The left and right chambers were equipped with electric heating devices, 

 cooling devices, and agitators „ The tank was filled with sea-water, the 

 cover was tightly closed so as to prevent contact with the air, the sar- 

 dines which were to be tested -- Sardinia melanosticta that had been in 

 captivity for two days were used ~ were placed in the tank, and as the 

 sardines consumed the limited free oxygen in the water and until they 

 began to respire with difficulty, water samples were drawn off from time 

 to time (from the sampling tap using a force pump) , and the degree of 

 diminution of free oxygen was determined by Winkler's method,, 



In the following Table 1, Table 2, and Table 3 the average number 

 of fish is 10, and the average total weight is 265 gnu In the experiments 

 recorded in Table 4, Table 5, and Table 6 these amounts were about doubled, 

 that is, the average number of fish was 20 and their average total weight 

 was 556 grtic The duration of the experiment was until all of the fish 

 being tested showed marked difficulty in breathings In the case of the 

 first experiment it was three hours, and in the later experiment it was 

 one hour and thirty minutes.. The amount of free oxygen is shown as the 

 number of cubic centimeters contained in 1 liter of sea-water- 



The diminution of free oxygen which gave rise to abnormal respira- 

 tion, as shown in each table, is shown graphically in the following 

 figures* In the first three, that is, in Figures 1, 2, and 3 corres- 

 ponding to Tables 1, 2, and 3, the slope of the curves is gentle. In the 

 latter three, that is, in Figures 4, 5, and 6, corresponding to Tables 

 4, 5, and 6, they are steep. It can be seen that, regardless of the 

 steepness of the curves, the values for the concentrations of free 

 oxygen that produced difficult respiration are all roughly equal. It can 

 be seen clearly that in the case of tne latter three, which involved 

 nearly double the number of fish (total weight) of the first three experi- 

 ments, the oxygen was consumed and the difficult breathing appeared with 

 nearly twice the speed shown in the first three The author has observed 

 and reported on the same relationship in the case of mixed groups of 

 sardines and anchovies<,4) 



Accordingly, if the number (total weight) of bait fish kept in a 

 bait tank is increased, either the amount of water circulated must be 

 amplified, or other appropriate means must be employed to supply enough 

 free oxyger; - 



b) Lethal level of free oxygen 



In the preceding section it has been described how the sardines begin 

 to breathe abnormally as they consume the limited free oxygen in sea-water 

 by their respiration, and how the concentration of oxygen finally gets so 

 thin that it will not support life* This section reports the results of 

 experiments on the concentration of free oxygen insufficient to support life, 



The experiments were carried out in the latter part of August, 1932, 

 and in late December, 1933, at the Kanagawa Prefecture Misaki Marine 



