Wait, How Big Can Goldfish Get? A Very Serious Investigation

Terrible news for anyone still recovering from those live-action photos of Clifford the Big Red Dog: another alarming, disproportionately sized pet has entered the chat (and also your nightmares). On Friday, the city of Burnsville, MN warned that officials had found exorbitantly big goldfish in Keller Lake. Some were as long as 18 inches, and as heavy as four pounds. But where did these behemoths come from? According to the city’s official Twitter account, the goldfish are coming from people’s homes. 

“Please don't release your pet goldfish into ponds and lakes!” pleaded Burnsville officials. “They grow bigger than you think and contribute to poor water quality by mucking up the bottom sediments and uprooting plants.”

Apparently, what's happening is that, rather than flushing unwanted goldfish down the toilet or whatever it is that people who can't wait for their goldfish to die of natural causes do, unwilling goldfish-owners are getting rid of their erstwhile pets by releasing them into local lakes, ponds, and waterways. But, once freed of their tiny bowls and tanks, goldfish can grow shockingly large. “Their size is limited in the tank, but when you release it into the wild, that doesn't exist anymore,” Kate Wilson, an aquatic invasive species coordinator at Alberta Environment and Parks, told The Washington Post in 2015. So while goldfish kept in tanks typically weigh 0.2 to 0.6 pounds, in the wild, they can top five pounds, according to National Geographic.

These five-pound fish might look unsettling, but Adam Jones, editor and founder of The Goldfish Tank, says they aren’t cause for concern. “The reason that people think of goldfish as small fish is that we're used to seeing young goldfish kept in small tanks or even bowls,” Jones tells Refinery29. “These containers are actually far too small for them, which means their growth is stunted, they don't live as long as they should, and they never have a chance to grow to their full potential.”

The solution here isn't to throw your goldfish into a pond, but rather to get a bigger tank. Jones says that it’s possible we’re seeing so many big goldfish in the wild precisely because pet owners don’t know what to do when their fish start growing larger than expected, but that it doesn't matter how well-intentioned the owners are, because releasing "goldfish into the wild... is a very bad idea.”

Goldfish might be unthreatening when kept in an enclosed tank, but they can cause serious harm to local ecosystems. In 2018, an influx of large goldfish in West Medical Lake, WA took over and drove away local trout. In years past, biologists have expressed concern about how goldfish could impact Lake Tahoe’s water. This is partially because they’re bottom-feeders: Caleb Ashling, a Burnsville natural resources specialist, told The Washington Post on Sunday that, when goldfish feed, they uproot oxygen-producing plants and spread sediment throughout the water. They’re also forced to compete with native fish for food, shelter, and space, and they can spread disease, reported NPR. 

Furthermore, just one fish can cause a frenzy. Goldfish live a long time — up to 30 years, according to National Geographic — and reproduce rapidly, multiplying and causing further disruption. In one Minnesota county, not far from Burnsville, at least 30,000 of these fish were removed from a chain of lakes in one day.

Somes states, Minnesota included, have actually made it illegal to introduce goldfish into ponds and lakes. With all this in mind, Jones says it’s important to seriously think about your decision to adopt a goldfish.

“If you think that you don't have enough room for a goldfish tank in your home, you'd be better off getting a smaller type of fish, rather than keeping a goldfish in unsuitable cramped conditions,” Jones advises.

If you do get a goldfish that you’re then looking to get rid of, the U.S. Fish and Wildlife Service suggests either rehoming your fish or reaching out to a veterinarian for advice on humanely putting it down. Or, you can always get a really big tank, let your fish grow to be as big as a foot-long hot dog, name it Clifford, and impress all your friends with your Big Red Fish. Fun as that joke would be, just remember that the real gag is how long that goldfish might live: 30 years.