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Photo: The Norwegian Ministry of Fisheries and Coastal Affairs.Photo: The Norwegian Ministry of Fisheries and Coastal Affairs

Salmon lice

01.01.2014 // The strategy for an environmentally sustainable Norwegian aquaculture industry states that parasites shall not not have a regulating effect on stocks of wild fish. Salmon lice is the most common parasite in salmon farming.

Salmon lice are ectoparasites that occur naturally on salmonides in sea water.  However, it is an example of a parasitic disease, the consequences of which are exacerbated in fish farms due to the large number of hosts found there. In addition to the spread of parasites inside and between cages at fish-farm sites, the parasite can also be spread over larger areas by coastal currents.

New methods continue to be developed

The regulations in force require compulsory treatment of salmon lice before the number of lice exceeds a certain limit. An increasing number of fish farmers are using wrasse (which eats lice) to control the levels of salmon lice in the cages. Other methods, such as mechanical removal or the use of veterinary medicinal products, are also in use. New methods continue to be developed and the aim is gradually to replace and reduce chemical treatments through the introduction of alternative methods of action.

Regulations to ensure food safety

The pharmaceuticals in use today for treating salmon lice are approved by the Norwegian Medicines Agency, in accordance with the general EU rules for approval of veterinary medicinal products. In order to be approved, information must be available on environmental impact and food safety considerations. To ensure that only approved veterinary medicinal products are used and that they are used correctly, only authorised veterinarians and fish health biologists are allowed to issue prescriptions for use on fish. To further ensure food safety, there are also regulations specifying the length of time necessary between treatment with veterinary medicinal products and slaughtering (withdrawal time). In addition, the Norwegian Food Safety Authority keeps records of all pharmaceuticals ordered by veterinarians and fish health biologists for use in aquaculture.

Lice can develop reduced sensitivity to pharmaceuticals, making it difficult to determine the effectiveness of different methods of treatment. This represents a significant challenge. Where a veterinary medicinal product for the treatment of salmon lice proves ineffective, the fish farmer is obliged to repeat the treatment with a different pharmaceutical. If this also proves ineffective, the Food Safety Authority has the power to take any decision necessary to control the situation, including the slaughter of stocks. To reduce the development of resistance among lice, the focus is on efficient implementation of delousing through coordinated delousing in larger areas and coordinated fallowing of fish farms.

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