the lineso They are extraordinarily strongs, and it is not 

 unusual for a large black tuna to drag a glass ball float 30 

 cnio in diameter deep down into the water, sometimes so far 

 that it is burst by the water pressurOo 



According to Dro Kishmouyej the tunas do not seek food on 

 the bottom of the ocean^ but it appears that one cannot make 

 an absolute statement to that effecto As a concrete examples, 

 the author has seen dead leaves and gravel among the stomach 

 contents of several yellowfin, Since these yellowfin were 

 taken in the vicinity of Halmahera I„ and Sangi lo , it may be 

 thought that there is a possibility that these fish seek food 

 on the bottom near small islands and reefso Of coursej it is 

 hard to believe that these dead leaves and gravel were eaten 

 by the yellowfin as food^ so it should probably be considered 

 that they were swallowed along with some animals from the 

 bottomo 



Figure 3o— Juvenile /blaoV^ tuna (after Gamahara) 



iiic Spawning and growth 



The facts that are known concerning the spawning of "che 

 fishes of the family Thunnidae are extremely fewj only a 

 certain amount of information being available in regard to 

 the black tuna and the yellowfinc. 



The spawning season of the black tuna which migrate into 

 Japanese waters is thought to be about June to July, and it is 

 believed that they spawn in the offshore waters of the Pacifico 

 Dro Kishinouye says "in June and July the gonads become extra- 

 ordinarily large and the fish congregate at the surface, 

 frequently showing their dorsal fins above the water. This 

 phenomenon is seen in the northern coastal waters of Japan on 

 both the Pacific and Japan Sea sidesc These ripe fish are 

 mixed in with immature fisho I have not yet seen any completely 

 ripe gonads, but in August the gonads are already spent,, For 

 these reasons it is thought that the black tuna spawn in the 

 offshore waterso In late summer and early autumn small 

 juvenile fish appear off southern Kyushu" and central Honshu, 

 however, tuna with ripe gonads are unknown from these waters » 

 Ripe adult fish are seen farther north, but it is hard to believe 

 that these juvenile fish have migrated down from the northo" 

 Kawana (1935) has also reported spawning in the Japan Seao 



At the time when Dro Kishinouye voiced the above views, 

 the southern limit of the distribution of the black tuna was* 

 thought to be in the waters adjacent to Tanegashima, In 1935 



13 



