216 Fish Behavior and Angling 



magnifies objects on the shore— magnifies them, that is, as compared with 

 their apparent size when the window is smaller. To see the fishermen 

 optimally, then, the fish must seek a depth from which the improvement 

 of visibility through enlargement is not cancelled by the loss of light 

 through the greater distance of water through which the rays must travel 

 to his eyes. The poor fish is thus fated never to see us as we are— even 

 through the flat glass side of an aquarium tank." (figure references in 

 parentheses mine) 



The eyes of most kinds of fish protrude enough and are located on the 

 body in a position to give a full visual field. This is necessary because a 

 fish has no neck, a situation that is not compensated for by his buoyancy 

 and ability to rotate on his vertical axis. 



Changing Pigmentation 



Many years ago while stationed at the Rock Creek Hatchery in south 

 central Nebraska, I observed some very large black rainbow trout in the 

 small spring-fed rocky stream that meandered through the hatchery 

 grounds. The hatchery superintendent told me they were blind "spawners" 

 (fish used for stripping eggs and sperm in artificial trout propagation) 

 that had been injured and later released in the creek. For something to 

 do on a Sunday afternoon, four of us decided to catch one of these black 

 trout; using two minnow seines, one above and below a fish, we tried to 

 trap him in the bag of one or the other of the seines. He always escaped, 

 usually by finding an opening under the seine when a rock caused a 

 momentary lifting of the lead line. The fish was as capable of avoiding 

 capture as if it had functional eyes, except that once it escaped the net 

 it did not seek cover as a normal trout would do. The dark color of these 

 trout is characteristic of fish that are totally blind. 



The relationship of light to the intensity of a fish's pigmentation is 

 described by Walls ^": (1) When no light is striking a fish (with or with- 

 out functional eyes) the melanophores (dark pigment cells) "contract." 

 (2) When light strikes only the skin (whether the eyes are present or 

 not) the melanophores "expand." (3) If more of any light entering the 

 eye strikes the upper part of the retina, the melanophores "contract" 

 despite the tendency mentioned in (2). (4) If more of the light entering 

 the eye strikes the lower part of the retina, the inhibitory effect of the 

 tendency given in (3) upon the tendency in (2) is ineffective and the 

 melanophores expand. Thus the extent of pigmentation depends upon a 

 combination of stimuli upon the skin and eyes. A fish that is completely 

 blind darkens in the light because there is no functional eye to inhibit 

 the innate tendency of the illuminated melanophores to expand. Fish 

 taken from muddy water are usually light in color because they are 

 exposed to limited light. 



