492 Illinois State Lahoratonj of Natural History. 



SUMMARY OF THE FOOD OF THE YOUNG.* 



By an examination of three hundred and seven specimens, 

 representing twenty-seven species, twenty-six genera, and twelve 

 families of Illinois fishes, I learn that the food of many species 

 differs greatly according to age, and that, in fact, the life of 

 most of our fishes divides into at least two periods, and that of 

 many into three, with respect to the kinds of food chiefly 

 taken. 



In the first of these periods a remarkable similarity of food 

 was noticed among species whose later feeding habits are widely 

 different. The full grown black bass, for example, feeds prin- 

 cipally on fishes and crayfishes, the sheepshead on mollusks, 

 and the gizzard shad on mud and Algge, while the catfishes are 

 nearly omnivorous; yet all these agree so closely in food when 

 very small, that one could not possibly tell from the contents 

 of the stomachs which group he was dealing with. 



I will now summarize the facts concerning the earliest 

 food of the principal species, taken seriatim. 



The food of six common perch (Perca Intea) from an 

 inch to an inch and a quarter long, consisted wholly of Ento- 

 mostraca (ninety-two per cent.) and minute larvse of Chiron- 

 omus. No very small white bass (Labracidse) were found, the 

 youngest being an inch and a quarter long. Half the food of 

 this consisted of Entomostraca, and the other half of minute 

 gizzard shad. Forty-three sunfishes (Centrarchidse) from five 

 eighths of an inch to two inches long, had made ninety-six per 

 cent, of their food of Entomostraca and the small larvse of 

 gnats (Chironomus) already mentioned, seventy per cent, of 

 the first and twenty-six of the second. This group comprised 

 five specimens of black bass under three quarters of an inch 

 in length, two rock bass of similar size, two of the large- 

 mouthed sunfish (Chasnobryttus) from seven eighths of an 

 inch to an inch long, nineteen of the commoner sunfishes 

 (Lepomis) ranging in length from an inch to two inches, five 

 of the genus Centrarchus, one inch and under, four croppies 



* For detailed treatment of this topic see Bull. 111. St. Lab. Nat. 

 Hist., Vol. I., No. 3, p. 66, and No. 6, p. 95. 



