Giant goldfish and sewer alligators: Why releasing household pets into the wild is a very bad idea

Emergence of fish the size of American footballs in Minnesota lakes poses serious threat to sensitive ecosystems already under duress

A town in the midwestern state of Minnesota has been forced to issue an appeal to local residents asking them not to dump their unwanted pet goldfish in local waterways after a number of giant specimens, some as large as American footballs, were discovered in a lake.

“Please don’t release your pet goldfish into ponds and lakes!,” the City of Burnsville implored in a tweet. “They grow bigger than you think and contribute to poor water quality by mucking up the bottom sediments and uprooting plants. Groups of these large goldfish were recently found in Keller Lake.”

Ten of the fish had already been discovered before a further 18 were caught last week, some weighing as much as 1.8 kilograms and stretching 46 centimetres in length.

“Most of them were definitely bigger than you’d find in your typical aquarium,” Daryl Jacobson, the city’s natural resources manager, told The Star Tribune.

“I would not be surprised if they’re in a lot of lakes, especially in low numbers. Goldfish are a pretty hardy species.”

As the council of the Twin Cities suburb suggests in its post, the release of domestic goldfish into the wild might seem like a humane gesture but is in fact a seriously bad idea because of their disruptive influence over delicate ecosystems they are not native to.

They have few predators of their own and compete with other species for algae, uproot existing plant life growing on the beds of lakes and ponds - meaning no more oxygen is generated - and disrupt the sedimentary soil, which releases phosphorus into the water and interferes with its purity.

They can also survive in frozen lakes or those with poor water quality because of their ability to go without oxygen for long periods.

According to National Geographic, goldfish can come to weigh as much as 2.27kg in the wild and stretch to 41cm in length, living for more than 40 years compared to 10 in captivity.

“Goldfish go from cute to villainous when released into the wild. They’re known to carry disease and parasites, as well as breed with wild carp in the area,” the nature periodical warns.

Burnsville has been working with local firms to tackle the problem, “electroshocking” the fish to temporarily stun them so that they can be measured, tagged and then re-released into the waters to establish where they spawn.

Similar measures have been undertaken in the city of Chaska in the same state, implemented as part of a three-year plan to resolve the problem of their overrunning Big Woods Lake and Lake Hazeltine.

“Last fall we removed close to 100,000 goldfish,” Tim Sundby of Carver County Water Management told CBS Minnesota, explaining that the ultimate goal is to bring down their numbers so that the water and vegetation can recover and other species like bluegills and sunfish return.

The everyday household goldfish we know today is descended from the Prussian carp and was first domesticated 2,000 years ago in China, where they were admired for their tranquil presence and came to be regarded as symbols of good fortune during the Song Dynasty.

They were introduced to Europe in the 17th century as a novelty and to North America in the 19th, where the habit of giving them away in bags at funfairs developed, a trend that has been blamed for the widespread modern perception that the species is disposable.

In addition to Minnesota, instances of giant goldfish being caught by delighted fishermen in recent years have been reported across the US, from New York and Washington to Missouri, South Carolina, Virginia and Kentucky, as well as in Canada, Australia and the UK.

In Britain, Lawrence King, an angler from South London, caught a whopping 3.8kg goldfish in 2018 and, eight years earlier, Surrey GCSE student Nick Richards landed a 2.2kg bloater while on holiday in Poole, Dorset.

The whole idea of pet animals being released into the wild and thriving in mutant form is a potent one and relates to the popular urban myth about feral crocodiles dwelling in the sewers beneath the streets of New York City, which dates back to at least 1907 and really caught the public’s imagination in the gloomy Depression years of the 1930s when baby gators were commonly advertised for sale in newspapers and dispatched by mail.

A number of incidents were recorded at that time, most famously the eight-foot East Harlem crocodile hauled out of a storm drain by two local youths in February 1935.

The obsession enjoyed a particular revival in the 1980s, a decade that began with the release of the B-movie Alligator that explored the theme and also saw the creation of both the Batman villain Killer Croc (1983) and the Teenage Mutant Ninja Turtles antagonist Leatherhead (1987).

Sadly, however, the truth is more pedestrian.

While The New York Post does record a caiman on the loose in Central Park in 2001, a four-foot croc spotted in Alley Pond Park in Queens in 2003 and an 18-incher (“but mean looking”) crawling out of a drain on Newtown Avenue in August 2010, they are hardly running an underworld down there.

“The tales are sort of true,” Corey Kilgannon wrote in The New York Times last year. “The city rescues several alligators a year, typically former pets that have been abandoned after having outgrown their cute phase.”

As with so many things, the threat is far more real in balmy Florida, where a nine-foot alligator was lugged out of a manhole in Tampa in March 2017.

Other famous nightmare scenarios involving commonly-domesticated animals on the loose include the horrifying experience of Bangkok resident Attaporn Boonmakchuay, whose penis was bitten by a 10-foot python that reared up out of his toilet in May 2016.

“The snakes just follow the trail of the rats. All over the world rats go down in sewers and the snakes go in there after them,” Australian wildlife expert Geoff Jacobs told the BBC at the time.

The moral of the story? Give your unwanted pets up for adoption. While returning them to the wild might seem like the kindest option, the knock-on consequences of introducing a non-native species to carefully calibrated habitats are rarely positive.