Q2 ANIMAL COMMUNITIES OF STREAMS 
conditions and being also positively rheotactic. The fish are able to 
meet the current and to withstand the conditions of the stagnant pools. 
The crayfishes live in the water in the spring and burrow in the 
37 
PIONEER STREAM FISHES 
Fic. 35.—Black-nosed dace (Rhinichthys atronasus) (from Forbes and Richardson). 
_ Fic. 36—Common sucker (Catostomus commersonii); length 18 in. (from Meek 
and Hildebrand after Forbes and Richardson). 
Fic. 37.—Blunt-nosed minnow (Pimephales notatus); length 2 to 33 in. (from 
Forbes and Richardson). 
dry weather; adults of the aquatic insects creep into moist places 
when the stream dries. Allee (53) has found that isopods are positively 
rheotactic and that they can be acclimated to extreme conditions. 
