Disease is a major welfare and production challenge in salmon aquaculture. Sea lice, bacterial infections, and viral diseases cause suffering affecting millions of fish and require welfare-conscious management approaches.
Salmon disease management involves difficult welfare trade-offs at every decision point. Sea lice infestation causes chronic welfare harm through skin damage, osmotic stress, and discomfort. However, chemical treatment baths used to control lice involve crowding salmon into treatment vessels — itself a significant acute stressor — followed by chemical exposure that can cause toxic effects at high doses. Biological lice control through wrasse deployment reduces chemical treatment need but raises welfare questions about wrasse themselves — these small fish have poor survival rates in cage environments and may experience significant mortality from cold temperatures and predation. Vaccination against bacterial diseases has dramatically reduced antibiotic use in Norwegian salmon farming — a model for sustainable disease management that benefits fish welfare by preventing disease rather than treating it. The path to better disease welfare runs through prevention, monitoring, and developing treatments that minimize both disease burden and treatment stress.