ELLSWORTH, Maine — The little orange fish are a staple in home aquariums and Asian restaurants. They are a rite of passage for young children, who receive them as a test-run for bigger, furrier pets.

But goldfish also are an invasive species and a risk to Maine’s indigenous fishes, said a state biologist Tuesday. The Maine Department of Inland Fisheries and Wildlife is responsible for enforcing a state law banning goldfish from outdoor bodies of water.

Greg Burr is a regional fisheries biologist for the DIF&W. He and a small crew were at Birdsacre Stanwood Wildlife Sanctuary in Ellsworth on Tuesday. There, a small pond is overrun with goldfish, he said, some of them up to a foot long.

It’s unclear how the fish got there, Burr said, but he knows they were placed by human hands. Despite the common name “goldfish,” the Carassius auratus auratus is not always the familiar golden color. They’re often brown or even black, Burr said, and are mistakenly identified as carp or sunfish.

Because they’re so easily misidentified, goldfish outside of aquariums are sometimes moved by anglers who trap them for live bait. The mistake proliferates the species.

The goldfish is a domesticated version of the Prussian carp. Keeping them outdoors is illegal because their escape could lead to ballooning goldfish populations in Maine’s rivers, streams, ponds and lakes.

“We don’t want them getting into public waters,” Burr said. “They’re very prolific and we can’t have them competing with native species.”

In the past two years, DIF&W scientists have “reclaimed” 11 ponds from goldfish infestations. Two more — Birdsacre and a pond in Mount Desert — are slated for reclamation within the next two years.

Reclamation is achieved by dispersing rotenone, a naturally occurring piscicide that’s found in several beans and legumes in South America. DIF&W crews don hip-waders and spray the chemical into the infested water. Over the next few weeks, all the fish in the water are dead.

Joe Overlock, another fisheries biologist, said the rotenone is safe for plants and nongilled animals. Birds or other critters that may eat the dead fish will be unharmed, he said.

“It gets broken down really quickly by stomach enzymes,” he said. “The reason it kills fish is that it goes right into the bloodstream via the gills.”

Overlock and Burr were scheduled to treat the Birdsacre pond Tuesday, but a survey of the site showed that the water level had risen because of recent rainfall. The DEP permit for rotenone requires that the chemical not move to other bodies of water. With the water level up, the crew couldn’t guarantee that wouldn’t happen.

Overlock said it would likely be next summer before the water level is low enough to treat the pond, so the goldfish in Ellsworth have a one-year stay of execution.

Stan Richmond, former president of Birdsacre and son of the bird sanctuary’s founders, said the goldfish aren’t the only ones who will be pleased by the delay.

“There’s one guy that will be pretty happy,” he said. “The great blue heron.”

Follow Mario Moretto on Twitter at @riocarmine.

Mario Moretto

Mario Moretto has been a Maine journalist, in print and online publications, since 2009. He joined the Bangor Daily News in 2012, first as a general assignment reporter in his native Hancock County and,...