Channel and returns north. The sane species found In Nagasaki Prefecture, from 

 which the noted product of that prefecture, dried mullet-roe, is manufactured, 

 journeys to the Sfikishima Islands in Okinawa to spawn in the Kuroshio. Therefore, 

 since skipjack and tuna are fish which inhabit warm waters of constant temperature, 

 I believe it is logical to search for their spawning grounds in areas providing 

 these condltioris, namely, in the Celebes Sea, the Sulu Sea, etc. There are, however, 

 localities where small skipjack are caught throughout the year such as in the 

 Senkaku Islands off Miyako, Then there are some areas to which skipjack do not mi- 

 grate except for certain periods. What these facts suggest is as yet questionable, 



I believe the necessity exists for studying whether skipjack and tuna remain 

 in specified localities at any certain period during their development, if coastal 

 schools differ from migratorj schools, and if a single large group migrates in the 

 warm waters of the vast Pacific. In order to do this, however, it is important to 

 study by. some means the age of fish caught in the various areas. One method is by 

 examining the rings appearing on scales and vertebrae, I feel that the selection 

 of Palau as a principal research point is ideal as skipjack and tuna can be caught 

 there throughout the year and it is near their presumed spawning grounds, 



Mr. Takeda, did you visit the Philippines and Borneo areas? 



Takeda : I was informed of this meeting by Mr. Marukawa, but now that I am here, I 

 find I have verj' little to contribute to the discussion. Because I specialize in 

 fishing, I have experimented with fishing techniques but not in biology. With the 

 recent increase in the price of skipjack and tuna livers, the entrails of these 

 fish are being retained. Therefore, I believe the collection of reproductive or- 

 gans has been simplified. 



In 1930, 1 went to the Sulu Sea between November and December to fish for tuna. 

 Skipjack, however, are abundant in this season. In Japanese waters, the fishing 

 vessel is generally directed to a sighted school of fish, but in the Sulu Sea, 

 skipjack approach the boat. At first, small carangids gather around the buoy tied 

 to the longllne and these gather around the stem of the ship after following the 

 longllne when it is hauled In. The skipjack strike for the carangids as the vessel 

 proceeds to take in the line. These skipjack, weighing about one kan (8.27 lbs.) 

 were brought back to Japan and their ovaries measured over 1.2 ahaku (1.19 ft.) In 

 length [t J . These are presently preserved at the Kochl Prefectural Fisheries Ex- 

 perimental Station. Thereafter, I went to Borneo at the request of Mr, Marukawa to 

 experiment in the artificial fertilization of skipjack. When I arrived there, how- 

 ever, I discovered that the ovaries of skipjack were not as large as described. 

 Ovaries about 5 to 6 sun (6 to 7.2 inches) can be found almost all year round, but 

 I never found many which were ready to extrude mature eggs. Dried skipjack sticks 

 are made of female and male skipjack. It is very difficult to distinguish between 

 males and females by observation. We once thought that fish with large bellies 

 were females, but were surprised to find them males. As a consequence, it is Impos- 

 sible to conduct experiments on artificial fertilization haphazardly aboard skipjack 

 vessels. Actually, we never did conduct this experiment because we couldn't dif- 

 ferentiate between a male and female skipjack. I believe that research would gain 

 through study of the egg, 



Marukawa : The simplest way to tell between a male and female skipjack is to observe 

 the shape of the tip of the head. Fish with pointed lii^when observed from over- 

 head are males and those with rounded lips are females. I don't think that there 

 are any other methods for distinguishing between the two sexes. When fish are 

 observed from posteriorly, those iriiich become narrow from the eyes forward and have 

 sharply pointed lips are males j females are those with somewhat rounded lips. 



