Formerly pet, giant goldfish threatens the Great Lakes – 01/01/2024 – Science

In an aquarium, goldfish — a species of carp native to East Asia bred for aesthetic pleasure and, it is believed, for good luck — are little more than home decoration. Usually just a few inches long, it is one of the easiest pets to care for.

But when released into the wild, the seemingly humble goldfish, freed from glass barriers and no longer limited to modest meals, can take on monstrous proportions. There is also the risk of killing native marine life and helping to destroy fragile and economically valuable ecosystems.

“They can eat anything and everything,” said Christine Boston, an aquatic research biologist at Fisheries and Oceans Canada, the federal agency responsible for managing fisheries resources.

For the past few years, Boston and his colleagues have been tracking invasive goldfish in Hamilton Harbor, which sits at the western tip of Lake Ontario, which is 35 miles southwest of Toronto. The bay has been devastated by industrial and urban development, as well as invasive species, making it one of the most environmentally degraded areas of the Great Lakes.

The study, published last November in the Journal of Great Lakes Research, could help identify populations of goldfish for slaughter, according to Boston, lead author of the work. “We find out where they are before they start reproducing,” she said. “This is a good opportunity to get rid of them.”

Female goldfish, which grow quickly, can also reproduce multiple times in a season. “They have the resources,” Boston added, “and they can leverage them.”

Goldfish were first spotted in Hamilton Harbor in the 1960s, but largely died out in the 1970s due to industrial contamination. In the early 2000s, its population appeared to recover. Goldfish tolerate a wide range of water temperatures, reach sexual maturation quickly and can eat almost anything, including algae, aquatic plants, eggs and invertebrates, Boston said.

Their football-shaped bodies can reach a size that makes them an oversized meal for predators — up to about 40 cm long. “A fish would have to have a very big mouth to eat them,” said the researcher.

Wild goldfish are also destructive, uprooting and consuming plants that are home to native species. They help generate harmful algal blooms by consuming the algae and expelling nutrients that promote its growth, Boston said, creating intolerable conditions for native fish.

To track the goldfish, researchers captured and sedated 19 of the larger adults and implanted AA battery-sized tags in them. The items, which sent signals to acoustic receivers around the bay, provided researchers with a map of the animals’ locations.

Eight of them died. The other 11 led Boston and his colleagues to discover that the fish tended to spend the winter in deep waters and move to shallower habitats in the spring, where they prepared to reproduce.

Some options for removing goldfish, she said, include catching them with specialized nets deployed under the winter ice or using “electric fishing,” which involves stunning them with an electric current and pulling them out of the water. Both techniques, the researcher added, would avoid killing native fish.

Nicholas Mandrak, a professor of biological sciences at the University of Toronto Scarborough, said that although goldfish were introduced to North America in the late 19th century, the wild population began to “increase dramatically” in the last two decades. Their breeding boom, he said, resulted in part from residents of densely populated areas releasing pets into urban ponds.

Climate change may play a role, due to goldfish’s ability to adapt to warm, poorly oxygenated waters, he added.

“There are literally millions of goldfish in the Great Lakes, if not tens of millions,” Mandrak said.

Despite the threat, he added, environmental managers tend to forget about goldfish. “They just assume, ‘It’s been there for 150 years — there’s nothing we can do about it.'”

The problem is not unique to Canada.

In Australia, a handful of unwanted goldfish and their offspring have taken over a river in the southwest of the country.

Wild goldfish have flooded waterways in the UK, and in Burnsville, Minnesota (USA), the discovery of football-sized creatures in a lake in 2021 left authorities begging residents: “Please, Don’t release your pet goldfish into ponds and lakes!”

Anthony Ricciardi, professor of invasive ecology at McGill University in Montreal, noted that not all invasive goldfish become giants, but even small ones are problematic, outgrowing native fish populations and damaging the environment.

People mistakenly believe that because goldfish are “small and cute” they won’t pose a problem when released into the wild, Ricciardi said. “It’s the ‘Free Willy’ syndrome.”

Goldfish, he added, are just a small part of a vast invasion of non-native species whose results can be unpredictable and, in some cases, are worsened by climate change.

“Under human influence, creatures are moving faster, further and in greater numbers, reaching parts of the planet they could never reach before,” he said. “We’re talking about the redistribution of life on Earth.”