Thousands of goldfish threaten a whole lake ecosystem

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Officials in the US are seeking information on the person(s) responsible for releasing goldfish into a Colorado lake.

The alien goldfish have multiplied so successfully that what may have started out as four or five unwanted pets released a couple of years ago into Teller Lake #5 in Boulder, has become a population of 4,000 or more.

"Goldfish are not a native species and are very harmful to the local aquatic ecosystem," said Kristin Cannon, district wildlife manager for Boulder. "We strongly encourage the public not to dump their unwanted pet fish in our waters. It is bad for our environment as well as illegal."

Fish that are being threatened by the goldfish include channel catfish, bluegills and sunfish.

Wildlife officials say they have two options: draining the lake and rebuilding the natural fish stock from scratch, or electrofishing the lake to collect the goldfish, which would then be sent to a raptor rehabilitation centre for food.

"Most people don't realise the far-reaching effects of introducing exotic species to the environment," said Ken Kehmeier, senior aquatic biologist for Colorado Parks and Wildlife (CPW).

"Non-native species can be devastating to native populations by causing disease outbreaks and creating competition unbalance. It's an issue that anyone concerned with our environment should know about."

Also of concern is the "bucket brigade" — anglers who choose to dump sport fish of their choosing into Colorado waters. While some non-native fish are stocked at times, aquatic biologists only do so after a rigorous biological assessment to determine what can be stocked and where for a balanced ecosystem.

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