mm in length, three more characters are useful 

 — number of dorsal rays, shape of the dorsal fin, 

 and the nature of the lateral line. 



Another problem with some of these characters is 

 that they are very difficult to use. The number of 

 dorsal fin rays that I have compiled in Table 1 ex- 

 hibits a greater range than those given by Ueyanagi 

 (Table 3). Therefore, a young specimen with ray 

 counts at the extreme of the range — for example, a 

 spearfish with 47 dorsal rays — is within the range of 

 the sailfish. This specimen could be further compli- 

 cated by having its dorsal fin fixed in the retracted 

 position. Such a specimen is difficult to evaluate 

 because it is almost impossible to erect the dorsal 

 fin to determine its shape. Measurements are very 

 difficult to make, particularly on the very small 

 specimens less than 8 mm in standard length and, 

 more often than not. the bodies are bent and the 

 opercles are expanded. This latter feature makes it 

 very difficult to maintain the animal on its side for 

 making measurements under a microscope. Even 

 when opercles are flattened in their normal posi- 

 tion, measurements are difficult because the ob- 

 server has to carefully manipulate the specimen in 

 order to maintain the two points of measurement on 

 a plane parallel to the plane of the measuring device. 



Determining whether or not the anterior edge of 

 the orbit projects is very difficult to evaluate. I have 

 trouble with this character when I am simultane- 

 ously comparing this feature on specimens which 

 have it projected and those which do not. Invari- 

 ably, there are specimens for which this decision 

 cannot be made. I have this same trouble with the 

 character of whether or not the tip of snout is 

 above, below, or on the same plane as the eye. If 



the specimen is fixed with its mouth open the tip of 

 the snout is invariably above the center of the eye. 

 Attempts to close the mouth generally distort the 

 specimen so that this character is unusable. 



I am suspicious of the premise that Indo-Pacific 

 cognate species will resemble those from the Atlan- 

 tic. Both white marlin juveniles collected in the At- 

 lantic have 4 or 5 prominent ocellus-like spots 

 (bright orange in life) on the dorsal fin. Its cognate 

 from the Pacific, the striped marlin, as illustrated by 

 Nakamura (1968), has a solid black dorsal fin. 



In order to evaluate these identification methods 

 more fully, I examined 86 istiophorid young ranging 

 in standard length from 2.8 mm to 20.8 mm. Six of 

 these specimens were collected and identified by 

 Ueyanagi — five were Pacific blue marlin and one 

 was an Atlantic blue marlin. The remaining 80 were 

 all collected in the vicinity of Miami or in the cen- 

 tral Gulf of Mexico and the distribution of adults 

 from these areas could reveal the presence of the 

 young of four species — sailfish, blue marlin, white 

 marlin, and longbill spearfish. Only 11 specimens 

 were 12 mm or longer in standard length. For each 

 specimen I made the following measurements: 

 standard length (tip of snout to the end of the 

 notochord or hypural plate), snout length (from the 

 tip of the snout to the anterior edge of the orbit), tip 

 of snout to center of eyeball, horizontal diameter of 

 the eye, horizontal diameter of the orbit, head 

 length, distance upper jaw extended beyond the 

 lower jaw, and length of the pelvic fin. On a few 

 specimens, the vertical diameter of the eye and 

 orbit were taken, but I eliminated this measurement 

 because on many specimens the upper jaw bones 

 projected above the lower rim of the orbit and eye. 



Table 3. — Diagnostic characters usable in distinguishing the istiophorid larvae more than 

 20 mm in standard length modified from Ueyanagi (1964). 



Species 

 characters 



Tetrapturus 

 angustirostris 



Istiophorus 

 platypterus 



Tetrapturus 

 auda.x 



Makaira 

 mazara 



Makaira 

 indica 



Number of first More than 48 

 dorsal fin rays 



43-47* 



Less than 45 Less than 45 Less than 45 



Shape of first Anterior-high Poterior-high Anterior-high Anterior-high Anterior-high 

 dorsal fin type type type type type(presumed) 



Lateral line Single Single Single Complex-having Not single (?) 



branches (obscure)** 



*This range is estimated from a small number of specimens. 

 "Lateral line pattern not yet ascertained. 



67 



