Sea lice infestation is the most significant chronic welfare problem in open-net pen salmon farming, causing tissue damage and stress to millions of fish while treatments create additional welfare impacts.
Sea lice welfare represents a welfare dilemma in salmon aquaculture — the infestation causes chronic suffering, but the available treatments cause acute stress and welfare compromise of their own. The ideal solution is prevention through site selection, fallowing periods, and biological barriers rather than reactive treatment of established infestations. Non-treatment biological control using wrasse cleaner fish has expanded, but wrasse welfare in salmon pens is a growing concern, creating a welfare trade-off between species. The development of enclosed sea pen technology that prevents sea lice from accessing farmed salmon would address the welfare problem at its root. Current open-net pen production continues to involve chronic sea lice-related welfare compromise for millions of farmed salmon.