The Wisconsin Department of Natural Resources (DNR) fisheries division has confirmed its workers found a giant snakehead fish in the Rock River between Janesville and Beloit earlier this month, the Milwaukee Journal Sentinel reported Tuesday. A year ago, discovery of northern snakeheadsa close relative to the giant snakeheadin a Crofton, Md., pond touched off concern among fisheries officials because the snakehead is a voracious, predatory fish that can wriggle short distances on land. The northern snakehead was described then as Frankenfish for its ability to survive in oxygen-depleted water, move from pond to pond and eat other fish. Maryland officials poisoned six adult and more than 1,000 juvenile northern snakeheads in that pond. The discovery of the 2-foot-long fish in the Rock represents the first time the non-native snakehead has been found in Wisconsin waters, and it underscores the states vulnerability to exotic species, the Milwaukee paper reported. This was a real wake-up call, said Mike Staggs, director of fisheries at the DNR. We have been concerned about people releasing the snakehead here in Wisconsin and this is prima facie evidence. If theyre worried about it in Wisconsin, fisheries officials elsewhere have to be worried, too. The Rock, of course, enters Illinois at South Beloit, flows through the Rockford area and eventually empties into the Mississippi River at Rock Island. For years, this columnist has been harping about the cost to all of us for the few people who want to bring non-native species into this country. True, many aquatic invaders arrive in the ballast water of ocean-going ships which then exchange that ballast water once they enter the Great Lakes. But a lot of people who bring in exotic species are doing so to have them as pets or for food. Officials believe that is how live snakeheads got into the U.S. from China and the Far Eastto be used as food. At least 17,000 snakeheads have been important live by Asian fish markets and pet stores since 1997, according to a CNN Web site report. And snakeheads have been spotted in six states besides Maryland. Controlling and repairing the damage from invasive species, including the snakehead and other aquatic pests like mitten crabs and zebra mussels, costs the United States an estimated $10 billion a year, according to the CNN story. With the appetite of a northern pike or muskie, the giant snakehead can grow past 3 feet and is capable of eating loads of native Wisconsin fish, said the Journal Sentinel. With no natural predator, it could alter the resident fish population or introduce new diseases. For years, Wisconsin officials have been concerned about an array of invasive speciesfrom sea lampreys to zebra musselsthat threaten to destroy native aquatic communities, said the Milwaukee paper. More recently, they have been keeping an eye out for Asian carp, another exotic fish, which has been found on the Mississippi River and the Illinois River. A 38-pound Asian bighead carp also was found in Chicagos McKinley Park Lagoon, within a few miles of Lake Michigan this summer. A native of Southeast Asia, the snakehead species can grow to more than 40 pounds, and according to the Wisconsin DNR, can be purchased in pet shops or at fish markets in metropolitan Chicago. The Wisconsin DNR found the giant snakehead during a routine fish survey of the Rock River on Sept. 4, reported the Journal Sentinel. However, the snakehead was misidentified by a DNR employee who threw it back after mistaking the snakehead for a bowfin (dogfish), a fish native to Wisconsin that bears a close resemblance. DNR crews photographed the fish before releasing it. An employee of the department later concluded that it was a snakehead, Staggs said. The DNR sent two crews back to the Rock River on Thursday and three more crews back on Tuesday to look for any evidence of snakeheads, Staggs said. They found nothing. After working parts of the river between Janesville and Beloit and finding no other snakeheads, Staggs does not think the fish is widespread in the river. The best bet, he said, is that a hobbyist tired of having such a large fish in his aquarium released it into the river. Releasing aquarium fish into the wild in Wisconsin is illegal, the DNR said. One saving grace for the Rock, or any other Wisconsin river where the fish might have been released, is that the giant snakehead cannot tolerate cold water. Staggs said he thinks the fish could not survive a Wisconsin winterunless it inhabits waters near power plants, where the water is warmer. There are power plants on the Rock, including at Byron in Illinois. Warmer water is discharged into the Rock from the Byron plant. The Wisconsin DNR would like to see legislation banning the ownership of snakeheads. The U.S. Fish and Wildlife Service has listed all snakeheads as injurious species, meaning the federal government bans importing, or moving the fish within the United States. The ban does not make it illegal to own the fish in Wisconsin, however. Kevin Boettcher, an employee at Aqua Exhibits in Milwaukee, said his shop was selling snakeheads as recently as six months ago. But because of the restrictions on sales in neighboring states, the fish have been hard to find. They were pretty popular, he said. They are aggressive. They eat other fish, and some people like to see that. Snakeheads are known to be very durable fish that can live out of water for hours, and even days if kept moist. Some species can burrow in mud in a drying pond and live for months before water returns, said the Milwaukee paper.