BRIEF NOTES ON FISHES. 407 



variety that closely approached the boundary of a " spe- 

 cies." Since then I have found these blue roach in Cross- 

 wicks Creek, and always in swiftly running, clear, cold 

 water. It would seem, therefore, that the fish varies in a 

 marked degree in accordance with its environment ; and 

 being a hardy species, capable of living almost anywhere, 

 that variation is necessarily considerable. Considered 

 from the evolutionary stand-point the only rational one 

 it is an instance of the instability of species, GO called, 

 and shows how little change is necessary to bring about 

 even permanent " specific " changes in the anatomy of a 

 fish. Once let there occur a decided change of habits, 

 and a change of structure will ultimately follow. 



The next in importance among the cyprinoids, and 

 one exceeding the roach in size, is the beautiful fall-fish, 

 or rosy chub. 



How great a change in habits may exist among the 

 fishes of a family can be seen when comparing the habi- 

 tat of this chub with that of a muddy-pool roach. !Nb 

 water is too clear, too cold, too rapid for the chub. They 

 delight in stemming the swiftest currents of the river, 

 and die at once if confined in quiet, sun-warmed waters. 

 To find them in all their glory, I have but to go to the 

 swift ripples about the rocks in the river. Here they 

 congregate in large numbers in April and May, but wan- 

 der about singly later in the season. Except during the 

 spring months, they are not a social species, as is the 

 roach. Chub are not confined to the river, however, for 

 I find many of them wandering up Crosswicks Creek to 

 the limit of tide-water. Here they delight in deep holes, 

 and often I have caught specimens of the largest size by 

 carefully sinking a grasshopper into some known deep 

 hole in this creek. 



