16/08/2016 3:03 PM AEST | Updated 16/08/2016 4:18 PM AEST

Giant Feral Goldfish Are Taking Over Australian Rivers

It begs the question: are they huge or are aquarium goldfish being stunted?

Murdoch University
Stephen Beatty holds one that got away from its owners.

The world's biggest goldfish can be found in a river in Western Australia but local researchers aren't cheering, they're trying to eradicate the pests.

In the warm, nutrient-rich waters of the Vasse River feral goldfish grow up to 1.9 kilograms and they're destroying the habitat of endemic native species.

That's right. Goldfish. 1.9 kilograms. This is real.

Murdoch University Centre of Fish and Fisheries researcher Stephen Beatty said feral goldfish grew so much larger than the ones in aquariums because of availability of resources.

"It depends on the physiology of species but they really grow to their environment," Beatty told The Huffington Post Australia.

"There's a maximum size genetically inbuilt, but for a really good growth rate, they need nutrient-rich water and warm temperatures.

"Unfortunately we have both and they've just exploited the environment really -- it's a bit of an anomaly."

Murdoch University
Yes, that's a goldfish.
Stephen Beatty
A typical haul from the nearby Warren River.

A 2007 review found they grew the largest, followed by a goldfish population in Lake Egirdir, Turkey.

Beatty said most of these goldfish were once owned by people who let them go.

"I don't think it's malicious. A lot of these wetlands are fed by stormwater pipes. If they're flushed down a toilet they could definitely end up here."

In a new study published in journal Ecology of Freshwater Fish, Beatty and team showed they were highly mobile, with one fish moved over 230 kilometres in a year.

As for the damage they cause, Beatty said more than 80 percent of freshwater fish in south west Western Australia were not found anywhere else.

"Any species that predate on these endemic freshwater species' eggs and disturb water quality are a concern."