THE re-discovery of an exotic aquarium fish in the Swan River near Eden Hill and Caversham has sparked fears it could have a negative impact on native species in the upper reaches of the river.
Department of Fisheries officers suspect the feral pearl cichlids, found by a member of the public last week, were dumped into a local waterway that feeds into Bennett Brook.
Subsequent surveys by researchers have not yet located any further samples.
In many cases it is impossible to eradicate unwanted species when they are established.
Director of Aquatic Management Greg Paust said the species was first located in Bennett Brook in 2006 and action was taken in a bid to control their spread.
“Likely impacts on the Swan River ecosystem are unknown because, while the cichlids could dominate native species in freshwater environments, their ability to reproduce, spread and compete in the more saline sections of the river is unknown,” he said.
“The Department of Fisheries has spent approximately $300,000 over the last three years on the difficult and challenging control program.”
Mr Paust said last year the fish poison rotenone was applied in Bennett Brook to try and limit downstream movement of cichlids.
“But unfortunately it appears that this may not have successfully contained the feral population,” he said.
The Department of Fisheries will continue to monitor the Swan River in the area where the cichlids were found.
Mr Paust urged aquarium owners to never release exotic fish, algae or other aquatic life into waterways.