The invasion begins innocently enough: a goldfish paddles through the secluded waters of a home aquarium, minding its own business, not disturbing any native habitat.
The real problem comes later, when the human who put it there decides it’s time to change. Not wanting to hurt the fish, but also unwilling to keep it, the owner of the animal decides to release it into a local lake, pond or stream. The move, experts say, is well-intentioned but misguided – and potentially dangerous.
Officials from Burnsville, Minnesota, a town about 15 miles south of Minneapolis, demonstrated why last month when they shared photographs of several massive goldfish recovered from a local lake. Abandoned animals can swell and wreak havoc, the city has warned.
“Please don’t release your goldfish into ponds and lakes!” The city wrote in a Twitter post, which had been liked and retweeted more than 15,000 times. “They get bigger than you think and contribute to poor water quality by messing up bottom sediment and uprooting plants.”
Burnsville, along with neighboring Apple Valley, began studying the lake’s goldfish population after residents complained of a possible infestation. In collaboration with the company Carp Solutions, which specializes in the fight against aquatic pests, the cities sent a team to investigate, and even it was surprised by the size of the fish found.
“You see goldfish in the store and it’s those little fish,” Burnsville natural resources specialist Caleb Ashling said in an interview. “When you take a football-sized goldfish out of the lake, you wonder how it could be the same type of animal. “
Far from being a harmless domestic animal, a goldfish released into freshwater is an invasive species, an organism that is introduced into an environment, can reproduce quickly, supplant native species and destroy habitat. And even though they receive less attention than invasive organisms such as Asian carp or zebra mussels, goldfish appear to be a growing problem in water bodies in the United States and around the world, triggering warnings from government officials in Virginia, Washington State, Australia. , Canada and elsewhere.
“A few goldfish may seem like a harmless addition to the local body of water to some – but they are not,” the Minnesota Department of Natural Resources advised this year.
The problem has worsened in recent years, said Przemek Bajer, owner of Carp Solutions and professor of aquatic invasive species at the University of Minnesota. The most likely sources are former pets and their offspring, he said.
“They seem to be becoming more and more prevalent,” Bajer said. “You think of how many of these fish are sold nationwide and how many are released. It’s a pretty big introductory vector.
Also known by the scientific name of Carassius auratus, goldfish can live up to 25 years, weigh up to four pounds, and grow to well over a foot long. They are also surprisingly hardy – they can survive harsh conditions and can survive winters in frozen bodies of water, living for months without oxygen. This quality, Bajer said, “makes them really, really difficult and allows them to dominate certain types of ecosystems.”
Goldfish, like their cousins common carp, feed on the bottom of lakes, where they uproot plants and stir up sediment, which in turn damages water quality and can lead to algae blooms, harming d ‘other species.
“Goldfish have the ability to dramatically change water quality, which can have a cascade of impacts on plants and other animals,” Ashling said. “They are a major concern.”
Once goldfish are in a body of water, they can move on to others and it can be difficult to expel them. The Minnesota Department of Natural Resources said the fish are able to “navigate their way through city stormwater ponds and downstream lakes and streams with great impacts, reproducing rapidly,” by surviving harsh winters and feeding and stirring the bottom “. It is illegal to release goldfish into state public waters.
In Carver County, near Burnsville, goldfish have plagued a chain of lakes for at least two years, frustrating water officials and costing the community money as it tries to combat the problem.
Last year, county workers removed about 30,000 to 50,000 fish in one day. The root of the problem, the county said, is likely “one or more individuals illegally dumping pet goldfish over the years.”
This year, Carver County signed an $ 88,000 contract with a consulting firm to study how to manage and eliminate schools of goldfish.
Paul Moline, director of planning and water management for Carver County, told county commissioners that fish “are an under-studied species” with “a high potential to negatively impact water. water quality of lakes “.
In 2018, officials in Washington state said they would spend $ 150,000 to rehabilitate a lake near Spokane that had become so overrun with goldfish that it was harming the trout population. An invasive species expert from Alberta called the problem in the Canadian province “frightening.” And about two months ago in Virginia, state wildlife officials certified a record after an angler stung a 16-inch goldfish, but they warned that ” animals should never release their aquatic organisms into the wild “.
Ashling and her colleagues at Burnsville are trying to determine the extent of their problem, but they hope their early findings will discourage other pet owners from abandoning their fish in public waters – which in the land of 10,000. lakes, are sacred.
“People try to be nice, but they don’t realize that goldfish can really have a lot of unintended consequences,” Ashling said. “Most people genuinely care about their lakes and ponds, but you might cause problems you weren’t aware of if you let them go. “