Author: marina02

The North American strain of Tetracapsuloides bryosalmonae utilises the salmonid Oncorhynchus mykiss and bryozoan Fredericella indica

In Europe, the myxozoan parasite responsible for Proliferative Kidney Disease (PKD), Tetracapsuloides bryosalmonae (T. bryo), cycles between salmonid fishes and freshwater bryozoans. However, in North America no active hosts (species that shed viable, infectious spores) have been identified. To assess the active host status of steelhead trout Oncorhynchus mykiss and the bryozoan Fredericella indica, we conducted fish-to-bryozoan and bryozoan-to-fish transmission experiments. Specific-pathogen-free F. indica colonies were first exposed to effluent from naturally infected O. mykiss and monitored weekly using stereomicroscopy for overt T.bryo infections. Malacospores from infected colonies were then introduced to naïve O. mykiss, which were held at 16°C and sampled for PCR and histology at 2 and 8 wks post-exposure. Additionally, to investigate vertical transmission of T.bryo, statoblasts and hatched zooids from overtly infected F. indica colonies were screened with stereomicroscopy and qPCR. We observed the development of overt infections in exposed F. indica, indicating that subclinically-infected O. mykiss shed viable fish malacospores of the NA strain of T. bryo. Sequentially, malacospores shed from the bryozoan induced clinical PKD in naive O. mykiss; extrasporogonic stages of the parasite were observed in histology, and T. bryo DNA was detected. We found no evidence of vertical transmission within F. indica. Given that O. mykiss is widely reared and stocked across North America, these findings highlight the importance of pre-release surveillance in susceptible stocks to prevent dissemination of T. bryo into habitats where infected, active host populations may overlap.

1. Das, Nilanjana, Oregon State University, Author
2. Atkinson, Stephen, Oregon State University, Author
3. Hallett, Sascha, Oregon State University, Presenter

BIOAQUA Cost project “enhancing knowledge of biomolecular solutions for the well-being of European aquaculture sector”: opportunities for young researchers

Over the past decade, there has been a significant surge in interest surrounding the development of innovative technologies aimed at enhancing the sustainability of the aquaculture sector. As global demand for sustainable seafood continues to grow, the need for alternative scientific and technical solutions in fish-farming has become increasingly urgent. In response to this, a forward-thinking project called Bioaqua has been launched within the EU COST actions framework with the goal of establishing a dynamic and collaborative European network. This network seeks to bridge the gap between researchers, aquaculture industry professionals, and key stakeholders to facilitate the efficient exchange of knowledge and best practices. By fostering collaboration and encouraging co-creation between academic, industrial, and societal actors, the initiative aims to explore advanced research pathways and accelerate the development and implementation of innovative technologies. Key thematic areas of focus include biomolecular approaches for water treatment and disease prevention, as well as novel engineering and treatment solutions designed to safeguard the health of aquatic environments and enhance fish welfare. Equally important is the project’s commitment to evaluating the impact of these technologies on fish welfare and environmental sustainability. Through rigorous assessment, the project ensures that the proposed solutions are not only scientifically sound but also practically applicable in real-world aquaculture operations. Another strength of Bioaqua is the interdisciplinary collaboration that is ongoing with other COST actions in order to increase synergies across different but complementary scientific sectors. A major emphasis is also placed on the training and development of researchers, with the objective of stimulating European research in biomolecular solutions for aquaculture challenges. The project offers targeted grants to support researcher mobility and skill development, with a focus on early-career scientists. It also provides training through webinars, workshops, and masterclasses to promote ongoing learning, collaboration, and strong research networks across Europe. In addition to financial support for short term missions, the project provides a range of training opportunities such as webinars, workshops, and masterclasses. These events are designed to promote ongoing learning and knowledge sharing among participants and are scheduled to continue in the coming years. By investing in both innovation and lifelong education, the project plays a crucial role in advancing sustainable aquaculture practices and reinforcing Europe’s position at the forefront of this vital sector.

