The Michigan attorney general's office said David Shane Costner, 42, of Harrisburg, Ark., sold two grass carp last month in Midland to undercover officers from the state Department of Natural Resources. He had been driving around the southern part of the state selling the carp from store parking lots for use in ponds, where they eat nuisance plants, investigators said.

Grass carp are among four species of Asian carp that infested U.S. waterways after being imported decades ago to clear fish ponds and sewage treatment lagoons of unwanted vegetation or grubs.

Two other Asian varieties — bighead and silver carp — have migrated up the Mississippi and Illinois rivers and are poised to invade the Great Lakes, where scientists say they could out-compete native fish for food. The federal government has spent more than $100 million on an electric barrier and other steps to keep them out.

"Invasive species in general and the Asian carp in particular pose one of the most serious current threats to the economy and the ecology of the Great Lakes," DNR Director Rodney Stokes said.

Possession and sale of live Asian carp is illegal in Michigan.

Bighead and silver carp are a particularly serious threat because they eat plankton — microscopic plants and animals that are essential components of aquatic food webs.

Grass carp eat larger vegetation, which makes them attractive to people wanting to rid ponds and lakes of weeds. But they have such voracious appetites that they can strip a water body of all plant life, hurting native fish that depend on the vegetation for habitat. They were declared illegal in Michigan in the late 1970s.

It's unclear whether Costner sold grass carp to anyone other than the two undercover agents, DNR spokesman Ed Golder said.

"We're still looking into that," he said.

Golder said Costner had 112 grass carp, which he kept in tanks inside a semi-truck. Officials said the words "grass carp" were imprinted on the side of the vehicle, along with the names of several legal species Costner was selling, including channel catfish, largemouth bass and fathead minnows.

Costner is charged with 10 counts of possessing an illegal species and two counts of selling an illegal species. Each carries a maximum sentence of two years in prison and a fine of $2,000 to $20,000. Costner is in Arkansas and will be arraigned in Michigan later, said Joy Yearout, spokeswoman for Attorney General Bill Schuette.

Calls to a phone listing for Costner went unanswered.

The Associated Press left a message seeking comment with Farley's Arkansas Pondstockers, which the attorney general's office said furnished the truck Costner was using.

Canadian border authorities in recent years have arrested several truckers hauling live Asian carp into Windsor, Ontario, after crossing the Ambassador Bridge at Detroit.

"Once destructive Asian carp enter our waterways, the damage cannot be undone," Schuette said. "We must remain vigilant and use every tool available to protect Michigan's tourism and sport-fishing industries from this dangerous threat."