MADISON, Wis. — Wisconsin and Minnesota scientists are studying a little-known and vulnerable fish whose disappearance could mean smaller musky, pike and walleye in the states’ inland lakes.

The Wisconsin Department of Natural Resources is three years into its first comprehensive study of the cisco, a slender white fish that scientists say is an important food for other fish and may serve as an early warning of problems in fisheries.

“Cisco are a key component to how a lot of lakes operate,” said John Lyons, a DNR fisheries scientist on the study.

Lyons and two other Wisconsin scientists have chosen nearly 200 public and private lakes with good cisco habitat. They’re trying to measure the abundance of the fish in Wisconsin’s lakes where sometimes the only evidence comes from old photos, rumors or inadvertent catches from unrelated studies.

They’ve never focused solely on cisco, which some anglers call lake herring or tullibee. Results from the study will become a foundation scientists will use as they assess which fish are at risk of disappearing.