Gill disease in farmed salmon is a major welfare and production challenge. Healthy gills are essential for oxygen uptake, osmoregulation, and overall fish welfare.
Gill health is fundamental to salmon welfare because gills perform the critical functions of breathing and salt-water balance. Salmon with compromised gills experience the equivalent of breathing through damaged lungs - chronic oxygen insufficiency causes fatigue, stress, and immune suppression. The treatments for gill disease - freshwater or hydrogen peroxide immersion baths - are themselves stressful experiences requiring handling and water transfer. Prevention through biosecurity, optimised stocking densities, and monitoring represents the most welfare-positive approach, as it avoids both disease suffering and treatment stress.