation of seal predation, and the development of automated monitoring tools.

Conclusions
Overall, the surveys highlight the need for authorities and researchers to improve welfare practices in Finnish fish farms through targeted research. Both fish farmers and veterinarians demonstrated strong motivation to deepen their understanding of fish welfare and willingness to invest resources in improving the welfare of farmed fish. The surveys provide a solid foundation for developing targeted training programs to strengthen fish farmers’ capacity to assess welfare more holistically and veterinarians’ role as professional advisors in fish welfare.

1. WESTERBACK, JENNI, FINNISH FOOD AUTHORITY, Presenter
2. Eriksson-Kallio, Anna Maria, FINNISH FOOD AUTHORITY, Author
3. Airaksinen, Susanna, Natural Resources Institute Finland/Alltech Fennoaqua Ltd, Author
4. Hellström, Ella, Natural Resources Institute Finland, Author
5. Kauppinen, Tiina, Finnish Centre for Animal Welfare, Author
6. Korkea-aho, Tiina, Finnish Food Authority, Author
7. Raussi, Satu, Finnish Centre for Animal Welfare, Author
8. Vielma, Jouni, Natural Resources Institute Finland, Author

Opercular shortening and deformities in salmonids (Salmo salar and genus Oncorhynchus): A scoping review

In the 2023 Norwegian Fish Health Report, opercular shortening was identified by fish health personnel as one of the five main causes of reduced growth and welfare in the hatchery phase of salmon and rainbow trout production. Opercular shortening is also cited as a significant cause of mortality in juvenile rainbow trout. When the operculum is shortened or deformed, the gills are exposed to varying degrees and may become injured, and the fish’s ability to effectively pump water over the gills is reduced. Since operculum shortening and deformities is a significant problem in commercial aquaculture, there is a need to review and summarize available knowledge on causes, risk factors, prevalence, temporal development, consequences, and preventive and mitigating measures for opercular lesions in salmon and trout. From 2023 to 2024 we performed a scoping review of the scientific and grey literature on opercular lesions in salmonids, specifically genus Salmo and Oncorhynchus. A systematic literature search was performed, identified publications screened and reviewed, and additional publications was identified in reference list of included publications. A total of 60 studies and 59 publications were identified. 44 studies were identified that describe possible risk factors or causes across six main areas: Genetics, hormones, infectious agents, management and production routines, nutrition, and finally, toxic or other harmful influences. All these factors can cause or increase the risk of opercular lesions, but more research impact on management routines is necessary. In most studies where fish were followed from hatching opercular lesions were first reported during or after first feed, though opercular lesion were also described in alevins. In 18 studies the opercular status of fish were examined more than once, allowing for description of temporal development, while 6 studies report on healing of opercular lesions. In most studies the severity and/or frequency of opercular lesions decreased of time in the hatchery phase and healing of opercular lesion were reported in both induced and spontaneously occurring opercular shortening and erosion. A total of 11 studies described or investigated the possible impact of opercular lesions on other health outcomes. The literature indicated an association between opercular lesions and weight, length, survival, mortality, and gill status in affected fish, though more research in this area is necessary. The search did not identify any scientific articles or grey literature describing investigations of measures to prevent opercular lesions or resolve and mitigate the issue once it has occurred.

1. ØSTEVIK, LIV, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Presenter
2. Kjønstad, Mari, Åkerblå AS, Author
3. Gundersen, Idun, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Author
4. Kortner, Trond, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Author
5. Stormoen, Marit, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Author

Development of an Auxotrophic Transformed Chlorella for Environmental Safety in Recombinant protein Production

