394 



Scientific Proceedings (131) 



These experiments serve to indicate that migration in the 

 cooler water may be influenced somewhat by the action of light, 

 and may even be in part due to light. However, the well-known' 

 fact that hibernating fish come out and swim around under thin 

 sheets of ice, after the sun has risen, may be directly correlated. 

 It is quite possible that before the sun has warmed the water, 

 its rays may serve to stimulate surface swimming. The clear 

 sky contributes to attractiveness of the shallower waters offshore. 



Alewives are known to rest in small pools at night and to 

 travel only by daylight. On the other hand, shad, although they 

 travel by daylight, evince great fcar of shadows. Light sensitiv- 

 ity is well marked in many of the migratory fishes, although it is 

 quite variable. 



2. Dark adaptation 12 hours, room darkened, monochromatic 

 lights used. 



When monochromatic lights were used, the reactions to red, 

 blue and green seemed attributable to intensity rather than to 

 color. The investigations of White, Reeves, Reighard and others 

 will be discussed in another more complete resume of the sub- 

 ject of fish responses. 



3. Light adaptation 3 hours, room darkened at time of ex- 

 periment. 



The average percents of positive heliotropism were so remark- 

 ably low in the case of both the normal temperature of 20.5°C. 

 and the lower one of 18°C. that the movements were considered 

 as random movements. After one-half hour of darkness, the 

 fish began to react definitely to light stimuli. Since the fish were 

 in their troughs undisturbed by agitation, the distinctly negative 

 results thus obtained may be considered as more reliable than 

 those reported by Hess under exaggerated stimuli from moving 

 the aquaria to the window and then into a dark-room. 



II. Temperature of troughs graduated from left to right; 

 fish dark adapted 12 hours, illumination stimuli changed from 

 warmer end to cooler end. 



Temperature 



Positive heliotropism 



Left 



Right 



Left illuminated 



Right illuminated 



32 C. 

 30 C. 

 17 C. 



28 C. 

 26 C. 

 21 C. 



60 per cent. 

 05 per cent. 

 60 per cent. 



70.25 per cent. 

 72.5 per cent. 

 75. per cent. 



