Gill health is a critical determinant of salmon welfare in sea pen aquaculture. Gills are the primary organ for gas exchange and osmoregulation, and gill disease causes significant suffering and is a leading cause of mortality in commercial salmon farming.
Gill disease causes respiratory distress analogous to breathing difficulties in mammals - a genuinely aversive and potentially painful experience. The high prevalence of AGD in sea pen salmon reflects the challenge of managing sensitive animals in environments where pathogens are endemic. Treatment itself involves handling stress. Prevention through site selection, genetic resistance, and proactive monitoring reduces the frequency and severity of gill disease, with direct welfare benefits for individual fish.