Gill health is critical to Atlantic salmon welfare in aquaculture, with gill disease representing a major welfare and production challenge in sea cage farming.
Gill health is the single most critical physiological system for salmon welfare because gills perform multiple life-supporting functions simultaneously. Compromised gills cause chronic hypoxia and osmoregulatory stress even when fish appear clinically normal. Assessment of gill health requires examination beyond visual observation, including scoring microscopic changes. Treatment for gill disease involves handling and freshwater bath treatments that cause acute stress, raising the welfare calculation between treatment stress and ongoing disease burden. Prevention through site selection, stocking management and monitoring is preferable to treatment.