Cleaner fish — primarily wrasse and lumpfish — are deployed in salmon sea cages to eat sea lice. Their welfare is a significant and often overlooked concern in the aquaculture welfare chain.
Cleaner fish welfare represents a significant and largely invisible welfare problem embedded in Atlantic salmon aquaculture. Tens of millions of lumpfish and wrasse are deployed in salmon cages annually, where they are expected to consume sea lice from salmon. Their welfare is affected by the conditions of salmon cages — water quality, access to their preferred microhabitats, and the density of salmon with which they share space — that were designed for salmon rather than for them. High cleaner fish mortality rates — often exceeding 50% over a production season — indicate that cage conditions are far from welfare-optimal for these species. The development of welfare standards for cleaner fish, including monitoring of mortality rates as a welfare indicator and cage design standards that accommodate cleaner fish habitat needs, represents an important and achievable welfare improvement.