304 BULLETIN OF THE BUREAU OF FISHERIES. 
QUALITATIVE AND QUANTITATIVE FOOD DETERMINATIONS. 
Perch were usually examined while fresh, but in a few instances they were preserved 
in 95 per cent alcohol before examination, as in the case of those collected in Oconomowoc 
Lake. In the laboratory the contents were stripped from the alimentary canal on a 
microscopic slide. A little water was added to the mass; it was then teased apart under 
a binocular microscope and after being well spread out was again examined with a 
compound microscope. The volume of all constituents of the food was estimated and 
recorded in percentages. As a rule, the larger constituents were counted, and in many 
instances the number of microscopic animals was also noted. It was not practicable 
to measure the volume of the food, because it was mixed with more or less mucous 
secretion, so that in the intestine it formed a cylindrical “string.” 
The total number of adult perch for which we made such volumetric percentage 
food estimates in the lakes studied was 1,147. Considering together those of various 
localities, habitats, and ages, the food, as a whole, was made up of 38.3 per cent insect 
larve, 21.4 per cent entomostracans, 9.5 per cent insect pup and adults, 6.1 per cent 
silt and débris, 5.5 per cent macroscopic Crustacea, 5.5 per cent plants, 4.5 per cent 
fish, 2.4 per cent molluscs, 1.4 per cent oligochzetes, + leeches, + arachnids. 
The maximum amount and number of the particular species of animals observed 
in the food have also been recorded, and a number of important examples are given in 
Table 10. No particular discussion of the different items in the food is necessary. 
Tables 6 to 9 show that entomostracans and insect larvae are most important; but 
there is also a good representation of other animals, plants, and mud from the lake 
bottom. 
SEASONAL VARIATION. 
Though the diet of perch is made up of the same general kinds of food throughout 
the year, there is considerable seasonal variation in all the important constituents, 
some of which are eaten only during certain months. The seasonal appearance of 
various items as constituents of perch food is represented graphically in figures 6 to 30, 
the curves showing the fluctuations in each throughout the year. From a study of these 
the annual food cycle may be outlined somewhat as follows: Perch at all seasons feed 
largely on or near the bottom. During the spring they come inshore, probably chiefly 
for breeding, and feed more or less among the aquatic vegetation. This is indicated 
by the rise in the percentages of plants, gastropods, Corethra larva, silt, and fine débris 
in the food at that time. In summer perch leave the deep water on account of its 
stagnation and feed on the bottom near the thermocline, as is indicated by the increase 
of chironomid larve, crayfishes, and midge pupe# in the diet. After the autumnal 
overturn the perch return to deep water and feed largely on Cladocera and Corethra 
larve. During the winter they remain in the depths of the lake, as shown by the 
preponderance of cladocerans, silt and débris, chironomid larve, and Sialis larve. 
Some foods (like Corethra and chironomid adults, crayfishes, Corethra and 
chironomid pupz, mites, and ostracods) were eaten only during the warmer months; 
some (copepods, oligochztes, alge) were eaten throughout the year in small quantities; 
other foods (Corethra larve, chironomid larve, Cladocera, silt and débris, Sialis larve, 
etc.) appeared at all seasons but showed rather striking maxima during certain months. 
The time at which a particular food was taken in greatest quantity often coincided with 
