How did an Amazonian fish invade a California pond?

A California fisherman’s latest catch had an unexpectedly human grin.

When Juan Gallo cast a line in a Petaluma, Calif., pond, he expected to pull up a typical fish, perhaps a catfish. Instead, he reeled in a pacu fish, a relative of the piranha with humanlike teeth.

The problem: Pacu fish aren't native to California and are illegal to own in the state. But they are widely available in pet stores throughout the United States.

"It landed on the dirt and you could tell it wasn't anything we had seen before," Mr. Gallo told The Press Democrat. He said he would first try giving the fish to the California Department of Fish and Wildlife or consider getting it stuffed and keeping it if officials did not want it.

Invasive species can be highly disruptive to their newly adopted ecosystems. In Florida, Burmese pythons and, more recently, even Nile crocodiles, pose an onerous threat to the state's native wildlife. Reports suggest 99 percent of south Florida's raccoon population and 98 percent of its opossum population have been destroyed from invasive species.

Outside of Florida, invasive species are also wreaking havoc in the Great Lakes region. The Great Lakes now contain a large population of goldfish, known as golden carp, and their cousins the Asian carp.

The golden carp is being hailed as an example of an ambivalent non-native species, which doesn't harm the ecosystem, and is actually helping local fisherman turn a profit. However, the Asian carp is another story entirely.

The Asian carp likely found a way into the Great Lakes by traveling up the Mississippi River. It's seen as a threat to the local ecosystem and the $7 billion fishing industry.

"It's very sobering," Marc Gaden, spokesman for the Great Lakes Fishery Commission, told the Associated Press. "Lake Erie is one of the most productive inland fisheries in the world. It wouldn't be as valuable by any stretch of the imagination if one out of every three pounds of fish were Asian carp."

So as new invasive species continue to pop up in areas where they aren't wanted, like the pacu fish in California, Nile crocs in Florida, and carps in the Great Lakes, what can be done to help?

Chowing down could be a good start. Whole Foods in Florida is now offering the invasive lionfish as an alternative snack. Shoppers with an appetite for the unusual could help reduce the number of the invasive species in their local lakes and rivers. And the principle of using invasive species for food to cut down their numbers has been propagated by other sources as well.

The Institute for Applied Ecology began an Eradication by Mastication campaign and sponsored an Invasive Species Cook-off in Florida. Turkey, bullfrogs, wild boar, garlic mustard, and kudzu were highlights on the menu.

Alternatively, Indiana has had some success combatting the influx of Asian carp with a two-mile-long, 7.5-feet-tall wall. The Eagle Marsh berm helps keep Asian carp that find their way into the marsh from using flood waters during heavy rain events to sneak into Lake Erie, as The Christian Science Monitor reported earlier this month. Ideally, the wall would be deconstructed once the threat of Asian carp and other invasive species is brought under control.

"My dream is that one day we can tear down this berm," Betsy Yankowiak, director at Little River Wetlands Project, which co-owns the marsh where the berm is built, told the Monitor.