Forget sewer-dwelling gators. Toronto biologists are saying it’s giant goldfish that should be worrying us.

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Last summer, biologists in Toronto discovered more than 20,000 goldfish in a single stormwater drain. Freed from the confines of a fishbowl, some had bulked up to three pounds. And don’t think you’re safe from supergoldies if you live outside of Toronto. Around North America, goldfish flourish in ponds built to capture runoff and rain.

Related: These goldfish learned to drive with the help of scientists

It turns out that goldfish, which originated in East Asia, are more than pampered pets. They’re climate change survivors who have learned to thrive in the warm and ever-fluctuating environment of stormwater ponds. They’ve even adapted metabolically to survive without oxygen for up to five months. Scientists are worried these puffed-up climate warriors could edge out native species as global warming further depletes oxygen levels in rivers and lakes.

Goldfish have a messy eating style that involves gulping fine sediment from river and lake bottoms and swirling it in their mouths before spitting it back out. Then they gobble whatever food separates from the sediment. This makes the water murky. Without enough light filtering through the water, aquatic plants can die and species that rely on vision for hunting may go hungry.

“Are we creating these ‘superinvaders’ that are likely to have incrementally greater impacts in the wild under climate change?” asks Nicholas Mandrak, a biologist at the University of Toronto Scarborough, as reported by Scientific American. Mandrak is one of the scientists studying the adaptations of pollution-tolerant fish.

Since stormwater ponds are usually isolated from waterways, experts are trying to figure out how to keep it that way. One strategy for separating supergoldies from more desirable fish is to place signs around ponds asking fish owners to not dump their unwanted pets. Additionally, land developers could be encouraged to build barriers between ponds and other waterways, or to stock ponds with largemouth bass and other native goldfish predators.

Via Scientific American

Lead image via Pixabay