Wrasse and lumpsucker fish used to control sea lice on salmon farms are themselves welfare-deprived animals whose own wellbeing is often neglected.
Wrasse transported from inshore collection to offshore salmon cages experience transport stress and abrupt habitat change from complex reef environments to open cages. Mortality rates among deployed cleaner fish are often high, exceeding 50% in some operations. Cleaner fish are small and vulnerable in sea cages, facing predation by salmon and exclusion from food in competition. Their welfare needs including shelter, appropriate density, and compatible tank mates are frequently unmet. The ethical inconsistency of using billions of cleaner fish as tools while conducting welfare monitoring only for the salmon they service is increasingly recognised.