The invention relates to a system and method for reducing exposure to sea-lice (Lepeophtheirus spp. and Caligus spp.) for fish in marine fish farms by inducing controlled doses of sound energy which destroy specific organs (sensory, nervous and secretory systems) of the sea-lice present in the volume of water containing the farmed fish and/or seal-lice attached onto the fish. The sound is characterised by having one or more frequencies is/are in the range of from 300 to 550 Hz, and a sound pressure level, SPL, at 1 metre distance from the transducer in the range of from 140 to 180 dB re 1µPa2, and the sound is maintained until the cumulative sound dose reaches a sound exposure level, SEL, of at least 180 dB re 1 10 µPa2∙s or higher.
