Giant goldfish invasion warning by scientists in Alberta Canada

There is a giant goldfish invasion underway in Alberta, Canada, which has prompted local authorities and scientists to urge residents to refrain from flushing their unwanted aquatic pets down the toilet. Several goldfish, about the size of a small dog, are being pulled from lakes and ponds all over the province.

How big is a goldfish? The typical answer is ‘That depends on how large your fish tank is.’ So, if they grow to the size of their aquarium, what happens when there is no fish tank – do they just keep up growing and eventually become mega goldzillas?

Alberta zoologists are starting to answer that question, and that answer is rather disconcerting, and perhaps a little scary too.

Giant goldfish invasion in AlbertaWhen an invasive species spreads, it can push out native species and cause ecological chaos. According to The Nature Conservancy: “When a species is introduced—accidentally or intentionally—into a new landscape that is not used to its presence, the consequences can be devastating.” (Image:

Wild Albertan goldfish are growing

Invasive species experts in Alberta say that over the past few years, goldfish in lakes and ponds are getting bigger – they will probably continue growing, especially if there is lots of food about and plenty of space.

Since 2013, goldfish have been reported as far south as Lethbridge and as far north as Fort McMurray – an area spanning 800 kilometres (497 miles) says Kate Wilson, who recently joined Alberta Environment & Sustainable Resource Development (ESRD), part of the Alberta Invasive Species Council, as an engagement specialist.

In an interview with CTV’s Canada AM, Ms. Wilson said:

“It really is becoming an issue. Once released from your small aquarium, a lot of these species can get quite large because they’re not constrained by the size of the tank.”

Last summer, over thirty goldfish were pulled from a Fort McMurray storm pond – some of them more than eight inches (20 cm) long.

Goldfish length of small dogMany of the giant goldfish pulled out of the water in Alberta are over 20 centimetres long, that is about the same length as a Russell Terrier (smaller than Jack Russell).

Wild goldfish surviving cold Canadian winters

Evidence suggests that the goldfish are breeding and making it through Fort McMurray’s cold winters. If this is the case, which experts say is highly likely, their populations are increasing.

Wildlife experts say that the last thing Alberta wants is goldfish breeding in the wild like this – in effect, it means there is another major invasive species problem.

When an invasive species (not native to the location) thrives, some native species tend to suffer as a consequence. They can also be devastating not just for the environment, but also the economy.

Alberta has already reported a serious increase in invasive Prussian carp numbers, and is trying to prevent lampreys and zebra mussels from gaining a foothold.

These invasive species could disrupt the delicate balance of Alberta’s aquatic fauna and flora, gobbling up native fish species or competing with them for food and space.

Experts have not yet determined what impact invasive goldfish might have on native species, but their rapidly-growing population is disconcerting. Goldfish, which are avid eaters of fish eggs, can also compete successfully with native species for food.

Goldfish sizeMany factors determine how big a goldfish can become, including the available space, how many there are in that space, how much food there is, the quality of the water, and its genetic make-up. In Alberta they have plenty of space, lots of food, and excellent quality water – ideal conditions for growth.

Don’t flush pet fish down toilet!

According to the Alberta Fisheries Act, anybody caught flushing live fish down the toilet, or any contents of their home fish tank, is liable to a fine of up to CAN$100,000.

Flushing the contents of your aquarium down the toilet can spread foreign diseases into the ecosystem, as well as non-native plants and parasites, experts say.

Flushing a fish is definitely not a humane way of getting rid of it, Ms. Wilson pointed out. “It’s a really cruel thing to do to a pet. It will probably die a horrible death, but some of them are so robust that they will survive, and they will actually do potentially huge damage.”

Video – Giant goldfish growing and multiplying in Alberta

Kate Wilson talks about the giant goldfish invasion in Alberta and what the Government is doing to combat this problem.