Food Belations of Fresh-Water Fishes. 499 



meager food resources of their localities. Two of the comnjon 

 blunt-jawed minnows (HijbognatJiNS nnchalis) had fed here 

 almost wholly upon mud mixed with Algte and miscellaneous 

 vegetation; while three of the little pirate perch (Aphredod- 

 erus) had eaten little but (Jhironomus larva, half the food of 

 one of the specimens being wholly small fishes, and insignif- 

 icant quantities of Entomostraca occurring in the stomachs of 

 the others. 



A small collection, made from the Little Fox River, in 

 White county, in southern Illinois, Oct. 5, 1882, of four speci- 

 mens each of Labidesthes and Zi/gonectes notatus enables us to 

 bring into comparison the food of two extremely different 

 species taken together from the same pools in a running stream. 

 The Labidesthes, although predaceous in habit and feeding 

 most commonly upon Entomostraca, was here giving its atten- 

 tion wholly to terrestrial insects, — more than two thirds of 

 them winged Chironomus; while the Zygonectes had eaten in 

 addition to thirty-seven per cent, of terrestrial insects (scarcely 

 any of them Chironomus imagos), about thirty per cent, of 

 aquatic vegetation, nine per cent, of Entomostraca, eleven per 

 cent, of aquatic insects, and fourteen per cent, of mollusks. 

 These differences in food have no apparent relation to the 

 essential structural differences of the species, but must be 

 considered an illustration of the various effect of like conditions 

 when applied to different species. 



On the other hand, three bull-heads (Amiurus nehulosus) 

 and six common perch (Perca) taken from Fox River, at 

 McHenry, May 9, 1880, did not differ remarkably in food, both 

 groups having eaten crayfishes, mollusks, aquatic insects, and 

 vegetation. One of the catfishes had taken another fish, and 

 one had eaten leeches. It is to be noted, however, that these 

 species are both bottom feeders, and that both lots of these 

 specimens had taken about the average food of their kind.* 



The above are examples of the food relations of fishes 

 widely separated from each other in the classification and 

 decidedly different in alimentary structures and in feeding 

 habits. Illustrations of the differences in food apparent in 



* See Bull. 111. St. Lab. Nat. Hist., Vol. I., No. 3, p. 35. 



