Unpublished study reveals molecular keys to gill damage during Complex Gill Disease

Complex Gill Disease (CGD) is a particularly challenging syndrome for salmon farming, as it largely affects the gills of fish, producing lamellar vascular changes, inflammation, cell death, and epithelial cell hyperplasia. Other symptoms include very pale gills and increased mucus.

Additionally, this disease also impacts production, increasing production costs by 20% due to treatment costs, and has been reported to increase mortality rates by up to 80% in some cases. To date, CGD is known to be influenced by a multifactorial interaction of environmental variables and pathogens.

Given the impact of CGD and the lack of molecular studies aimed at its characterisation and modulation, a group of Chilean scientists conducted a study in which they analysed the modulation of genes and biological processes that occur in the gill filaments affected by this pathology in Atlantic salmon.

In the study, the specialists took gill samples from fish affected by CGD at a fish farm in the Aysén Region. They then divided the gill tissue into damaged (CGDdt) and undamaged (CGDndt) for total RNA extraction and subsequent transcriptomic analysis using RNA-Seq to identify differentially expressed genes and their biological functions.

Pro-inflammatory

As a result, the authors found that the damaged tissue had overexpression of key genes such as mmp9, ccl19, and il8, which would indicate the promotion of a pro-inflammatory environment. "Conversely, the dysregulation of processes associated with cellular homeostasis, cellular communication, and structural development suggests altered tissue homeostasis and regeneration," the scientists explained.

In contrast, undamaged tissue showed inhibition of the immune response and processes associated with maintaining tissue homeostasis, "suggesting the promotion of mechanisms aimed at controlling the inflammatory environment and tissue damage due to proximity to the branchial filament affected by CGD," the authors added.

Overall, the researchers concluded that this study provides valuable insights into transcriptomic responses to CGD and immune regulatory and tissue repair mechanisms in the mucosal tissues of aquatic organisms.

Review the abstract of the study titled “Modulation of immune response and tissue repair mechanisms in the gill filaments of Atlantic salmon (Salmo salar) affected by complex gill disease (CGD) in a marine open sea-cage environment”, here.