Biological Survey — Genesee River 51 



not become well established in cold streams and we have never 

 found it occurring commonly in association with the trout. 



Some of the main factors of environment in determining the 

 kinds and numbers of fishes which any given stream might support 

 are: (1) size of stream, (2) current, (3) type of bottom, (4) tem- 

 perature, (5) chemical and gaseous content of water, (6) type 

 and abundance of food, (7) shelter, (8) spawning grounds. 

 Although these factors are usually inter-related they may be 

 treated separately. 



(1) Size of Stream. — The black-nosed dace {EJunichfhys atro- 

 nasus) is an example of a species which prefers small streams. 

 Although commonly in nearly all small tributaries of the Genesee, 

 it is rare in the river and large tributaries. Another minnow, the 

 river chub (Nocomis higuttatns) , was taken only in large streams 

 as the Genesee river and Black creek (Monroe county). 



(2) Current. — All of our specimens of the stone-cat (Noturus 

 ff(wu.s) came from rapid water. Another catfish (Amemnis 

 nehuJosus) prefers still waters. 



(3) Type of Brjttom. — The fan-tailed darter {Catojiotus flahel- 

 laris) is an example of a fish which prefers a stream with hard 

 bottom, usually rubble or gravel in this region. The common 

 bullhead {Amehirus nehuJosus) seems to be most common in waters 

 having a soft mud bottom. 



(4) Temperature. — As a cold water fish we have already named 

 the brook trout (SalveUnus fontinalis). As a warm water fish we 

 might name the small-mouthed black bass (Mieropterus dolomieu). 



(5) Chemical and Gaseous Content of Water. — A test made In 

 a milk polluted stream at Lakeville August 31, 1926, showe 1 

 that fishes representing minnows (Hyhorhynchus notatus, Notropis 

 rornutus, ExogJossum m((.rillingua) , one species of perch (Perca 

 pivescens) and one species of sucker {Catostomus commersonnii) 

 died within a few minutes in a stream having a low dissolved 

 oxygen content accompanied by a high carbon dioxide content 

 (Fig. 6). The absence of fishes in a salt water stream (Wolf 

 creek) could be considered evidence of the dislike of fresh water 

 species for a high concentration of this chemical substance. 



(6) Type and Abundance of Food. — Embody and Gordon 

 (1924) give as the total com])osition for the ration of the brook 

 trout (based on analysis of the food of wild fishes from 4 to 13 

 inches in length) the following: 



Per cent 



Crude protein 48 . 73 



Fat 15.50 



Carbohydrates 



Nitrogen free extract 17 . 90 



Crude fiber 7.97 



Ash 9.90 



100.00 



