Posted by Cheva Heck, Lake Tahoe Basin Management Unit, U.S. Forest Service in Conservation

Brianne O’Rourke, with the California Department of Fish and Wildlife, holds a large goldfish found in the Tahoe Keys of Lake Tahoe. (Photo courtesy of the California Department of Fish and Wildlife)

Lake Tahoe, the country’s highest alpine lake, is no goldfish bowl.

But U.S. Forest Service fish biologists with the Lake Tahoe Basin Management Unit said they’re well-acquainted with the big goldfish – several pounds and up to 4 to 8 inches long – living in the large freshwater lake along the border between California and Nevada.

The warm-water fish recently made the news when University of Nevada researchers displayed photos of an enormous goldfish found in Lake Tahoe. While the goldfish may seem innocent and beautiful in a glass fish bowl, they like other invasive species can wreak havoc on the lake’s natural ecosystem.

Invasive species can harm native fish by destroying their habitat, preying on them directly or interfering with their food source. In the case of the giant goldfish, researchers believe they may actually be harming lake clarity by fueling algae growth with their waste. When biologists find warm water fish during surveys, they remove them.

Forest Service biologists have surveyed streams in the Lake Tahoe Basin since 2007 looking at numbers of native fish versus invasive species. They found that nonnative species such as brook trout, rainbow trout, blue gill and brown bullhead accounted for more than half of the fish surveyed.

“We’re already seeing some of these invasive species move upstream, but we’re expecting the expansion to greatly increase if we don’t continue and even increase control efforts in Lake Tahoe’s near-shore environment,” said aquatic biologist Maura Santora.

Climate change plays a role in that potential increase.

“As Lake Tahoe’s waters warm, invasive species can more easily breed in the near shore and travel to other parts of the lake,” said Sarah Muskopf, a fish biologist with the agency. “We’re most concerned about marinas, canals and wetlands that are closely connected to Lake Tahoe.”

Lake Tahoe Basin Management Unit staff work with a multitude of partners, including the California Department of Fish and Wildlife, the University of Nevada at Reno, and the Tahoe Regional Planning Agency, to complete the surveys and on other invasive species prevention, control and eradication efforts.

However, it’s the public that may have the greatest role to play in stopping this threat.

“We believe that these goldfish were originally introduced to Lake Tahoe by well-intentioned pet owners,” said Santora. “If we can persuade the public not to release their aquarium fish or leftover bait fish into the lake, we will have made a critical step in addressing the problem of invasive species.”

And for the record, the largest goldfish on record, according to Guinness World Records, was recorded in 2003 as being 18.7 inches from snout to tail-fin. The weight was not provided.

Forest Service crews survey fish species in Lake Tahoe Basin streams. Data shows that invasive species now outnumber native fish. (Maura Santora/U.S. Forest Service)