RECENT STUDIES ON TUNAS AND MARLINS IN JAPAN 171 



same method. Ban (1941), Higashi (1941), Ikebe (1939, '40, '41) re- 

 ported the growth of K. pelamis, N. macroptenis, P. mehachi, G. germo 

 by the method of size composition of the catch. Kimura (1932, '35) 

 worked on the same problem about T. orientalis and N. macropterus, 

 by the seasonal change of size of catch in the Izu Region. Recently 

 Moore (1951) reported that of N. macropterus near Hawaii. The 

 growth rates obtained by these workers have big differences from each 

 other. For example, about that of N. macropterus a. big difference 

 exists between Aikawa & Kato, Kimura and Moore. To examine the 

 numerous samples to get the accurate age composition of population, 

 instead of size composition, the centrum reading method is inconven- 

 ient. So now the scale reading method is going to be established by 

 Hiyama, as the scale samples can be collected easily from numerous 

 specimens before the fish is dissected. It is already affirmed by him that 

 the ring in the scale is formed once a year during a certain long season. 

 It will be published in the near future, and now the age determination 

 by this method is going on to get the age composition of the catch. 



(5) Feeding Habit 



Many reports have already been published on the stomach contents 

 of these fishes, but many of them are fragmental and not enough to 

 see the relationship between foods and migration. Nakamura (1936) 

 noticed the difference of the stomach content of N. macropterus in the 

 Celebes Sea between the fish caught during the Northeast wind season 

 and that caught during the Southwest -wind season, and by this he 

 guessed the seasonal change of the fauna in this region. Suyehiro (1936) 

 reported the stomach contents of K. pelamis and he also (1938) re- 

 ported that of N. macropterus, P. sibi, and T. orientalis. A group 

 of biologists with us are now working systematically on the stomach 

 contents of these fishes, but the results are not ready for publication. 

 In general, these carnivorous oceanic fishes have less tendency to be 

 selective as to food, as so many various fishes may be found in their 

 stomachs, sometimes including the garbage of vegetables thrown out 

 from boats. Marlins are generally taking larger fish having greater 

 swimming power than tunas. And the latter, though variation accord- 

 ing to species is shown, generally has a tendency of a plankton feeder 

 in any degree, and it is most conspicuous at G. germo. With reference 

 to fishing, the reason why some school of tunas would not take the bait 

 was investigated by Suyehiro (1938) and others. 



Literature Cited 



Aikawa, H., 1933. Fishery conditions on the Pacific coast for skipjack, tuna, 

 and sauries. Proc. Sci. Fish. Assoc, vol. 5, No. 4, pp. 354-369. (Jap.) 



