76 
BULLETIN OF THE BUREAU OF FISHERIES. 
LAKE MENDOTA, WIS. 
For purposes of comparison some specimens of the yellow perch ( Perea fla- 
vescens ) were obtained from Lake Mendota at Madison, Wis., and the contents of 
their digestive tracts were examined. During this investigation some perch were 
caught each month from January to August, 1913. During the winter months 
they were caught with hook and line in the deep water, but the summer catches 
were made near the shore in shallow water. The following table (5) gives the per- 
centages of the different kinds of material found in the alimentary canals of the 
perch while the lake was covered with ice. 
Table 5. — Food from stomachs of 67 yellow perch caught in winter months, Lake Mendota, Wis. 
Date. 
Number 
of perch. 
Cyclops. 
Daphnia. 
Corethra 
larvae. 
Debris. 
Miscella- 
neous. 
.Tan. 14 
1913. 
12 
Percent. 
10 
Per cent. 
80 
Per cent. 
Percent. 
7 
Notholca. 
Jan. 27 
10 
2 
85 
10 
3 
Crayfish. 
Feb. 15 
10 
3 
80 
7 
10 
Mar. 1 
15 
2 
95 
3 
Algae. 
Amphipod. 
Mollusca. 
Mar. 15 
10 
5 
60 
10 
20 
Apr. 1 
10 
2 
70 
10 
15 
The stomachs of all of these perch contained relatively small amounts of 
material, but a great deal was found in the intestines. Daphnias were the pre- 
dominant portion of the food, but Cyclops and Corethra larvae were found in con- 
siderable numbers at times. Over 600 Daphnias were counted in some of the 
stomachs. A few Notholca longispina were noted in the stomach of one fish caught 
on January 14. A crayfish completely filled the stomach of one fish caught January 
27. A most interesting discovery was a large number of algae in a fish stomach 
obtained on March 1. Such algae as Melosira, Cyclotella, Tabellaria, and Fragilaria 
were found. In the stomachs of several fish caught on March 15 a number of 
amphipods were noted, and on April 1 a few univalve Mollusca were found. The 
food at this season consisted entirely of aquatic life and largely of Micro-Crustacea. 
During the months of May, June, July, and August, perch were taken only 
once a month. The results are shown in the following table (6). 
Table 6. — Food from stomachs of 42 yellow perch caught in summer months, Lake Mendota, Wis. 
Date. 
Number 
of perch. 
Corethra 
larvae. 
Amphi- 
poda. 
Daphnia. 
Mayflies. 
Debris. 
Miscellaneous. 
Mav 15 
1913. 
12 
Per cent. 
95 
Per cent. 
3 
Per cent. 
Per cent. 
Per cent. 
2 
Hydrachnidae. 
June 10 
10 
12 
2 
2 
July 10 
12 
2 
50 
3 
40 
5 
Claw of crayfish. 
Minnow; Chaetophora. 
3 
40 
50 
7 
In the stomachs of the perch caught on May 15 Corethra larvae constituted 
nearly the entire amount of food. Beginning in June we find a few mayflies (Ephe- 
merida). Again in August large clusters of Chastophora were found in some of the 
stomachs. Several pieces of the larger aquatic plants were also noted. The pro- 
portion of mayflies increases very rapidly during July and August, and in some 
