THE BEHAVIOR OF BROOK TROUT EMBRYOS 53 



In the experiments tabulated the trout were placed in the 

 center of the dish with right and left sides alternately toward 

 the light, so as to eliminate complication from a propensity to 

 turn toward a particular side of the body. Each fish was ob- 

 served for five minutes. The strengths of the lights given are 

 approximately what the fish actually encountered in the center 

 of the dish. It may be noted that a somewhat greater percentage 

 reacted negatively to a light 2.3 candlemeters than to a light 

 1.5 candlemeters. Above 2.3 candlemeters, however, the in- 

 crease in the strength of light seems to make little difference. 

 Brook Trout less than a week old in general react more strongly 

 to a weak light (2.3 candlemeters) than to a strong one (16 

 candlemeters). With the older fish this does not seem to be 

 true. 



The conclusion that young Brook Trout larvae are negatively 

 phototropic was corroborated by other incidental observations. 

 When a dish containing fish was placed before a window, they 

 almost invariably sought the side of the dish away from the 

 light. The same was true of the Rainbow Trout. 



In order to discover whether a Brook Trout is photokinetic, 

 a Nernst lamp was suspended about eighteen inches above a 

 dish containing them. When the light was first turned on, the 

 trout darted about vigorously, many seeking the corners of the 

 dish. After a few minutes' exposure, however, they came to rest 

 quietly as before. The same experiment was tried with Rain- 

 bow Trout with like results. It was observed that the raising 

 of a window curtain suddenly allowing the sunlight to fall on a 

 dish of Rainbow Trout, stimulated them to unusual activity 

 for several minutes. 



From these experiments it is evident that Brook Trout are 

 photokinetic and negatively phototropic. 



7. Light and Current 



It has been shown that Brook Trout are negative to light 

 and positive to current. It is desirable to know how they react 

 when the two stimuli conflict. Fish-hatchers claim that when 

 a light is placed at the head of the current, the trout go away 

 from the light, thus reversing the usual reaction to current. 

 In order to study this matter, the trough used for the current 

 experiments was entirely covered except for an opening 3 cm. 



