94 ILLINOIS BIOLOGICAL MONOGRAPHS [94 



THE CISCO LEUCICHTHYS ARTEDI (LE SUEUR) 



INTRODUCTION AND DESCRIPTION 



Among the most abundant of the food fishes of the great lakes is the 

 Lake Herring or Cisco, Leucichthys artedi (Le Sueur). Either this species 

 or a variety of it is an inhabitant of all the great lakes and is particularly 

 abundant in Lake Michigan, the southern end of which marks the southern 

 limit of the fish. It is found also abundantly in most of the larger lakes of 

 Wisconsin, and must be considered as a characteristic fish of the deeper 

 inland bodies of water of that state. In southern Wisconsin, within the 

 limits of Waukesha county, the species has been taken in the following 

 lakes: North, Pine, Nagawicka, Okauchee, Oconomowoc, Fowler, La 

 Belle, Upper and Lower Nashotah, Upper and Lower Nemahbin, Silver 

 and Dutchman's. In the largest lake of the county, Pewaukee, the species 

 does not occur as the lake is too shallow to accommodate it. 



The family Salmonidae comprises two great groups of fishes, the white 

 fishes or Coregoninae and the salmon and trout series, the Salmoninae. 

 Three genera make up the Coregoninae: Coregonus, the true whitefish; 

 Stenodus, a peculiar trout-like whitefish from the Mackenzie river, a 

 genus represented by a single species, mackenzii; and Leucichthys, the lake 

 herring or cisco, represented by about ten species, which may or may not 

 prove valid. The exact number of species is not known, as the ciscos are 

 extremely variable; hence it is probable that many of the present so-called 

 species will be shown to be synonymous. Variability is, as a matter of fact, 

 characteristic of the whole family. This variability, taken in connection 

 with the fact that no salmoid fish is known in a fossil condition except from 

 very recent deposits, forces the conclusion advanced by Gunther that the 

 group is of recent origin. Certain it is that, though the ciscos from the 

 above mentioned lakes are all alike in essential structures, if one is familiar 

 with the fish from the different lakes, it is possible to sort out a mixed 

 collection according to the lakes from which the fish came on the basis of 

 variations in color or body proportions, length and depth of caudal pe- 

 duncle, and other characters. Yet the writer believes that, until a much 

 more careful study of the genus Leucichthys is made than has appeared 

 to date, all the fish should be considered as merely local environmental 

 variations of the single species Leucichthys artedi. (Fig. 3.) 



Leucichthys artedi was described by Le Sueur in 1818 from specimens 

 taken in Lake Erie, near Buffalo, under the name of Coregonus artedi. In 



