Vision 213 



VISION 



Most fishes have eyes, which in many species are very functional. All 

 of the so-called game fishes and pan fishes have well-developed ones and 

 use them in finding and capturing their foods. Color vision has been 

 tested in a number of species, and no fish is known to be without it. 



Color Vision 



Investigations of color vision in largemouth bass ^^ indicated that bass 

 vision was similar to that of a man looking at objects through a strong 

 yellow filter, i.e., the yellow filter made it difficult for the man to separate 

 colors at the blue end of the spectrum. Tests of color vision in bluegills 

 using red and green lights at variable intensities demonstrated the ability 

 of these fish to distinguish these colors. After 100 practice trials, bluegills 

 made 94 correct selections out of 101 tests.^^ Other investigations in- 

 dicated that various fishes differed in their ability to separate colors al- 

 though they had little difficulty in separating colors from shades of gray 

 of equal intensity. The elritze (a minnow) could distinguish blue from 

 green but confused red with yellow. The stickleback could discriminate 

 red from green, but not blue from yellow. ^"^ 



Most of the kinds of fishes tested seemed to respond well to red, and 

 either to shun or prefer it. In one series of experiments, untrained mud 

 minnows and common shiners were stimulated by red. In daylight the 

 mud minnows had a respiratory rate of 30 per minute. When a ruby glass 

 was placed over the source of light, the fishes settled to the bottom, had 

 fits of trembling, and more than doubled their rate of opercular move- 

 ment. The common shiners "breathed" 60 times per minute in diffuse day- 

 light, 85 times per minute when a carbon filament light was turned on in 

 addition, and 150 times per minute when a ruby filter was placed over 

 the light. 



When trained to feed in response to a definite color, small fishes that 

 were offered a whole spectrum on the wall of the aquarium gathered in 

 the particular region of color to which they had been conditioned, and 

 followed the movement of the spectrum. Carp were trained to give a 

 positive response to a voilet disc but a negative one to a blue disc, and to 

 move to a white triangle in preference to a white square. When confronted 

 with a violet square and a blue triangle, these fish went to the violet 

 square in preference to the blue triangle, suggesting that the stimulus 

 of color was stronger than the stimulus of shape. 



These laboratory experiments indicate the importance of color in the 

 vision of fishes. Most fishermen are aware of the preferences shown by 

 largemouth bass for red, orange, and yellow. In an Illinois lake, red and 

 white casting baits had a catch rate for largemouth bass of 3.5 times that 



