FISHES OF GREEN LAKE, WIS. 27 1 



though ciscoes are present in Lake Mendota they are few in number and the perch is the 

 abundant fish in deep water, except when stagnation forces it out during the summer 

 (Pearse and Achtenberg, 1920). The perch appears to be about equally abundant in 

 both lakes in shallow water. 



There are perhaps two reasons why ciscoes are not abundant in Lake Mendota 

 and why perch are comparatively scarce in Green Lake. These are concerned with tem- 

 perature and food. The perch may live in shallow water at rather high temperatures, 

 but because the summer stagnation has made Mendota unsuitable for ciscoes, it has 

 also been able to dominate the deep water. To flourish, the cisco appears to require 

 cold water in surmner and finds ideal conditions in the depths of Green Lake. There 

 appears to be no good reason why the perch should not occur in the deeper parts of 

 Green Lake. Perhaps it has never crossed the "barren zone" between the depths of 

 20 and 40 m. Perhaps the "attractive" food which takes it to the bottom of Lake 

 Mendota is lacking. The characteristic animals in the bottom of Lake Mendota are 

 enormous numbers of midge larvse (Corethra, Chironomus, Protenthes, etc.). Little 

 clams, oligochsetes, crustaceans, and protozoans are also present. On the bottom of 

 Green Lake the fauna is much the same, except that the crustaceans (particularly am- 

 phipods) are very abundant and midge larvae are few. 



The relatives of the cisco are usually found in the depths of lakes and in the cooler 

 parts of the ocean. The relatives of the perch are mostly found in shallow regions of 

 fresh water. The ciscoes apparently invaded fresh water from the ocean as the glaciers 

 receded and have remained in the cooler parts. The perch has probably migrated into 

 the depths of lakes from adjacent shallow waters to take advantage of the abundant 

 stores of food there. Reighard (1915, p. 242) even classifies the perch in his "Vegeta- 

 tion Community," though he also found it in deeper water in Douglas Lake. 



Not only are the fishes which feed on the bottom most abundant in both lakes, 

 but the animals found in or on the bottom are most used for food by all the fishes in the 

 lakes; that is by all species of fishes considered together. In Lake Mendota, however, 

 more plankton is consumed by the fishes than in Green Lake, and this probably for two 

 reasons: (i) There is actually more plankton in the lake, and (2) a large portion of the 

 bottom is not readily accessible on account of stagnation. 



The shallow waters in the two lakes under consideration are quite different. Green 

 Lake has sandy and stony shores, with comparatively little vegetation ; Lake Mendota 

 has varied shores and large numbers of aquatic plants. These differences are 

 reflected in the two basses, the smallmouth being the common one in Green Lake and 

 the largemouth in Lake Mendota. The smallmouth in Green Lake feeds largely on 

 shallow water cladocerans, insect larvae, and fishes. The most important foods of the 

 largemouth in Lake Mendota during the summer are fishes, adult insects, crayfishes, 

 amphipods, and algae. In this lake the smallmouth partakes largely of adult insects. 

 The largemouth apparently becomes the dominant bass because it feeds more during 

 the summer, which is its chief growing period, on food which is found in the shore vege- 

 tation rather than on the bottom. 



Why is it that Lake Mendota has a greater number and variety of fishes than 

 Green Lake in spite of the fact that (i) it has half the volume and (2) that a consid- 

 erable portion of its bottom with much food is cut off by stagnation for three months 

 during each year? The writer has thought over the whole question with care and 



