Food of the Ycllozcstoiic Trout 473 



an arc of approximately 90 degrees. Beyond that point the surface 

 film becomes a mirror to the fish. These points can be easily tested 

 by any person with sufficient courage to keep his eyes open under 

 water for a few seconds. There is a slight difiterence in a stream 

 where the surface is mobile, as in rapids. Here the effect is primarily 

 that of a " freak " mirror, constantly moving like a dish of agitated 

 mercury or molten silver or lead, with bright streaks and dark bands, 

 the bands being transparent places. 



To the fish, then, the water surface is in good part a mirror, 

 through which he cannot see; but he does see objects beneath him 

 reflected plainly in the surface mirror — upside down, of course. 

 This is an advantage, for it aids him to find the food in the water, 

 to come upon his prey suddenly, unobserved, and from an unex- 

 pected angle. It is also to his disadvantage, for while it aids him 

 in finding his prey, it exposes him to his enemies in the water, 

 putting him in the position of prey. It places him at the further 

 disadvantage of not being able to see external enemies, such as man, 

 birds, and fishing mammals, except through the circumscribed area 

 directly above him. And finally, the mirror tricks him into accept- 

 ing bait that is poked through the surface mirror while preventing 

 him from seeing the fisherman on the shore who is ofi^ering the bait. 



Another point is that fish are more or less near-sighted and do 

 not recognize objects unless they move. Further, a good deal of 

 scientific evidence indicates that fish are color-blind, that they do 

 not see colors as we do. To' fish, all colors apparently must be more 

 or less shades of gray, much as to a color-blind person. If this is 

 true, in just what way are colored flies so useful when used as bait 

 for fish, since fish are not supposed to recognize colors as we do? 

 Again, since a fish generally strikes from below and sees the colors 

 of bait against light, of what use are colors under such conditions.-' 

 To test this, let the reader try to recognize colors of an opaque object 

 held against light, ^^'hether a fish recognizes colors as such, or 

 merely as shades of gray, is as yet an unsettled question which oflfers 

 splendid opportunity for experimental study. 



For the observer who wishes furthei" information on this interest- 

 ing subject, the following references are suggested : 



The Senses and Learning in Fishes, by Jacob Reighard. In Trans- 

 actions Amer. Fisheries Soc., Vol. 46, No. 3, 1917, pp. 133-170. 



Marvels of Fish Life, as Revealed by tJie Camera, by Francis 

 Ward. 2nd ed., pp. 1-196. London, 1912. 



Animal Life Under IVater, by Francis Ward. Pp. 1-178. New 

 York. 1920. 



