56 UNIVERSITY OF WISCONSIN STUDIES 



which are directly or indirectly supported by it." It is doubtless 

 true that there is a reciprocal relation between the larger vege- 

 tation and the phyto-plankton, but Kofoid ignores the bottom 

 fauna and detritus feeders which constitute an important part 

 of the food resources in a lake. Furthermore, some shallow 

 lakes (Wingra) have much aquatic vegetation and much plank- 

 ton. 



Bottom. The soft bottom mud in lakes may support an abun- 

 dant fauna of insect larvae, Sphaeridae, annelids, and proto- 

 zoans. These animals live on the remains of plankton animals, 

 the organic ooze, fragments of leaves, sticks, and other organic 

 materials from land. Bottom mud and the animals inhabiting it 

 are important fish foods. If the bottom is sandy fewer fishes 

 frequent it (compare Lake Pepin and Green Lake, Tables II, 

 VI). 



Variation in height of water. Lake Pepin is the only lake 

 studied that shows a marked variation in the height of the water. 

 Shira (1917) has suggested that the buffalo is dependent on over- 

 flowed bottoms for spawning. In this connection the experience 

 of Mr. W. E. Wiedner, who has operated a commercial seine in 

 Lake Mendota for six years, is of interest. He has never seen a 

 small buffalo, but frequently catches adults. He believes the 

 fishes entered the lake from the Rock River years ago and, since 

 the outlet has been dammed, find conditions unsuitable for 

 spawning. The writer has seined extensively along the shores 

 of Lake Mendota and has never caught a small buffalo. The 

 overflow of the shores of lakes enables fishes to invade new feed- 

 ing grounds. The writer once examined a carp from Lake Mo- 

 nona which had eaten bluegrass from a pasture. The bullhead 

 mentioned in this paper as having eaten a young bird doubtless 

 got its meal from overflowed land. Falling water often leaves 

 fishes stranded, and many die annually. 



Current. Currents are usually not important in lakes. 

 Some fishes, like certain darters and the smallmouth black bass 

 which frequent swift, clear streams, are also found along the 

 rocky or sandy shores of clear lakes. In Lake Geneva there are 

 many bass, but no darters. The absence of the latter has no 

 apparent explanation. 



Gases. In thermally stratified lakes it is important for 

 fishes whether the deeper parts become stagnant or not. In 



