Biological control of sea lice using cleaner fish is increasingly used in Norwegian salmon farming. The welfare implications for wrasse and lumpfish used as lice-pickers deserve more attention than they currently receive.
The shift toward biological sea lice control represents a genuine welfare improvement for salmon by reducing chemical treatment stress. However, this benefit has been achieved at significant welfare cost to the cleaner fish deployed in enormous numbers. Wrasse — small, warm-water fish — suffer extreme thermal stress in cold Norwegian waters where salmon are farmed, with mortality often exceeding half of deployed fish within a season. Those that survive face predation by salmon, disease transmission, crowding, and behavioral frustration in an environment completely unlike their natural rocky reef habitat. Lumpfish are better cold-adapted but show signs of chronic stress in cage environments. Neither species is covered by existing aquaculture welfare regulations, meaning their welfare has been systematically overlooked in the industry transition toward biological sea lice control. Improving cleaner fish welfare requires investment in species-appropriate housing, thermal management, reduced stocking ratios, and regulatory inclusion.