Funded by the European Union Cost Action grant n°CA22160

1. MARSELLA, ANDREA, IZSVE, Presenter
2. PASCOLI, FRANCESCO, IZSVE, Author
3. TOFFAN, ANNA, IZSVE, Author

the effect of photoperiod stimulation in smoltification on salmon health and production, a common garden lifetime study

introduction

successful smoltification in norwegian salmon aquaculture is crucial for optimal fish health, welfare, and further production at sea. traditionally, smoltification is induced by simulating the natural framework of seasonal photoperiodic changes, exposing salmon to a “winter signal” (12 hours of light and 12 hours of darkness (ld12:12)) for 5-7 weeks. currently, there is no gold standard or best practice guidelines for smolt production, and many producers maintain a constant light regime throughout smoltification (ld24:0) to primarily avoid a reduction in growth during this period. this study aims to compare two smoltification regimes and investigate the effects of photoperiod stimulation during smoltification on atlantic salmon in a longitudinal study.

methodology

at vaccination, 80.000 salmon were separated, fin clipped, and exposed to a ld12:12 light regime for 6 weeks. simultaneously, another 80.000 salmon were placed in a neighboring tank and maintained at ld24:0. at seawater transfer, both groups were moved to the same unit in a common-garden setup and produced until harvest.

we examined smoltification status, growth metrics, heart morphology, nephrocalcinosis, serology, and expression profiles of key genes involved in growth, smoltification, and immune response.

results.

our results show that the ld24:0 salmon had higher growth rates during the freshwater and early seawater phases, while the ld12:12 salmon demonstrated a quicker recovery after seawater transfer and higher growth rates in mid to late production. smoltvision analysis indicated that the ld12:12 regime accelerated gill osmoregulatory gene expression, although smolt status was satisfactory in both groups at transfer. gene expression analysis suggests that the winter signal influences expression profiles of numerous genes, particularly those related to smoltification and pituitary adaptation to marine environments.

plasma analyses support these findings, showing that the winter signal causes an initial reduction in thyroid hormones, followed by a sustained increase and elevated t3/t4 ratios after the termination of the winter signal. no significant differences were observed in immune-related gene expression. however, the ld24:0 salmon exhibited a markedly higher mortality trend in the early seawater phase, a significantly higher prevalence of aberrant cardiac morphology, and increased trends towards greater severity of nephrocalcinosis.

conclusion

our results indicate that a preparatory winter signal significantly influences salmon physiology and health both immediately and over time, particularly in terms of gene expression, welfare, and production-related metrics such as growth and mortality.

1. FIGENSCHOU, ALEXANDER, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Presenter
2. Lund, Hege, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Author
3. Stormoen, Marit, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Author
4. Persson, David, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Author
5. Klykken, Christine, Aqua Kompetanse AS, Author
6. Kavaliauskiene, Simona, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Author
7. Ciani, Elia, Edmund Mach Foundation, Author
8. Hodne, Kjetil, NORWEGIAN UNIVERSITY OF LIFE SCIENCES, Author

Exploring natural protective immunity against Tetracapsuloides bryosalmonae in Rainbow Trout Aquaculture.

Emerging infectious diseases driven by climate change pose a major and growing challenge to the future of sustainable aquaculture. Proliferative Kidney Disease (PKD), caused by the myxozoan parasite Tetracapsuloides bryosalmonae (Tb) is highly temperature sensitive and has emerged as one of the most significant parasitic diseases affecting rainbow trout (Oncorhynchus mykiss) aquaculture and wild brown trout (Salmo trutta) populations around Europe and the USA.

This study uses PKD as a model system for linking disease ecology and environmental immunology to the drivers of pathogen tolerance and resistance. We present findings from 2 years of parasite environmental DNA (eDNA) monitoring via qPCR in the inlets of four UK farms, allowing profiling of infectious propagule pressure. In parallel, host adaptive immunity was evaluated using a parasite antigen-specific ELISA in naïve, previously exposed, and fish exposed at different timepoints to track immune profile development relative to infection pressure. These data have enabled temperature sensitivity modelling of the seasonality of infection, disease and the development of natural protective immunity, which are crucial for reducing fish mortality and morbidity in the following season.

