Examining complex gill disease in Scottish salmon

In recent years, Scotland’s salmon sector has been affected increasingly by gill health challenges. Across marine farms, inflamed and damaged gills have been observed which can lead to respiratory issues, reduced growth, emergency harvests, and significant economic losses.

The cause of gill disorders in marine-farmed salmon is complicated and, often, gill disease is believed to be the result of many interacting factors. These factors include infectious agents such as amoebae, bacteria and viruses; and environmental stressors such as harmful plankton, in adverse water temperature, or poor water quality. When no single primary causative agent can be identified, the condition is known as complex gill disease By 2017, the term was being used widely but without a clear or consistent definition, making it difficult to compare data or design effective management strategies.

Recognising the scale and complexity of the problem, the Sustainable Aquaculture Innovation Centre (SAIC) announced its funding of the ‘Gill Health in Scottish Farmed Salmon’ project, which brought together academic researchers, diagnostic experts, and industry partners from across Scotland. It aimed to produce an evidence-based understanding of gill disease from two complementary strands of work:

Work Package 1: investigation of the epidemiology of CGD, identified risk factors, diagnostic performance, and prevalence.
Work Package 2: characterisation of the community of microorganisms living on fish gills, or the microbiome, to understand its relationship with disease.
Together, these studies sought to build the foundations for improved monitoring, diagnosis, understanding, and management of gill health in Scotland’s farmed salmon.