70 



Thirty young suckers weic studied, representing tive genera of their 

 family. The very smallest were found feeding on Entomostraca only, and 

 it is possible that these usually ferm the first foofi of the family: but later 

 they resort to elements still more mirnite: viz.. rotifers. I'rotozoa. and 

 unicellular Alga*, quantities of which were found in the intestines of 

 young suclcers six inches or more in length. Vouug stone rollers (H\'pen- 

 telium) not more than an inch and a half long, had taken chiefly iarva' 

 of Chironomus (ninety per cent.), the remaining tenth ijeing principally 

 Entomo.straca. A single small black sucker (Minytremai had eaten little 

 but Cyclops. Four chub suckers (Erimyzoni. two three-quarters of an inch, 

 and two an inch and a ((uarter long, had eaten only P^ntomostraca and a 

 trace of water mites. In two larger specimens, however, still minuter 

 forms were the leading feature of the food, including rotifers. Protozoa, 

 and unicellular Alga-. Another example, three inches long, had eaten a 

 trace of Chironomus larva-, but for all the rest, one of the smallest of 

 the Entomostraca (Canthocarai)tus). Ten young red horse (Moxostomai, 

 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 liad taken a considerable amount of Entomostraca. — 

 notably the bivalve cyjjrids occurring on the bottom. Two of the com- 

 monest l)uffalo tish (Ictiol)us). seven-eighths of an inch long, had eaten 

 most freely of unicellular Alga' (sixty-three per cent.i. the remainder of 

 the food consisting of rotifers and Entomostraca. Four of the river carp 

 (Carpiodes), seven-eighths of an inch to tw'o inches long, had fed like the 

 preceding, except that the Entomostraca amounted to nearly half the food, 

 while the rotifers were comparatively few. 



Young catflshes, only three-eighths of an inch in length, belonging to 

 the genus Amiurus, l)ut quite too small to be specitlcally determinable, 

 were filled with various Entomostraca and Chironomus larva^. Other ex- 

 amples of this genus, making thirteen in all. none longer than an inch 

 and five-eighths, had fed almost wholly on Entomostraca and larva? 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 iNo- 

 turus), varying in length from seven-eighths of an inch to one and a half 

 inches, had taken more Chironomous larva' and scarcely any Entomostraca. 



A single dogfish (Amia), one and three-fourths inches long, had eateu 

 seventy per cent, of Entomostraca. a few larva? of Chironomus. some small 

 crustaceans, and aquatic insects. Others of the species, under an inch in 

 length, had the intestine packed with Entomctstraca. Of the common 

 river gars one, an inch and a quarter long, had tilled itself with minute 

 Entomostraca, while two other specimens had eaten only the smallest fry 

 of fishes. 



To recapitulate, I find that, taking togetiier the young of all tlie genera 

 studied, considering each genus as a unit, and combining the minute dip- 

 terous larva^ with the Entomostraca as having essentially the same relation, 

 about seventy-five per cent, of the food taken In- young fishes of all de- 

 scriptions, is made up of these elements. 



From the above if is clear that young fishes in general depend at first 

 on Entomostraca and certain small insect larva' ichiefly those of two genera 

 of gnats), beginning with the suuillesf of fhese forms, or with those espe- 

 cially exposed to their attack. One-celled plants and animals are also 

 eaten freely by the young of two of the largesi families. 



Correlated with these facts. I find that two at least of the genera, which 

 are toothless when adult, have minute raptaforial teeth in this early stage, 

 viz., Coregonus and Dorosoma. Otherwise young Hslies liave no apparatus 

 siHH'ially adapted to the capture of their miiuite prey, but this is brought 

 within their reach merely by their own small size and the corresjxuiding 

 minuteness of their structures of food prehension. Later, as the larger 

 species grow, this apparatus becomes too coarse to retain objects so minute, 

 but other food resources are made available, usually througli some adaptive 

 modiflcat ioti of tlie fishes lliemselves. 



