An invasive fish species, which scientists say is implicated in the decline of native fish, is taking over Queensland's freshwater catchments, and authorities concede they are powerless to stop the spread.

Fisheries Queensland said tilapia were first discovered in Townsville in 1978 and are now established in more than 20 coastal catchments, including tributaries of the Brisbane River.

In Queensland, it is illegal to have tilapia in your possession. This includes eating them.

The maximum penalty for possession is $200,000.

Tilapia removed from a Queensland water body. ( Amanda Dimmock: www.mdbc.gov.au )

The 2011 floods helped tilapia disperse and they are present in many freshwater bodies throughout the south-east, including the Kedron Brook catchment, the Nudgee Waterholes and the Bulimba Creek catchment.

An aggressive species that competes with native fish for food and space, tilapia are listed on the International Union for Conservation of Nature's top 100 world invasive species.

Tilapia are "mouth brooders" and can carry more than 1000 eggs at a time in their mouth, to protect the eggs from predators.

When the eggs hatch, tilapia will also nurse their babies in their mouths.

University of Queensland's Professor of Ecology, Hugh Possingham, said tilapia are built for survival and can take over dams, creeks and rivers.

"They can deal with poor water quality, they decrease water quality, they're certainly implicated in the decline of native fish," he said.

"They're extremely competitive. Some of the introduced species are predators but these are just super competitors."

Professor Possingham said tilapia were imported into Australia for the aquarium trade.

"It wasn't deliberate, it wasn't for food, it was an accidental introduction," he said.

"They seem to be inexorably spreading across subtropical and tropical Australia."

Professor Possingham said total eradication of tilapia in Queensland is impossible.

"Do we try and slow them down?" he asked.

"It would've made sense to find the southern edge of their range 10, 20 or 30 years ago and try and hold a boundary."

People still helping tilapia spread

The Freshwater Fishing and Stocking Association Queensland said it is disappointing that tilapia have spread so widely and so quickly throughout Queensland.

It is illegal to possess tilapia in Queensland, including for eating. ( Supplied: BCMI )

Treasurer Charlie Ladd said tilapia are present in every dam in the south-east.

"If the local stocking groups throughout Queensland weren't stocking the waterways with fish to try and achieve a balance, we wouldn't have any native fish in our waterways at all," he said.

"The Australian bass and Mary River cod certainly have the capacity to survive and compete with them.

"But you're more likely to catch tilapia because they're prolific breeders and prolific survivors."

Mr Ladd said people had to stop spreading and stocking tilapia for food purposes.

"They are taking over our waterways. It is hard to convince people their actions are creating a worse situation for our natives," he said.

"The human assistance they're receiving in spreading around the state, that is certainly very disappointing."

Fisheries Queensland said they were unable to eradicate tilapia once they became established in large, open bodies of water.