According to an Environment Agency report, illegally or accidentally introduced goldfish could be a serious threat to our native Crucian carp.
The Crucian carp, Carassius carassius, is a close relative of the goldfish, Carassius auratus, and it's possible for the two species to hybridise and produce viable offspring.
Fish geneticists from Hull University examined the DNA of a number of Crucian carp populations to determine the level of contamination through hybridisation.
The Environment Agency believes that the genetic makeup of some British Crucians has already been damaged through goldfish hybridisation.
Environment Agency Fisheries Officer Phil Bolton said: "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.
"Native crucian carp could be wiped-out as a result.
"It is a serious biodiversity issue because what is happening is not natural evolution but the hand of man."