HABITS OF YELLOW PERCH. 319 
. Insects—Corixa, Plea nymphs, Notonecta nymphs, damselfly adults, crickets, midges. 
. Chironomus decorus larve alive. 
. Fish cut into small pieces. 
. “Normal’’ diet, consisting of all the kinds of food fed under 1 to 6, but no single one in large 
enough quantity to give complete satisfaction by itself. The two jars in which these fish were kept 
contained also Elodea. 
g. Starved. 
ona an 
The fish ate all classes of food readily except the insects. Although Corixa and 
other varieties which occurred in perch of similar size in nature were offered, they were 
never taken in any quantity and were often refused altogether. The practice with 
all the foods was to change the water each morning and in midafternoon to add a fresh 
supply of food, which exceeded what might be eaten before the next day. 
The results of these experiments are given in Table 20. The foods would come in 
the following order, as judged by the rate of gain in weight and volume: Earthworms, 
Entomostraca, chironomid larve, amphipods, fish, ‘‘normal,” liver, and flour. The 
three perch fed adult insects lost almost as much as those which had nothing. It will 
be noted that there is no correlation between the gains in weight and volume. It is 
difficult to understand why the three “‘normal” individuals which were fed a variety 
did not gain as much as others which received only one kind of food during the entire 
month. Perhaps the extra energy required to digest a variety more than compensated 
for the diversity of chemical substances obtained. 
COMPARISON OF FOOD OF PERCH IN LAKE MENDOTA AND IN LAKE WINGRA. 
The fact that perch are individually smaller in Lake Wingra than in Lake Mendota 
is probably due to a number of causes, but one would naturally turn first to differences 
in food for an explanation of such variance. In Table 21 the various foods eaten by 
the perch in each lake is given by months. The averages show that fish, insect larve, 
insect pupz, adult insects, isopods, and copepods are eaten in greater amounts in Lake 
Wingra than in Lake Mendota; the opposite is true of mites, crayfishes, amphipods, 
ostracods, cladocerans, snails, clams, leeches, oligochztes, plants, silt and débris, and 
CaCo, crystals. In all but two months in Lake Wingra, insects as larve, pupe, or 
adults form half, or more than half, of the food. In Lake Mendota the months are 
equally divided, as regards the particular foods eaten in maximum amounts, between 
Cladocera and insect larve. 
An examination of figures 6 to 29 will show many other minor differences in details 
between the two lakes. Among the insects the chironomids do not differ much, but 
Wingra excels in chironomid pupe and in odonate and mayfly nymphs. Among the 
cladocerans the amount.of Leptodora was about the same in the two lakes (4.6 to 4.7 per 
cent); Daphnia was in excess in Mendota (20.9 to 4.8 per cent), and Eurycercus in 
Lake Wingra (0.1 to 30.3 per cent). 
Another difference between the perch in the lakes under consideration is shown in 
Table 22, which demonstrates that there are two seasons in Wingra when many of the 
perch have little or no food in them and only one in Mendota. The empty perch in 
April are doubtless due to the neglect of feeding on account of breeding. The fasting 
period in Wingra during August and September has no counterpart in Mendota and is 
equally characteristic of both sexes. It is probably due to the continued high tempera- 
ture, from which there is no escape, as there is in Mendota, and to the extreme turbidity 
