54 UNIVERSITY OF WISCONSIN STUDIES 



The most abundant bottom fish in Lake Pepin, the hackleback, 

 secured only one third of its food from the bottom; the re- 

 mainder consisted largely of plankton. That the river itself is 

 not an important habitat for fishes is also indicated by the fact 

 that Lake Pepin is the only lake among those studied in which 

 a large number of fishes were caught in the shallowest zone. 

 The fishes, except in winter when larger fishes eat little or noth- 

 ing (Pearse and Achtenberg, 1920, p. 313), are largely in shal- 

 low water, not in the lake itself. 



There are certain fishes that belong ecologically to rivers, 

 small streams, swamps, or lakes. Some species of fishes are re- 

 stricted to certain habitats in particular communities; others 

 range through a wide variety of habitats and communities, but 

 there is of course no fish that is not limited by the factors in its 

 environment. The more limited a fish is, the more restricted is 

 its range and the fewer it is in numbers. If all the lakes studied 

 are considered together, the most abundant species are those 

 which are least limited and are therefore able to take advantags 

 of the greatest number of chances for growth, survival, and re- 

 production. Darters are most abundant in streams and ciscoee 

 in the depths of lakes; perch and carp are found in' a variety of 

 habitats. The common eel of northern South America has the 

 greatest ecological range of any fish studied by the writer (1920) 

 from the depths of lakes to the ditches and drain pipes in 

 cities. 



In temperate regions there are three types of lakes, the 

 classification depending primarily on the temperatures and 

 dissolved gases (Birge and Juday, 1911): (1) shallow lakes which 

 have a rather uniform temperature from top to bottom at all 

 seasons, (2) deep lakes which are at times thermally stratified 

 but which contain oxygen throughout at all seasons, (3) deep 

 lakes which are thermally stratified and in which oxygen is ab- 

 sent from the deeper, cooler parts during certain seasons. In 

 the following paragraphs some of the important factors which 

 limit the distribution of fishes are discussed. 



Shores vary in their nature and the different types are im- 

 portant for fishes. Boulders and rocks are associated with cur- 

 rents and wave action; mud, with quiet water; and sand with 

 intermediate conditions. The rock bass, fantail darter, and 

 miller's thumb are found on rocky shores. Among the lakes dis- 



