EVVIRONMENT Agency scientists fear that goldfish, the popular household pets, could force native crucian carp out of existence.

Goldfish get into the wild by escaping from ponds during floods; being released illegally or accidentally stocked by fishery managers.

Now, in-depth research commissioned by the Agency has revealed that the ornamental fish are not only competing for food and living space, but are mating with crucian carp. Their hybrid offspring are subsequently causing further competitive problems.

Environment Agency Fisheries Officer Phil Bolton said: “The crucian carp is a fish that should have no problem thriving in the British Isles. It is hardy and adaptable.

“But man’s interference has tipped the balance in favour of goldfish. Crucian carp are already suffering from habitat loss and introduced disease. This new research has revealed that the presence of introduced goldfish and common carp has led to interbreeding and hybridisation in wild populations.

“Native crucian carp could be wiped-out as a result.

“Our research shows cause for major ecological concern because not only are the offspring capable of out-competing crucian carp but they are also capable of reproducing and further interbreeding with pure stocks.

“It is a serious biodiversity issue because what is happening is not natural evolution but the hand of man.”

The findings follow six months of in-depth research contracted to genetic experts at Hull University where molecular DNA testing was used to distinguish true species from hybrid carp.

Visual identification has proved difficult for fisheries managers in the past because the hybrids and brown goldfish look similar to crucians.

The new study has allowed the Agency to improve identification techniques and will support fisheries managers whose vigilance can help restrict the impacts and pinpoint pure crucian populations.

The findings will also be used to refine the Agency’s own policy on fish introductions into new waters.

Phil Bolton said: “We are developing a crucian carp conservation plan that will be available within the next few months and we’ve nearly completed a field guide that will give anglers and fisheries managers detailed information on identifying crucian carp.

“This will enable accurate data to be drawn up showing the whereabouts of crucian populations and will aid their long term protection.”


Goldfish are native to Asia – believed to have originated in northern China and Korea.

Goldfish were first introduced into the British Isles in the 17th Century.

Parent goldfish can give birth to non-gold offspring. These are thought to be a throwback to the goldfish’s wild ancestor and are mistaken for crucian carp.

The crucian carp is among the best freshwater fish for enduring pollution, low oxygen levels and cold. In extreme conditions it has been known to hibernate in mud while the water above it has frozen.

Goldfish grow quicker than crucians.