Fish Net Pen Welfare: Salmon and Sea Lice

How sea lice infestation in salmon net pen aquaculture harms fish welfare and what integrated management approaches look like.

Key Facts

Sea lice cause tissue damage, osmotic stress, and open lesions on farmed salmon, causing significant welfare harm
Infestations in net pen systems can reach levels of 10+ lice per fish, far above accepted welfare thresholds
Chemical treatments including hydrogen peroxide and azamethiphos are stressful and not always effective
Cleaner fish (wrasse and lumpsucker) eat lice from salmon, providing a welfare-positive biological control method
Closed containment systems and submerged feeding systems reduce sea lice exposure significantly

Welfare Considerations

Sea lice represent one of the most significant chronic welfare problems in Atlantic salmon farming. The parasites damage the salmon's skin and scales — their primary barrier to infection and osmotic regulation — causing chronic pain-like distress and secondary infections. At high infestation levels, affected fish show behavioural changes consistent with chronic pain including altered swimming patterns and reduced feeding. The treatments used to control lice add additional welfare burden: bathing treatments stress fish, and mechanical removal methods cause physical damage. Moving toward biological control using cleaner fish, closed systems, or selective breeding for lice resistance are the most welfare-positive directions for the industry.

What You Can Do

Choose farmed salmon from operations using biological lice control methods where this information is available
Support research into selective breeding for sea lice resistance in farmed salmon
Advocate for lice infestation thresholds to be included in mandatory welfare monitoring for salmon farms
Follow Fish Welfare Initiative's work on sea lice management and welfare in salmon aquaculture
Reduce farmed salmon consumption and choose certified, welfare-audited sources when you do purchase