CHICAGO (CBS) — Biologists at the Shedd Aquarium were hoping the addition of three Asian bighead carp to the Invasive Species exhibit would persuade visitors to help keep the voracious fish out of Lake Michigan.

Shedd vice president Roger Germann said the three Asian carp were caught in the Humboldt Park lagoon in October, and didn’t get there by themselves.

“The reality is it’s not connected to any waterways,” he said. “While we may never know how they got in there, I think all of us kind of agree that there’s a couple ways that we find invasive species like Asian carp making their way in these lagoons, through unintentional discharge of bait, or it could have been through an unintentional stocking at that time.”

Illinois Department of Natural Resources assistant director John Rogner said people can also help keep the carp out of the Great Lakes, by making sure they dump their bilge water and clean their boats before shifting from one body of water to another.

“Remove any visible mud, plants, fish, or animals before transporting equipment like boats and trailers, and things like that,” he said. “Don’t dump bait after a day of fishing, don’t dump that bait into that water body.”

The three bighead carp now in the Invasive Species display at Shedd range in length from three to four feet long, and in weight from 35 to 60 pounds.

Rogner said he’s confident that, between the U.S. Army Corps of Engineers and cooperation of boaters, Lake Michigan can remain free of bighead carp.

“I don’t think it’s a foregone conclusion that, in particular, that Asian carp will get in the Great Lakes. I think we have good defenses in place against them,” he said.

The Army Corps of Engineers has set up electric fish fences in the Chicago Sanitary and Ship Canal, which connects the lake to the Mississippi River. Officials also conduct extensive sampling of the canal to check for Asian carp.

The fish pose a significant threat to the ecology of the Great Lakes, to the point where several states have called for an order to close the Sanitary and Ship Canal.

So far, federal courts have rejected the lawsuits, and the U.S. Supreme Court has decided not to hear the cases.

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