Cleaner fish — wrasse and lumpfish — are used in salmon farming to eat sea lice. They are introduced with minimal welfare consideration and suffer high mortality rates, raising questions about whether this lice control method is truly welfare-positive overall.
The use of cleaner fish in salmon farming has created a welfare paradox: reducing sea lice welfare harm to salmon by introducing another species that suffers at high mortality rates in the process. This trade-off has been largely invisible in welfare discussions focused on salmon, but represents a significant welfare problem in its own right given the enormous numbers involved. Wrasse dying of cold stress, disease, or salmon aggression in inadequate cage environments represent welfare harm caused by a welfare intervention. The industry is beginning to acknowledge this, with some producers committing to improved cleaner fish welfare standards. The long-term solution may be non-biological sea lice control — laser systems, snorkel barriers, selective breeding for resistance — that eliminates cleaner fish welfare entirely.