PISHES OF THREE WISCONSIN LAKES 53 



GENERAL DISCUSSION OF THE FOOD AND DISTRI- 

 BUTION OF FISHES IN WISCONSIN LAKES 



As an environment for fishes a lake possesses certain qualities 

 which differ from those in a swamp or a river. Perhaps the 

 chief characteristic of a lake, as compared with other aquatic 

 habitats, is stability. It is comparatively quiet; its water level 

 does not fluctuate much; if it has sufficient depth, its water 

 stratifies and the deeper parts are always cool; its supplies of 

 food are about the same each year; its seasonal cycles occur 

 with regularity. A lake is dependable. A swamp or a river 

 cannot be relied upon temperatures vary to extremes with 

 seasons and weather; floods or droughts change the whole en- 

 vironment, affect the food supplies, and often interfere with 

 reproduction. The fishes in a lake have a limited range, but 

 enjoy the advantages of a stable environment. 



The observations discussed in this paper indicate that as the 

 conditions in lakes approach those in swamps the number of 

 fishes per unit of area becomes larger. In other words a shallow, 

 vegetation-filled lake contains more fishes in proportion to its 

 area than a larger lake with fewer aquatic plants. The reason 

 for this is probably that the great stores of foods occurring in 

 swamps are associated in these lakes with some of the stability 

 inherent in lake habitats. Yet small, shallow lakes are not the 

 optimum habitats for lake fishes. The species which flourish 

 in them (crappie, sunfishes, dogfish, bullheads, black basses, etc.) 

 are those which frequent aquatic vegetation. The true lake 

 fishes (ciscoes, trout, lawyers, yellow perch, etc.) are usually 

 absent, and when present, though sometimes abundant, never 

 attain great size. 



The observations also indicate that rivers, at least in sum- 

 mer, contain fewer fishes per unit of area than lakes. For fishes 

 a river is a highway and a refuge. It gives access to the stores 

 of food in swamps and lakes, and in winter furnishes an environ- 

 ment which is fairly stable. However, a river is not capable of 

 producing much fish food within itself. The food resources 

 available to lake fishes in the bottom mud cannot occur in 

 quantity in rivers because the bottom is continually changing. 



