CIV FISHES OF ILLINOIS 



Kaskaskia and the Big Muddy also. Species of the Ohio group 

 sometimes seem to spread into the headwaters of adjacent streams, 

 especially into the branches of the Kaskaskia where these come near- 

 est to the Embarras, and into those of the Big Vermilion of the Illi- 

 nois which are nearest to the Little Vermilion of the Wabash. Some 

 species, however, remain carefully within the tributaries of the Wa- 

 bash system. 



It seems possible that this appearance of an approach to the state 

 and entrance upon its territory from opposite directions is not alto- 

 gether deceptive, and that the annual movements of the fishes of the 

 state, up the streams at the time of the spring floods, downwards 

 with the recession of the waters, and still farther downwards, for 

 many species, into deeper water in the winter, may take these two 

 contingents of our fish population in opposite directions, from and 

 tow^ards local centers of population for the species, situated on oppo- 

 site sides of the state. Whether and where such local centers of 

 population actually exist, is a question which can not be answered 

 definitely for lack of numerical or statistical data in the faunal 

 lists and other literature of geographical distribution for the sur- 

 rounding states. If they exist, the Wabash fishes would constitute 

 one such system, and those of the Mississippi and its tributaries, 

 another. 



If we may speculate still further upon this subject, we may per- 

 haps surmise that a general critical analysis of the fish population of 

 the larger area of which Illinois forms the central part, would enable 

 us to distinguish fairly well-defined districts, each with its charac- 

 teristic assemblage of prevalent species, so associated and ecologic- 

 ally related as to form a balanced assemblage of species, all so ad- 

 justed to each other and so advantageously placed in their environ- 

 ment as to constitute a closed system, which the characteristic 

 species of adjacent areas can not enter, or in which they can not 

 permanently remain. 



Distribution chiefly in the Ohio Drainage 



Brindled stonecat Pirate-perch 



Green-sided darter Notropis illecebrosus 



Boleichthys fusiformis Ericymha buccata 



Chub-sucker Long-eared sunfish 



Distribution chiefly in the Mississippi Drainage 



Short -nosed gar White bass 



Stonecat Yellow bass 



Lake carp Common bullhead 



Notropis cayuga Short-headed red-horse 



