Laboratory and on the coast at Mitsu, Tagata-gun, Snizuoka Prefecture. 

 Materials used were sardines and anchovies. It would have been all right 

 to have used the same method as that employed in the experiments described 

 in the preceding section, placing the fish in a perfectly tightly closed 

 container of sea-water of a definite volume, leaving them until they 

 died of a lack of free oxygen, and then determining the oxygen content at 

 the time the fish died, however, the point to be particularly noted here 

 is that there is considerable variation in the resistance to oxygen 

 deficiency as between individuals and between different sizes of fish 

 (see Table 7). Therefore when a large number of bait fish are suffocated 

 at one time and an attempt is made to determine the lethal level of 

 oxygen,-^ in the end the fisn with the highest resistance are left alive. 

 Consequently the value for the lethal oxygen level obtained at this time 

 is thought to be inaccurate for tnese fish, Tnerefore the author made 

 several score experiments on individual fish using a bowl-shaped glass 

 vessel of known capacity as shown in Figure 7, This glass was placed 

 in the water in a vessel of large size in which a number of bait fish had 

 already been released.. Then, taking care not to excite the fish, one 

 was caught inside the vessel and it was quickly sealed by a cover ground 

 to fit perfectly. The experiment was then kept under close observation 

 until the fish suffocated. When it was completely suffocated, the vessel 

 was removed, shaking it during the removal, the cover was taken off, 

 and the water was immediately sampled The water temperature and the 

 free oxygen content, were determined, and by repeating such experiments 

 several score times and finding the average values the lethal level of 

 free oxygen for bait fish was obtained. 



At this time, in order to judge accurately the instant of suffoca- 

 tion of the fish, care must be paid to the following items When the fish 

 is first shut up in the glass bowl, it immediately becomes more or less 

 agitated, but with the passage of time it settles down and as it does so 

 its breathing rate returns to normal and becomes about 60 per minute 

 (in the case of the sardine) . However, as tne concentration of free 

 oxygen becomes thinner and approaches the lethal point the fish again 

 becomes excited and shows marked uneasiness and restlessness. The rate 

 of respiration exceeds 100 per minute, showing the so-called hyperpnoe. 

 In a bait tank at this time tne fish stick their snouts above the surface 

 of the water in the so-called hanaage /~nose-raising_7. When the oxygen 

 is gone and the lethal level is finally reached, the fish are almost 

 still, the depth of respiration is great, and tne breatning rate diminishes 

 greatly to 2 - 3 per minute,. Then the fish appears to be unconscious, 

 lies on its side, and the only movement that it makes is to bend its body 

 to the left and right from time to time, in many cases with the mouth 

 wide open, Wnen this condition is reached respiration by means of the 

 gills has already completely ceased, and consequently the sardine no 

 longer consumes the free oxygen in the water. Thereafter the fish 

 carries on so-called airless breathing, and according to the studies of 



IV, Technician Kinosuke Kimura is carrying on experiments by this method. 



11 



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