Invasive Pet: Dumped Goldfish Threaten Local Fish

We've all heard about rabbits overpopulating city parks, having been released by their owners a few months after, say, Easter.

But the new story is goldfish, which the Alberta government is trying to get Canadians to stop dumping into ponds. Because those goldfish are getting bunny-size (nearly) in the wild. 

"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 a CBC broadcaster. 

Apparently, these goldfish are not just growing large, they're tough enough to survive Canadian winters. According to CBC News, the municipality of Wood Buffalo pulled 40 goldfish from a stormwater pond.

"Their size is limited in the tank, but when you release it into the wild, that doesn't exist anymore," Wilson told The Washington Post.

That's because domestic Carassius auratus, like other species of carp, will keep growing as long as food sources and water temperatures support it.

There are also many reasons that dumping domestic goldfish means tossing an invasive species into the local pond: The large goldfish will compete with local fish for resources; goldfish feces might help support certain types of algae, causing algal blooms that disrupt the ecosystem; and the water in the aquarium, once dumped into a pond with the fish, can carry disease and parasites. 

Expanding goldfish have also been sighted in Lake Tahoe, Maine, Salt Lake City, Michigan, Colorado, and many other areas. Examples are below:

"Super-Sized Goldfish Pose Giant Problem for Lake Tahoe" (USDA)

"Giant goldfish in Belfast's Muck? The state says that has to change" (Maine's Bangor Daily News)

"Dumping pet fish into the wild harms ecosystem, experts say" (KSL/Salt Lake City)