Preliminary results suggest that antigen-specific antibody responses begin to develop 12-14 weeks post-exposure, with peak antibody production occurring at 17-19 weeks in naturally exposed farmed fish. Notably, antibody levels persist throughout winter gradually falling early spring, with a subsequent increase following re-exposure during the following spring/summer when river parasite loads increase.

By coupling eDNA detection with immunological profiling, we aim to improve on the reliability of a pre-exposure challenge program, which is informed by the ecology of PKD in naturally occurring hosts and the dynamics of natural resistance to symptomatic PKD. Together, these findings help highlight the potential for integrating environmental monitoring with immune profiling to support adaptive management strategies, enhancing aquaculture sustainability and the conservation of wild fish populations in a changing climate.

1. King Wolf, Lisa, University of Nottingham, Presenter
2. Hartikainen, Hanna, University of Nottingham, Author
3. Holland, Jason, University of Aberdeen, Author
4. Robinson, Oliver, British Trout Association, Author
5. Tharindu Hewage, Malintha, University of Aberdeen, Author

Teaching about fish at veterinary schools in France

Introduction:
There are currently 4 public veterinary schools and one private veterinary school in France. Historically, a chair of aquaculture was created at the public veterinary school based in Nantes when it was founded in 1979. This is still the school with the largest volume of aquaculture teaching, but it was decided to pool the teaching so that veterinary students from other schools could have a first-hand look at this production. The teaching is also provided as part of continuing education, opening up to a wider audience (researchers, technicians, etc.).
Methodology:
For initial training, all students at the Nantes veterinary school, Oniris VetAgroBio, have 22 hours of teaching, including lectures, practical work and farm visits. For the other public schools, the volume of teaching is different but all the students have a presentation of the major productions with a focus on rainbow trout for the section on the role of the veterinarian (diseases and treatments). The concepts of environmental impact and sustainable farming are also covered. Students from the 4 public schools who wish to do so in their final year can take the course further with a 15-day module including visits to different farms, lectures by field veterinarians or people working in the aquaculture sector and handling in a controlled structure.
Specific modules are also offered as part of continuing education and are open to people working with fish. They are more oriented towards experimentation and surgery on aquaculture species, and cover animal welfare and protection.
Results and Conclusions:
All French veterinary students who graduate (n = +/- 700/year) receive an introduction to aquaculture production and the role of the veterinarian. Although few of them end up practising aquaculture veterinary medicine, students are generally satisfied with their knowledge in this specific field. With regard to the ongoing training of research staff using the fish model for scientific purposes, the regulatory aspect of training means that all people working with fish must be trained. For the Oniris VetAgroBio school, this represents the training of around forty people, researchers or technicians, in the module devoted to aquaculture species and around twenty in the surgical training module each year.

1. Ségolène, Calvez, Oniris, INRAE, BIOEPAR, 44300 Nantes, France, Presenter
2. Nora, Navarro-Gonzalez, Oniris, INRAE, BIOEPAR, 44300 Nantes, France, Author
3. Céline, David, Oniris, INRAE, BIOEPAR, 44300 Nantes, France, Author
4. Lionel, Pineau, Oniris, INRAE, BIOEPAR, 44300 Nantes, France, Author
5. Jean-Claude, Desfontis, Oniris, NP3, 44300 Nantes, France, Author

Effect of fallowing and other biosecurity measures on bacterial and viral pathogens in a controlled RAS experiment with Atlantic salmon

Introduction

The introduction or presence of pathogenic microorganisms in Recirculating Aquaculture Systems (RAS) may result in disease outbreaks leading to fish mortality and reduced fish welfare in general, both in the current fish population and in later populations. The effect of fallowing and other biosecurity measures between production cycles of Atlantic salmon is questioned when biofilters are re-used between fish groups.

Methodology

We used experimental RAS units and biofilter reactors in triplicate, and investigated the establishment, survival, and inactivation of pathogenic agents. The effect of biosecurity measures such as fallowing, cleaning, and disinfection of biofilters on these pathogens was characterized.

