Hatal ; The subject seens to be somewhat clearer due to the various enlightening 

 discussions, I wish to call now upon Mr. Amemiya. 



Amemlya : I should like to refer to some ooints which come to mind. Imon* skipjack, 

 there are those which live in tropic waters where temperatures remain constant 

 throughout the year, and those which frequent the temperate zone. The latter group 

 migrate as far as eastern Hokkaido. Although fishery technologists have probably 

 noticed that the quality of the meat of tropical skipjack and migratory skipjack 

 differ, this should be carefully lnvestlgat<^d. It would probably be helpful to 

 consider the problem of skipjack spawning In reference to other fish having iden- 

 tical living habits such as the flying fish. 



TTie skipjack and flying fish are both tropical forms, except in that one group 

 of skipjack migrates In summer. Since the temperature of sea water in the tropics 

 Is constant with no seasonal change, what factors determine the spawning season of 

 fish inhabiting these waters? In fact, it yet remains to be confirmed whether a 

 set reproductive period exists. Flying fish spawn In waters adjacent to Japan 

 prior to the rainy season which approaches at the end of spring. Adult flying fish 

 are even seen in October near Kishia. The spawning season of this species is not 

 fixed an'' fish with we 11 -developed eggs are occasionally seen between these periods. 

 Similar conditions may prevail for skipjackj the spawning season is probably not 

 uniform. A veteran fisherman named Yaichl Tosa, who lives at Isosone on Koniya- 

 shlma in Satsunan, says that a number of skipjack with mature eggs are seen there 

 In spring, in summer, and even in October. Towards the end of August skipjack 

 with mature and Immature ovaries can be seen at Yamakawa and Makurazaki in southern 

 Kyushu, It can be Inferred from these facts that there is no fixed spawning season 

 for skipjack in the south and that spawning probably extends over the whole year 

 with periods of peak spawning. The Japanese anchovy and the English herring spawn 

 periodically but throughout the year. This tendency is believed to prevail with 

 skipjack. Of course, it does not mean that skipjack spawn independently. T^e 

 spawning of individuals continues over a long period of time so that when observed 

 in total, it appears thnt the spawning periods are interlinked. Although the 

 gonads of skipjack inspected at the Misakl Fish Market in the summer of 194.0 af>- 

 peared to be of the same shape, there was a narked variation in development. TTils 

 indicates that the spawning of skipjack is continuous and that there nay be peak 

 spawnings which are not necessarily confined to any definite period. Keitaro 

 Uehlda and Yaichl Tosa both state that skipjack do not spawn near the surface but 

 at considerable depths. They say that tbs eggs probably float to the surface 

 after deposition. Although there is no accurate bsisls for these statements, there 

 are some points which nust be taken into consideration. 



The spawning grounds of tuna are definitely not localized but are widespread. 

 The blue fin tuna seems to spawn around July in Tbyama Bay in the Japan Sea as 

 schools of adult fish with mature reproductive organs appear in this area. This, 

 however, does not happen every year* 



Marukawa x The tunas in Formosa carry extremely large sggs in May. 



Okada ; The study of the spawning grounds of skipjack is a major problem comparable 

 to the previous study on eels by Schmidt, It apnears that the tunas of the 

 Atlantic have been fairly well studied while research concerning those of the 

 Pacific has been neglected. In referring to Mr. Amemlya' s statement that flying 

 fish spawn continuously, I feel that this phenomena occurs in localities where 

 there are slight changes in water temperature. For example, the six-pointed sponge 

 which is found at a depth of about 250 fathoms carries eggs throughout the year. 

 The change in watar temperature at such a depth is very slight during the year. 



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