Large Scale Eradication of Parasite Infested Atlantic Salmon (Salmo salar) in Six Norwegian Rivers Using the Rotenone Based Piscicide Cft-Legumine

The introduced Atlantic salmon ectoparasite Gyrodactylus salaris is one of the greatest threats to wild Norwegian Atlantic salmon (Salmo salar). The Norwegian Environment Agency has developed a strategy to achieve total removal of the parasite from Norway. An eradication strategy using rotenone to kill the parasite host has been the only effective measure.

The eradication effort is demanding and it is necessary to employ robust planning and apply a coordinated effort to substantiate a possible success following treatment.

This talk describes the effort of eradicating Atlantic salmon from six G. salaris infected rivers in the Romsdal fjord in Norway. The largest river Rauma has an anadromous stretch of 42 km and a mean annual discharge of 36.3 m³/s. In total we treated 82.4 km of infected rivers including anadromous tributaries during 10 days in 2013 and 2014. The methods and techniques involved are outlined. We used the formulation CFT-Legumine, containing 3.3 % rotenone. The eradication involved rotenone concentration analysis in all rivers treated.

The Norwegian Veterinary Institute has been performing fish eradications since 1997. Through our own experience and international advice, a great number of improvements have been made to the techniques used and the implementation of treatment plans.