Sydney, Aug 16 (IANS): Researchers in Western Australia have found that unwanted pet goldfish dumped into rivers were growing as large as 1.9 kg and damaging the habitat of other native fishes found in the waterways.

Stephen Beatty from the school of Veterinary and Life Sciences at Perth's Murdoch University said on Tuesday that goldfish released into the waterways have grown to over 1 kg, with the largest weighing at 1.9 kg, Xinhua news agency reported.

"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," said Beatty.

"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."

Beatty said goldfish like carp can cause a host of problems once they become established in a freshwater system including bringing unknown diseases to the native populations.

"We know that one disease has been introduced and we think it has probably come in on goldfish," Beatty said.

Beatty's most recent research which involved attaching acoustic transmitters, similar to those used to track sharks in the ocean, spotted 15 monster-sized goldfish in the Vasse river in Western Australia' South West in the last 12 months.

"What we found is that they actually migrate off the main channel into the Vasse river into a wetland system to spawn," he said.

Beatty said the ideal strategy was to prevent goldfish from entering the rivers in the first place.

He advised people who had unwanted fish in tanks at home to return them to a pet shop.