FISHES OF THREE WISCONSIN LAKES 57 



deep lakes which stagnate (Mendota, Geneva) the perch is the 

 dominant deep-water fish. In those which have oxygen at all 

 depths throughout the year (Green, Michigan), the ciscoes are 

 the most abundant fishes in deep water. 



Size of lake. The size of a lake has a direct effect on wave 

 action along its shores. A small lake usually has much aquatic 

 vegetation at its margins while a large lake, like Lake Michigan, 

 has rather barren, rocky or sandy shores. The total body of 

 water in a lake is important in connection with contamination, 

 temperature cycles, etc. For commercial fishing on a large 

 scale a large lake is best, because it has greater resources and 

 will last longer before its fishes are exhausted. Such a lake is 

 not inexhaustible, however. 



Behavior. The behavior of fishes limits them to certain 

 areas. Some species react to the stimuli that they encounter so 

 as to remain in deep water, others respond so as to remain in or 

 near vegetation, etc. It is important to remember that fishes 

 choose the habitats in which they are found. 



Reproduction. Fishes of course cannot persist where they 

 are cut off from suitable conditions for breeding. Some species 

 require rocky shoals, others vegetation, etc. If the proper en- 

 vironment for spawning is lacking a fish is excluded from a lake, 

 though food may be abundant and other factors important for 

 everyday life may be favorable. 



Food. The foods of fishes in all lakes are, in order of impor- 

 tance, insects, plankton crustaceans, larger crustaceans, mol- 

 luscs, mud, plants, and certain minor aquatic animals. The 

 results discussed in this paper show that in a lake (Pepin) where 

 conditions most resemble those in rivers, plankton, bottom sedi- 

 ment, and crayfishes are the important foods. There are fishes 

 present with specialized food habits which feed primarily on 

 these particular foods mooneye, spoonbill, duck-billed gar, 

 red-horses, quillbacks, etc. In the more isolated inland lakes, 

 fishes, insects, molluscs, and plants are the important foods. 

 In Lake Michigan the important fishes feed largely on the deep 

 water crustaceans. 



Civilization. The activities of man are important for lake 

 fishes. The decrease of many species is doubtless due to the 

 "march of civilization." Examples are the buffalo and spoonbill 

 in Lake Pepin, the whitefish in Lake Michigan, and the ciscoes 



