NOW there’ll be no excuse for the one that got away. Britain’s rivers and lakes are to be restocked with trout carrying genetic alterations that make them easier to catch.

The move has been ordered by the Environment Agency which wants to prevent interbreeding between native brown trout and those introduced for anglers.

However, its research has shown that the genetic changes, which are designed to render the fish infertile, also make them easier to hook.

“It is an unexpected bonus,” said Dr Dafydd Evans, the agency’s head of fisheries. “It means anglers can catch more and so get more sport out of them.”

The study was prompted by concerns about the ecological impact of the annual restocking of lakes and rivers with 900,000 farm-reared brown trout. They are needed because the low numbers of native fish mean that Britain’s more than 2m anglers would otherwise stand little chance of catching anything.

However, the problem is that farm-reared fish can interbreed with wild ones and so pass on undesirable genes. “We knew one answer could be to release so-called triploid fish — which have been altered to have an extra set of chromosomes,” said Evans. “This makes them infertile so they cannot interbreed with native fish.”

Evans asked the Game & Wildlife Conservation Trust to examine the impact of releasing such fish into rivers including the Honddu in mid Wales and Arrow in Herefordshire as well as lowland chalk rivers such as the Avon, Allen, Frome and Piddle in the south of England.

Dylan Roberts, the trust’s head of fisheries, said: “Releasing farmed fish is a bit like letting battery chickens into the jungle.

“They are bred for eating and have lost many of the genes vital for survival. We don’t want them giving those genes to native populations,” he added.

In his research Roberts tagged about 1,000 triploid farmed fish and released them into the rivers. He attached alternative tags to a similar number of farmed fish with normal genes and released them too.

Then he surveyed fishermen, asking them to declare how many of each they caught and how they fought.

The results are being written up for publication in a scientific paper but show that dozens more of the triploid fish were caught.

One reason for this could be that fish with normal genes stopped feeding when they were ready to spawn.

The triploid fish, by contrast, had no interest in sex and just kept eating.

Restocking British lakes and waterways with fish for anglers has become big business because of the soaring popularity of the sport. Besides brown trout, about 2m rainbow trout, which originate from America, are poured into British waters every year. Research suggests that rainbow trout are unable to breed in British waters, probably because water temperatures and quality are not right for them.

The brown trout reared by fish farms are mostly derived from a handful of lineages, most of which began with fish caught in Loch Leven, Scotland in the 1850s. This was when the first fish farms were established.

The practice of restocking with farm-reared fish remains highly controversial among anglers as well as environmentalists. Some critics argue that the mass release of farm-reared brown trout simply for capture is akin to releasing cows into the woods and then shooting them.

However, supporters argue that recreational fishing is an industry that generates millions of pounds for rural areas and which offers urbanites a healthy hobby that gets them out of doors.

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