Release of pet fish into local waterways resulting in boom of pest fish

Bicentennial Park in Riverton, where Koi Carp have recently been seen feeding in the river.
Bicentennial Park in Riverton, where Koi Carp have recently been seen feeding in the river.

THE release of ornamental fish is thought to be responsible for 22 of the 34 species of pest fish established in Australian freshwater environments.

In 2012, the Department of Fisheries set out to find how many native and introduced fish species were living in the permanent wetlands and lakes in the Perth metropolitan area and goldfish and koi carp were the most common established pest fish found.

Throughout metropolitan waterways, ornamental fish have also been released and some of the species, including the pearl cichlid and Mozambique tilapia, have spread rapidly and now dominate some water bodies.

Aquatic pests and diseases can pose economic, social, cultural, human health and environmental impacts.

They can arrive in Western Australia in various ways and once established are virtually impossible to eradicate.

Recent sighting of the vermin-like koi carp in Canning River and Kent Street weir were likely the result of people dumping fish into the waterways, according to Department of Fisheries biosecurity branch manager Victoria Aitken.

“Aquarium or pond fish that are not native are often more aggressive than native species and can outcompete them, consuming their food and taking up their space,” she said.

“They can also spread disease, kill local species and damage natural habitats. Koi carp can stir up mud and reduce water quality, making it harder for native fish to survive.”

Ms Aitken urged the public to come forward to report any sighting of the destructive fish to give the Department a wider understanding of the problem and aid in ways to manage it.

“These reports are very useful as they are added to the Department’s database that helps to build a picture of exactly where (carp) are,” she said.

“To increase the chances of a timely response and eradication, early detection is essential. Aquatic biosecurity is a shared responsibility. You can play an important part by reporting anything unusual you have seen or found, including a fish kill… which can be a sign of disease.”

City of Canning chief executive Arthur Kyron said sightings should be referred to the Department of Parks and Wildlife.

Members of the public who see carp in the river are encouraged to contact the Department of Fisheries Fishwatch on 1800 815 507 or via www.fish.wa.gov.au.