Central Queensland anglers say the release of a highly predatory fish from South America that could wipe out local species in just two years is an "act of environmental bastardry".
Mackay Area Fish Stocking Association (MAFSA) founding chairman Keith Day says the Peacock Bass, which was caught at the Dumbleton Weir in Mackay's Pioneer River on Monday, was almost certainly deliberately released from a private aquarium.
Mr Day says unless urgent action is taken, it could decimate the 2.5 million barramundi and sooty grunter MAFSA had cultivated in the river over the past 25 years.
"I can just see everything that we have worked for going down the gurgler," he told AAP on Wednesday.
"Why anybody would think it was a good idea is beyond me - it's an act of environmental bastardry."
The fish - which are popular pets in Australia and can be bought through online classifieds website Gumtree for as little as $20 each - are "bucket-list" catches for many recreational anglers.
They have already caused rapid devastation in areas of Brazil where they have been introduced.
The Department of Agriculture and Fisheries said in a statement the discovery was the "first confirmed capture of this species in Queensland waters" and has advised anglers to humanely kill the fish instead of releasing it.
Catchment Solutions fisheries biologist Matt Moore said authorities needed to act immediately to contain what was a potential environmental disaster.
"They are a high order apex predator - they will eat anything they can fit in their mouth," he said.
"This has the potential to affect commercial, recreational and indigenous fish stock."
He said it was vital to investigate how many of the fish were in the river and where.
"We then need to eradicate them as quickly as possible," he said.
He said electrofishing - where fish are stunned with an electric shock, then netted and sorted so pests can be killed and indigenous fish released - was one possible method.