Human erythropoietin (hEPO) is a glycosylated cytokine that stimulates erythropoiesis and is widely used to treat anemia and chronic kidney disease (CKD), with additional therapeutic potential in diabetes due to its blood glucose-lowering effects. Currently, hEPO is primarily produced in Chinese Hamster Ovary (CHO) cells; however, this system has limitations, including high production costs and the risk of contamination. In this study, recombinant hEPO (rhEPO) was produced in Chlorella vulgaris, a eukaryotic green microalgae recognized for its scalability, cost-effectiveness, and capacity to perform post-translational modifications (PTMs). Since genetically modified C. vulgaris constitutes a living modified organism (LMO), there are concerns regarding its unintentional release into the environment, which could result in horizontal gene transfer (HGT) or ecological disruption. Therefore, this study aimed to introduce the hEPO gene into C. vulgaris and develop an auxotrophic strain in order to evaluate both the biological activity of the expressed protein and the ecological safety of the host system. The hEPO gene was codon-optimized for expression in C. vulgaris PKVL7422, a strain isolated in our laboratory. The expression vector was designed with the codon-optimized hEPO gene driven by the Cauliflower mosaic virus (CaMV) 35S promoter and the Chlamydomonas reinhardtii RBCS2 terminator, and flanked by nitrate reductase (NR) genes to facilitate homologous recombination-based selection. For auxotrophic strain development, the same strategy was applied to disrupt genes involved in essential amino acid biosynthesis by inserting a codon-optimized enhanced green fluorescent protein (eGFP) gene between the promoter and terminator, enabling visual selection. C. vulgaris PKVL7422 was cultured in BG-11 medium, and transformation was performed via electroporation using 1 × 10⁷ cells mixed with the PCR product of each vector. Integration of the hEPO gene was confirmed by PCR, and successful expression of the target protein was validated by Western blot analysis, which detected a band at approximately 18.4 kDa. The auxotrophic strain containing eGFP was isolated and analyzed via fluorescence-activated cell sorting (FACS), and was found to be incapable of growing in media lacking essential amino acids, in contrast to the wild-type strain. In conclusion, we successfully achieved expression of functional rhEPO in C. vulgaris and developed an auxotrophic host strain. These results suggest that C. vulgaris is a promising and environmentally safer platform for the cost-effective production of rhEPO.

1. Sung, Minkwan, PUKYONG NATIONAL UNIVERSITY, Presenter
2. Ahn, Heejin, PUKYONG NATIONAL UNIVERSITY, Author
3. Jo, Sohyeon, PUKYONG NATIONAL UNIVERSITY, Author
4. Jang, Sujin, PUKYONG NATIONAL UNIVERSITY, Author
5. Kim, Suyeon, PUKYONG NATIONAL UNIVERSITY, Author
6. Choi, Taejin, PUKYONG NATIONAL UNIVERSITY, Author

EFFECT OF DISINFECTANTS ON WATER QUALITY AND COLONIZATION OF FISH BY INFECTIOUS ORGANISMS

Parasites and bacteria are common causes of disease and may be one of the factors slowing down the current development of aquaculture. Preventive water disinfection eliminates dangerous pathogens and residual disinfectant concentrations should be used to treat fish for external parasitic and bacterial diseases.

The effects of two disinfectants – peracetic acid (PAA) and hydrogen peroxide (H₂O₂) on the hydrochemical properties of water and the parasitic and bacterial load on the skin and gills of carp are described in this paper. Three groups (n=6) of common carp (Cyprinus carpio) were exposed to PAA (1.5 mg·l^-1) and H₂O₂ (5 mg·l^-1) applied daily for a duration of 4 days. The test was triplicated. After exposition, bacterial and parasitological examinations of the gills and skin were conducted using bacteriological smear and microscopy of tissue scrapes. Hydrochemiacal parameters were measured before and after the trial. Parasitological and bacterial load of the skin and gills was classified into five categories and subsequently statistically evaluated using the Mann Whitney test.

Parasitological examination revealed a statistically significant (P<0>) effect of PAA on Trichodina sp. These parasites were eliminated on the skin and on the gills of the fish from PAA group. No other statistically significant differences were mentioned among group tested.

Semiquantitative bacteriological examination revealed a statistically significant reduction (P<0>) in the bacterial load of skin in both PAA and H₂O₂ exposed groups. Conversely, there was no statistically significant difference in the bacterial load of gills.

The results show that the application of PAA and H₂O₂ in the tested concentrations for four days has antibacterial effect, while PAA showed also antiparasitic effects.

1. Zusková, Eliška, South Bohemian University in České Budějovice, Presenter

Impact and population dynamics in a German biofloc aquaculture: ‚What happens in an aquaculture stays in an aquaculture‘?

