The Food of FIs/u's. 31 



Food of the Young, 



Findinc; that the food of most fishes differs with age, I 

 have grouped the young according to size, and averaged 

 the food for each group separately, — the first group con- 

 sisting usually of those under an inch in length, the second 

 of those from one to two, etc. 



.. Two perch under an inch in length had eaten nothing 

 but Entomostraca — a1)out equal quantities of Cyclops and 

 Daphnias. It was not until the specimens reached an inch 

 and a half in length that insects of any considerable size 

 appeared in the food. A single smaller fish had eaten a 

 a few^ minute larvae of Ohironomus, but otherwise the food 

 at this age consisted wholly of Entomostraca. 



About thirty-four per cent, of the food of nine specimens 

 ranging from 1^ to two inches in length consisted of in- 

 sects, and sixty-six per cent, of crustaceans. The only 

 insects recognized were the larvse and pupae of Ohironomus 

 (eleven per cent. ), small water-bugs, — Corixa tumida^\J\i\.^ 

 C. alternata, Say, etc. (twenty-three per cent.), — and a 

 trace of larvte of May-flies (Ephemeridse). The Crustacea 

 were chiefly Cladocera and Copepoda — thirty-six per cent. 

 and twenty-four per cent, respectively. Four of the nine 

 had eaten small quantities of a small ami^hipod crustacean, 

 Allorchestes dentata, which is very abundant north, and 

 has, in fact, about the same distribution in the state as 

 the perch itself. The Cladocera were chiefly Daphniidae 

 (twenty-seven per cent.), including Daphnia pulex, L., Sl- 

 mocephalus americanus^ Birge, and Bosmina longirostvis. 

 Specimens of Chydorus and Pleuroxus made up the prin- 

 cipal part of the nine per cent, of Lynceidae eaten. The 

 Copepoda were all Cyclops and Diaptomus. 



Four specimens two and a half inches long, all taken at 

 Peoria, in November, 1878, had eaten nothing but Hemip- 

 tera (twelve per cent.) and Neuroptera (eighty-eight per 

 cent.). The Hemiptera were all Corixa alternata^ and 

 the Neuroptera were nearly all the extremely common 

 larva of one of our most abundant May-flies {PaUngenia 

 hilineata, Say). Larvae of small dragon-flies (Agrionini) 

 made five per cent, of the food. The simplicity of the 

 food of these specimens is probably due partly to the fact 



