Goldfish helping to kill off frogs by spreading 'devastating disease', scientists warn

Stocking ponds with non-native species puts the amphibians at greater risk of deadly ranavirosis

Ranavirosis causes bleeding, severe ulcers and the loss of limbs and can be fatal to frogs

Goldfish and other non-native fish should not be put into garden ponds because they help spread a “devastating disease” that is killing off thousands of frogs every year, scientists have said.

The researchers, who published a paper in the PLoS One journal, also said the use of common garden chemicals was weakening frogs’ immune systems which put them at greater risk of deadly ranavirosis. Amphibians are also among the animals most at risk from climate change.

Alexandra North, of Exeter University and lead author of the study, which looked at frog deaths from 1992 to 2000, told The Daily Telegraph: “It is important to stop stocking ponds with non-native species like goldfish. Our results show that we can all help limit the impact of this devastating disease.

“Crucially, people should not move fish, frog spawn, pond weeds or ornaments from one pond to another as this could spread the disease.”

She added people should “reduce the use of garden chemicals like slug pellets and weed killers, which weaken the immune systems of frogs”.

Ranavirosis is not native to the UK but is thought to have arrived in this country through the international trade in pets. It causes bleeding, severe ulcers and the loss of limbs and can be fatal.

Dr Amber Griffiths, another author of the paper, said: “We are currently undergoing a mass extinction of species and amphibians are particularly under threat. The unprecedented loss of amphibians indicates widespread environmental degradation.”

The main problem was climate change, she said, but gardeners could help make an “immediate difference” to frogs by not stocking ponds with non-native fish and reducing the amount of chemicals they use.

Dr Silviu Petrovan, of the charity Froglife, which compiled the frog mortality figures, said: “In recent years diseases have significantly affected populations of frogs in garden ponds.

“Introducing species such as goldfish into a pond not only increases the severity of diseases for amphibians but also greatly reduces the variety of the species living in the pond and its overall value as a wildlife area.”