Supersized goldfish are threatening native species in this region of Canada

For those who ever wondered what would occur to your goldfish within the wild, then take a have a look at these giant examples. Pet goldfish released into stormwater ponds have gotten a supersized problem in Canada.

The fish, native to East Asia, are ‘intermediate growers’, meaning they will proceed to grow throughout their lifetime and can grow larger if conditions are right.

While it’s a myth that goldfish only grow to the dimensions of their tanks – living in an enclosure that is just too small for them causes the fish stress, which stunts growth – in the best conditions, goldfish will grow greater than those you commonly see in pet shops.

By releasing hormones, they’re even in a position to regulate their size and people of the fish around them, depending on the provision of natural resources. And with such abundant food sources in Canada’s waterways, they’re growing to epic proportions.

Where are the invasive goldfish living?

Scientists from Fisheries and Oceans Canada have been tracking the movements of invasive goldfish for quite a lot of months now using acoustic tags – a tiny sound-emitting device that’s attached to the fishes’ belly.

In October 2021, biology professor Nick Mandrak from the University of Toronto Scarborough discovered over 20,000 goldfish living in a stormwater pond outside of Ontario.

“These ponds are extreme environments,” Mandrak told the university’s magazine.

“Not only is the water shallow, oxygen levels are extremely low and temperatures can reach 30-plus degrees in the summertime.”

It’s their ability to survive in such harsh environments which is resulting in large shoals within the wild. Goldfish reproduce rapidly too, and this, coupled with their ability to thrive in water with low oxygen levels, is worrying scientists.

As water oxygen levels fall because of climate change, they fear the fish may have a competitive advantage over native species, potentially resulting in monocultures, as Mandrak points out,“**Are we creating ‘super-invaders’** which are more likely to have incrementally greater impacts within the wild under climate change?”

Unlike many fish species, the goldfish can survive in water with toxic blue-green algae, and will even be helping it to grow.

How are these super-invaders affecting native fish?

In addition to being quick breeders, goldfish are also big eaters. Large schools of the fish can quickly destroy aquatic habitats by tearing through plants.

They’re eating habits kick up sediment too, which clouds the water and reduces sunlight levels, restricting plant growth.

In addition to stormwater ponds, the fish have been present in Ontario’s Hamilton Harbour, a key spawning site for native fish species like Northern Pike. Scientists fear they might even find yourself in Canada’s Great Lakes in the longer term if their numbers usually are not reduced.


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