Goldfish thrive when released into local waterways ... a little too well.
Residents of western Australia have learned this the hard way, as a number of pet goldfish that were released into local waterways have grown to incredible sizes and have begun damaging the delicate habitat of native fish.
The problem is not new. In fact, Dr. Stephen Beatty of the school of Veterinary and Life Sciences at Perth's Murdoch University has been working on a control program for the Vasse River in Busselton, Australia for over 12 years. In his work, he and his colleagues have found goldfish that weigh over 1kg (2.2 pounds). They even found one fish that weighed 1.9kg (over four pounds).
Though the goldfish had been innocently released, Beatty said, in an interview with 720 ABC Perth, they were now ruining the habitat for other fish.
"Perhaps they were kids' pets where the family have been moving house and their parents, not wanting to take the aquarium, have dumped them in the local wetlands," Beatty said.
"Unfortunately a lot of people don't understand that wetlands connect up to river systems and introduced fish, once they get in there, can do a lot of damage to native freshwater fish and the aquatic habitat."
Once established in a freshwater system, goldfish can cause a number of problems. They swim along the bottom of the lake or river stirring up substrate, which can re-suspend nutrients into the water column and exacerbate algal blooms. They also disrupt aquatic plants and eat the eggs of other fish and, like any introduced species, have the potential to bring diseases to the native population of fish.
"We know that one disease has been introduced and we think it has probably come in on goldfish," Beatty said. "It causes lesions on the skin, it's pretty horrible to look at."
Beatty's team has had success eradicating carp in the Darch Brook, which flows into the Margaret River.
"We did actually eradicate them there before they became established in the Margaret River," he said. "You can have success but you have to act really early and throw quite a lot of resources at it. And quite often it is still unsuccessful."
The best method for protecting these freshwater systems is simply prevention.
"Whatever you do, don't release fish into waterways," Beatty said.
All images via ABC.