Wrasse and lumpfish are deployed in salmon sea cages as biological control agents for sea lice. Their welfare has received increasing attention as their numbers used exceed salmon numbers in some operations.
Cleaner fish welfare represents a compounding problem: these fish are deployed in welfare-challenging conditions (high temperatures, predation risk from salmon, no refuges) with welfare standards far below those applied to the salmon they serve. The use of 50+ million cleaner fish annually, with extremely high mortality rates, constitutes a massive welfare burden largely invisible in seafood welfare discussions. The precautionary principle applied to fish sentience suggests that this scale of preventable cleaner fish mortality warrants urgent attention. Alternatives including mechanical and chemical lice control all have their own welfare implications but should be compared holistically.