Goldfish booming in Hamilton Bay.

Posted on April 18th, 2019

Beneath the murky surface of Hamilton Harbour thousands of giant goldfish are teeming, tearing up vegetation and threatening native species. But now, thanks to a first of its kind study, researchers are have a new weapon in the battle to keep the harbour from becoming a giant goldfish bowl. It’s called acoustic telemetry. About a dozen of the fish were sedated and fitted with sound-emitting tags about the size of an AA battery, allowing scientists with Fisheries and Oceans Canada to track where they move.

“There’s only one other study of goldfish in a fresh water system and that’s in a river, so there are no other telemetry studies on goldfish in freshwater lakes,” explained aquatic research biologist Christine Boston. It might be hard to believe, but many of the bulky, pumpkin-coloured behemoths pulled from Cootes Paradise and other area wetlands most likely began their lives in fishbowls or backyard ponds. “Lots of people have goldfish as pets and don’t always get rid of them the right way,” said Jennifer Bowman, an aquatic ecologist with the Royal Botanical Gardens (RBG) in Burlington. “That’s how they got into these areas and they’ve been able to survive.”

Millions of eggs and an explosion of goldfish.

Not only survive, but thrive. In 2018, staff at Hamilton’s fishway —designed to keep carp out of the marsh— pulled out 1,690 goldfish. Three years ago, that number was closer to 2,500 large goldfish, along with about two million young. “They’re one of the most dominant fish in the fish community,” said Boston. “They’re in the top 10 for most abundant that we have.” That explosion of goldfish has only happened in the past decade or so.  The early 1990s saw just a few of the invaders, but in 2012 low water levels allowed researchers to pull out about 8,000 carp, allowing aquatic vegetation to grow like crazy, according to Bowman. With the carp gone and plenty of plants to scatter their eggs in, millions of baby goldfish were born. A mature female goldfish can lay up to 100,000 eggs, said Bowman, and they’re capable of spawning multiple times in a season. “When there’s a million babies produced, even if not of them survive that’s still a lot of fishing growing up.” – Article courtesy CBC News

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