Introduction: The genus Vibrio has the potential to exert a considerable influence on the field of aquaculture. While some species are classified as pathogenic to fish and seafood (e.g., V. campbellii/V. harveyi complex), other species, including V. vulnificus, V. cholerae and V. parahaemolyticus, have the potential to cause intestinal and extraintestinal infections in humans. In order to mitigate the risk of public health threats posed by aquaculture products, it is essential to gain a deeper understanding of the prevalence and impact of potentially human pathogenic Vibrio species. Methodology: The isolates were characterized by phenotypic and genotypic methods incl. antimicrobial susceptibility testing and biotyping. WGS sequencing and bioinformatics analysis was conducted to determine the population structure and to assess the impact of the isolates regarding virulence potential and transmissible resistance determinants. Results: As part of a qualitative Vibrio spp. monitoring of a German biofloc aquaculture in 2022, the occurrence and diversity of V. parahaemolyticus in shrimps and water samples over a period of one year were determined by conventional typing and SfiI-macrorestriction profiling, respectively. A further investigation was conducted 16 months after the last monitoring sampling in order to provide a comparison. In total, 214 strains of V. parahaemolyticus, originating from twelve shrimp and two water samples from one aquaculture basin, were investigated. Overall, the strains exhibited minimal variability in their SfiI-PFGE profiles across all sampling approaches, with 22 subclade clusters assigned to one clone, indicating the persistence of the predominant clonal type. In addition, antimicrobial susceptibility testing (AST), plasmid characterisation and whole-genome sequencing (WGS) was conducted to characterized the strain diversity in-depth. The observed differences between strains were mainly attributed to the presence of plasmids, which were identified in some of the strains. Conclusion: The study provides an overview about Vibrio spp. occurrence and insight into the impact of V. parahaemolyticus on human health and the persistence of a predominant clone.

1. HAMMERL, JENS ANDRE, GERMAN FEDERAL INSTITUTE FOR RISK ASSESSMENT, Presenter
2. BARON, SANDRINE, ANSES, Author
3. LeDevendec, Laetitia, ANSES, Author
4. Goellner, Cornelia, GERMAN FEDERAL INSTITUTE FOR RISK ASSESSMENT, Author
5. Nekat, Jonas, GERMAN FEDERAL INSTITUTE FOR RISK ASSESSMENT, Author
6. Manta, Diana, GERMAN FEDERAL INSTITUTE FOR RISK ASSESSMENT, Author
7. JAECKEL, CLAUDIA, GERMAN FEDERAL INSTITUTE FOR RISK ASSESSMENT, Author

A 3R approach for improving monitoring of salmon migration and health status

The 3R’s are beneficial regardless of whether animals are used for research, wildlife management or health monitoring. The Baltic salmon (Salmo salar) struggles with health issues, and the number returning to spawn has decreased in the last years. River Torneälven with its tributaries produce approximately 60% of all wild Baltic salmon smolts. Torneälven constitutes the Swedish-Finnish border from Haparanda and 190 km north to the junction with the tributary river Muonioälven, where Torneälven diverges west into Sweden and Muonioälven instead constitutes the border further north. Research & monitoring of this population has been long-time ongoing, but methods used require capture. In health studies, fish are euthanised for harvest of organs. Tagging requires sedation and surgery. Some fish suffer from prolonged stress and die after release. Every spawning fish is crucial for survival of the population, but fish in post-capture distress can transmit disease to several other fish and new methods to mitigate the need for capture are vital. A 3R approach is data collection from cameras, providing a non-invasive information method. In dammed rivers, cameras can be placed in fish ladders. In wild rivers such passages don’t exist. The purpose of this project is to develop a new non-invasive method for collecting basic data to support research on fish health and population monitoring in unexploited rivers.

In June 2025, we will mount a camera, observing the river from above, under a bridge approximately 20 km downstream the Torneälven – tributary river Lainioälven junction. At this bridge, the main river channel is shallow, and the water is typically crystal clear. This allows visual detection of salmon from the bridge. A first set of footage from 2024 suggests that skin lesions and moving patterns will be possible to use as biomarkers for disease with this new approach. During the spawning run of 2025, data will be collected. In the autumn, data will be manually assessed to estimate the number of migrating salmon as well as their health status. A massive amount of information is expected to be recorded with this new type of camera surveillance, and in the long run manual assessment of all the fish that pass the camera will not be feasible. Therefore, to ensure efficacy and usefulness, recordings must be automatically assessed with high accuracy and quality. Funding has been applied for to develop an AI for evaluation of footage during the spawning runs of 2026-2028.

