In the wild, goldfish can grow to be the size of footballs and wreak havoc on the ecosystem

By Kelli Bender
September 23, 2016 03:10 PM
Education Images/UIG via Getty
Credit: Education Images/UIG via Getty

The low maintenance pet many remember having as a kid is causing serious problems in the wild.

According to The New York Times, goldfish “are one of the world’s worst invasive aquatic species.”

As an example, the newspaper offers an anecdote about a creek in southwestern Australia. Twenty years ago, researcher believe someone dropped a few unwanted goldfish into the creek. Over time, these tiny swimmers swam downstream to Vasse River, spawned and have now taken over the whole river.

Goldfish invasions like this are popping up all over the world, with recent takeovers in Nevada, Colorado and Alberta, Canada. The rapid growth of wild goldfish in Australia’s Vasse River is being tracked by researchers from Murdoch University, who say some of the usually small fish have now grown to be 16 inches long, about the size of a two-liter soda bottle.

Since the Vasse River appears to have the fastest growing goldfish population in the world, researchers hope finding a way to control this problem will help goldfish management efforts around the world.

One of the researchers biggest obstacles is changing the way people view goldfish in the wild.

“Once you introduce something into a new environment — even if it’s a cute, cuddly aquarium fish — it can have quite unexpected, serious biological consequences,” Dr. Stephen Beatty, a researcher at Murdoch University, told the Times.

The issue appears to start with the goldfish’s transition from an esteemed symbol of luck in China to an everyday pet in the United States and elsewhere. In the United States, the spread of the goldfish, which is a type of carp, is linked to the government. In the late 1800’s it was common for the Commission on Fisheries to give out goldfish to Washington D.C. residents, with an estimated 20,000 being passed out in just a few decades.

This publicity stunt led to goldfish being given away as carnival prizes and cheap gifts, making the fish seem dispensable. And in enough cases it seems, people did just that, disposing goldfish they no longer wanted into wild water.

Left to their own devices in rivers, lakes and ponds, the tiny goldfish from the fair can turn into a 4-lb. behemoth covered in yellow and brown scales in just a few generations. This much larger fish wreaks havoc on the waters it populates: uprooting plants, spreading diseases, overeating, and multiplying rapidly. Goldfish are capable of mating with other species of carp, and, in most cases, have no natural predators to hamper reproduction.

So, how do you solve a problem like rapid goldfish growth? That’s what the research team from Murdoch University is working on. After tracking the fish for a year, the group learned that goldfish can swim long distances, often migrate to spawn and are smarter than we think.

Dr. Beatty hopes to trap a large group of goldfish in the future to further his team’s research and find a goldfish management solution. For now, the best thing to do is to take measure to prevent the problem from getting worse.

If you have a healthy, living goldfish you no longer want, don’t free it into wild, instead find a pet store, aquarium or fellow fish owner who is willing to take the pet. In some states local wildlife commissions will also take in unwanted pets.

As for ill goldfish, it’s best to find a humane way to kill the fish, such as putting them in an ice slurry. Disposing of a goldfish, or any other pet, by flushing them down the toilet is not recommended.