The salmon are believed to have escaped from farms in Finnmark, but their origin is still unknown, Finnmark Dagblad reports.
According to the newspaper, fishermen in the area caught some 400 farmed salmons in the night of Saturday May 29 to Sunday May 30.
The fish were caught in an area close to salmon farms and wild salmon rivers.
Both Grieg Seafood Finnmark and Mainstream told the newspaper that no signs of escapes have been found at their local farms.
Now Norway's fisheries directorate, Fiskeridirektoratet, is sampling the fish to determine its origin.