1. AXÉN, CHARLOTTE, Swedish Veterinary Agency, Presenter
2. Weijmers, Daniel, Swedish Veterinary Agency, Author
3. Törnqvist, Elin, Swedish Veterinary Agency, Author

Microplastic occurrence in the digestive system of the European squid (Loligo vulgaris) from the Mediterranean Sea

Microplastics (MPs) in the marine environment pose a potential threat to marine organisms worldwide. While MP ingestion in fish is well documented, much less is known about cephalopods, an ecologically important but understudied group. This study aimed to investigate, for the first time, MPs ingestion in the European squid (Loligo vulgaris), a key Mediterranean species and evaluate the preliminary risk assessment.

In February 2023, a total of 22 L. vulgaris specimens were collected using fishing rod during the “MARE2023” survey in the southern Tyrrhenian Sea (Italy). Each specimen was measured (mantle length, ML, mm) and weighted (total weight, TL, g), and rinsed with ultrapure water before dissection. The digestive system (DS) was removed from each individual and subjected to chemical digestion. The solution was incubated at 50°C for 48 h and filtered through fiberglass filters using a vacuum system. Suspected microparticles were then identified using Raman spectroscopy.

A total of 22 adult L. vulgaris specimens were analysed, with mantle lengths ranging from 130 to 280 mm and total weights from 72 to 492 g. The frequency of occurrence was 22.7%, with an average of 0.32 items/specimens. Only microfibers were detected, ranging in lengths from 0.3 to 2.2 mm. Blue was the dominant colour (43%), followed by transparent (29%), red and black (14% each). Most microparticles were coloured cotton (43%). The main polymers identified were polypropylene and polyamide, each accounting for 14%.

This study represents the first assessment of MP ingestion in L. vulgaris in the Mediterranean Sea, highlighting a previously unexplored facet of marine pollution. Based on the preliminary risk assessment indices, the PLI indicated that the surrounding environment was polluted, although the PRI classified the pollution level as low. This study provides a valuable baseline for further environmental and human health risk assessments, as well as for the development and implementation of targeted measures and effective management policies at both local and regional levels.

Funding: This study was funded by the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.4 – Call for tender No. 3138 of 16 December 2021, rectified by Decree n.3175 of 18 December 2021 of the Italian Ministry of University and Research funded by the European Union – Next Generation EU. Award Number: Project code CN_00000033, Concession Decree No. 1034 of 17 June 2022 adopted by the Italian Ministry of University and Research, Project title “National Biodiversity Future Center – NBFC”.

1. FABRIZI, FRANCESCA, CNR-IRBIM, Author
2. MANCUSO, MONIQUE, CNR-IRBIM, Presenter
3. PIRO, MARIA GIOVANNA, University of Messina, Author
4. FALLETI, ROSA, University of Messina, Author
5. BRANCA, CATERINA, University of Messina, Author
6. CONTI NIBALI, VALERIA, University of Messina, Author
7. D’ANGELO, GIOVANNA, University of Messina, Author
8. BOTTARI, TERESA, CNR-IRBIM, Author

Fat necrosis – a key histological feature of melanized focal changes in farmed Atlantic salmon

Melanized focal changes (MFCs) in the fillet of farmed Atlantic salmon represent a significant quality issue. These changes are believed to originate as acute red focal changes (RFCs) that evolve into chronic MFCs. Recent research suggests that hypoxia may play a crucial role in their development, potentially causing necrosis that affects myocytes and adipocytes. This study aimed to examine potential hypoxic conditions in RFCs and the subsequent inflammatory responses and adipose tissue lesions in RFCs and MFCs. We analyzed samples of RFCs, MFCs, and control muscle from various groups of farmed salmon. Immunohistochemistry revealed activation of the hypoxia-inducible factor 1 pathway in RFCs. Histological analysis of RFCs and MFCs showed various stages of fat necrosis. MFCs displayed accumulations of foamy macrophages, suggesting lipid degradation and phagocytosis. In situ hybridization identified amelanotic cells expressing tyrosinase and tyrosinase-related protein-1 in RFCs, which subsequently became melanized in MFCs. In conclusion, we propose a sequence of events leading to MFC formation, emphasizing the critical roles of adiposity, hypoxia, and fat necrosis.

1. Bjørgen, Håvard, NMBU FACULTY OF VETERINARY MEDICINE, Presenter
2. Koppang, Erling Olaf, NMBU FACULTY OF VETERINARY MEDICINE, Author