104 ILLINOIS BIOLOGICAL MONOGRAPHS [104 



the bottom, largely Ephemerida and Plecoptera, Chironomus and an 

 assortment of adult insects picked up off the surface during the summer 

 when the fish occasionally come to the surface on a quiet evening. The 

 fishes eaten are usually in such a state of digestion that identification was 



Table 26 



THE PERCENTAGE OF VARIOUS ITEMS OF FOOD OF THE CISCO 

 THROUGHOUT THE YEAR IN OCONOMOWOC LAKE 



utterly impossible, but scales found in the stomach has hinted that these 

 are often young of the cisco itself. The vegetable matter includes algae and 

 plant debris from the bottom. The inorganic matter is largely fine silt or 

 sand, taken in as the fishes nose around on the bottom. The miscellaneous 

 item includes forms not found in any great numbers, such as water mites, 

 rotifers (Anuraea) and unidentifiable matter. 



Certain facts in connection with the food habits deserve mention. 

 During the winter months it is a common occurrence to find a stomach 

 simply packed with entomostraca. One such stomach, from a fish 31 cm 

 long and weighing 446 grams, was carefully washed out and the contents 

 preserved in alcohol. This mass was then diluted in 250 cc of alcohol 

 and five samples of 2 cc each were carefully counted on a squared plate. 

 The average of the five counts gave the following: 



Daphnia 541 ; in 250 cc 67,625 



Cyclops 263; in 250 cc 32,875 



Bosmina 121; in 250 cc 15,125 



Total: 115,625 



This gives some idea of the tremendous numbers of organisms these fish 

 consume. A stomach was found in January, 1924, which contained nothing 



