The invention provides a method of treatment of farmed fish to combatinfestation by multicellular ectoparasiteswith exoskeletons, which method comprises topically exposing farmed fish,especially salmon in sea cages, to a first and a secondsea lice treatment agent, said first sea lice treatment agent being acarbamate or organophosphate and said second sea lice treatmentagent being a pyrethroid or pyrethrin.
