CX1V 



FISHES OF ILLINOIS 



A more precise statement and a fuller discussion of the 

 ecological relations of our fishes, including statistics of com- 

 panionship for the various species, as shown by the frequency 

 of their joint occurrence in collections, must be left for later 

 contributions. 



Attention may be profitably called, in conclusion, to the 

 economic significance of the details of distribution of the various 

 species, as influenced both by geographical and ecological con- 

 ditions, since a proper understanding and application of these 

 facts will prevent wasteful efforts to introduce species where 

 they do not belong and can not thrive. Indeed, the more de- 

 tailed our knowledge of favorable, and even optimum, conditions 

 for the different species, and the more exact, also, our acquain- 

 tance with the relations of each species of fish to its companion 

 species in any associate assemblage, the more intelligent, and 

 hence the more successful, in the long run, will be our efforts to 

 extend the range and multiply the numbers of the more useful 

 species and to lessen the numbers of those especially injurious. 



*The figures of this table, except those in the columns for available collections, are ratios 

 of frequency of the species in our collections, computed with due reference to the comparative 

 numbers of collections of all kinds made in each situation. 



