Pet Goldfish Released into the Wild Are Getting Really Huge

Monster goldfish are trouble for native fish

Pet goldfish in a tank, where it belongs Benson Kua/Flickr (CC BY 2.0)

Goldfish are some of the easiest pets to keep. With the proper sprinkling of food and a clean tank, those low-maintenance pets can live for decades. For some people, that may be a bit long and perhaps that’s why they set the fish free. That can be a problem. A big one.

"Their size is limited in the tank, but when you release it into the wild, that doesn’t exist anymore," Kate Wilson, the aquatic invasive species coordinator at Alberta Environment and Parks told Sarah Larimer at The Washington Post. The Alberta government has just issued a plea asking goldfish owners not to release their discarded pets into the wild. Larimer writes:

Like other species of carp, the domestic goldfish Carassius auratus will basically keep growing as long as water temperatures and food resources support it. There are obviously limits — you're not going to accidentally create fishzilla if you overfeed your goldfish — but given a big body of water with tons of food and warm summers, a fish is bound to get supersized.

Researchers worry that the large, invasive goldfish can outcompete local fish. Their feces also seem to encourage algal blooms that disrupt the pond and lake ecosystem. 

The municipality of Wood Buffalo in Alberta recently pulled 40 non-native fish from a stormwater pond, writes a reporter at CBC News. This problem isn’t just a Canadian one. Teller Lake #5 in Boulder Colorado has thousands of feral goldfish. Fish biologists at Lake Tahoe in California has grappled with goldfish weighing several pounds and at least one that stretched 1.5 feet long.

Goldfish may get much bigger. A teenager in Dorset caught a 5-pound goldfish in a lake in southern England in 2010. Guinness World Records has a fish owned by Joris Gijsbers down as holding the record for longest goldfish, ringing in at 18.7 inches from nose to tail. The report of a 30-pound goldfish apparently caught by a French fishermen seem a bit more fishy.

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