Invasion of the Giant Goldfish

Researchers recently pulled a real barn-burner of a goldfish out of Lake Tahoe: the specimen weighed in at more than four pounds, and it was one among a colony of similarly large fish living in a cozy area of the lake. The story makes for some bizarre headlines and good-natured ribbing, but behind the humor lies a very serious issue, because goldfish don’t belong in Lake Tahoe. These warm-water fish are adapted for other climes, but they’re hardy, and that means they can readily become an invasive species, just like their other relatives in the carp family, who have been plaguing waterways across the U.S. for more than a decade.

While goldfish in a tank might not seem like much, they have the ability to grow quite large in the right location, and Lake Tahoe provides just that. There’s plenty of fresh, nutritious food, and as goldfish grow, they can out-compete native species while destroying oxygen-producing plants and disturbing the equilibrium of this famous body of water. Their activities can make the water warmer, which can push out native fish, especially juveniles, who are very sensitive to temperature swings. With all that eating, there’s also a lot of, uh, output, which, to put it bluntly, could put a serious dent in Tahoe’s famous clear reputation.

The stunning blue water and impressive visibility in Tahoe’s waters are both under threat from goldfish colonies, who can produce nutrient pollution that encourages algae growth as well as choking out other fish and plants. Since goldfish breed readily and quickly, they’re hard to get rid of. Scientists have spotted them in the lake’s waters since the 1990s, but despite their best efforts, the population is difficult to control.

Where are they all coming from? Researchers point the finger solidly in one direction: pet owners who dump their aquarium animals. Whether they drop them off directly in the lake in the mistaken belief that they’re giving them freedom or flush them down the toilet and think that solves the problem, pet owners who tire of their aquatic charges are contributing to a nationwide invasive species problem. Overall, the aquarium trade is believed to account for around one third of invasive species in U.S. waters, and a lot of that is due to the lack of public understanding about the risks of releasing pet fish.

Pets are a lifetime commitment, and in an ideal world, people wouldn’t get bored with their fish and decide to move on to something else. If they do, though, researchers and officials warn that they shouldn’t just dump them in a body of water and hope for the best. A dealer may be interested in taking the fish back if they’re rare or interesting, or they could be sold privately on the secondary market, depending on legal restrictions. Fish and wildlife officials may also be able to help people who need to rehome their fish.

Related posts:

Environmental Groups Demand EPA Provide Better Protection for Great Lakes

Invasive Species Arrive in Oregon on Tsunami Dock (Video)

Controlling Invasive Species Through Brunch and Birth Control


Photo credit: Protographer23

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Carrie-Anne Brown

very sad news, thanks for sharing

Connie O.
Connie O.2 years ago

When I moved across country, my local pet store took the fish from me. They were to go into quarantine, and then be resold.

Sarah Hill
Sarah Hill2 years ago

Why do people continue to get pets and then decide they really don't want them?

Bill K.
Bill K.2 years ago

sounds like a 1950's B horror movie

stacey t.
Stacey Toda2 years ago

Thanks for sharing this story, good thing to learn about as most people never think about things like this.

Vernon Wong
Vernon Wong2 years ago

According to some reports of owners, goldfish can grow up to 9 lbs and 23 inches. They can grow large in large spaces like lakes. They can also survive under ice in winter as long as the water does not freeze solid. I breed a type of goldfish called shubunkins and my biggest one is about 13 inches. She lives in my 1000 gal koi pond. I don't understand what all the fuss is about "giant goldfish." I suspect the young goldfish are food for the trout in Lake Tahoe. Koi and goldfish make good pets because they are never aggressive.

Gysele van Santen

if someone can't take care of a goldfish that's just pathetic. every action has a consequence & dumping a pet fish into a lake thinking it's all good is not responsible at all.

Marie W.
Marie W.2 years ago

Some people should NOT be allowed to have any pets or kids.

Isabel Araujo
Isabel Araujo2 years ago

Irresponsible people!

Beth Cook
Beth Cook2 years ago

I had a fantail goldfish for nearly 6 years before he died. He was pretty big by the time he died too--from nose to tail he was about 5 inches long, maybe an inch or so across and I think about a pound or so in weight. I loved him--he liked his top fin rubbed and was very demanding if the water temp in his tank was too cold or hot, he would play around with his thermometer, loudly, until I turned the heater up or down. These guys make great pets if you are willing to put in the time and effort to make sure that they remain happy and healthy--including buying a larger tank when its needed.