MADISON, Wis. (AP) — Scientists in Wisconsin and Minnesota are studying a little-known 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 a long-term study of the cisco, or lake herring. Cisco are slender white fish that need cold, clean water to survive. Wisconsin is studying about 200 lakes that at one time had the fish. They say cisco are an important food for other fish and may serve as an early warning of problems in fisheries. Pete Jacobson, a fisheries research supervisor with the Minnesota Department of Natural Resources, says Minnesota scientists have found cisco may live in about 650 lakes there, but populations have rapidly declined since 1975.