ONE of the world's most invasive species of fish has found its way into the Condamine River.
The Department of Agriculture, Fisheries and Forestry discovered the pearl cichlid while doing regular sonar scans for fish and habitat this week.
The local fish-stocking group is calling for someone to come forward and let them know how many were dumped before it's too late.
The aggressive pest fish, about 15cm in length, was caught near the Grafton St Bridge.
"Pearl cichlid or Geophagus braziliensis are a popular aquarium species and this fish is likely to have been dumped by someone who no longer wanted it," Condamine Alliance river manager Kevin Graham said.
"Native to South America, this fish, when released in the wild, can potentially become a significant pest, based on their size, hardiness and aggressive behaviour."
The department is conducting monitoring throughout the Condamine catchment on behalf of the Condamine Alliance.
"Monitoring is a vital part of the work we do in rehabilitating our waterways," Mr Graham said.
"Without monitoring we would have no understanding of what is in our waterways and pest fish numbers could potentially get out of control.
"The monitoring program is primarily focused on tilapia as part of a broader tilapia exclusion strategy project to help keep tilapia out of the Murray-Darling Basin.
"Whilst we are lucky that so far it is only one fish, and it isn't a tilapia, it does highlight that we do need to remain vigilant.
"Our rivers are only for our native fish."
Pearl cichlids have been found over the Great Dividing Range, but to date this is the first official sighting in the Murray-Darling Basin.
Warwick Fish Stocking Group member Ed Kemp said if they did not find the rest of the fish it could potentially destroy the ecosystem.
"They will eat all the food and the native fish will die," he said.
"Once tilapia are established in a flowing river or creek, it is impossible to eradicate them.
"We just want someone to call us and tell us how many are in there so we can solve the problem before it gets worse."
Mr Kemp said it was a timely reminder that aquarium fish belonged only at home in a fish tank.
"Give unwanted aquarium fish to friends or a pet shop, rather than letting them go in the wild," he said.
Mr Kemp said pearl cichlids were called Brazilians in aquarium shops.
If anglers catch or sight a fish that could be a tilapia, take a photo of it if possible and phone the Queensland Fisheries hotline on 132 523 to report the location. Do not return the fish to the water.
Condamine Alliance manager Kevin Graham said it was illegal to release a non-indigenous fish in Queensland waters and penalties up to $220,000 applied.
However, if you would like to notify Warwick Fish Stocking Group how many pearl cichlids were placed in the river you can phone 4661 3095.
How to identify them: The dorsal (upper) fin is continuous and ends in an extended point. Most native fish have a dorsal fin with a dent or gap in the middle and a rounded end.
The two pelvic (belly) fins are long and almost touch the front of the anal (bottom) fin, whereas most natives have short pelvic fins.
Never throw tilapia back into a waterway, don't use tilapia as bait (dead or alive) and don't stock dams or ponds with tilapia.
Native fish include: Murray cod and golden and silver perch.