Sea lice infestations are among the biggest welfare problems in Atlantic salmon aquaculture, and the treatments used to remove them carry their own significant welfare costs.
Delousing procedures impose acute welfare costs on salmon including thermal injury, physical trauma from mechanical handling, and osmotic stress from freshwater exposure. Research using behavioural and physiological indicators has shown thermal treatments cause pain responses and elevated cortisol. The fish endure multiple treatments over a production cycle. The welfare of cleaner fish — wrasse and lumpfish sourced from wild capture or aquaculture — is also a growing concern, as these species have high mortality rates in salmon cages. Industry and researchers are actively seeking less harmful lice control strategies.