Minnesota authorities have called on aquarium owners to stop releasing pet fish into waterways, after several huge goldfish were pulled from a local lake.
Officials in Burnsville, about 15 miles south of Minneapolis, said released goldfish can grow several times their normal size and wreak havoc on native species.
“Please don’t release your goldfish into ponds and lakes!” ” the city tweeted Friday. “They get bigger than you think and contribute to poor water quality by dirtying bottom sediment and uprooting plants.”
Last November, authorities in nearby Carver County removed up to 50,000 goldfish from local waters. County water management official Paul Moline said goldfish “are an understudied species” with “high potential to negatively impact lake water quality.”
Goldfish, a member of the carp family, can easily reproduce and survive on low oxygen levels during the Minnesota winter.
“A few goldfish may seem to some like a harmless addition to the local body of water – but they are not,” advised the Minnesota Department of Natural Resources.
The ecological destruction caused by released aquarium animals is nothing new. The carnivorous lionfish, native to the Indo-Pacific but believed to have been released by Florida pet owners after Hurricane Andrew in 1992, killed dozens of Caribbean species, allowing algae to overtake reefs.
Goldfish have received less attention than other invasive species, including Asian carp and zebra mussels, but warnings have been issued in Virginia and Washington state, as well as Australia and Canada.
In 2013, Scientific American reported that researchers trawling Lake Tahoe caught a goldfish that was nearly 1.5 feet long and weighed 4.2 pounds. The author of a report on the California aquarium trade said: “Globally, the aquarium trade contributed to a third of the world’s worst aquatic and invasive species.”
Wildlife officials in Virginia recently warned that “pet owners should never release their aquatic organisms into the wild” after an angler caught a 16-inch goldfish.
The costs of rehabilitating watercourses infested with goldfish are considerable. Carver County in Minnesota signed an $88,000 contract with a consulting firm to study how to eradicate shoaling.
The Washington Post reported that in 2018 Washington state officials said they would spend $150,000 to rehabilitate a lake near Spokane. In Alberta, Canada, an invasive species expert called the goldfish problem “scary.”
It is estimated that up to 200 million goldfish are farmed each year, with most ending up in national exhibition.