Image: Murdoch University, screenshot from ABC News Twitter

Common goldfish dumped from household aquariums into rivers in Western Australia are growing into four pound monsters and endangering native species.


The behemoth fish are being found with alarming regularity, according to Australia’s ABC News.

While they appear small and harmless in captivity, Carassius auratus are bottom-feeders who send nutrient-rich sediment back into the water column, which can create algae blooms. Goldfish have also been known to eat the eggs of native species and a paper published by researchers from Perth’s Murdoch University is calling them “one of the world’s worst invasive aquatic species.”


Goldfish can act as carriers for diseases that don’t naturally occur in these rivers, according to the study, and one new disease has already been detected. It’s believed the former goldfish owners who released them into the wild—are to blame for the outbreak. Dr. Stephen Beatty, who helped author the paper, told ABC News, “It causes lesions on the skin, it’s pretty horrible to look at.”

Aquarium dumping is a huge problem worldwide, and Godzilla-sized goldfish are not without precedent. A similar incident occurred in the waters of Lake Tahoe in 2013, where conservationists from the University of Nevada found carassius auratus growing up to 1.5 feet in length.

While releasing a captive fish into the wild can feel merciful, it tends to do a lot more harm than good.

[Ecology of Freshwater Fish via ABC News]