The salmon farming industry, a cornerstone of the coastal economies in northern Europe, North America, and Chile, faces significant challenges to gill health, often stemming from interactions with planktonic organisms. Understanding the specific planktonic taxa involved is crucial for developing effective mitigation strategies.
A study published in the journal by scientists from the University of Glasgow, NatureScot, Heidelberg University Hospital, Scottish SeaFarms, Mowi Scotland, and UiT the Arctic University of Norway presents a comprehensive approach to identifying the biological drivers of proliferative gill disease (PGD) and associated fish mortality in salmonid aquaculture.
The growing challenges of marine aquaculture
Marine aquaculture has experienced rapid expansion but is increasingly vulnerable to environmental stressors. Climate change, along with anthropogenic activities, is causing shifts in coastal ecosystems, including increased phytoplankton and zooplankton blooms, reduced dissolved oxygen levels, and parasite proliferation. These factors pose significant threats to the health and survival of farmed fish, particularly salmonids.
Gill health issues in salmonid aquaculture
Gill health has become a major concern in salmonid aquaculture, and losses due to gill-related diseases have steadily increased in recent years. Gills play a vital role in fish physiology, and their health is influenced by a multitude of factors, including parasites, viruses, bacteria, and plankton.
Limitations of traditional monitoring methods
Traditional plankton monitoring methods based on morphological identification have several drawbacks, including:
- Time and labor-intensive: Morphological identification requires significant expertise and can be slow and prone to errors.
- Limited taxonomic resolution: Distinguishing between morphologically similar species can be challenging.
- Inaccurate abundance estimates: Traditional methods may not accurately quantify plankton abundance.
A comprehensive approach to plankton identification
To address the limitations of traditional methods, this study employed a comprehensive approach combining both morphological and molecular techniques. Environmental DNA (eDNA) barcoding was used to identify and quantify a wide range of planktonic organisms, while morphological analysis provided additional taxonomic information.
A longitudinal study of plankton diversity and gill health
To investigate the link between plankton diversity and gill health, the study conducted a longitudinal assessment at two marine aquaculture facilities in Scotland. Daily data were collected during the 2021 growth season (March-October), covering both sheltered and exposed sites. By combining morphological and molecular identification methods with robust statistical models, the researchers aimed to identify the key planktonic drivers of PGD and mortality.
Key findings:
- Diverse planktonic threats: The study revealed a wider range of planktonic threats to salmonid gills than previously recognized. In addition to established culprits like hydromedusae and diatoms, unexpected taxa such as doliolids and appendicularians were identified as potential drivers of PGD and mortality.
- Delayed effects: The research demonstrated that plankton impacts on gill health can be delayed, highlighting the importance of considering historical plankton data when assessing risks.
- Comparison of identification methods: The study compared the effectiveness of environmental DNA (eDNA) metabarcoding and microscopy in identifying and quantifying plankton species. Both methods proved valuable, emphasizing the need for a combined approach to capture the full diversity of planktonic organisms.
Implications for the salmon industry
The findings of this study have significant implications for salmonid aquaculture management:
- Early warning systems: Identifying the key planktonic drivers enables the development of early warning systems to detect potential threats and implement preventive measures.
- Targeted treatments: A better understanding of the biological causes of gill diseases can lead to the development of more targeted and effective treatments.
- Sustainable aquaculture practices: By addressing the root causes of gill health problems, the study contributes to the development of more sustainable and resilient aquaculture practices.
Future research directions
To further advance our understanding of plankton-related threats to salmonid aquaculture, future research should:
- Expand spatial and temporal coverage: Conduct similar studies across multiple aquaculture sites over several years to establish long-term trends and regional variations.
- Investigate interactive effects: Explore how interactions between different planktonic taxa and environmental factors influence gill health.
- Develop predictive models: Create predictive models based on plankton data to forecast potential gill disease outbreaks.
Conclusion
This research underscores the importance of a comprehensive approach to understanding the complex interactions between salmonid gills and planktonic organisms. By combining molecular and morphological identification methods with rigorous statistical analysis, the study has shed light on the diversity of planktonic threats and their potential impact on aquaculture. The findings provide valuable insights for developing effective management strategies to ensure the long-term sustainability of salmonid aquaculture.
The study was funded by BBSRC, the Scottish Aquaculture Innovation Centre, and The Royal Society of Edinburgh.
Contact
Martin Llewellyn
School of Biodiversity, One Health and Veterinary Medicine, University of Glasgow
Glasgow, UK
Email: martin.llewellyn@glasgow.ac.uk
Reference (open access)
Algueró-Muñiz, M., Spatharis, S., Dwyer, T., Cheaib, B., Liu, Y. W., Robertson, B. A., Johnstone, C., Welsh, J., Macphee, A., Mazurkiewicz, M., Bickerdike, R., Migaud, H., McGhee, C., Præbel, K., & Llewellyn, M. (2024). High-Resolution Longitudinal eDNA Metabarcoding and Morphological Tracking of Planktonic Threats to Salmon Aquaculture. Environmental DNA, 6(5), e70005. https://doi.org/10.1002/edn3.70005
