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Dumping pet goldfish into reservoirs can turn them into predators

Posted at 1:59 PM, Apr 27, 2021
and last updated 2021-04-27 16:57:34-04

ST. GEORGE, Utah — Dumping unwanted goldfish or other aquatic pets into reservoirs might seem like a humane way to dispose of them, but these invasive species can wreak havoc on fisheries, the St. George News reports.

Problematic fish include large koi in the Baker and Ivins Reservoirs, though nearly all community fisheries in the St. George area have them, the Utah Division of Wildlife Resources (DWR) says.

“Koi are not very desirable for table fare, and they compete with species like rainbow trout that people tell us they want to catch,” said Southern Region Aquatic Program Manager Richard Hepworth.

“Smallmouth are a very direct threat to the native species within the Virgin River system. If they got out into the river system, not only would they compete, but more likely they would prey on and eat these native species that we’re trying to keep from being endangered, ” Hepworth added.

In 2015, the population of smallmouth bass overwhelmed the Gunlock Reservoir; DWR treated the entire reservoir with rotenone, a pesticide so powerful it will kill all fish in the treatment area.

“We try to do removal efforts,” Hepworth said. “If you catch a smallmouth bass in Quail Creek, it’s against the law to let that go: you have to kill that fish. With these koi in community fisheries, such as Ivins, I’d encourage them (fishermen) to kill those fish.”

Though some like the sport of catching a large koi, they will disrupt the ecosystem in the waterway where they are dumped.

“It is against the law to release a pet into a pond or lake in the wild,” Hepworth said. “You’re doing a lot of damage. We don’t necessarily want to give people tickets or citations, we just want the people not to do it. That’s the bottom line.”