Giant goldfish suddenly menacing the Great Lakes
Inside a fishbowl, the goldfish — a species of carp native to East Asia, bred for aesthetic delight and traditionally believed to bring good fortune — is hardly more than home décor. Usually just a few inches long, it is among the easiest of pets to keep.
But released into the wild, the seemingly humble goldfish, freed from glass boundaries and no longer limited to meager meals of flakes, can grow to monstrous proportions. They can even kill off native marine wildlife and help destroy fragile and economically valuable ecosystems.
“They can eat anything and everything,” said Christine Boston, an aquatic research biologist with Fisheries and Oceans Canada.
Over the past several years, Boston and her colleagues have been tracking invasive goldfish in Hamilton Harbour, which is on the western tip of Lake Ontario, about 35 miles southwest of Toronto. The bay has been decimated by industrial and urban development as well as by invasive species — making it among the most environmentally degraded areas of the Great Lakes.
Their study, published in November in the Journal of Great Lakes Research, could help pinpoint goldfish populations for culling, said Boston, who is the lead author. “We found out where they are before they start spawning,” she said. “That's a good opportunity to get rid of them.”
The fast-growing female goldfish, Boston noted, can also reproduce several times in one season. “They have the resources,” she added, “and they can take advantage of them.”
Goldfish were first spotted in Hamilton Harbour in the 1960s, but largely died off in the 1970s because of industrial contamination. In the early 2000s, their population appeared to recover. Goldfish can tolerate a wide range of water temperatures, reach sexual maturation quickly, and can eat nearly anything, including algae, aquatic plants, eggs and invertebrates, Boston said.
Their football-shaped bodies can swell to a size that makes them too large a meal for predators — up to about 16 inches long. “A fish would have to have a really big mouth to eat it,” she said.
The feral goldfish are also destructive, uprooting and consuming plants that are home to native species. They help spawn harmful algal blooms by consuming the algae and expelling nutrients that promote its growth, Boston said, creating conditions that are intolerable to native fish.