Disease is the primary welfare and economic threat in aquaculture. Managing disease with minimal fish suffering requires prevention-first approaches and welfare-conscious treatment protocols.
Disease management in aquaculture creates welfare trade-offs: treatment is necessary to prevent suffering from disease progression, but many treatments are themselves stressful or painful. Chemical sea lice treatments applied as bath treatments expose entire populations including wrasse cleaner fish to compounds that can be toxic. Handling stress during treatment procedures adds to the welfare burden. Prevention through vaccination, biosecurity, and appropriate stocking density is the most welfare-positive approach. When treatment is necessary, protocols should minimize handling stress, use the most targeted treatments available, and include monitoring for treatment-related mortality and distress. The welfare case for precautionary stocking density limits is strong: lower densities reduce disease transmission and treatment frequency.