29 



In very swift water of shallow riffles, where their bodies were 

 out of water much of the time while working at the gravel. 

 The only undoubted horned dace nest found in Campus creek 

 was located in one of the tributaries of the stream in a nar- 

 row, shallow piece of swift water ; but a number have been 

 found in other streams in the region and all were located in 

 a good current. Some silver-mouthed minnows were found 

 spawning upon a sandy shoal where there was a moderate cur- 

 rent last spring. The shoal with swift water seems to be least 

 frequented by fish of all habitats in Campus creek except at 

 night and by certain species at the spawning time. Its main 

 function for fish appears to be that of a general highway con- 

 necting their diurnal dwelling places, the pools and deep nar- 

 rows. 



The current also has an indirect effect upon the distribution 

 of fish by changing the bottom topography; for example, I 

 noticed this winter that there is a broad shoal where a deep 

 jpool existed last fall; and in another place, where there was 

 an extensive area of riffles used by stone rollers for nesting 

 purposes last spring, there is now a deep pool. These changes 

 will necessitate biotic changes involving fish as well as other 

 organismis ; and an opportunity will thus be afforded to observe 

 directly the succession of forms inhabiting a particular part of 

 the stream due to a change of environmental conditions. After 

 a hard rain last April, the swift water completely denuded an 

 area of gravel, which formed a piece of riffles used by many 

 stone rollers for nesting purposes, and left in its place a shal- 

 low area a few inches deep, having a hard, blue clay bottom 

 with a few pot holes and scattered cobble stones. Fish were 

 found using these objects as places of concealment. Thus in 

 a few hours one type of habitat was transformed into another, 

 and each had a fish fauna different as to the species present and 

 the way they reacted to their surroundings. 



Food. This is undoubtedly a strong factor in determining 

 the distribution of fish in Campus creek. Diatoms, entomos- 

 tracans, and Chironomus larvae are the chief objects that I 

 have found by dissecting many examples of the common species. 



