UDN is a disease mainly affecting wild salmon, sea trout and brown trout. It usually occurs in adult fish returning from the sea and starts as small lesions on the scale-less regions of the fish, mainly the snout, above the eye and on/ above the gill cover. On entry to fresh water lesions ulcerate and may become infected. For further information please click the following link:
UDN occurs in cold water temperatures only and disappears over the summer. The last major outbreak was in the late 1960’s/early 1970’s and caused huge losses in the wild salmon population.