Commercial fishermen caught a 47-pound bighead carp in the Mississippi River near Frontenac.
Department of Natural Resources officials said the catch last week adds weight to the evidence that Asian carp are moving upstream.
Bighead carp have been turning up occasionally in the St. Croix and Mississippi Rivers for 15 years. But the DNR said this bighead found in Lake Pepin is the largest yet.
Bighead and silver carp — both from the Asian carp family — are established in the Mississippi River in Iowa, the agency said.
The fish do not appear to be reproducing in Minnesota waters yet, said Tim Schlagenhaft, who studies Asian carp for the DNR.
"We've never caught multiple Asian carp of the same species at the same time," Schlagenhaft said. "It's always been kind of an individual catch. We've never had larger numbers of them, and we've never had any evidence of any natural reproduction, which is a good thing."
Many public officials fear Asian carp will upset the rivers' ecosystems if they outcompete other fish for food.
"They do consume a large quantity of plankton. They're big fish. They eat 10 percent of their body weight a day. And plankton are the basis of the food chain," Schlagenhaft said. "At current levels, I wouldn't anticipate any impact."
The Minnesota legislature set aside $7.5 million this year for Asian carp barriers, and a bill in Congress would close the Upper St. Anthony Falls Lock if the fish are found north of Hastings.
However, critics of those efforts say the cost is too high and the environmental consequence is uncertain.