But the problem of the invasive fish has only ballooned along with their bodies—at least in the Great Lakes.
“There are literally millions of goldfish in the Great Lakes, if not tens of millions,” Nicholas Mandrak, a biological scientist at the University of Toronto Scarborough, tells the New York Times, which reports the carp species native to East Asia grows “monstrous” when “no longer limited to meager meals of flakes.”
Reaching up to a foot and a half long, often too large for predator fish to consume, goldfish wreak havoc on ecosystems, spreading disease, rooting up plants, and eating just about anything, including native marine life and vegetation.
Luckily, researchers have come up with strategies to deal with them.
Researchers inserted trackers into 19 goldfish that were at least a foot long, collected from the westernmost shores of Lake Ontario in Hamilton, Ontario, and documented their movements for up to two years, finding some unexpected patterns.
With few exceptions, “they overwintered in the same areas each year and returned to the same spawning habitat each spring,” Christine Boston, an aquatic research biologist with Fisheries and Oceans Canada and lead author of a study on the findings published in the Journal of Great Lakes Research, tells Great Lakes Now.
They also congregated in specific areas earlier in the year and in colder water (around 50 degrees Fahrenheit) than expected before moving to their spawning grounds, as was predicted by models.
“If we can get our hands on them, we can make a real dent in their population,” says Boston. She and her colleagues suggest grabbing the fish in nets beneath winter ice or shocking them with electrical currents and taking them from the water.
Similar methods have been used to cull invasive carp, which are related to goldfish.
“We’ve seen significant drops in invasive carp populations, so we know control works,” Boston tells Great Lakes Now.
And neither method would kill any native fish, she tells the Times. Still, all the effort could be for nothing if pet owners continue to deposit their goldfish in ponds and lakes. A tiny goldfish might seen harmless, but “they reproduce several times in one mating season and they can even live up to 25 years,” per Popular Science.