Gyrodactylus salaris is a parasite which infects the skin, gills and fins of salmon, trout and some other types of freshwater fish. The parasite is less than a half millimetre in size, is barely visible to the naked eye and causes serious mortalities to Atlantic salmon. The parasite is very hardy and may be introduced by fishermen returning from infected countries as it is capable of surviving for several days in damp conditions such as plastic bags, wet angling equipment and on the surface of dead fish.
Gyrodactylus salaris occurs naturally in the Baltic rivers of Finland and Russia, where the native fish are tolerant to the parasite and normally any infection causes them no harm. In areas where the parasite does not occur naturally, salmon trout and other freshwater fish have little or no tolerance.
In Norway between 1970 and 2002 salmon stocks on 44 rivers have been infected as a result of infection by Gyrodactylus salaris. Means to eradicate the parasite are very costly. The Norwegian remedial work is very destructive and this work has involved treating whole catchment areas.
At present the UK is free from this parasite, and Working Group was formed in 2005 to raise the public's awareness of this parasite. This group also looked at how the parasite could be contained and eradicated, should it ever appear in the UK.
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