Goldfish infestations threatening native fish species in B.C. lakes

Don Agnew of Penticton, B.C., enjoys spending his retirement fishing on picturesque Yellow Lake southwest of the city.

But two years ago he raised the alarm about the invasion of a non-native species lurking in its depths.

Much to his surprise, Agnew hooked a pair of goldfish, which likely came from a household aquarium.

Concerned, he contacted environment officials and the media.

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“They’ll clean up the food supply that the trout and the kokanee rely on,” he said on Thursday.

Goldfish are native to eastern Asia and continue to proliferate in B.C.’s lakes and rivers.

In June, officials closed Lost Lake near Terrace, B.C., to recreational fishers due to a goldfish infestation.

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Gail Wallin, the executive director with the Invasive Species Council of BC, said the non-native species poses ecological trouble.

“When you introduce a voracious feeder like the goldfish, which will grow to a kilogram in size, that will outcompete many of the native fish that are in there,” she told Global News.

Goldfish have also been shown to prey on native fish species and can disturb sediment while feeding, which increases water turbidity.

The Okanagan and Similkameen Invasive Species Society (OASISS) said it discourages the release of pets such as goldfish into local lakes and wetlands.

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“Such introductions are inhumane and illegal,” executive director Lisa Scott said in a statement.

“Often the non-native species reproduce and thrive, causing untold impacts to our native fish and wildlife though spread of disease, predation and direct competition for food.”

The Ministry of Environment and Climate Change Strategy received its first report of goldfish in Yellow Lake back in 2015.

When Global News requested an update on the ecological preservation efforts at Yellow Lake, the ministry said the issue is still being studied with findings expected next year.

“The Yellow Lake goldfish are surviving over winter and the temperature tolerances of goldfish and their ability to survive in BC lakes will be looked at as part of the risk assessment,” the statement said.

Wallin said the most effective way to eradicate the pesky intruder is to poison them with a natural pesticide called Rotenone.

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“If you’ve got goldfish that you need to get rid of, you’re going to actually have a ripple effect on some of the native fish there, so you’re going to watch the timing of it and you’re going to want to reintroduce that, but then you can actually restore that lake back to its natural ecosystem,” she said.

Meanwhile, anglers like Agnew hope the goldfish will be eradicated from Yellow Lake before they pose a greater threat to trout and kokanee populations.

“I know they’re dragging their heels — they always have — but just get them to do something,” he said.