The infected fish showed no clinical signs of the disease, according to Defra.
The discovery was made through comprehensive sampling. Cefas is continuing to test wild fish in the river, both below and above the infected farm to determine the extent of infection.
Although there is no scientific evidence that VHS infection causes significant disease outbreaks in wild freshwater fish stocks, any persisting infection in wild stocks could be a source of infection or re-infection for trout farms in the vicinity through VHS virus contamination of the river supply to the farms.
There have been no further cases of the disease on trout farms in the Ouse/Don catchments of North Yorkshire affected by the current case. The first round of testing on all farmed sites has returned negative results so far and is due to be completed later this week. A second round of testing began last week with results expected by the middle of July.
Results of the further testing will be made known when they have been completed. Fish farmers in the affected area and other stakeholders are being kept informed of the situation.
VHS has no implications for human health.
For more information, view the Viral Haemorrhagic Septicaemia Fact Sheet
TheFishSite.com News Desk