A SIGHT REFLEX SHOWN BY STICKLEBACKS. 



WALTER E. CARREY. 



The casual observer of the aquaria of the United States Fish 

 Commission at Woods Hole, Mass., always evinces considerable 

 interest in the behavior of the schools of sticklebacks (Gaster- 

 osteus bispinosus) which are exhibited annually, the attention be- 

 ing attracted by the very characteristic way in which these little 

 fish swim about. During the summer of 1900, while at the 

 Marine Biological Laboratory, the author made some observa- 

 tions bearing on these movements and extended them during the 

 summer of IQO./).. 1 



In walking past the aquarium it was noticed that all the fish 

 were oriented with the long axes parallel and that the whole 

 school swam in a course parallel to, but in a direction opposite 

 to that of the moving observer. When the observer stoos the 



o j. 



fish may also stop, but usually continue swimming in the same 

 course, although at a slower rate, till they reach the end of the 

 aquarium, where they usually remain as long as the observer is 

 quiet. If the observer retraces his steps they again orient them- 

 selves and swim back to the other end of the aquarium. At first 

 sight this looks like simple fright with movements limited by the 

 walls of the aquarium, but this is not the case as the following 

 experiments will show : 



If the observer remains stationary opposite the center of the 

 aquarium and moves some object, preferably a white one held in 

 the hand, horizontally, the little fish at once respond, show a 

 most beautiful orientation and movement, slow and uniform, 

 opposite to that of the moving object. This movement can be 

 arrested at any instant, or the path of motion completely reversed 

 by moving the light object in the opposite direction. This 

 reversal may be produced when the fish are in the center of 

 the aquarium and has no relation whatever to the walls of the 

 aquarium. 



1 I wish to thank the research staff of the Fish Commission for placing the aquaria 

 at my disposal. 



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