4-pound goldfish among invasive species at Tahoe

RENO — Researchers at Lake Tahoe are raising new concerns about non-native, warm-water fish invading the mountain lake’s chilly waters, including giant, minnow-gulping goldfish weighing as much as 4 pounds.

Studies in the mid-2000s prompted funding for a warm-water fish control program at the University of Nevada, Reno. Since the project began in 2011, scientists have removed thousands of fish, including about 90 goldfish, mostly on the south end of the lake around the Tahoe Keys.

It’s not clear why the goldfish are populating near-shore regions in Tahoe, but some suspect it most likely is from aquarium dumping. The problem is they eat native minnows, one of the main sources of food for naturalized species such as Mackinaw and trout.

“It is a big deal because it is not just in Nevada. This is something that has gone on throughout the country,” Nevada Department of Wildlife spokeswoman Teresa Moiola told the Reno Gazette-Journal. She said the Nevada Legislature in 2011 passed a law to make it illegal to dump invasive fish.

Christine Ngai, a fish researcher at UNR, thought it was an orange soda can or plastic cup the first time she spotted one of the unwelcome visitors back in 2006 near the Tahoe Keys in South Lake Tahoe, Calif.

“As it approaches you realize it is some sort of fish,” Ngai said. “And you scoop it up, remove the vegetation and there it is — a goldfish that is the size of your head.”

Since 2011, about 35,000 warm-water fish have been removed from water near Tahoe’s shore through the program, the vast majority of them large-mouth bass and bluegill. The minnow population declined 58 percent from 1988 to 2009, according to a UNR study.

Large-mouthed bass numbers spiked at Tahoe in the 1980s, Ngai said. Their numbers and the numbers of several other warm-water fish in Lake Tahoe have thrived in the region partly because of climate change, she said.

But the goldfish, even with its population well below that of its other warm-water brothers, might pose another threat.

“They end up excreting nutrients causing near-shore algae to grow, which affects the clarity of the lake,” UNR fisheries expert Sudeep Chandra told the Gazette-Journal.

Ngai described goldfish as omnivores efficient at eating and excreting, which creates algae growth and green water. She and other members of the non-native warm-water fish removal program will move into the third year of the three-year pilot program .

They count fish through electric shock, which stuns the fish in water. The shock lasts two to four seconds depending on the type of fish, Ngai said, and the mortality rate is low.

Invasive fish, such as the goldfish, are gathered and removed from the water. Ngai said the program will look to filet them and donate them to food banks.