The Goldfish Threat: Why Your Pet Might Turn Into a Giant Menace

Admit it, goldfish sound like innocent, harmless creatures. And that holds true when they live in an aquarium or in the wild with numerous predators. But what happens when goldfish owners release them into freshwater lakes with no natural enemies? They grow to monstrous proportions, weighing up to two kilograms or more.

Predators play a crucial role in our world: they prevent animal populations from taking over ecosystems. Many examples exist of such invasive species becoming ruthless conquerors: goats brought to the Galapagos Islands decimating local vegetation and endangering native tortoises, or the New Guinea flatworm scientists warn could obliterate Europe’s snail populations, thus depriving birds of a vital food source. Goldfish have become the latest focus of attention, following irresponsible abandonment by those who once kept them as pets.

"These could have been children's goldfish, discarded by families who moved and didn’t want to take the aquarium with them. People don’t realize that every stream eventually connects to larger river systems, allowing these fish to invade and harm native freshwater species," explains Steven Beattie, an Australian researcher studying this phenomenon of goldfish growing excessively in Australia.

Australia is not the first to face this issue. In 2015, the Canadian government formally requested pet owners stop releasing goldfish into local waterways. The fish have caused trouble in lakes across the United States as well.

Why are goldfish so dangerous? Because their growth potential is nearly unlimited. With plenty of resources and an absence of predators, they burgeon significantly. In the wild, they don’t stick to fish food from the pet store – they become predators, eating other fish.

In other words, if you're tired of your goldfish, take them back to the store instead of tossing them into local waters. Otherwise, that small, boring aquarium fish could transform into an unrecognizable monster.