232 EIGHTH PACIFIC SCIENCE CONGRESS 



open sea, as no experimental studies iiad been carried out, although such 

 relations were commonly discussed. 



Laboratory experiment: 



In a black colored tank, I m. in diameter, 20 cm. in water depth, 

 a 20W electric bulb was set so as to throw its light horizontally in the 

 water, on one side of the tank called F-light, after fish lamp and the 

 other one, called M-light, which compared to the moonlight was at- 

 tached 2 meters above the water surface. The light showed 0.068 lux 

 on that surface as the light intensity of the full moon on the surface of 

 the sea was measured from 0.06 to 0.07 lux. 



Under these equipments, the gathering rate of fish to tlie F-light 

 \vas calculated for fifteen minutes at water temperature of 13°— 14°C in 

 the dark room. 



From the experiments of the gathering rates of fishes to the F-light 

 under varying intensity of the M-light in different species of fish, it 

 was found that the gathering rates of Girella punctata had almost the 

 same in either one light or two lights, while those of Pempheris japonica 

 were more considerably decreased in the two lights than in one. 



And the result of the experiment on SpJieroides niphoblse coincided 

 with that of Pempheris in spite of change in the intensities of the M- 

 light. It was observed that the gathering rates of fishes decreased in the 

 field of F-light according to the increase of intensity of the M-light; 

 and the rate increased in the field of green color of the F-light and 

 decreased in the red of it. 



From the experiments above mentioned, the relation between the 

 gathering rates of fish and spectral luminosities which were calculated 

 from the product of the relative radiant energies in place of the light 

 intensities and relative visibilities for light of the same wave lengths, 

 (Kawamoto and Konishi, 1952) will be shown as the following equa- 

 tion: 



Ga Ha 



Gb ~ Hb 

 where Ga and Gb are the values of rates of fish gathered under the F- 

 light and the M-light except in the field of the former respectively, and 

 Ha and Hb are the spectral luminosities under the fields of the two 

 lamps. 



Open sea experiment: 



A rectangular net of 20 m. x 6 m. x 3 m. was let down off the coast 

 about 200 meters from the shore near our Ichthyological Laboratory 

 and ten horse-mackerels (Trachurus trachurus L.) about 16 cm. in body 

 length and 30 gm. in body weight were set free in that net at tlie time 

 of each experiment. 



