A serious new disease has been found in salmon on Scottish salmon farms. The disease, cardiomyopathy syndrome (CMS), produces heart failure in the fish.
Although CMS presents no threat to humans it is invariably fatal to the fish as there is no known treatment. It has been found in one and possibly two Scottish farms: in the first case, where it has been positively identified, it wiped out 60 per cent of a stock of 27,000 large adult salmon in a west coast sea loch over five weeks, with the remainder having to be destroyed at a cost of many thousands of pounds.
The outbreak of CMS in Britain is reported for the first time in the current edition of The Veterinary Record. It is the third of a trio of severe disorders of farmed salmon that have occurred first in Norway, where salmon farming was pioneered, before turning up in Scotland. The other two, sea-lice infestation and infectious salmon anaemia, are now established in Scotland and have caused serious economic and environmental problems.
CMS itself is "probably one of the most serious diseases in some fish farming areas of Norway", where more than 100 farms have been affected, according to the authors of the Veterinary Record paper, Hamish Rodger and Tom Turnbull.
Dr Rodger, formerly of the University of Stirling and now at the University of Pennsylvania, and Mr Turnbull, an aquaculture vet for a big Scottish salmon-farming company, examined eight fish from the west coast sea loch incident, which occurred in December 1997 and January 1998. They found them to have symptoms indicating CMS, including bulging eyes, pitting of the skin, haemorrhaging of the stomach and heart abnormalities.
Tissue samples of fish from a second farm, which was experiencing significant mortalities", displayed similar symptoms, they report.
Dr Rodger said at the weekend that it was too early to say whether CMS presented a serious economic threat to the Scottish salmon farming industry. "But if there were more cases, it would be," he said.
Gordon Rae, technical director of Scottish Quality Salmon, the trade association for most of the industry, said there had been no further reports of CMS since the incidents described. "There is no cause for concern," he said.
What is not known is how CMS arises but an infectious agent is strongly suspected, although none has been detected so far. Dr Rodger said the cause was possibly a virus carried by salmon, which was harmless in wild fish but became malignant in the more stressed conditions of salmon farming. "There is no known treatment because we don't know exactly what we're dealing with," he said.
The £260m Scottish salmon farming industry, mainly based in the Highlands and Islands region, employs 6,500 people and produces 120,000 tonnes of fish a year.
Salmon fishermen are angry at disease spreading to wild fish from the farm cages, in particular infestation with sea lice. Last year Professor David Mackay of the Scottish Environmental Protection Agency said it was "beyond reasonable doubt" that sea lice damage from farm cages could be very serious to wild fish.
Infectious salmon anaemia, which broke out in farm cages two years ago, is also fatal but even more serious in its environmental effects as it can spread into wild fish populations, as it is now believed to be doing in Scotland. Farms where it has occurred have had to destroy their stocks and go into quarantine.
But there was no evidence that CMS could spread into wild fish, Dr Rodger said.