A system is disclosed for protecting fish from parasite infection. The system comprises a fish guidance system for deterring fish from moving into a first region bordering a water surface and/or for can move from the second region into the first region so that they can reach the water surface bordering the first region. The system further comprises a radiation disinfection system that is configured to provide disinfection radiation to the first region, the disinfection radiation being configured to disinfect water from parasites.