Source: BBC News
Ulcerative Dermal Necrosis (UDN) is a naturally occurring dermatological disease that leaves salmon with lesions, which can become infected and anglers visiting the Spey have been urged to disinfect their equipment, although officials have said it is not yet known how infectious this particular strain of UDN is.
The Spey River Board said many anglers and ghillies had reported salmon entering the river this season with lesions and ulcers on their head. Samples taken by inspectors from the Marine Laboratory in Aberdeen confirmed one of the fish was suffering from UDN and the Association of Salmon Boards has alerted river authorities across Scotland.
In a letter to proprietors on the river, the Spey River Board said deaths from UDN tended to come as a result of the secondary fungal infection Saprolegnia. The letter said:
“The disease can affect sea trout and brown trout but juvenile fish do not appear susceptible. Previous outbreaks have died out naturally after a period of time. It is important to note that fish affected by UDN can and do survive to spawn normally.
As an interim measure it is recommended that all fresh run fish exhibiting head lesions, but otherwise free of fungal infection should be returned in the hope that they will recover and spawn naturally.”
There have been two serious outbreaks of UDN in Scotland, one in the 1880s and another in the late 1960s and early 1970s.
