Using cleaner fish including wrasse and lumpfish for biological sea lice control in salmon farms creates welfare responsibilities for a second species alongside the salmon they protect.
Cleaner fish welfare represents an ethical complication of biological sea lice control — solving a salmon welfare problem through the deployment of another species whose own welfare is poorly protected. Wrasse that evolved for shallow reef environments and lumpfish adapted for cold Norwegian waters both face welfare challenges in salmon pen environments, including inappropriate temperature, density, habitat complexity and diet provision. High mortality rates in cleaner fish deployed in salmon pens indicate welfare compromise at a significant scale. The industry obligation to address cleaner fish welfare as a condition of using biological control is increasingly recognized, but implementation has lagged significantly behind deployment scale.