Amoebic gill disease (AGD) caused by Neoparamoeba perurans is a major welfare and production challenge in Atlantic salmon farming, particularly in warmer waters.
Amoebic gill disease welfare encompasses both the disease burden and the treatment stress. Gill lesions from AGD accumulate mucus that impairs oxygen uptake, causing the equivalent of partial suffocation in affected fish. Behavioural signs including lethargy and surface congregation indicate significant welfare impairment. Freshwater bath treatment removes the marine amoebae but involves crowding, net transfer, and environmental change that cause acute stress. Treatment frequency of every 2-6 weeks in severely affected farms means repeated welfare events. Climate change is worsening AGD as water temperatures rise. Prevention through site management, genetics, and biological control methods that reduce freshwater bath frequency are welfare priorities.