Sea lice and other ectoparasites feed on their host causing fish to lose skin and scales, which can cause deadly infestations to both farmed and wild fish. The problems often arise from farms of fish due to the higher density of fish found there. Without means of treating the farmed fish, the farmed fish may infest the wild fish population.
Commonly used treatments cover both chemical treatment and mechanical treatment. A suitable example of a mechanical treatment is found in WO 98/24304, which discloses a method and a device for removing exterior parasites from salmon in fish farms. The method is described as mechanical stripping, wherein the fish is led through a water current and subjected to water jets from a number of nozzles. The device is described as comprising four or more nozzles, which are all connected to a water pump. When fish is led past the nozzles, they are subjected to strong water jets ejected from the nozzles.
Another example is found in WO 2015/043603, wherein a system and a method are described. The system is described to suck up water and fish using a suction tube connected with a pump system. The fish is thereby transported upwards from the first volume and onwards to another volume via the suction tube. On the upwards part of the transportation path, that is where the fish is moving upwards, the suction tube is provided with a number of nozzles, which ejects water jets towards the fish in order to spray off parasites. The discrete nozzles treat the fish in a point-wise fashion in which some part of the circumference of the fish is left untreated. The untreated or under-treated part of the fish increases the possibility of the parasites to remain on the fish skin after the treatment.