Regardless of how it first ended up in America, how did this little exotic fish become the ultimate affordable pet?

Oddly enough, the government had a lot to do with it. The United States Commission on Fisheries received the first official import of goldfish from Japan in 1878. The Commission was only seven years old then, and as a publicity stunt, it offered free goldfish to D.C. residents. Throughout the 1880s and 1890s, these fish were bred in ponds in Washington and Baltimore, and anyone who sent a request through a member of Congress would receive one, along with a glass globe to keep it in.

At the height of this campaign, the Commission was distributing 20,000 fish annually, and nearly a third of households in the District owned pet fish from the Commission. According to a New York Times article from November 1894, "The business of distributing free goldfish to the people of the District of Columbia has become such a tax on the Fish Commission that it appears they must choose between running a goldfish bureau for Washington exclusively and conducting the legitimate work of the bureau."

In the 20th century, goldfish became a staple as prizes at fun fairs. Many American adults can remember seeing rows of single fish in plastic bags next to the sideshow games. It's a less common sight nowadays, likely due to all the fish that expired in hot plastic bags in the backseats of cars, or in the grip of overexcited children.

But the spread of these fish has had unanticipated consequences. Goldfish are members of the carp family. Their radiant color is the result of centuries of breeding -- first in China, where they were allowed to be owned only by members of the Song Dynasty, and then in American pet stores. But goldfish can also interbreed with common carp. When they're flushed down the toilet, or washed away from private ponds, goldfish find their way into American rivers and lakes, where they meet up with their cousins -- the food carp that were brought to American from Europe in the early 19th century.

Together, these fish breed prolifically and disrupt the ecosystem. They scour the bottom of rivers for food, vacuuming up practically everything in sight and leaving very little behind for the native forage fish. They can even eliminate frogs from an area by eating tadpoles. Their success at muscling out native species has made them a concern for conservationists.

As early as 1941, goldfish had become such a menace to game fish in Crystal Lake, California, that the state fish and game commission set out to eradicate them. They dragged the lake with bags containing a temporary paralytic affecting the gills of all fish, which enabled them to separate the goldfish from the other fish in the lake when they floated up to the surface. (The other fish were allowed to remain and recover, while the goldfish were scooped up and killed.) The Crystal Lake colony apparently originated the way many do: with a private individual deciding to set pet goldfish free into a local waterway.