Three brackish water systems were set up to mimic smolt production conditions in RAS. Each tank holding fish was connected to its own water treatment unit with mature biofilter. Salmon infected with Ca. Branchiomonas cysticola, Infectious pancreas necrosis virus (IPNV), and Piscine reovirus (PRV-1) were transferred from a commercial farm to the challenge facility at Marineholmen RASLab (Bergen, Norway). Swabs from RAS unit surfaces, biofilter chips, tank, and water were sampled regularly and analysed for pathogens over a period of three weeks after introduction of the infected fish. After three weeks, the fish were removed and the the effects of fallowing studied by introducing healthy naïve fish into the tanks at three different time points, as well as environmental monitoring.

After the initial experiment, some of the biofilter chips from the tanks were distributed into 3 smaller units, and different biosecurity measures such as changing the water and ozonation were tested.

Results and conclusion:

It was possible to detect all three agents in both environmental samples and in fish during the first phase of the trial. During the second phase, to test impact of biosecurity measures and disinfection procedure, Ca. Branchiomonas cysticola could be detected for one week, while IPNV could be detected for a much longer period. At conclusion of the trial, the naïve fish introduced to the tanks were negative for Ca. Branchiomonas cysticola infection, but positive for PRV and IPNV using real time rt-PCR. Histological and IHC detection will confirm possible pathological changes.

1. COLQUHOUN, DUNCAN, NORWEGIAN VETERINARY INSTITUTE, Presenter
2. Patel, Sonal, Norwegian Veterinary Institute, Author
3. Nilsen, Hanne, Norwegian Veterinary Institute, Author
4. Weli, Simon, Norwegian Veterinary Institute, Author
5. Furne, Miriam, Norwegian Veterinary Institute, Author
6. Roalkvam, Irene, Norwegian Veterinary Institute, Author
7. Øvredal, Lisa, Norwegian Veterinary Institute, Author
8. Fernandes, Paulo, Norwegian Institute for Water Research, Author
9. Hess-Erga, Ole-Kristian, Norwegian Institute for Water Research, Author
10. Larsen, Sondre, Akvaplan NIVA, Author
11. Andrews, Melanie, Marine RASlab, Author
12. Handegaard, Reidar, ILAB, Author
13. Dale, Håkon, University of Bergen, Author

Simultaneous detection and quantification of fish parasites and invertebrate hosts in riverine systems using environmental DNA

Knowledge of how host species, vectors and infection reservoirs are distributed and disperse in the environment is crucial for management and control of disease outbreaks. Wildlife diseases caused by pathogens with multiple host life cycles or broad host ranges are particularly challenging as effective control strategies often require assessing the distributions of multiple hosts species across complex landscapes. Using environmental DNA (eDNA) isolated from filtered water samples across a network of sites among a one river catchment in the UK (Erewash), we assessed simultaneously the occurrence of an invertebrate host and a range of myxozoan parasites. Despite many of myxozoans targeted here causing little virulence, Tetracapsuloides bryosalmonae in particular causes epidemic outbreaks of Proliferative Kidney Disease in salmonid fish populations. A quick ‘catch-all’ water filtration method was developed using adaptable and recyclable components, allowing for a range of pore sizes. We employed targeted detection of bryozoan host Fredericella sultana and the PKD parasite T. bryosalmonae through qPCR, alongside a myxozoan-specific metabarcoding approach. Comparison of field surveys and eDNA detection showed that eDNA detection and quantification of F. sultana eDNA in rivers performed well (~85% congruency with visual surveys). Detection of parasite in the same eDNA samples revealed the absence of the T. bryosalmonae in the river, which was further confirmed by metabarcoding. However, we detected several myxozoan parasites including Buddenbrockia sp. which are known to infect F. sultana. We demonstrate that one can efficiently capture small particles such as sloughed host eDNA and the much larger parasite spores using a single, simple and flexible sampling technique. While the invertebrate host is spread throughout the river network, co-occurrence with the parasites is focused on the main river with side and upstream section showing no presence.

