Biological Survey — Genesee Rr^r 53 



The brook trout feeds lar^'ely iijion aquatic insects, such as 

 mayflies {Ephemerida), stoneflies (Plecoptera), and caddis flies 

 {Trichopfera). These organisms are mostly absent in polluted 

 waters and we have not found the trout in such waters. 



Some of the fishes which were found tolerating rather serious 

 organic pollution are: C^ommon sucker {Catosforniis commer- 

 soniui), liog sucker {HifpenfrJiu))} iiir/rirans), red-horse sucker 

 {Mo.rosfonia aurfoJnm) , stone roller ((himposfoma anomalnni) , 

 horned dace (i^rwofiJvs afromaruhifys) , common shiner (Nofropis 

 cornufus), trout perch (Perropsis otnisco-mayctis), black bass 

 {Mirropffnis clolomini) . Most of these species are able to subsist 

 upon algae, and small bottom-living organisms, such as can occur in 

 polluted waters. Young black bass Avere found feeding upon 

 midge larvae {Chironornidae) which were present in water pol- 

 luted by cannery wastes. 



It is dangerous to assume, however, that pollution of a stream 

 is harmless to fish life merely because fishes exist there. The 

 number and kinds of fishes must be taken into account. Also, it 

 should be borne in mind what we do not know, from the existence 

 of individuals (young or old) or a species in the polluted part 

 of a stream, that conditions are favorable for the propagation of 

 that same species there. The environmental requirements of eggs, 

 young stages, and adult fishes may be, and probably are, very 

 different. 



Typical Fishes of a Trout Stream. — In cold streams, where 

 brook, brown, or rainbow trout occur there are usually but few 

 species of other fishes. A list of fishes commonly taken associated 

 with trout is as follows : 



Black-nosed dace {Rhinichthys atronasus) . 



Horned dace (SemotiJus atromacidatus) . 



Common sucker (Catostomus commersonnii) . 



Pearl minnow {Margariscus margarifa). 



Red-sided minnow (CUnostormis eJongafus) . 



Common shiner (Nofropis cornniiis) . 



Sculpin {Cot fits hairdii). 



Fan-tailed darter (Catonofus flaheUaris). 



Brook stickleback (Eucalia inconsfans) . 



Stone-roller minnow (Camposfoma anomaJum). 



Other species sometimes enter trout waters in limited numbers. 

 These are likely to be found in the lower, warmer waters of the 

 stream. They include the following: 



Blunt-nosed minnow (Hyhorhynchus notatus) . 



Fat-head minnow (Pimephfdes promeJas). 



Long-nosed dace {Ehmichihys cafaracfae) . 



Johnny darter (Boleosonia nignim). 



By far the most common trout associates are the black-nosed 

 dace, the horned dace, and the common sucker. All of these occur 



