Gyrodactylus salaris (Gyro) are parasites that infect salmon in fresh water. In Norway, they have so far proved to be lethal for all concerned strains of Norwegian salmon.
As of 27 October 2011 20 rivers have been recovered after chemical treatment. Steinkjer region has been infected for three years now and is now in the middle of a clean bill of health process, while the Laerdal and Vefsna regions are to be treated for the last time this year.
Gyro fighting is mainly by means of chemical treatments. In addition, the treatment area is reduced as much as possible by the closure of fish ladders and the use of physical barriers where possible. Chemical treatments implemented either as pure rotenone treatments or using the combination method, where the acidic aluminum is used as the main chemical and rotenone as a supplement in peripheral areas.
The difference between the methods are roughly the rotenone treatments aim to eradicate the gyro by taking the life of the salmon, while the acidic aluminum aims to remove the gyro without the fish dying.
In Lærdalselva, treatment started on Thursday 9 August. Before the autumn is over the river will have gone through two treatment periods.
Here, the treatment used is acidic aluminum, supplemented with rotenone in peripheral areas where the use of acidic aluminum is not appropriate.
Lærdalselva has been designated as test waters for use of acidic aluminum. The aim of the ongoing campaign is to eradicate the parasite within two years, starting in 2011.
National Veterinary Institute is responsible for the part that requires rotenone treatment and is also very involved in the part that requires treatment with acidic aluminum. After treatment in the autumn, work will start to enhance salmon stocks and monitor the river to see if the parasite is gone.
If the parasite disappears after the treatments, it will be the first time G. salaris has been eradicated from a watercourse by means other than rotenone. In this case one has found a new tool in the fight against the salmon parasite which avoids damage to salmon stocks in the river.
