DPI&F fisheries biologist Sam Hedge demonstrates the use of electrofishing, a technique used to temporarily stun fish for identification.
Fisheries biologist Sam Hedge, who is based at DPI&F's Northern Fisheries Centre in Cairns, said no tilapia populations had been found during previous surveys in these rivers.
"This is good news, but we need to keep a close eye on these catchments because of their proximity to catchments infested with tilapia in the Cairns and Tablelands areas," Mr Hedge said. "The only waterway from the coastal area that feeds into these Gulf catchments is from Tinaroo Dam, and a fish screen at that location has effectively kept out tilapia and eggs."
Mr Hedge said the Great Dividing Range was an effective natural barrier to the spread of tilapia. "The major cause of infestations is people moving them between waterways," he said. "This is why we advise people who catch tilapia to destroy them and then bury them away from waterways.Tilapia are mouthbrooders, and hundreds of eggs can hatch from the head of a tilapia even if it is dead; these fish then end up in a waterway," he added.
Tilapia competes aggressively with native fish, such as barramundi, and disturbs and takes over their environment. Other introduced pest fish that are illegal in Queensland include carp and gambusia (or mosquitofish).
"They are not as aggressive as tilapia, but they compete with native species and ecosystems," Mr Hedge said.
DPI&F carries out pest fish surveillance three times a year, sampling 50 sites across the three catchments.
"We have a range of techniques, such as electrofishing and netting, to detect, and in some cases eradicate, pest fish if we can find them early enough," Mr Hedge said.
The community can help in the early detection of incursions.
"If you see any unusual fish, please let us know on 13 25 23, as early detections will make a difference."
Mr Hedge said all unusual fish caught would be kept for identification and for further research by other fisheries scientists.
"We accumulate data of all species in the areas we sample to help other fisheries researchers," he said.