An outbreak of ISA in 1998 severely damaged the Scottish salmon industry
A second case of the fish disease Infectious Salmon Anaemia (ISA) has been confirmed on Shetland.
Scientists said the disease was found at a fish farm close to the one in the Burra area which was confirmed with the infection on 2 January.
The Scottish Government said owners Hjaltland Sea Farms would "depopulate" its site as soon as possible.
The disease does not affect humans but can cause serious damage to stocks of farmed Atlantic salmon in seawater.
A controlled zone was set up on 2 January after the virus was found at an empty fish farm off Burra.
The virus was also suspected at two other sites in the area.
The movement of fish and equipment has been restricted.
Fish health inspectors will continue investigations in the area.
An outbreak of ISA on Shetland, the Western Isles and Orkney in 1998 and 1999 was estimated to have cost the industry £100m and led to the loss of 200 jobs.