Setting a pet fish free in a local lake or waterway is not an act of liberation — it’s ecological sabotage.

According to researchers at Australia’s Murdoch University, once pet fish are introduced into lakes and rivers they have the potential to decimate an ecosystem.

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While a goldfish or koi might remain miniature when housed in a bowl or aquarium, once freed into a larger environment the fish are able to grow at an exponential rate. They also eat up food that native species depend on and introduce exotic diseases.

A study published last year by Murdoch University’s Freshwater Fish Group and Fish Health Unit claims “introduced freshwater fishes are one of the major global threats to aquatic biodiversity.”

“They are eating up the food resources and using up the habitat that our native fish would otherwise be using,” Jeff Cosgrove, a Postdoctoral Research Fellow at Murdoch University, told the Australian Broadcasting Corporation.

In addition, once they’ve been introduced into a new ecosystem they can be “extremely difficult to eradicate,” says Cosgrove.

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