Food Bdiitions of Frcsli-Wnter Fishes. 495 



Chironomus larvio, but for all the rest, one of the smallest of 

 the Entomostraca (Canthocamptus). Ten young red horse 

 (Moxostoma), varying in length from an inch to two and 

 three fourths inches, had fed largely upon Protozoa, — especially 

 the largest of the specimens, — but the smallest of them had 

 taken a considerable amount of Entomostraca, — notably the 

 bivalve cyprids occurring on the bottom. Two of the com- 

 monest buffalo fish (Ictiobus), seven eighths of an inch long, 

 had eaten most freely of unicellular Algae (sixty-three per 

 cent.), the remainder of the food consisting of rotifers and 

 Entomostraca. Four of the river carp (Carpiodes), seven 

 eighths of an inch to two inches long, had fed like the 

 preceding, except that the Entomostraca amounted to nearly 

 half the food, while the rotifers were comparatively few. 



Young catfishes, only three eighths of an inch in length, 

 belonging to the genus Amiurus, but quite too small to be 

 specifically determinable, Avere filled with various Entomostraca 

 and Chironomus larv«. Other examples of this genus, making 

 thirteen in all, none longer than an inch and five eighths, had 

 fed almost wholly on Entomostraca and larvas of Chironomus, 

 the latter, however, composing seventy-four per cent, of the 

 food of all, and the former eighteen per cent. Six small stone 

 cats (Noturus), varying in length from seven eighths of an 

 inch to one and a half inches, had taken more Chironomus 

 larvai and scarcely any Entomostraca. 



A single dog-fish (Amia), one and three fourths inches 

 long, had eaten seventy per cent, of Entomostraca, a few 

 larvye of Chironomus, some small crustaceans, and aquatic 

 insects. Others of the species, under an inch in length, had 

 the intestine packed with Entomostraca. Of the common river 

 gars one, an inch and a quarter long, had filled itself with 

 minute Entomostraca, while two other specimens had eaten 

 only the smallest fry of fishes. 



To recapitulate, I find that, taking together the young 

 of all the genera studied, considering each genus as a unit, and 

 combining the minute dipterous larva3 with the Entomostraca 

 as having essentially the same relation, about seventy-five 

 per cent, of the food taken by young fishes of all descriptions 

 is made up of these elements. 



