Lumpfish and wrasse are deployed in salmon cages to eat sea lice. As living tools for another species' welfare, their own welfare is often overlooked but scientifically significant.
Cleaner fish welfare represents one of aquaculture's most ethically complex situations. Lumpfish and wrasse are deployed as living biological tools to serve the welfare interests of salmon — reducing the sea lice burden that causes suffering in the more commercially valuable species. The welfare of the cleaner fish themselves is treated as secondary, despite accumulating evidence that both lumpfish and wrasse are sentient, pain-capable fish with their own behavioral needs.
Mortality rates in cleaner fish are staggering — the Scottish salmon industry deploys millions of cleaner fish annually, with majority mortality within six months. These deaths occur from salmon aggression, inappropriate habitat conditions, disease, and the physiological stress of cold-water deployment. The welfare cost of cleaner fish mortality has rarely been quantified against the sea lice control benefit provided.
The salmon industry and welfare organizations are now developing specific welfare standards for cleaner fish production (hatchery conditions) and deployment (sea cage conditions). Key requirements include providing substrate for lumpfish to rest (they are poor swimmers requiring substrate contact), shelter from salmon aggression, and appropriate stocking density in combination with salmon. These welfare improvements should be adopted as standard practice given cleaner fish sentience evidence.