Wrasse and lumpfish are used as biological control agents for sea lice in salmon farms. These cleaner fish have received growing welfare attention as their use has scaled dramatically.
Cleaner fish welfare is one of the most under-addressed issues in salmon aquaculture. Wrasse and lumpfish have their own complex welfare requirements — wrasse are territorial reef fish that hide in structure, lumpfish use adhesive discs to rest on surfaces — that are largely unmet in salmon net pens. Being stocked at high densities in open-water pens with a completely different species exposes them to conditions entirely unlike their natural ecology. High mortality — sometimes exceeding half the stocked population within a production cycle — reflects welfare failure at scale. In Norway alone, tens of millions of cleaner fish die annually under poor welfare conditions. The Norwegian and UK governments have begun developing welfare standards for cleaner fish, but implementation and enforcement remain early-stage. Breeding programs for lumpfish are improving availability of purpose-bred stock with potentially better adaptation to farm conditions.