Disease is a major welfare challenge in intensive aquaculture. Effective biosecurity and early treatment prevent suffering for millions of farmed fish.
Disease in farmed fish causes welfare harm through the direct effects of infection — tissue damage, organ failure, systemic inflammation — and through the stress of crowding and deteriorating conditions in affected populations. The relationship between intensive production conditions and disease risk is well-established: crowding, poor water quality, and nutritional stress predispose fish to infection. Prevention through better husbandry and biosecurity is both the welfare-positive and economically preferred approach. Treatment with antibiotics, when necessary, has welfare benefits by resolving bacterial infections, but their use must be targeted rather than routine to prevent resistance development. Vaccination programs for salmon have been particularly successful, reducing antibiotic use by over 99% in Norway while maintaining welfare and production outcomes.