style tank, with pump circulation, are over the old type$, particularly 

 from the point of view of the lack of free oxygen . 



The figures shown in Table 9 are the results of experiments in the 

 new bait tanks of the Fuji Maru» Because this was the very beginning of 

 the tests and the operators were unfamiliar with the equipment, a great 

 quantity of bait was too quickly placed in the tank at one time, and the 

 spray pump was not used, so the excited fish congregated densely near the 

 surface, and the increased circulation was almost without effect,, Barely 

 30 minutes after the fish were placed in the tank the free oxygen concen- 

 tration had fallen far below the lethal level for sardines and anchovies, 

 and all of the bait quickly suffocated and perishedo 



This indicates that when placing bait fish in the tanks one should 

 avoid putting a great number in at one time, and the spray pump should be 

 utilised fully to prevent the fish^, immediately after they have been 

 placed in the tank, from congregating densely near the surface and creating 

 a localized lack of free oxygen 



t 



The experiments shown in Table 9 utilized new "wild" bait fish 

 while the results of previous experiments using tame bait were as shown 

 in Table 10 c Because the fish had become accustomed to confinement in a 

 net live-pound and the number put into the tank was comparatively few, 

 not many of the sardines crowded together near the surface when they were 

 placed in the tank, and so, even though the spray pump was not used, and 

 the free oxygen content 30 minutes after the fish had been put in the 

 tank was only a thin 2 o 70 cc per liter , as the fish settled down the 

 effectiveness of the pump circulation was apparent, the free oxygen in- 

 creased quickly j, and it was possible to complete the experiment without 

 mishapo 



From the two examples cited above it will be seen that when bait fish 

 are held in a new pump-type bait tank, the oxygen supply must be made 

 ample during the first hour or so when the fish are excited and liable 

 to crowd together near the surface and that thereafter there is absolutely 

 no need to worry about a lack of free oxygen., On the other hand, in the 

 old-fashioned bait tanks used hitherto,, which depend wholly on natural 

 circulation, even though it is possible to get the bait into the tank 

 safely in the first place, if the motion of .the vessel becomes slight, it 

 often happens that because of insufficient oirculation a lack of free 

 oxygen develops and the fish begin to stick their noses out of the water. 

 In Tables 12 and 13 are shown the results of actual tests in which the 

 new and old style tanks of the Fuji Maru were compared by putting into 

 them an approximately equal number, in relation to their respective 

 water capacities, of wild bait fish caught 5 hours before and then 

 cruising for a long period of time in the calm waters of Suruga Wan» 



As can be seen from these two tables, in both cases good success 

 was attained in reducing to a very great extent the diminution of free 

 oxygen in the critical first hour after the fish were placed in the bait 



16 



