Heavy sea lice infestations cause skin lesions, osmotic stress, secondary infections, and immune suppression. Affected salmon show reduced feeding, abnormal swimming, and chronic stress responses. Untreated infestations can be fatal, particularly in smolts.
Hydrolicer, thermolicer, and laser (Stingray) systems remove lice without chemicals. Hydrolicer uses pressurized water; thermolicer uses warm water (34°C briefly). These methods reduce chemical resistance but carry risks of scale loss, stress, and mortality if not managed carefully.
Hydrogen peroxide and azamethiphos baths are licensed treatments applied in tarps or well boats. Overdose and underdose both harm fish — the former causing acute toxicity, the latter promoting resistance. Precise dosing protocols and oxygen supplementation during treatment are critical welfare measures.
Emamectin benzoate (slice) delivered in feed targets sea lice systemically. Resistance has developed in many regions. Withdrawal periods must be observed to protect fish welfare and food safety. Strategic rotation with other treatments manages resistance.
Cleaner fish — wrasse (Labridae species) and lumpfish — eat sea lice from salmon. They provide a chemical-free control option when stocked at appropriate ratios. Cleaner fish welfare is itself a growing concern, as they need appropriate habitat and feeding.
Best practice combines all available tools in an integrated pest management framework, guided by real-time monitoring (sea lice counting protocols) and coordinated with neighboring farms. Reducing peak infestations protects both salmon welfare and wild salmonid populations nearby.