Sea lice infestations are one of the most significant welfare challenges in salmon aquaculture, causing painful skin lesions, secondary infection, and contributing to high mortality rates in affected fish.
Lice welfare in salmon farming illustrates how a single pest problem generates multiple layers of welfare harm. The lice cause direct pain and tissue damage; the treatments — baths, mechanical brushing, thermal exposure — cause acute stress and can themselves cause injuries; and the cleaner fish deployed as biological control experience chronic welfare neglect. Fish welfare science has established that salmon have the neurological capacity for pain experience, making the scale of lice-related suffering in global aquaculture significant. Regulatory frameworks are beginning to impose lice count thresholds above which treatment is mandatory, but the welfare quality of available treatments remains an open question.