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This "Disposable" Pet Hardly Looks Like an Invasive Species, But...

Story at-a-glance -

  • Pet goldfish dumped in natural bodies of water are creating an ecological disaster
  • Unconstrained by the limitations of an aquarium, goldfish in ponds and rivers can grow to an enormous size
  • Giant goldfish compete with native species for food, and win. In addition, their excrement is thought to promote algal blooms
  • Pet owners needing to relinquish aquarium fish should call the store where they bought them or their state department of fish and wildlife

By Dr. Becker

Some people who grow tired of their aquarium fish seem to believe the kindest way to “relinquish” them is to set them loose in a local body of water like a pond or river.

For example, a few years ago researchers from the University of Nevada, Reno were checking Lake Tahoe for invasive fish species and captured an enormous goldfish that measured a foot and a half long, and weighed a whopping four pounds, two ounces.

More recently, the government of Alberta, Canada asked residents to stop dumping their fish tanks into ponds, because the ponds are overflowing with goldfish that are able to grow impressively large in the wild.

‘Goldfish the Size of Dinner Plates Are Multiplying Like Bunnies’

“It’s quite a surprise how large we’re finding them and the sheer number,” Kate Wilson, Aquatic Invasive Species coordinator at Alberta Environment and Parks, told CBC News.

In Wood Buffalo, 40 domestic fish species were discovered in a storm water pond.

"That's really scary because it means they're reproducing in the wild, they are getting quite large, and they are surviving the winters that far north," said Wilson.1

In a home aquarium, the growth of the fish is limited by the size of the tank. However, once fish are released in a natural body of water, size limitations disappear.

Domestic goldfish (Carassius auratus), which are a species of carp, and other aquarium fish will just keep growing in favorable water temperatures with ample food sources.

This results in a group of XL goldfish that then compete with native species for food. Scientists also fear that goldfish poop might promote algal blooms, further disrupting the ecosystem.

‘Don’t Let It Loose’ Campaign

Alberta has kicked off a Don’t Let It Loose campaign designed to educate residents about the dangers of releasing domestic fish into the wild.

According to Wilson, about a third of the invasive fish species currently threatening native aquatic environments came from aquariums and the ornamental trade.

The Don’t Let It Loose campaign targets pet stores, pond and aquarium suppliers, Asian markets that sell live fish, and spiritual groups that release captured animals as acts of good karma.2

Another problem is that when people dump their aquarium fish, they also dump the aquarium water, which can harbor parasites and disease.

Goldfish Overtake a Colorado Lake

Earlier this year, Colorado Parks and Wildlife (CPW) announced that goldfish had taken over a lake in Boulder.3 Officials believe a handful of pet fish were dumped into Teller Lake a few years ago, and that handful multiplied to thousands.

“These are domestic fish actually,” said Jennifer Churchill of CPW. “These are fish from a store I imagine. They can out-compete the native fish.”

While CPW officials were trying to decide what to do about the fish, pelicans took care of the matter with a giant fish feast.

Goldfish Are Capable of Creating ‘Ecological Disaster’

Experts warn that even though a goldfish looks harmless, it's capable of creating ecological disaster.

According to KSL.com in Salt Lake City:

“The fish hardly look like an invasion force when they're blubbing along in an aquarium. But make no mistake: these fish and others can quickly become nightmares for wildlife managers.”4

Drew Cushing of the Utah Division of Wildlife Resources says that each year, the agency must spend hundreds of thousands of dollars to control non-native fish that are dumped by fish owners who grow tired of them.

"They think they're doing the fish a favor when, in fact, they're doing the natural resources of Utah a disservice," says Cushing.

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How You Can Help

Aquarium dumping is a common problem in the U.S. and other countries. In addition to goldfish, other invasive species have also been discovered, including bluegill, crappie, largemouth bass, tropical fish, snails, and seaweed.

In the case of Tahoe, aquarium dumping isn’t the only way non-native fish invade the lake and other natural ecosystems. Other sources of introduction include aquaculture (farming of aquatic organisms), live seafood and bait, and fishing and recreational boats.

Studies show that the size and aggressiveness of fish are the two main reasons pet owners decide to dump them. However, the better option is to call the store where you bought the fish to see if they’ll take them back (many stores will), or your state department of fish and wildlife.

Euthanasia is an option if all other alternatives have been exhausted. No one should ever consider flushing fish down the toilet.

When you visit a natural body of water:

  • Remove all aquatic plants and animals from boats and transported gear
  • Do not release aquarium pets, plants, or live bait into aquatic ecosystems
  • Do not move live fish and other aquatic organisms from one water body to another
  • Report non-native species