A. Tunas 



These fishes all belong to the family Thunnidae, amd are very closely related to the 

 mackerels and bonitos. 



The body is almost perfectly spindle-shaped and is adapted to swimming at high 

 speed. The root of the tail (caudal peduncle) is extraordinarily slender and is broader than it 

 is deep. This form is well-adapted to a violent, side to side motion of the tail fin. The tail fin 

 is large and strong. As the majority of these fishes are essentially warm-water fish, they are 

 most numerous in warm seas, and they characteristically make large-scale migrations along 

 warm currents. A very great number of species has been reported from the seas of the world, 

 but in actuality it is doubtful whether the number of species is so large. Even though the species 

 may be numerous, they do not after all have any great concern for us, so only the five species 

 which occur in Japajiese waters will be described here. 



1. Black tuna, Thunnus orientalis (Schlegel) 



Bluefin tuna (America). 



Depending on the locality and the size of the fish, this species has nnany names, such 

 as, inaguro, kuromaguro, kuroshibi, mejimaguro , yokowa, kakinotane . This is the largest 

 species in the family Thunnidae, attaining a length of 2.5 meters and a weight of 300 to 350 kilo- 

 grams. 



The species is characterized by short pectoral fins, the tips of which do not reach to 

 below the middle of the first dorsal fin. They can easily be distinguished from the other species 

 by this character alone. The back is a light black and the sides are greyish white. The finlets 

 (the disconnected smaill fins) behind the dorsal and anal fins are yellowish on the back and silvery 

 white on the belly. There are very sintiilar fish on the American side of the Pacific and in the 

 Australian area and by some scholars they are considered to be the same species, but it is said 

 that the dorsal finlets are blue, a characteristic which is indicated by the name bluefin. 



The flesh is dark red with something of a blackish tinge. The flesh of the belly con- 

 tains a great deal of fat, causing its color to vary in different parts from the white-spotted 

 so-called "middle belly meat" to the almost pure white "great belly meat." This part of the 

 flesh is prized as material for sliced raw fish and rice balls garnished with fish. This species 

 is delicious during the winter, but fish taken in the summer are poor eating, except for the small 

 specimens. This is related to the spawning season of these fish, the fish being fat and well- 

 flavored before spawning but lean and tasteless in-imediately after spawning. It is said that they 

 spawn in Japanese waters around June and July. The fish taken during the summer from the 

 waters off northeastern Japan and the coast of Hokkaido are fish that have already spawned. 

 These are called Sendai tuna and are regarded as inferior fish. 



This species can withstand low temperatures better than any of the other tunas, and 

 because it has the characteristic of coming connpar atively close into shore, it is taken with sta- 

 tionary gear. As far as is known at present, the southern limit of its distribution is in the vi- 

 cinity of 15 N. latitude on the east coast of the island of Luzon. It is not clear whether it occurs 

 farther to the south, but it is though^ that its range probably extends south of the Equator. Until 

 recent years it was believed that the southern limit of the distribution of this species was in the 

 vicinity of 30 N. latitude, however, this fish began to be taken in Formosa in 1935 and before 

 the war its annual production there reached a value of 1, 500, 000 ye"- The northern limit of 

 distribution is around 45 N. latitude. In the western Pacific during the winter there are some 

 catches of this species over an extensive area fronn east to west in the vicinity of 30 N. latitude. 

 Before the war splendid catches were made in January and February to the south of Kyushu, but 

 this fishery has completely died out in recent years. The schools which appear to the south of 

 Kyushu moved to the northeast as it grew warmer, and a part of them followed the Tsushima 

 Current into the Sea of Japan. 



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