Cleaner fish are widely used in salmon farming to control sea lice biologically. Their own welfare is poorly understood and largely unmanaged in most operations.
Cleaner fish represent a welfare blind spot in salmon aquaculture welfare discussions. Used to address sea lice welfare problems in salmon, cleaner fish — primarily wrasse and lumpfish — face their own profound welfare challenges. Mortality rates exceeding 50% on some farms indicate conditions that are deeply unsuitable for these fish. Wrasse evolved in complex coastal habitats with abundant structure, hiding places, and territory — the open water environment of a salmon cage provides none of these features. Lumpfish, cold-water specialists, struggle in the warmer temperatures increasingly prevalent in salmon farming due to climate change. The welfare science for cleaner fish is underdeveloped compared to salmon, meaning welfare problems are poorly characterized and management is correspondingly poor. As biological pest control, their welfare should be included in any honest assessment of salmon farm welfare.