ANCHORAGE, Alaska (AP) — A murky pond in the middle of Anchorage has some unwanted guests.

Cuddy Pond, near the city’s main library, is home to dozens of goldfish, The Anchorage Daily News reports. Wildlife officials say they likely were put there by pet owners who didn’t want to kill them.

State officials classify goldfish as an invasive species. The aquarium pets are domesticated carp originally bred in China. Goldfish can carry diseases and bacteria that harm the ecosystem and other marine animals and among other misplaced aquatic species causing damage in Alaska.

“This is a real clear example here in the heart of Anchorage — here’s all these goldfish, over 150 of them I counted last week, swimming around,” said Krissy Dunker, an invasive species research biologist for the Alaska Department of Fish and Game.

The department has increased efforts to investigate how invasions start, Dunker said, using sophisticated forensic technology in genetic sampling and water chemistry.

Northern pike have decimated salmon and trout populations in southcentral Alaska and have cost millions to kill. Officials documented largemouth bass in Sand Lake, red-ear slider turtles in other Anchorage lakes and creeks and crayfish in Kodiak.

State officials eradicated muskellunge from the Kenai Peninsula and worked with geneticists in Wisconsin and Minnesota to trace the fish back to the Midwest, Dunker said.

Releasing non-native fish in Alaska can result in a criminal misdemeanor charge and a $10,000 fine because of the ecological and financial consequences.

Fish and Game officials have been aware of the goldfish in Cuddy Pond since at least spring 2018. Goldfish also have been found in Jewel, Cheney and Taku lakes, though there’s no evidence they reproduced, Dunker said. A population was also found in Gustavus in southeast Alaska.

Fish and Game employees used nets to sample goldfish from Cuddy Pond. The orange, white and red fish had grown as long as 10 inches (25.4 centimeters). A pathology lab bested them for parasites and disease.

The department last year tried using electroshock equipment, which sends pulses through the water, to stun fish and make them easier to catch. The fish simply swam deeper and the equipment was not effective, Dunker said.

Officials would like to find out if the Cuddy Pond goldfish are reproducing and where they came from.

The department also wants to collect reports of wildlife that looks out of place, Dunker said.

“Obviously, those big, orange fish by the Loussac Library don’t look right,” she said.

Goldfish are not the only unnatural wildlife occurrence at Cuddy Park. The park is home to flocks of ducks and geese. Some overwinter because people feed them over the pleas of the Anchorage Waterways Council, which says it harms birds.

Dunker says it’s more humane to euthanize unwanted pet fish than to release them into the wild, where they’re likely to starve in winter.

“People think they’re doing something kind for the pet, but you’re actually causing it to suffer,” Dunker said.

At least one Anchorage specialty fish store takes unwanted fish pets.

“We will always take in fish, no questions asked,” said Cody Hall, a manager at Alaska Coral and Fish.

The store tries to find unwanted fish new homes.

“We’re sort of like the pound for fish tanks,” Hall said.

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