howoTer, the tips of the second dorsal and the emal are white* This fish ooours 

 along the ooaats of tropioal and subtropioal regions* It is fo\md in the Ogasavara 

 Is*, the Isu Shiohito, and the Red Sea* It is not a numerous species* The fish 

 ar« said to attain a length of several feet and a weight of several tens of kan 

 [l kan ~ 8*27 pounds]* It prefers to feed on deoapterids, and the flesh is said to 

 be soft and inferior in quality* 



Family Thunnidae (ehibi -ka) 



The body is generally short and thick and very slender at both ends* The 

 dorsal surface of the head is flat, and the caudal peduncle is compressed dorsoven- 

 trally with a soaleless keel on each side* The corselet is well developed and is 

 oovei*ed by a membr«ine* The scales on this part of the body are much larger and 

 thicker than the rest; ther« are many minute scales anterior to the base of the 

 pectoral fin* Except in the genus Thunnus the posterior extension of the corselet 

 follows roughly along the lateral line, and except for the same genus there are no 

 scales aside from those on the corselet* The lateral line generally follows the 

 dorsal outline of the body* The posterior end of the maxillary does not reach the 

 middle of the eye, the teeth are small, conical in shape, and bend somewhat imrard* 

 It is uncertain whether or not there are teeth on any bones other tdian those of the 

 Jaws. 



The fins are well developed, especially in the genus Thunnus * The first dorsal 

 is high and its spines are strong* The first spine is the longest* The rays of 

 the fins aire also well developed and only those of the ventrals are articulated 

 transversely* The caudal is stiff and forked* 



The pyloric caeca are remarkably well developed end consist of a mass of fine 

 tubules at the tips of large dendriform tubes* The whole mass is covered with a 

 membrane and is pale yellowish in color* It is very large* The skeleton is very 

 delicate, the dorsal surface of the skull is roughly triangular, and there is 

 oartilage between the f rentals, parietals, and oocipitals* The posterior ventral 

 foremen of the skull opens obliquely or vertically* The operculum is scaleless 

 and its dorsal edge is indented* The fi]*st vertebra is fused to the cranium (ex* 

 cept in the genus Auxi s)'^ and there is little variation in the number of vertebrae, 

 which is 42 in the genus Katsuwonus and 39 in all the other genera* The haemal 

 spines of the posterior thoracic vertebrae are long and their tips can be seen to 

 be attached to the ribs* 



There aire blood vessels of a special type which run along the surface of both 

 sides of the body from a point posterior to the pectoral fins* Groups of capilla- 

 ries branch off from these blood vessels and enfold a laminar strip of tissue on 

 each side of the spinal column* The muscle fascicles of the enfolded portion are 

 small and soft, and the tissue is dark red in color because of the abundance of 

 capillaries* This is what is commonly called the chiai * 



The fishes of this family sometimes attain tremendous sizes, but aside from 

 the genus Thunnus most of them weigh about 8*27 lbs* They are plentiful in the 

 open sea and are widely distributed in the tempertite and tropical zones* They form 

 schools and feed on anchovies, sauries, sand lances, carangids, flying fish, squid, 

 and planktonio crustaceans* The back is indigo in color and some of them have short 

 oblique stripes on the sides of the body, black spots or stripes on the belly, or 

 white spots and stripes on a gray background* 



8 



