Fish farmers warned to watch out for disease from wild salmonids
UDN is a wild fish problem 'but may be contagious'
Fish farmers in the Trøndelag region of Norway are being encouraged to increase vigilance for the unlikely but possible spread of a disease from wild to farmed fish.
Ulcerative dermal necrosis (UDN) has already been found in wild salmonids in Norway’s Orkla, Gaula, Verdalselva and Mossa rivers, and on Wednesday, November 4, the Norwegian Veterinary Institute issued a notification of UDN in the Stjørdalselva, a 43-mile long river that flows into the Trondheim Fjord.
UDN and saprolegniosis caused by Saprolegnia parasitica are the most prominent challenges in what the Veterinary Institute calls a complex disease picture facing wild salmonids. In addition to UDN and saprolegniosis, examinations of sick fish show the occurrence of bacterial sepsis (blood poisoning), various parasitic infections, and soft tissue calcifications.
Disease burden
Among parasitic infections, blood poisoning caused by nematodes (Anisakis spp.) is common. In addition, several other parasites occur with varying degrees of tissue damage and health effects.
Overall, the findings show a significant disease burden for individuals and at the population level, the Veterinary Institute said in a press release. Given that disease arises from the interaction between host, infectious agents and environment, and that climate change is changing the rules of the game, there is reason for concern about the future.
There is no information to suggest that farmed fish are affected, but there are indications from older studies that the disease may be contagious, and that it can also occur in the marine phase, the Institute said.
“UDN is considered a problem in wild fish. Nevertheless, we urge increased vigilance both at marine sites and at facilities that use freshwater from sources with runs of wild salmon and sea trout,” said Åse Helen Garseth, wild fish manager for the Veterinary Institute’s fish health and welfare department.
