Food ReJafions of Fresh-Wafer Fishes. 493 



(Pomoxys) from three quarters of an inch to an inch and a 

 half, and six indeterminable specimens, probably Lepomis, from 

 seven sixteenths to five eighths of an inch long. A single 

 sheepshead an inch and an eighth in length had eaten Chiron- 

 omus larvae (seventy-five per cent.) and larvae of the "river 

 fly" (Hexagenia). A single grass pickerel about an inch and 

 a quarter long had taken about sixty per cent, of its food from 

 Eutomostraca and young Amphipoda, the remainder consisting 

 of little fishes. 



The first food of the common white-fish was determined 

 experimentally, the breeding habits of this species making 

 direct observation impossible. Three hundred and forty very 

 young fry fed with fragments of the brook shrimp, Gammarus, 

 in a hatching house, were examined in January, 1881, and 

 thirty-five of them, which had apparently taken food, were dis- 

 sected. Minute fragments of Gammarus were found in but 

 eighteen of these, while five contained minute insect larvaj, 

 four, Entomostraca, and eight, small particles of vegetation, — 

 objects accidentally conveyed to them in the water of the 

 hatching house. In two hundred and forty-two others, con- 

 fined in spring water; only eight were found to have eaten 

 anything, and these had taken only Alga3 and vegetable frag- 

 ments. In February of the same year, fourteen specimens, 

 confined in a small aquarium and supplied with living objects, 

 plant and animal, from stagnant pools, were proven to feed 

 freely upon the smallest Entomostraca presented to them, — 

 chiefly Cyclops and Canthocamptus, ten of the fourteen eating 

 Cyclops, three Canthocamptus, and one a specimen of each. 



A little later, a more extensive experiment was conducted 

 by means of a large aquarium, in which there were placed sev- 

 eral hundred fry, kept constantly supplied with all the living 

 objects which a fine gauze net would separate from the waters 

 of Lake Michigan. Of one hundred and six of these, dissected 

 within the following fortnight, sixty-three had taken food con- 

 sisting almost wholly of the smallest Entomostraca occurring 

 in the Lake (a minute Cyclops and a slender Diaptomus). 

 The other objects encountered were rotifers, and diatoms and 

 other unicellular Algie, appearing, however, in such trivial 

 quantity as to contribute nothing of importance to the sup- 

 port of the fry. 



