FUNDAMENTAL STUDIES ON THE FISH LAMP 233 



At one side o£ the net, a fish lamp which directed horizontally to- 

 ward the other side was fixed one meter under the water from the sur- 

 face and a 20W, 60W or lOOW electric bulb was used as a light source 

 of the fish lamp, and attached to it was a gieen glass filter 18 cm. in 

 diameter which had a limit of transparency from 500 m/x to 570 m^ 

 and maximum wave length of transparency of 530 m^. 



The weather was frequently stormy during the experiment, as this 

 study had to be carried out from November to February in 1950—1951, 

 and difficulties had often been experienced for observing the phenomena 

 in the roughing sea. The water temperature measured from 14.0° to 

 15.5°C in these experiments. 



The numbers of fish which gathered in the area of light field with- 

 in three meters from the lamp were calculated as the rate of gathering 

 for twenty minutes in every thirty seconds. 



In the dark night experiments, the gathering rate attained about 

 80% within the time of two minutes and 30 seconds after the light 

 was switched on, and continued its rate at the light source of 20W of 

 the fish lamp. 



The rate of gathering in the night of the moon age of 9.8 decreased 

 to 77.8% as compared with the data of the rate of gathering in the 

 dark night and, moreover, decreased to 21% at the moon age of 10.7. 



The rate became zero at the 11.8 moon age, and no reaction of 

 fish to light was seen. 



As the light intensity of 11.8 moon age was almost equal to that 

 of 18.0 moon age, it might be supposed that the fish would not show any 

 reaction to the fish lamp in the period between those two ages. 



From these experiments, observation was made that the conditions 

 of gathering rates of fish differed according to the kind of bulbs, 20W, 

 60W, or lOOW respectively, and it was considered that the 20W electric 

 bulb was most adequate in the limit of the size of this experimental 

 net, since the rates of gathering became irregular in the light sources of 

 60W and lOOW. 



It turned out clearly that the effect of the fish lamp was influenced 

 by the moonlight from the results of experiments in the laboratory and 

 in the open sea; however, the authors concluded that the efficiency of 

 it might be kept in some limit by adjusting the strength of intensity 

 of the fish lamp. But the relation of those intensities has not as yet been 

 sufficiently studied, and it will be cleared in a later experiment. 



In the course of these studies, it was also understood that the ef- 

 ficiency of the lamp was considerably influenced by facts such as the 

 tidal current, direction of wind, and temperature of the sea water, etc.; 

 and the relation of these factors to the lamp will be studied later as 

 those must never be passed over. 



