Extermination of Gyrodactylus salaris – infected Atlantic salmon Salmo salar by rotenone treatment in the river Vikja, Western Norway

Abstract
Infections by Gyrodactylus salaris of Atlantic salmon in the river Vikja were discovered in 1981. To prevent further spreading of the parasite to neighbouring rivers in the Sognefiord area, the river was treated with rotenone in November 1981 and in May 1982 in order to exterminate the salmon population and consequently the parasite. Eggs of Atlantic salmon and Brown trout deposited in the gravel survived the rotenone treatment. Annual investigations of the river indicate a build-up of the Atlantic salmon population after 1982. In 1986 and 87 four yearclasses of young Atlantic salmon were present. No G. salaris have been found after 1981. Rotenone treatment seems to be a useful method for exterminating G. salaris from river populations of Atlantic salmon.

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