PEST FISH CLOG RIVER
Ross River being overrun by invasive species
THE Ross River, which runs through the heart of Townsville, has the worst proportion and diversity of pest fish of any river system on the east coast of Australia, according to a leading biologist.
One of the species which is in plague proportions is gambusia, a species introduced in an unsuccessful program to control mosquito numbers. Families dumping aquarium fish, including tilapia, into the Ross, are also to blame.
A walk along the river reveals the extent of the issue, with dozens of tilapia guarding nests in weed beds while bright orange oscars, a fish from South America, can be seen competing for food with turtles and small mosquitofish thriving.
A FISH species introduced to the Ross River to kill off mosquitoes is now in plague-like proportions.
Transient families are also to blame for the pest fish crisis after dumping pet fish species into the Ross, with numbers exploding because of the breeding conditions.
The river system that runs through the heart of Townsville has the worst proportion and diversity of pest fish in any river system on the east coast of Australia, according to a leading biologist.
Gambusia, also known as mosquito fish, were put into rivers throughout Australia in 1929 in a bid to control mosquito numbers but the program was unsuccessful and the fish overran native species.
Pest fish are known to eat native fish species eggs, as well as their natural food. They are also very defensive and will attack larger fish.
Catchment Solutions fish biologist Matt Moore said the Ross was now home to thousands of foreign pest fish, which likely started life in people’s aquariums.
A walk along the river reveals the extent of the issue, with dozens of tilapia guarding nests in weed beds while bright orange oscars, a fish from South America, can be seen competing for food with turtles and small mosquitofish thriving.
Tilapia and mosquitofish have been declared noxious fish under the Fisheries Act 1994.
“Tilapia will predate on the eggs and young fry of native fish,” Mr Moore said. “They outcompete with food resources. They also build their nests (and become protective). Native fish, they can be attacked by the tilapia, taking the mucus protective layer off the fish.”
Mr Moore suspected Townsville’s transient population was one of the issues, with people releasing pet fish into the wild before moving on.
It was a claim backed up by A1 Aquarium World’s Hayden Lyon.
The fish retail assistant said many people did not understand the size some fish could grow to. Larger cichlid species such as tilapia, oscars and red devils grow to about 38cm and have been known to attack other fish.
But Mr Lyon said smaller pest fish posed just as many issues. “All foreign fish pose a threat (to native species) regardless of their size,” he said.
A Townsville City Council spokesman said it was important to stop exotic fish from entering marine environments as they were typically impossible to eradicate.
“Under the Biosecurity Act 2014, tilapia must not be distributed, either by sale or gift, or released into the environment, they must not be kept nor fed, and captured tilapia must be killed and disposed of as soon as practical.
“The only other restricted invasive fish known in Townsville is gambusia, also known as mosquito fish.”
Other exotic fish, such as oscars, that do not have legislated pest status but are also in Ross River. >>Pest fish sightings should be reported, with a photo if possible, at daf.qld.gov.au/fisheries/pest-fish/report-a-pest-fish-sighting or by calling 13 25 23.