|
In common with trouts and grayling, the members of the whitefish subfamily possess both an adipose fin and an axillary process in the angle of each pelvic fin. The whitefish subfamily is distinguished from the rest of the salmon family by the larger scales (fewer than a hundred in the lateral line), and smaller mouth with weak teeth. Coregonines are included in the Salmonidae based on advanced osteological characters. Coregonines are restricted to the northern parts of Eurasia and North America. The total range fits roughly within the glaciated areas. All species spawn in freshwater and all but a few are confined throughout their lives to lakes and streams. There are three principal groups of whitefishes in the Great Lakes: the lake whitefish (Coregonus, subgenus Coregonus), the ciscoes (Coregonus, subgenus Leucichthys), including "chubs" of the commercial fishermen, and the round and pigmy whitefishes (Prosopium). All of these and their varieties inhabited the clear, cold or cool waters of the Great Lakes and deeper inland lakes. Great Lakes Coregonus species are seriously depleted or extinct, now, and only careful regulation of the fishery can hope to restore the remaining populations. Many northern lakes have two or three forms of whitefishes that occupy different depths and have different numbers of gill rakers. They colonized separately or populations diverged from each other through local habitat choice, spawning time, and competition.
|