Revenge of the Goldfish! Dumped Pets Growing Into Giant Monsters

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©. Murdoch University

It may be borne from the noblest of intentions. Who doesn’t love the idea of releasing the poor goldfish, who has spent his life swimming around in bowl-shaped circles, into the great wet wild?

The problem is that the domestic goldfish, Carassius auratus, will grow to be as big as its resources allow. And when lovingly released into a wetland, pond, lake or other aquatic habitat, the resources are aplenty! Those once-little-cutie-pies are growing to weigh as much as four pounds, if not more.

According to a new study from Australia's Murdoch University, goldfish were one of the first fishes to be domesticated and have been widely introduced across the globe; they are now considered one of the world's worst invasive aquatic species.

"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," study author Stephen Beatty from the school of Veterinary and Life Sciences at Perth's Murdoch University tells the Australian Broadcast Corporation (ABC).

"Unfortunately, a lot of people don't understand that wetlands connect up to river systems," he adds, "and introduced fish, once they get in there, can do a lot of damage to native freshwater fish and the aquatic habitat."

With the universal appeal of goldfish, and the seemingly universal appeal of setting them free, Australia is not unique in this problem. Both Canada and the United States have seen their share of the great goldfish invasion. And while a goldfish on a child’s dresser is fine with a sprinkle of fish flakes, in the free world they are downright gluttonous – as the Washington Post reports:

In the wild, goldfish are carnivorous. At best, their feeding habits — trawling along the bottom of the body of water — disrupt sediment and make it harder for other fish to eat. At worst, goldfish will fatten up on the eggs of native species. Goldfish may also be bringing new diseases to the wild fish population.

Beatty notes that the invasive fish can potentially impact water quality, introduce disease, disturb habitat and compete with native species putting them under serious pressure, which just adds to the existing threats associated with habitat and water quality decline.

Another eye-opening revelation from the study is the dogged persistence of the little fish that could.

“Our research discovered the fish displayed a significant seasonal shift in habitats during breeding season, with one fish moving over 230 kilometre during the year,” Beatty says.

Over 140 miles in a year! How many laps in a goldfish bowl would that be?

It’s actually all kind of a mess. Too many people consider goldfish as a novelty and even disposable. Think of all the fairs and carnivals in which kids are walking around with one of the poor creatures panicking in a plastic bag, only to be delivered to a small bowl, the equivalent of solitary confinement. Is it any wonder they thrive when given the chance? I know it may sound trivial, but people really need to consider what they’re doing when taking on a pet fish. Unwanted animals are a dismal enough problem, but ones that have the potential to take down whole ecosystems? The goldfish may be having the last laugh with this one.