In aquarium and sea cage experiments four wrasse species from Norwegian waters were identified as facultative cleaners, with lice infested salmon (Salmo salar) as the host: goldsinny (Ctenblabrus rupestris), rock cook (Centrolabrus exoletus), female cuckoo wrasse (Labrus ossifagus) and corkwing wrasse Crenilabrus melops). In this assumingly artificial cleaning symbiosis the wrasses played the active role while the salmon showed little response, neither aggressiveness nor invitation to cleaning. Experiments in sea cages have shown that wrasse might be utilized to control sea lice infestation on salmon postsmolts, as an alternative to treatment with chemicals.