Gill Health in Scottish Farmed Salmon

Gill disease poses a significant challenge to salmon aquaculture globally. It is associated with reduced performance and elevated mortality on affected sites, and can result in difficulties in maintaining effective sea lice control. Since the emergence of a form of gill disease (amoebic gill disease, or AGD) in Scotland in 2011, multifactorial gill conditions, often termed complex gill disease (CGD), have emerged as an even greater challenge. Several pathogens have been implicated in cases of CGD, but our ability to detect them has surpassed our understanding of their clinical significance. Furthermore, the importance of other potential contributors to CGD (for example, environmental factors and management practices) is poorly characterised, and effective means of disease mitigation or prevention remain to be determined.

The objective of this project is to identify actions and measures that can be used to prevent or reduce gill disease in farmed salmon, using a multidisciplinary approach that will combine novel methodologies with well tested techniques.

Further achievements are also expected in:

• Characterising cases of CGD to develop a consistent definition of the disease
• Improving our understanding of the factors that drive gill disease via epidemiologic studies
• Creating evidence-based information and decision support regarding gill disease and fish husbandry
• And providing knowledge on the gill microbiome, exploring its role in the molecular pathology of gill health, and assessing how it changes under different conditions

This project represents an unprecedented industry-wide collaboration of all major salmon producers in Scotland and other key industry stakeholders. All recognise gill disease as one of the greatest threats to sustainability, profitability, and growth of the Scottish salmon industry. The cooperative framework established for this project, together with the information collected and knowledge gained, will ultimately provide the basis for further work on health issues in Scottish aquaculture.