Goldfish thrive inside school classroom tanks, bright indoor aquariums and backyard ponds.
But when they end up in Ohio’s natural waterways, the starter pets have the power to disrupt entire ecosystems, according to new research from University of Toledo associate professor Bill Hintz, published in the Journal of Animal Ecology.
Goldfish are often released into the wild, but their impact on lakes and other waterways are understudied.
Hintz’s research findings reveal the small fish have a mighty impact. They can deplete the habitat and food source of native fish and even alter the look of waterways.
“When we add the goldfish to those experimental ecosystems, we found this kind of dramatic change in water clarity,” he said.
From pets to pests
Hintz and his partners from the University of Missouri conducted controlled experiments in artificial lakes to measure the impact of goldfish.
They found a major threat in the fish’s voracious appetite: Goldfish don’t technically have a stomach. They’re always eating.
“They ate a lot of the material within the tanks and what that did was it kind of resuspended a lot of sediments into the water column,” Hintz explained.
It reduced water clarity. In just a short 61-day window, the ornamental fish triggered a so-called “regime shift” – turning a once clear lake to a murky pool – with fewer food sources for native fish.
Their findings largely reflected what other research out of Europe have shown: Goldfish are a threat to water quality and native species.
“We have a pond outside of our research center and that pond is chock full of goldfish. That pond almost looks exactly the same as the photos we took in the experiment,” he said.
Their impact on Ohio’s waterways
Goldfish can be found in many of Ohio’s major waterways, Hintz said, including Lake Erie. Oftentimes, the ornamental fish escape backyard ponds or are released into the wild by well-intentioned pet owners. Then, they multiply quickly.
He said their exact number isn’t known, but the state often captures goldfish in their field surveys. Hintz estimates their population in the thousands in Lake Erie.
Although, they often look nothing like the goldfish that might swim around a small fish bowl. They can grow up to 16 inches, get up to nine pounds and lose their vibrant coloring.
“Goldfish can be kind of drab-looking in the wild. So they're not as noticeable as they are in our fish tanks,” he said.
But they’re important to watch out for. Hintz said his research concluded that natural resource managers should manage wild goldfish populations. He said there needs to be more efforts to prevent these pets from growing into sizable pests that alter ecosystems.
“Don't release your pet into the wild. We can return it to a pet store. We can consult a state wildlife professional to learn how to deal with these goldfish,” he said. “Removal efforts, education and outreach – all those are in the toolbox to kind of manage wild populations of goldfish.”
