“Monster” Goldfish Multiplying in Lake Tahoe: Freshwater Species of the Week

Giant goldfish have been found breeding in Lake Tahoe. Photo: University of Nevada, Reno

I’m posting Freshwater Species of the Week a day early because I just caught wind that biologists have discovered “monster” goldfish breeding in Lake Tahoe.

I visited Lake Tahoe a few winters ago, and can say with experience that it’s a stunning natural gem. Snow-capped peaks ring the crystal-clear blue water, which supports a diverse ecosystem.

The lake is a huge draw to tourists to the California-Nevada border. The region supports a booming ski industry, although locals told me it seems even busier in the summer, when city dwellers pour in to swim, boat, hike, and cycle, or just cool off in the serene waters.freshwater species of the week

To keep Lake Tahoe as pristine as possible, a team of biologists from the University of Nevada, Reno (where Water Currents’ own Zeb Hogan is based!) and California State Fish and Game patrol its waters throughout the year. They are monitoring invasive species like largemouth bass. The scientists use electric probes to stun fish, and then they scoop them up with their nets to count and examine them.

As KCRA in Sacramento reports, researcher Christine Ngai of the University of Nevada, Reno, said, “You can get 200 fish in one scoop.” (We reached out to Ngai and are hoping to speak with her.)

But hungry bass is not all that the scientists pull up. “You just see this bright golden orange thing starting to float up, and you’re like, what is that?

“Then you take your net and scoop it up, and it’s like, it’s a goldfish,” said Ngai.

Some of these non-native fish have reached almost a foot and a half long in the lake. And they seem to be multiplying, say the scientists. In one day, Ngai and her colleagues caught 15 in one small part of the lake.

How Did Goldfish Get There?

KCRA suggests that goldfish may have been released in the lake by well-meaning pet owners. A commenter on Huffington Post also noted that goldfish are often used as cheap bait for bass, so that seems to be another plausible intro point, if they wiggle off the hook, or if fishermen empty their bait buckets at the end of the day.

Ted Thayer of Tahoe Regional Planning Agency told KCRA, “Those small things people do can have a large impact, when you consider that it’s probably not just one person doing it.”

For now, goldfish aren’t thought to be as big a problem as the non-native bass, since they are outnumbered 100 to 1. But the fact that they are new arrivals, and are breeding, is pause for concern. The researchers also point out that goldfish can have big appetites, and they excrete a lot of nutrients, which can dirty that clear water and stimulate algae to grow.

Tahoe, like most of the world’s lakes, is already facing stresses, from pollution to climate change. Non-native species often can tip the balance to a radically different ecosystem.

goldfish caught in lake tahoe
Invasive species, not pets. Photo: University of Nevada, Reno
Invasive largemouth bass pulled from Lake Tahoe. Photo: University of Nevada, Reno