Quote:Goldfish (Carassius auratus) are cute and low-maintenance pets, but research has shown that when they end up in lakes and rivers, they can grow up to 10 times their original size and travel long distances, making them an incredibly invasive pest.

A team of Australian researchers has reported finding wild goldfish that weigh up to 1.9 kg (4 pounds), and they're wreaking havoc on the local ecosystem.

The researchers are studying the Vasse River in southwest Australia, which had goldfish introduced into it more than two decades ago, and has seen the population surge over the past 12 years. The most likely cause of the infestation was pet owners.

"Perhaps they were kids' pets where the family have been moving house and their parents, not wanting to take the aquarium, have dumped them in the local wetlands," lead researcher Stephen Beatty from Murdoch University in Perth, told ABC News.

"Unfortunately a lot of people don't understand that wetlands connect up to river systems and introduced fish, once they get in there, can do a lot of damage to native freshwater fish and the aquatic habitat."

Quote:Not only do the fish, which are native to eastern Asia, grow as large as resources will allow - which in this case, is pretty big - they're also carnivorous.

"They cruise along the bottom stirring up the substrate with their feeding strategy, this can re-suspend nutrients into the water column which exacerbates things like algal blooms," said Beatty. "They can also disrupt aquatic plants and eat other fish's eggs."

The team also suspects that goldfish have introduced at least one disease to the region already, and are responsible for a decline in native freshwater fish species.