Aquaculture Net Pen Welfare: Wild Salmon and Sea Lice

Sea lice infestations in salmon net pens cause significant welfare harm to farmed fish and threaten wild salmon populations migrating past farms.

Key Facts

Sea lice Lepeophtheirus salmonis cause skin lesions, osmotic stress, and secondary infection in salmon
Adult sea lice densities of more than 0.5 per gram body weight are considered welfare-relevant
Treatments including hydrogen peroxide baths cause acute stress and occasional mortality
Wild juvenile salmon migrating past net pen farms show dramatically elevated lice burdens
Norway alone uses millions of cleaner fish (wrasse and lumpsucker) to control lice
Resistance to pharmacological treatments is increasing, creating a treatment escalation cycle

Welfare Considerations

Sea lice infestation creates welfare harm through tissue damage, osmotic stress, and the physiological burden of parasite load. Heavy infestations cause open wounds on heads and backs that are comparable to chronic wounds in any vertebrate. Treatment stress compounds the harm: hydrogen peroxide baths and mechanical delicing cause acute distress. The use of cleaner fish raises additional welfare concerns — wrasse and lumpsucker are often not counted in welfare assessments despite being sentient fish. Alternative approaches including closed containment systems, single-use sites with fallowing periods, and selective breeding for lice resistance address the problem more systematically while reducing welfare burden from treatments.

What You Can Do

Choose farmed salmon products certified under schemes addressing sea lice management
Support development and adoption of closed containment aquaculture that eliminates sea lice risk
Advocate for monitoring and reporting requirements for sea lice levels on farms
Reduce farmed salmon consumption or shift to certified lower-impact products