Cleaner fish — wrasse and lumpfish — are deployed in salmon sea cages to control sea lice, but their welfare has received inadequate attention relative to their large numbers and documented welfare challenges.
Cleaner fish welfare represents a significant welfare gap in the salmon aquaculture industry: tens of millions of animals deployed annually with mortality rates that would be unacceptable for salmon, and welfare standards substantially less developed than for the primary farmed species they protect. The irony is acute — cleaner fish are deployed to reduce the welfare harm of sea lice on salmon, but their own welfare in the process is severely compromised. Wrasse, in particular, are cognitively complex fish whose behavioral needs are poorly accommodated in salmon cage environments. Shelter provision, temperature management, and species-appropriate conditions are known to reduce cleaner fish mortality substantially, but implementation is inconsistent. The welfare case for treating cleaner fish with the same seriousness as salmon is strong on numbers alone — in some operations, cleaner fish represent a substantial proportion of total fish present in a cage.