The import of cleaner fish for use in aquaculture of salmonids poses a moderate risk to biodiversity in Norway. The risk is associated with genetic change of local populations, the spread of species beyond their natural range, and the spread of pathogens and introduction of alien organisms.
Thus concludes the Norwegian Scientific Committee for Food and Environment (VKM), in their risk assessment of negative impact, commissioned by the Norwegian Environment Agency.
Sea lice are small crustaceans parasitizing marine fish. They are a threat to wild salmonids and cause disease outbreaks, and fish welfare issues in Norwegian aquaculture. The use of cleaner fish that prey on sea lice in Norwegian salmonid farms has increased substantially over the last decade and has created a demand for the import of cleaner fish from other countries. VKM has assessed the risk to biodiversity in Norway from the import of cleaner fish in terms of genetic change of local populations resulting from interbreeding with imported cleaner fish. The project group also assessed the risk from import to the spread of the species beyond their natural ranges, the risk from transferring pathogens and parasites among areas, and the risk from other ecological effects caused by imported cleaner fish.
VKM concludes that genetic changes caused by crossbreeding with imported cleaner fish could have a severe negative impact on local populations of corkwing wrasse and ballan wrasse, and may lead to a reduction in viability and adaptability of native populations of goldsinny wrasse and lumpfish.
The risk of negative impact from the spread of the species beyond their natural range was assessed to be moderate for corkwing wrasse and low for the three other species of cleaner fish.
There are considerable knowledge gaps considering infectious agents in the cleaner fish species, but it was assessed that the gill parasite Microcotyle donavini, if transferred from imported fish, might have a moderate negative impact on the viability of local populations of wrasses. It was further assessed that Viral haemorrhagic septicaemia virus (VHSV), if spread, could have a severe negative impact on any of the cleaner fish.
The project group assessed a moderate risk of negative impact on biodiversity in Norway following the introduction of alien species through by-catch or transport water.
Overall, VKMs Alien Organisms and trade in Endangered Species (CITES) concludes that the use of imported cleaner fish poses a moderate risk of having a negative impact on biodiversity in Norway.