New case study: enhancing salmon health through better understanding of stress and diet

Creating a realistic model of stress that mirror the experiences of Atlantic salmon

Farmed Atlantic salmon face regular health interventions to manage common parasites like sea lice. While necessary, these procedures can put the fish under stress, weakening their immune system and damaging the protective mucus layer on their skin. This project set out to understand how repeated stress affects salmon health, and whether specially designed dietary supplements could help fish become more resilient.

Valued at over £120k, the project partners were Lallemand UK Ltd, University of Stirling, and BioMar.

The aim was to create a realistic model of repetitive stress that mirrored what fish experience on farms, and test whether enhanced diets could lessen the negative effects. The project also sought to identify reliable biomarkers that farmers and researchers could use to measure stress and health in the future.

Salmon were placed into groups receiving different combinations of diets and stress events. One was a standard feed, while the other was enriched with antioxidants, nucleotides, and advanced yeast-derived ingredients known to support immune function and mucosal health.

The project team monitored how fish responded to either a single stress event or several in succession. They assessed hormonal and antioxidant responses, skin mucus quality, tissue health, gene activity, and overall performance.

The project found that repeated stress caused signs of chronic strain, including disrupted cortisol responses and reduced antioxidant defences. Importantly, the enhanced diet helped soften some of these negative effects, particularly at the immune and mucosal level. Growth rates were not affected.

The project also identified a shortlist of biomarkers, e.g., cortisol levels, antioxidant enzymes, and changes in skin mucus, that are especially useful for monitoring long-term stress.

Overall, the study demonstrated that repetitive stress can be modelled in a controlled, realistic way, and that targeted nutrition has the potential to improve fish robustness. This work supports more welfare‑focused parasite management strategies and opens the door to new dietary solutions that could reduce reliance on medicinal treatments and strengthen the sustainability of salmon farming.

The full title of this project is 'Enhancing mucosal robustness and immunity in salmon'.

Read the case study