1. MELZER, FLORIAN, UNIVERSITY OF NOTTINGHAM, Presenter
2. Sweeney, Emma, University of Nottingham, Author
3. King Wolf, Lisa, University of Nottingham, Author
4. Fiala, Ivan, Biology Centre CAS, Author
5. Hartikainen, Hanna, University of Nottingham, Author

Motivating systematic learning: evaluation of a points-based activity system in fish diseases education

As part of the “fish diseases” course, students were given the opportunity to earn activity points, which were added to their score on the final test. The aim of the point system was to encourage students to study systematically.
During classes, students could earn points in the following forms: a quiz, “pins” (naming organs during practical class), drawing questions in Kinder egg capsule, attendance at lectures, answering questions during class, working in a group – calculations on carp fish nutrition and profitability of fish farming, preparing a presentation on parasitic diseases. None of the activities were compulsory. At the end of the course, students were asked to complete a questionnaire on the point system. The first question asked students to rate the usefulness of the system on a scale from 1 (negative) to 5 (very positive). In the second question, students determined whether the point system mobilised systematic learning. In the third question, students chose the best (in their opinion) forms of earning points.
The overwhelming majority of respondents rated the usefulness of the points system as 5 (85%) and felt that it mobilised them to learn (87%). The best-rated form of scoring was pins, lecture attendance and a quiz. The least frequently ticked option was answering questions in Kinder egg capsule. Despite the lack of compulsory scoring, all students took the quiz and pins. Attendance at lectures was around 40%. The willingness to prepare the presentation varied from group to group. In some groups, not all of the prepared seminar topics were presented by the students, in which case the teacher discussed the topic. Individuals expressed the wish to prepare more than one presentation. Due to the points earned, students achieved higher scores in the final test. Students who did not pass in the first attempt were generally those who gained single points during the semester. This may indicate a positive impact of the credit system on the quality of education in “fish diseases”.  Students vary in the way they acquire knowledge. Some are auditory, others visual or kinesthetic. Many students are introverts and are reluctant to speak during class. Different forms of scoring help to activate students from different learning types and can be an easy teaching tool to facilitate learning.
Funding: Funded by the Minister of Science under „the Regional Initiative of Excellence Program”

1. Pajdak-Czaus, Joanna, University of Warmia and Mazury in Olsztyn, Presenter
2. Sadowski, Jacek, University of Warmia and Mazury in Olsztyn, Author
3. Platt-Samoraj, Aleksandra, University of Warmia and Mazury in Olsztyn, Author

Optimized methods for water-based pathogen detection in aquaculture systems

Specific and sensitive tools for detecting and monitoring pathogens in the aquatic environment can be crucial for preventing the spread of infectious agents in aquaculture facilities. Monitoring waterborne pathogens through water filtration and subsequent detection using target-specific (RT-) qPCRs and/or sequencing is an approach that can reduce or even replace the need to euthanize fish for monitoring purposes in aquaculture, allowing earlier biosecurity- and disease control measures. We first performed an in vitro work where we tested various filtration- and nucleic acid extraction methods for selected pathogens prior to target-specific (RT-) qPCRs to simplify and facilitate on-site water filtration without compromising detection probability. This was tested in combination with different filtration rates, lysis buffers, and filters for freshwater and seawater spiked with relevant salmon pathogens. The suitability and feasibility of the methodology was then tested in the field, where a fish group was followed over time from the hatchery to offshore Atlantic salmon aquaculture facilities until slaughter. Additionally, the third generation sequencing approach (MinION Oxford Nanopore Technologies) was used to correlate shotgun metagenomics sequencing for microbiome analyses to events in the production cycle. The results showed that a “sandwich” filtration method combining two different filters allows for the detection of various pathogens with a single filtration step and a single nucleic acid extraction step, followed by (RT-) qPCRs. This reduces both the costs and time required for analysis. Moreover, we showed that this methodology is feasible and effective under field conditions. This means that aquaculture facilities could implement these methods on-site, ensuring timely and accurate pathogen monitoring. Additional shotgun metagenomics sequencing for microbiome analyses with the MinION allowed a microbial screening technique which would lead to future real-time acquisition and analysis of data in the field. This dual qPCR-sequencing approach will provide a unique system to gain knowledge on the impact of real-time monitoring to detect various pathogenic specimens (e.g., viruses, bacteria, parasites).

