316 BULLETIN OF THE BUREAU OF FISHERIES. 
Five crappies (Pomoxis sparoides) had consumed of Chironomus fulviventris larve, 24.2 per cent; 
mayfly nymphs, 13 per cent; Callibetis nymphs, 7.2 per cent; Enallagma hagenit nymphs, 6 per cent; 
chironomid pupe, 13 per cent; Corixa adults, 3.6 per cent; Hyalella, 3.2 per cent; ostracods, 1.3 per 
cent; Cyclops, 26 per cent; Daphnia, 2.6 per cent; Bosmina, 0.6 per cent; Eurycercus +; calcium 
carbonate crystals, o.2 per cent. 
Thirteen perch contained of fish eggs, 0.7 per cent; minnows, 8 per cent; fish remains, 7 per cent; 
insect larve, 1.5 per cent; Protenthes larve, 2 per cent; Chironomus decorus larve, 7.6 per cent; 
C. fulviventris larve, 38.2 per cent; Probezzia pallida larve, 0.5 per cent; caddisfly larve, 0.6 per cent; 
Callibetis nymphs, 7.8 per cent; Enallagma hageni nymph, 1.4 per cent; chironomid pupe, 6 per 
cent; Hyalella, 1.5 per cent; ostracods, +; Eurycercus, 0.1 per cent; Physa, 6.5 per cent; Planorbis, 
0.2 per cent; Pleurococcus, +; Chara, 1.4 per cent; fine débris, 8 per cent. 
Though the perch is versatile, it selects preferred foods from the environment, 
and preferences apparently vary more or less at different ages, seasons, and localities. 
The staple articles of diet for adult perch throughout the year are chironomid larve 
and cladocerans, but with changing seasons there may be great variation in the pro- 
portions of either. Furthermore, perch of the same size caught at the same time and 
place have usually eaten the same kinds of food, but at times have not. As a rule the 
nature of the food indicates that it was secured on or near the bottom, but schools of 
perch are sometimes seen feeding at the surface of the lake. This is particularly true 
in the early morning. 
Judged by the success of line fishing, feeding is largely diurnal, for few perch can 
be caught at night. This indicates also that perch depend upon their sense of sight 
to a marked degree, and this view has been supported through the observation of 
individuals fed in glass aquaria. 
In order to discover whether adult perch ate different foods at various depths, 
comparisons have been made which include all catches in Lake Mendota. These are 
summarized in Tables 16 and 17. The first shows the percentage of food at different 
depths; the latter, the kinds of foods which exceeded all others in volume. Both 
tables show: (1) That food is more varied in shallow water and that it consists largely 
of chironomid larve, Corethra larve, Daphnia, Corneocyclas, and bottom mud in the 
deeper parts of the lake; (2) that the following foods decrease in amount eaten fn 
passing from shallow to deep water—small fishes, mites, adult insects, crayfishes, 
Hyalella, copepods, snails, leeches; (3) that the following foods increase in passing 
from shallow to deeper water—insect larve, insect pupze, bottom mud, Cladocera, 
small clams, oligochetes, plants; and (4) that in general the perch have eaten the 
foods which are most abundant at the depth where they are caught. This indicates 
that they do not change rapidly from one stratum to another; that is, there are usually 
no rapid vertical migrations. 
The fact that insect pupe, largely those of midges, are eaten mostly in deep water 
indicates that they are secured in the bottom mud before beginning their migration 
to the surface. Plants occur in greater amounts in perch from deeper water, and this 
is probably because remains of plants which have been washed loose and broken up by 
storms are so arranged as to be lying upon the bottom. Deposits of such plants are 
favorite resorts for insect larve. The tables just cited and evidence from many other 
sources show that the perch usually feed on or near the bottom. 
The contrast in the food of perch from different depths may, perhaps, best be 
indicated by the following specific instances where individuals were caught at the same 
time: 
