Cisco (Coregonus artedii) Mortalities in a Southern Michigan Lake, July 1968

Mortalities of the cisco (Coregonus artedii) in Halfmoon lake, Mich., in summer 1968, were investigated, and oxygen and temperature conditions in the lake were compared with those in nearby Pickerel lake where no mortalities have been recorded and which was well stocked with the fish. The dissolved oxygen in Halfmoon lake was found to be severely depleted in the hypolimnion and the thermocline, apparently forcing the fish into the epilimnion where they could not tolerate the high temperatures. The dissolved-oxygen profile of Pickerel lake showed that conditions were more favourable for the survival of this fish.