1. BENEDICENTI, OTTAVIA, NORWEGIAN VETERINARY INSTITUTE, Presenter
2. STRAND, DAVID A., NORWEGIAN VETERINARY INSTITUTE, Author
3. MOHAMMAD, SAIMA N., NORWEGIAN VETERINARY INSTITUTE, Author
4. AMUNDSEN, MARIT M., NORWEGIAN VETERINARY INSTITUTE, Author
5. SINDRE, HILDE, NORWEGIAN VETERINARY INSTITUTE, Author
6. VRÅLSTAD, TRUDE, NORWEGIAN VETERINARY INSTITUTE, Author

eDNA metabarcoding reveals effects of intensive aquaculture on aquatic parasite diversity

Introduction: Understanding biodiversity at the species and genetic levels remains a key challenge in ecological research, especially for microscopic fish parasites such as myxozoans, aquatic microsporidians, and amphizoic amoebae. Freshwater ecosystems are increasingly threatened by anthropogenic pressures, from habitat degradation to climate change, making the assessment of parasite diversity and community shifts an urgent research priority.

Parasite species richness within these groups remains poorly characterized. Human-driven changes to aquatic environments alter host community composition and, consequently, parasite assemblages. Disruptions to ecosystems can destabilize delicate host–parasite dynamics, with potential consequences for host health and population resilience.

Parasites are inherently difficult to detect, leading to major data gaps in ecological surveys. Environmental DNA (eDNA) metabarcoding offers a powerful means of overcoming this limitation by enabling the detection of parasite DNA directly from environmental samples. We applied this approach to investigate how human activities, such as river regulation and intensive aquaculture, affect the occurrence and diversity of fish parasites.

Study Site and Methods: Our study focused on the Lužnice River in the Czech Republic, a system that presents a natural experiment. One segment of the river remains undisturbed and meandering, while another is regulated and hydrologically connected to a network of fishponds used for intensive fish farming. Both regions share similar climatic conditions, and the area includes the historic Zlatá stoka canal, which supplies water to the Třeboň Basin ponds.

We sampled 29 locations along approximately 160 km of river and canal. From each site, water and sediment samples were collected for DNA extraction. eDNA-based metabarcoding was performed using specific primers targeting Myxozoa, microsporidians, and amphizoic amoebae. Amplicons were sequenced using Illumina NovaSeq platform, and custom bioinformatic pipelines were used to define operational taxonomic units (OTUs). Phylogeny was reconstructed using Maximum likelihood method in RAxML and Bayesian inference in MrBayes.

Results and Conclusions: We observed high parasite diversity, including many previously uncharacterized taxa. Differences in community composition were apparent between disturbed and undisturbed sites. We detected native parasites as well as taxa likely introduced via fish stocking. Several species appeared suppressed in heavily impacted areas. Parasite richness was notably higher in regions associated with intensive aquaculture.

These findings underscore how anthropogenic disturbance shapes parasite communities and can disrupt host–parasite equilibrium. Monitoring both pathogenic and non-pathogenic parasites is essential for early warning and disease prevention, especially as climate change and aquaculture expansion intensify ecosystem pressures.

The project is supported by MEYS (LUAUS24281).

1. FIALA, IVAN, Institute of Parasitology, Biology Centre CAS, Ceske Budejovice, Czech Republic, Presenter
2. Lisnerová, Martina, Institute of Parasitology, Biology Centre CAS, Ceske Budejovice, Czech Republic, Author
3. Pecková, Hana, Institute of Parasitology, Biology Centre CAS, Ceske Budejovice, Czech Republic, Author
4. Lazárková, Eliška, Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic, Author
5. Lövy, Alena, Institute of Parasitology, Biology Centre CAS, Ceske Budejovice, Czech Republic, Author