Melanin spots in farmed salmon indicate chronic infection and immune response, serving as a welfare indicator in aquaculture operations.
Salmon with high melanin spot scores have experienced significant immune challenges indicating health events causing welfare compromise. Melanin spots themselves are harmless to consumers but represent a record of health history in fish that experienced infections. Farms with lower melanin spot scores are managing health challenges more successfully, representing better welfare outcomes. Melanin scoring provides a practical welfare assessment method.