Invasion of the Giant Goldfish

By Samba Lampich

The tranquil, quiet waters of Lake Tahoe, the country’s highest alpine lake, have been invaded by monster goldfish, weighing several pounds and measuring more than a foot long.

A group of researchers from the University of Nevada at Reno (UNR) discovered and documented the oversized fish, and they say this household pet is an unwelcome visitor to the freshwater lake.

From Home to Lake

Researchers say aquarium dumping is to blame for the invasion. Owners don’t think twice about emptying their aquariums into lakes, which may contain no fish but might have fertilized eggs.

The goldfish in Lake Tahoe grow faster and bigger than in a bowl or aquarium because they have a high-protein diet, which increases their weight, and they feed more often. They are also exposed to warm water, which hastens their growth. They have few predators, allowing them to grow larger and rapidly reproduce.


Photo credit: Heather Segale, UC Davis

Disrupting the Ecosystem

The giant goldfish out-compete native species, such as trout, for food, leading to the decline of native fish. They also harm the lake clarity by rooting around the sediment for food and fueling algae growth with their waste, which interferes with food sources, disrupting the ecosystem’s food chain.

The California Department of Fish and Wildlife, Tahoe Regional Planning Agency and UNR partnered on a pilot project to remove warm-water fish species, such as large-mouth bass, from the Tahoe Keys during the summers of 2011 and 2012. Although only a small fraction removed in 2012 were goldfish, researchers found pregnant fish, which indicates that they are breeding quickly. Efforts to eradicate these invasive species will continue through the summer of 2013.

Classroom Discussion

  • What species of fish are goldfish and how were they domesticated?
  • How and why are non-native species of animals and plants introduced into an ecosystem? Could there be any benefits?