4/2 Roosevelt Wild Life Bulletin 



While dealing specifically with the trout streams of Yellowstone 

 Park, the facts here presented have a much wider application. It 

 is an axiom that like causes beget like results. In a broad sense 

 the mountain trout streams of the Park and their fish are typical 

 of the trout streams throughout the Rockies. The writer has had 

 the opportunity to make comparisons of physical conditions, and to 

 some extent of the biological conditions, in several of these states. 

 In the region studied, the conditions ailected but a single species 

 of trout — the native redthroat, cutthroat, or blackspotted trout 

 (Salmo clarkii) — ^ the only one foimd in the northeastern part of 

 the Park. 



The present account is not in any sense complete, as it deals with 

 only a few phases of the work, certain summaries presented in a 

 form be.ieved to be of most interest and value to the general reader. 

 The technical, detailed report is to follow at a later date. 



The illustrations accompanying this paper, with the exception 

 of figure 113, are reproduced from photographs taken in 1921 by 

 the author. 



FISHES AND THEIR ENVIRONMENT 



There are at least two points of view in dealing with fish, — that 

 of the fish and that of the fisherman. A fish wants something to 

 eat, and the fisherman, aside from a secondary " sporting " interest, 

 wants to eat the fish. What the fisherman thinks we known pretty 

 well. But no one has as yet succeeded in interviewing a fish directly 

 to find out what he "thinks" about the matter. Indirectly, scien- 

 tists have frequently forced fish to give us information by placing 

 them under special, controlled conditions. This method is called 

 experiment. To this is added observation. By combining the results 

 gained by the two methods a good deal of information has been 

 accumulated regarding a fish's habits, his likes and dislikes, and 

 something of the world in terms of a fish's life. 



Let us summarize briefly the conditions under which a fish lives. 

 Water is supposedly transparent. But have you ever looked at the 

 under side of the surface film of water in an aquarium? Seen from 

 an acute angle, this surface film is not at all transparent, but acts 

 as a mirror, reflecting the objects beneath. The more closely the 

 angle of vision approximates a right angle the less the mirroring, 

 and the greater the transparency. There is a further difference 

 whether one gazes toward the sunny or shaded side of the water. 

 A fish can see objects outside of the water, provided these are fairly 

 above him, at an angle of view not exceeding 45 degrees, or within 



