RECENT STUDIES ON TUNAS AND MARLINS IN JAPAN 169 



germo, down to the east of Bonin Island in March, and fades away. 

 Nakamura and others (1951) think that the spawning ground of this 

 fish would be in the South from subtropical convergence, because they 

 found so many juveniles of this in this area. 



(3) Spawning Habit 

 In general, Nakamura thinks these oceanic fishes have a long spawn- 

 ing season, sometimes almost all year round, and have their spawning 

 grounds widely distributed throughout tropical and subtropical, and 

 sometimes even in temperate zones in the Pacific, based upon the recent 

 data of collection of eggs and juveniles of these fish kinds, done inten- 

 sively by Japanese research vessels. Regarding the spawning grounds 

 of Katsimonus pelamis, many biologists, such as Schaefer & Marr 

 (1948), Shimada (1951), and Wade (1950, 1951) reported juveniles 

 from various parts in the Pacific. Yabe (unpublished) got ten indi- 

 viduals of 5 to 10 mm. long juveniles of this species from the collection 

 of our research vessels during 1947 to 1952 from near Ryukyu, off Hon- 

 shu and in Micronesia in April to September. Suda (unpublished) 

 found large numbers of juveniles from stomach contents of tunas and 

 raarlins caught from various parts of the Pacific, and found evidence 

 that the smaller (5 to 20 mm. long) juveniles are obtained from the 

 area south from subtropical convergence, and the larger ones (over 20 

 mm. long) were found in the area to the north. About Thunnus ori- 

 entalis, Kishinouye (1923) thought that this would spawn in June 

 and July in the area off Honshu, but later Kawana (1935) reported its 

 spawning in the Japan Sea, and Nakamura (1938, 1939) found the 

 ripened ovarium in the fish caught near the Philippines from the middle 

 of April through the middle of May. About Germo germo, Watanabe 

 (1939) reported that he obtained the ripened ovarium in the fish caught 

 near Midway Island, and Schaefer (1948) and Brock (1943) got some 

 idea on this matter. The data obtained by Japanese research boats are 

 now under investigation. About Parathinmus mehachi, Shimada (1951) 

 found ripened ova in the fish caught from the area 143-160'^E, 1-10°N 

 from June to September, and thought that the spawning season might 

 continue later than this period. Recently biologists on board the re- 

 search boat of Nankai Regional Fisheries Laboratory succeeded in the 

 artificial fertilization of this fish in the equatorial region. About N. 

 7iiacropterus, Nakamura (1939, '43, '49, '51) reported that he found 

 ripened ova in the fishes caught in the South China Sea from March 

 to May. Wade (1950) thought the season near the Philippines was 

 from May to August, and afterwards he obtained the juveniles (9.4-37.5 

 mm. long) and could assure both the locality and the season. Shimada 



