From Pet To Pest, Goldfish Tip Scales Of Survival In Lake's Ecosystem Colorado wildlife officials believe someone released four or five pet goldfish into Teller Lake #5 a few years ago. Now, the fish number in the thousands and threaten the lake's ecosystem.

From Pet To Pest, Goldfish Tip Scales Of Survival In Lake's Ecosystem

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Last month in Boulder, Colo., wildlife officials noticed some goldfish, like the kind you might get in a pet store or at a carnival, in Teller Lake #5. As it turns out, it wasn't just one or two goldfish, it was 3,000. Officials think someone maybe a year or two ago wanting to get rid of their pets released the fish into the lake where they reproduced wildly. The problem is the fish aren't native to the area, and now they're threatening the lake's ecosystem. Here to talk with us is Ben Swigle. He's an aquatic biologist with Colorado's Parks and Wildlife Service. Welcome to the program.

BEN SWIGLE: Thanks for having me.

BLOCK: So help us understand. With this number of fish, how do they threaten the ecosystem?

SWIGLE: Well, my biggest concern was the fish would escape downstream. And in Colorado, we have a very short transitional zone where we have a cool Rocky Mountain stream and 20 miles to the east, the stream transitions into a more warm water fishery. And the goldfish are super adaptive, and they can live in a variety of environments. So they have the potential to compete with other native species and potentially supplant those to a point they may no longer exist in Colorado.

BLOCK: Talk about some of the methods that you guys are considering to get rid of them.

SWIGLE: The first method is a mechanical removal where we use a process called electrofishing, which temporarily stuns the fish and allows us to net them up and transport them, you know, off-site and dispose of them. We usually give the fish to raptor farms where they're rehabilitating birds. The other method is using an organic plant-based material called rotenone. And that's applied to the water, and it kills everything that respires using gills. And then the final method that we're weighing is draining the lake. Each method has, you know, a varying cost associated with it, and we're working with the city of Boulder Open Space to determine what the best course of action is.

BLOCK: You know, when I hear you talking about having to electrofish - right? - electroshock the fish or drain the lake, it makes me think about how somebody probably thought they were doing their goldfish a favor, right? They thought that they were sitting it free or something.

SWIGLE: Right. I mean, I'm sure no matter what type of pet you have there is a sentimental value, but there's better methods of disposing of unwanted pets rather than harm a public water.

BLOCK: What would you suggest people do with their unwanted pet goldfish?

SWIGLE: Certainly if the fish is deceased, we recommend just putting them in the freezer overnight and disposing of it. If the fish is alive or a different aquatic species for that matter, then we recommend putting in the freezer overnight and then just disposing it in the trash.

BLOCK: Do you basically hate goldfish now?

SWIGLE: Absolutely not. I wish the education was stronger and folks would dispose of their unwanted pets and aquatic species in a better fashion that doesn't have the potential to have long-lasting effects for our native species.

BLOCK: Well, Ben Swigle, thank you so much for speaking with us and best of luck with Teller Lake #5.

SWIGLE: Well, thank you very much. Have a wonderful day.

BLOCK: Ben Swigle, he's an aquatic biologist for the Colorado Parks and Wildlife Service.

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