Salmon Parasite Management: Cleaner Fish Welfare in Aquaculture

Wrasse and lumpfish are used as biological control agents in salmon farming, but their welfare as cleaner fish is often neglected — high mortality rates signal significant problems.

Key Facts

Cleaner fish — primarily ballan wrasse (Labrus bergylta) and lumpfish (Cyclopterus lumpus) — eat sea lice off salmon in open sea cages
The Norwegian salmon industry uses tens of millions of cleaner fish annually, making them one of the most numerous farmed fish species
Wild-caught wrasse are still used in large numbers, raising sustainability and welfare concerns about capture methods
Mortality rates for cleaner fish in sea cages can exceed 50% within the first few months of deployment
Causes of cleaner fish mortality include salmon aggression, poor nutrition, disease, inadequate habitat, and thermal stress
Wrasse and lumpfish have different ecological requirements — wrasse need reef-like shelter structures; lumpfish prefer cooler, deeper water
Cleaner fish welfare has received increasing research attention since the mid-2010s, resulting in husbandry guidelines in Norway and Scotland
The welfare of cleaner fish is legally relevant in countries where fish sentience is recognised under animal welfare legislation

Welfare Considerations

Cleaner fish welfare has historically been treated as an afterthought in sea lice management, with mortality treated as an expected cost of biological control rather than a welfare problem to be addressed. However, wrasse and lumpfish are fish with pain nociception and stress responses, and their welfare deserves consideration equal to other farmed fish. The high mortality rates experienced by cleaner fish in salmon cages reflect fundamental mismatches between their ecological needs and the cage environment: wrasse are reef-associated fish that need shelter structures and appropriate prey; in the open water of a salmon cage with no shelter and subject to aggression from much larger salmon, they suffer significantly. Lumpfish are cold-water specialists poorly suited to warmer cage conditions in summer. Improving cleaner fish welfare requires providing species-appropriate shelter refugia within cages, feeding with supplementary diets (cleaner fish eat insufficient lice to meet nutritional needs), preventing salmon aggression through cage design, and breeding programmes that produce welfare-adapted strains. Welfare-conscious salmon producers are beginning to measure cleaner fish survival as a key performance indicator.

What You Can Do

Choose salmon certified to standards that include cleaner fish welfare requirements
Support research into improved cleaner fish husbandry including shelter provision and supplementary feeding
Advocate for inclusion of cleaner fish welfare in aquaculture welfare legislation and certification standards
Support the transition from wild-caught to hatchery-reared cleaner fish with improved welfare from birth
Raise awareness that cleaner fish are sentient animals whose welfare matters, not just biological tools
Encourage aquaculture producers to measure and report cleaner fish survival as a welfare indicator