Gill disease is one of the most significant chronic welfare problems in farmed Atlantic salmon, impairing respiration and requiring intensive management.
Salmon with gill disease experience chronic respiratory compromise from impaired gill function. Affected fish show reduced appetite, increased surface breathing, and lethargy indicating welfare impairment. Amoebic gill disease causes visible gill fusion and inflammation. Freshwater treatment for AGD is effective but stressful, requiring crowding and pump transfer. The welfare cost of chronic gill disease across a production cycle is substantial. Prevention through water quality management and early detection through regular gill scoring is the most welfare-positive management approach.