34 The Food of Fishes. ' 



I shall give here a description of the food of the family, 

 based upon a study of the contents of seventy stomachs 

 representing fifteen species, collected in all parts of Illi- 

 nois, in several months of four successive years. These in- 

 dicate much more than their number would imply, since 

 from those collected at each time and place, as many were 

 commonly studied as were necessary to give a full idea of 

 the food of the species then and there. The different in- 

 dividuals from the same date and locality usually agreed 

 so closely in food, that the study of from two to five gave 

 all the facts obtainable from several times as many. The 

 data here given, therefore, really exhibit the food of the 

 family at different seasons in twenty-nine localities with- 

 in the state. 



The genus Pleurolepis is comparatively rare in Illinois, 

 as there are few of the sandy streams in the state, which 

 it inhabits. Seven individuals were examined — four of 

 P. pellucidus and three of P. asprellus. The food of these 

 specimens was remarkably uniform^the only elements 

 found being the larvae of small Diptera and ephemerids. 

 Eighty-one per cent, of the food of all consisted of the 

 larvae of Chironomus,* — a small, gnat-like insect, — twelve 

 per cent, of the larvae of other small Diptera, and the re- 

 maining seven per cent, of ephemerid larvae (May-flies). 



Twelve specimens of the genus Alvordms were studied — 

 seven of maculatus and five of phoxoGephalus. These rep- 

 resented five different localities and dates. This is a lar- 

 ger species than the preceding, and to this fact is probably 

 due the predominance (seventy-five per cent.) in its food 

 of the larvae and pupae of May-flies (Ephemeridae). These 

 included four per cent, of the larvae of Palingenia hilineata,, 

 Say, one of the largest ephemerids in our streams. The 

 remaining kinds were larva; of dragon-flies (Agrionidae), 

 four percent., larvae of Chironomus, seven percent., Co- 

 rixa tumida, Uhl., thirteen per cent,, and Cyclops, one per 

 cent. 



*The larvae of Chironomus are amonp the most important elements of 

 fish food in our waters, appearing in abundance in the stomachs of the 

 young of a great variety of species. They have been too little studied 

 in this country to allow specific determination. 



