DISCUSSION 



It should be anphasi'?. ed that the experiments which have 

 been conducted were exploratory in nature^ and lead only to 

 tentative conclusions o If some of these appear to have practi- 

 cal application they should be checked by further studies con- 

 ducted according to planned experimental designs^ and with 

 suitable statistical analysis. 



It should also be emphasized that the strength of the re- 

 sponse to light stimuli varied to some extent from night to 

 night (apart from obvious extraneous sour'ces of interference) 

 indicating a variation in the responsive condition of the fisho 

 Therefore the results of individual experiments are not strict- 

 ly comparable from series to series o 



It should further be en5)hasized that the e}q)eriraents ware 

 conducted in a relatively small tank and hence under highly 

 artificial conditxonsr Although certain suggestions may be made 

 as to the response of tuna in the open sea to light stiraulij 

 these should be accepted with great cautionc 



Reactions to continuous white light 



The reactions of the tuna to continuous -vi^ite lights are 

 summarized in table 8^ omitting only those experiments which 

 were disturbed by known extraneous factor So From the many expe- 

 riments which showed positive results^ it is evident that the 

 tuna undergo a change in behavior when exposed to a continuous 

 white light of source intensity between 70 and k50 foot candles. 

 This change in behavior is judged to be a tropistic response to 

 the stimulus^ in that the fish approached closer to the source 

 under experLmental conditions as compared vvith control condi- 

 tions,, Moreover, with a horizontal beam, as opposed to light 

 radiated in all directions from a bulb 5 they approached the 

 source in a lin-. parallel to the beam and turned away only after 

 enterirxg the fifcji.d and approaching the baffle. There was no 

 conclusive difference in the strength of the reaction between 

 intensities of 70 and about i;^0 foot candles, although apart 

 from the results with the arc lamp (the higher estimated inten- 

 sity) there seems to be a tendency for greatest response (exper- 

 imental minus control entrances) at an intensity of I06 foot 

 candles o On the other handj vreak or no response was obtained 

 with light of low intensity (Ii7 foct candles) and also with 

 light of high intensity (530 foot cand]_es)o 



xt seems possible that tuna cculd be attracted to a light 

 at seao However,, this would have to be a very high intensity 

 to penetrate the water for any great distance , Although the 

 tuna might be attracted to a light of high intensity., it is 

 doubtful if they would approach very close tc the sourceo 



$h 



