THE Government has quarantined 72 fish farms in the Highlands in response to an outbreak of what may turn out to be the deadliest salmon disease ever seen in this country.

In addition, the bodies of tens of thousands of fish which have been infected on one fish farm are to be transported to Norway for disposal because no facilities exist in Scotland.

The disease, infectious salmon anaemia, devastated Norway a number of years ago and the Scottish outbreak is the first recorded instance within the European Union. The Scottish office has confirmed that there has been an outbreak at a fish farm on Loch Nevis, near Mallaig. More than 200,000 fish there are being destroyed.

Tests are continuing at a second farm on Loch Snizort, on Skye, which is also thought to be affected by the disease. The quarantined farms, all within 40km of the original outbreak, have been banned from moving live fish within the next 30 days while tests are carried out to ensure that all stocks are disease free. The move is a precaution and there is no evidence of any infection on these sites.

''This is a terrible disease,'' said Professor David MacKay, director of the Scottish Environment Protection Agency's north region. ''It does spread quite slowly, but it did eventually move throughout the whole of Norway. It caused a lot of damage before it was eventually brought under control.''

Inspectors were called in to the infected farm after it was noticed that large numbers of the fish were dying. The virus is identified by examining the blood cell count. It spreads through the liver, turning it black, and into the kidneys, before finally causing internal bleeding. Infected fish become listless, hanging around the side of farm cages before dying and sinking to the bottom.

Professor Mackay said the extraordinary steps taken to dispose of the infected fish were necessary because of the danger from the disease to Scotland's fish farm industry, which employs more than 5000 and produces 100,000 tons of salmon as year.

''Basically, the fish will be sucked out of the water into a tanker where they will be anaesthetised with carbon dioxide and then killed. Formaldehyde will be added and they will be turned into silage.''

He added that, because of the pressure of time and the need to ensure absolutely safe disposal, it was more sensible to ship the fish to Norway, where there was experience in dealing with infected carcasses.

An official investigation is under way into the source of the virus which can be transmitted by wild sea trout, who carry it unaffected, from an effluent discharge, or be brought by fish transferred from other farms. It poses no risk to humans, says the Government, as research shows it cannot be transferred from species to species.

A spokeswoman for the Scottish Office said there were two confirmations of outbreak of the disease. ''Beyond that we can't go into any numbers. On the disposal issue, no final decision has been taken. The fish could be disposed of in any one of a number of ways, including landfill or incineration.''

The confirmation that the virus is present in Scotland is likely to alter forever the way Scottish fish farmers go about their business.

The situation in Norway has been controlled through a series of strict curbs on the movement of live fish and continuous monitoring. It is extremely likely that the Government will be forced to implement similar measures to ensure that, if there is another outbreak, its effects are minimised.

No-one could be contacted for comment from the Scottish Salmon Growers Association.