Fish farming is threatening pristine wild stocks of the Arctic char, a cousin of the salmon and the trout, which have evolved undisturbed in Scottish lochs and some English and Welsh lakes since the last Ice Age, ecologists say.
Scottish farmers are experimenting with imported Canadian char, rearing them in moored cages. Conservationists fear escaped fish will sooner or later breed with wild stocks, irreparably polluting a genetic resource.
Peter Maitland, a freshwater biologist who runs the Fish Conservation Centre at Stirling in Scotland, said: "When I heard that Canadian fish were being brought in I was aghast. There should be a complete ban on the import of foreign stocks. If farmers want to experiment they should use only native fish."
The Scottish Office's fisheries department said: "We are aware of the danger of escapes. We try to persuade farmers to refrain from experimenting close to native stocks, but provided foreign fish are intended for farming and not for release into the wild there is no legal bar on their import."
Ron Greer, a former government fisheries scientist who is leading a campaign, to protect the Arctic char, said: "So far we only know of one or two farms experimenting with Canadian imports, but the escape of just one farmed fish into the wild could be enough to destroy 10,000 years of evolution."
Pressure to exploit Arctic char is growing as fish farmers seek to diversify. The multi-million-pound salmon farming industry has been hit by falling prices caused by reckless over-production, chiefly in Norway but also in Scotland, where output has grown from almost nothing to more than 45,000 tons in little more than a decade.
Arctic char is not only excellent to eat but thrives in extremely cold water and is ideally suited to Scottish conditions. Scottish entrepreneurs are importing from Canada because the fish is already being successfully farmed there and they believe that is the way to get hold of the best breeding stock.
Mr Maitland, who will attend an international conference on Arctic char conservation at Trondheim in Norway this week, says escapes of imported stock are inevitable. "Enormous numbers of fish have escaped from salmon farms, more than a million of them in a single incident," he said.
What effect such escapes have had on wild salmon is still being studied. The impact on Arctic char will be more devastating because British stocks of the fish have been left alone for so long. They are thought to have come here about 10,000 years ago. As the ice receded the fish were left trapped in lochs and lakes. In warmer parts of Britain the fish died out, but there are still nearly 180 populations in the Scottish Highlands, ten in the Lake District and four in Wales, which have lived in isolation for thousands of years.
In those unusual conditions, the fish have begun to diverge genetically. In this country they have become purely freshwater fish, but in Norway, Iceland and Canada, Arctic char still run to the sea like salmon.
