Cataracts — clouding of the lens — affect a large proportion of farmed Atlantic salmon and represent a significant but underappreciated welfare problem caused by dietary and management factors.
Salmon cataracts represent a welfare problem that is both entirely preventable and historically underappreciated. A salmon with significant cataract impairment is functionally partially blind, impairing its ability to locate food efficiently, navigate social interactions, and respond to environmental threats. The feeding difficulty caused by cataracts creates nutritional stress on top of the vision impairment itself. The cause — histidine deficiency in feed — is addressable through feed reformulation that is economically feasible and increasingly standard in higher-welfare salmon production. The persistence of high cataract prevalence in some salmon operations reflects inadequate attention to welfare outcomes in feed specification decisions rather than any technical impossibility of prevention.