such as the presence of visitors or an urge to chase a school 

 of baitfish wrdch was present in the tanko Experiments which 

 were attempted under these conditions gave erratic results and 

 were rejected o 



All expieriments were performed while the tank was illumi- 

 nated by two 60-watt bulbs (L and M in figo lii) which were 

 suspended about 6 feet above the water's siirface . These lights 

 were not extinguished during the experiments for fear of fright- 

 ening the fish and causing them to ram the walls » They served 

 to illuminate the tank sufficiently for observations to be 

 made of the behavior of the fish in waiting for the establish- 

 ment of control conditions and during the experiments o 



RESULTS 



Several series of experiments were conducted between 

 August 20 and September 18, 195l> each on a different night 

 and therefore each under slightly different environmental con- 

 ditions „ They are discussed below in the order in which they 

 were performed c 



S eries i— Reactions to white?/and colored beams o f light from 

 a carbon arc Ija j^ "" — — _ 



The results of experiments with & continuous horizontal 

 beam from a carbon arc lamp are sho^vn in table 2o The estimated 

 intensity of the beam, using white light, was about k50 foot 

 candles (the apparatus for measuring the intensity was not avail= 

 able at the tine of the experiments)., Only one yellowfin was 

 present in the tanko 



After control conditions were established^ the Masonite 

 shutter was slid from the window as quietly as possible and the 

 beam was allowed to penetrate the tank for 5 minutes » During 

 this period, the tuna entered the field llj times m Experiment 

 1 and 18 times in Experiment 2o The pattern of movement was 

 fairly regularo The fish swam across the beam of light at the 

 south end of the tank, then turned around = swimming parallel to 

 but outside of the beam towards the source „ After entering the 

 field at the north end of the tankj it again turned around, 

 passing through the light beam with its one side and eye illu- 

 minated, Tnis is considered to be a definite tropistic react- 

 iono At times, attraction was also indicated when the fishj on 

 leaving the fields described a small circle in the northern half 

 of the tank, and re-entered the field, l/ilhen the light was 

 turned off, the swimming pattern was maintained for but a minute 



1/ The word "White" is used in the sense that no light filters 

 "ere employed to regulate Iha emittincr light beam's freauency, 



43 



