HABITS OF YELLOW PERCH. 339 
g. Compared with the crappie, the perch eats a greater variety and shows other 
specificities of behavior. 
10. Though perch are able to recognize the proportions of oxygen and carbon 
dioxide in water, they enter regions where conditions are unfavorable for respiration 
and may remain in oxygen-free water for as much as two hours without dying. Whenin 
water without oxygen perch use part of the oxygen in the swim bladder. 
11. Perch may become sexually mature in two years. In the smaller lake inves- 
tigated they generally become mature when of much smaller size than do those in the 
larger lake. 
12. During the spawning season the males come into shallow water and remain for 
some time. The females remain on the spawning grounds only long enough to breed. 
13. Except during the spawning season and when the deeper water is stagnant, 
most of the perch in the large lake remain in deep water through the year. In the 
smaller lake similar migrations take place. 
14. There appears to be an upward migration at night. 
15. Perch swim more or less in schools throughout the year and apparently do not 
remain in one locality but move along the shore. 
16. Perch have many predacious enemies. The pickerel and lota are important. 
17. Perch are very generally infected with parasites. Those in the two lakes 
investigated contained cestodes and cestode larve (one or more species), trematodes (5s), 
acanthocephalans (2), nematodes (1). Leeches and an insect larva were found on the 
outside of the body. 
18. Perch are more abundant in inland lakes than other species because they are 
more versatile. 
19. Large inland lakes will generally contain more fishes per unit of volume than 
those of smaller size. 
20. Judging by the data presented in this paper the reason why the fishes in certain 
inland lakes attain a rather small maximum size is because there are various adverse 
conditions which prevent growth. In the present instance food does not appear to be as 
important as other factors, such as shallowness, exposure to wind, etc. 
TABLES. 
TaBLE 1.—CoOMPARISON OF LAKE MENDOTA AND LAKE WinGRA, EAcH 258.8 M. (849 FEET) ABOVE 
SEA LEVEL. 
Length. Breadth. Area, Maximum depth.| Mean depth. Shore line. 
Lake. 
: : Square A 
Kilo- . Kilo- . - Square Kilo- . 
meters,| Miles. | meters, | Miles. — miles, | Meters.| Feet. | Meters.) Feet. meters, | Miles. 
Mendota..... 95 5-8 4 45 39-4 15-2 25-6 84 12.1 39-6 32-4 20.1 
Wingra 2.6 1-6 1-4 8 
2.17 +79 4-25 14 1.6 5-3 73 45 
