Gyrodactylus salaris

Gyrodactylus salaris is a small monogenean ectoparasite (about 0.5 mm long) which mainly lives on the skin of freshwater Atlantic salmon. It attaches to the fish by a specialized attachment organ (haptor) with sharp hooks, which is situated at the parasite's tail end. When feeding, the parasite glues the mouth end to the salmon. Then, it everts its pharynx through the mouth and releases a digestive solution with proteolytic enzymes which dissolves the salmon skin. Mucus and dissolved skin are then sucked into the gut. This feeding activity results in ulcers and lesions in the fish skin.

Historically, Gyrodactylus-infected rivers has been treated with the indiscriminate pesticide rotenone. Recently, however, a new method of treatment has been introduced, dosing small volumes of aqueous aluminium and sulfuric acid into the river. A huge advantage of this method is the possibility to kill the parasite without harming the host. This new method has shown very good and promising results in Batnfjordselva River and Lærdalselva River, two rivers in Norway.