G. Wagner, 1910
The deepwater cisco (Coregonus johannae) was one of the largest ciscoes in the Great Lakes. Its average length was 30 cm (12 inches) and it was about 1.0 kilogram (2.2 pounds) in weight. Occurring only in Lakes Huron and Michigan, and inhabited waters between 50 and 150 metres deep, it was difficult to distinguish from other ciscoes and was possibly the same species as the shortjaw cisco (Coregonus zenithicus). The deepwater cisco was distinguished by usually having fewer than 33 gill rakers, relatively long pectoral fins, and unpigmented jaws. It was a silvery colour with a pink or purple lustre and a green or blue back. It spawned in August and September, earlier than most other ciscoes and, because of its large size, the deepwater Cisco was heavily fished commercially.
The last specimens of deepwater ciscoes were recorded in Lake Huron in 1952 and Lake Michigan in 1951. The main reasons for its extinction were competition from the invasive alewife and predation by the introduced sea lamprey.