Monster goldfish threaten Canadian lakes and rivers

Dylan Young
Daily Brew

It's hard to believe that those tiny goggle-eyed goldies could pose a serious threat to Canada's ecology. But whether they began as a stall prize at the county fair or some child's first purchase from a pet store, the moment they get into the wild they become a bonafide public enemy - bullying the local fauna and nabbing more than their fair share of nature's spoils.

Reports have the ornamental fish popping up in rivers and lakes from the U.S. to Fort McMurray, and in numbers that show they are not just surviving in the wild but actually thriving.

"We had a pretty shocking find last year when we discovered four different age classes of goldfish living in a Fort McMurray storm water pond," said Kate Wilson, the Aquatic Invasive Species Specialist for Alberta Environment & Parks.

"That means they're breeding in the wild. Which is remarkable considering how cold the winters are there. The biggest ones were the size of dinner plates."

It's too soon to know what sort of impact the invasive species will have. At best they will cause mischief. At worst they could set off a chain reaction that decimates an entire ecosystem.

"We still don't have enough data to know how a large goldfish is going to behave in the wild," Wilson admitted.

"Our best measure at the moment is to look at what Prussian carp have done since invading our flowing water systems."

The grey-green Prussian carp is a close relative of the goldfish: a popular theory of goldfish origin is that they were selectively bred from Prussian carp in China over a thousand years ago. Prussian carp are also an invasive species that has proliferated in Alberta waters at an alarming rate over the past several years, with the population topping 100,000.

"They're thriving everywhere, even in tributaries with very low flow and low oxygen," Wilson said.

"One biologist told me about leaving several Prussian carp in a bucket overnight, with no water. They were still alive the next day."

"They eat fish eggs, plants, plankton, small fish and amphibians. So they're not only competing for food, they're eating the native species as well."

Even with the amount of data scientists have collected on the Prussian carp's incursion into Alberta waters, it could still be years before they know just how bad the situation really is. What they can be certain of is that there is no way to dial back the damage — Prussian carp aren't going anywhere.

The big fear now is that the goldfish problem could very quickly spiral into a Prussian carp-sized one, with the sparkly fish not only feeding like their dull-looking cousins but breeding and spreading like them as well.

And the worst part of the whole phenomenon? It's all our fault.

"With the goldfish, I don't think it's coming from a bad place," Wilson admitted.

"People don't want their fish anymore but they don't want to kill them. So they let them go in a storm pond or a river. They don't know how damaging that is. They don't know that it's illegal."

Other seemingly benign human behaviour can also contribute to the problem. The popularity of stocking decorative ponds with ornamental fish allows for the possibility of them escaping into public waterways during heavy rains. And the ceremonial release of fish has become a popular method of spiritual balancing with certain groups.

"In all of these cases, I think if they knew how serious the impact was going to be — or that they could end up having to pay heavy fines — they'd happily change their behaviour," Wilson said.

So far Wilson and her peers are assuming that the invasive goldfish are the result of sporadic or accidental release. But there may be something different going on with the Prussian carp.

"Pet shops sometimes use less desirable fish as 'feeder fish' and it's possible that some of these were allowed to get free," Wilson said.

"But it's also possible that people have been actively stocking waters with Prussian carp so they can fish for them, which is highly illegal."

"People are known to catch and eat this species," she added.

"It's bad enough that people may be putting these fish into our waterways. But if people are eating the fish they pull out of storm water ponds that have poor water quality, low oxygen levels, and are full of pollutants, I can only imagine what they are putting into their bodies. It's a potential health issue."

This summer Alberta will be pressing forward with a campaign to draw a line under these issues. The 'Don't Let It Loose' campaign won’t just be delivering its message to hobby fishers and pet owners. It will be actively reaching out to pet stores, horticultural centres and fresh fish markets in the hopes of partnering with them to drive the message home.

If the urgency of the message seems out of proportion to many of us, it's because we don't fully understand the stakes. Though it may not be as severe in other regions of Canada, this issue is not isolated to Alberta. Maybe because the rest of the country doesn't have the Prussian carp example to show how bad it can get, most provinces have yet take the threat seriously — a threat that is not just a remote one.

Toronto, Canada's largest municipality, is already seeing the not-so-thin end of the wedge on this giant goldfish issue. But if a sense of gravity surrounding the phenomenon exists within the scientific community, it has yet to filter out to the public. A recent article in the Toronto Star even had a pond fisher espousing a catch-and-release approach to the invaders and a Conservation worker downplaying the issue.

"Nearly one-third of aquatic invasive species that threaten our ecosystem come from the aquatic ornamental fish trade," Wilson said.

"That's crazy! We need to educate people that it's not a humanitarian act to release your pet into the wild. If they don't survive, it's cruel; if they do survive, it presents a huge problem for the environment."

And if one of us should come across an outsized goldfish, Prussian carp or another invader in the wild?

"If you catch one of these unregulated fish, whatever you do, don't throw it back," Wilson said. "Catch it, kill it."