Istiophorus orientalis --Tanaka, Shigeo, Japanese Ichthyology, p. 373, 1921. 



Tanaka, Shigeo. Illustrated atlas of useful, harmful and adnnirable aquatic 

 animals and plants, 1933. 



Jordan and Evermann. Occasional Papers, Calif, Acadenny of Sci, XII, page 46, 

 1926. 



Morphology - D. Ill, 9, XXXII-XXXV, 6-7. A. II, 11, 6. V, I, 2. 



Vertebrae-24 (12 + 12) 



Body length 3. 19 times head length, body depth 6.3 times body depth (a), 7.8 times body 

 depth (b); head length 1.40 times snout length and 7.6 times interorbital space. 



(a) Regular body depth. 



(b) Body depth at the origin of the 1st anal. Subsequent references to body depth will be to this 

 measurement. 



The length ratio of the jaws measured fronn the posterior end of the maxillary is 2. 19, 

 and the ratio of snout length to the length of the head without the snout is shown by 2. 83. The 

 body is conspicuously compressed in the anterior part, but in the caudal region it becomes 

 almost cylindrical. There are two pairs of keels on the caudal peduncle. The Ist dorsal fin is 

 greatly developed and high and has rather strong spines in its anterior portion. The length of the 

 3rd spine is slightly more than 1.3 times the body depth. The 1st dorsal fin profile is high in 

 front and gradually curved in a concave shape after which there are again very long large spines 

 dropping off gradually in the form of an arc to the end of the fin. The pectoral fins are well 

 developed, their length being 1. 1 times the body depth. The ventral fins are the most highly 

 developed among the istiophorid fishes, their tips extending approxinnately to the anus. The 

 second dorsal and the second anal are approxinnately the same shape; the number of rays in the 

 former is 6 to 7, in the latter 6. The caudal fin is greatly developed; its upper and lower lobes 

 are long and narrow and meet at a large angle. The dorsal surface is a deep purple black and 

 the belly is brownish. There are more than 10 transverse bands of cobalt spots on the sides. 

 Black spots the size of soy beans are scattered over the 1st dorsal fin. The vertebral formula 

 is 12 + 12 and all of the vertebrae are long. The rasp-like teeth are developed in both jaws, but 

 the teeth on the palatines are poorly developed and vestigial, and there is only one row of them. 



Among past reports of the ray counts for the dorsal and anal fins. Dr. Tanaka gives 44 

 soft rays for the Ist dorsal, 6 rays for the 2nd dorsal, 10 soft rays for the Ist anal, and 6 soft 

 rays for the 2nd anal, while Jordan and Evermann give 41 for the dorsal. The results of the 

 author's study differ quite nnarkedly from these, but since there are no other innportant morpho- 

 logical differences this fish is considered to be the same species as Istiophorus orientalis of 

 Japan proper. Hitherto the ventrals have been considered to have only one ray, however, it has 

 been ascertained by dissection that this is an error and it should be corrected to 1 spine and 2 

 soft rays. The second dorsal fin has 6 to 7 rays, 7 in most specimens, with 6 fish out of a 

 sample of 8 having 7 rays in the fin. 



H abits 



The seasons of migration of this species are completely different from those of the other 

 istiophorid fishes. It is most abundant in the waters adjacent to the island in the summer and 

 characteristically approaches very close to the coast. Unlike other species, the catch remains 

 comparatively high throughout the year. The juveniles are remarkably phototropic and are often 

 taken as they congregate around a night light. The fish which migrate into the waters around the 

 island in the summer have rather highly developed gonads. 



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