follows: ". . . the profile of head, tip of snout and 

 center of eye are on a nearly equal level" (Ueyanagi, 

 1963a). In addition, the shape (arrangement) of the 

 pterotic and preopercular spines is diagnostic for lar- 

 val identification (Ueyanagi, 1974). 



On the vertical distribution of billfish larvae, 

 Ueyanagi (1964) indicated that larvae appear to be 

 distributed most abundantly in the surface layer dur- 

 ing the daytime and vertical, diurnal migration seems 

 to occur in the upper 50 m of waters (Table 3.). 

 Billfish larvae appear from time to time in the 

 stomach contents of the larvae and juveniles of 

 sailfish and swordfish, Xiphias gladius (Arata, 1954; 

 Gehringer, 1956). It is assumed that striped marlin 

 larvae are therefore preyed upon by many surface 

 feeding species, including the billfishes. Considering 

 the very large numbers of eggs spawned by the striped 

 marlin (see 3.15), it appears that mortality at the lar- 

 val stage is extremely high. 



Time of first feeding: No direct information is 

 available. There is an observation that five copepods 

 were seen in the stomach of a 3.9-mm sailfish larva 

 (Gehringer, 1956). 



Type of feeding: There is no information pertaining 

 to the larvae of striped marlin. Of the larvae of sailfish 

 in the Atlantic, Gehringer (1956) noted that 

 "copepods constituted the food of specimens less than 

 6 mm. long. At this size fish larvae also were eaten, 

 and no specimen exceeding 13 mm. had copepods in 

 its stomach." Furthermore, it is also known that 

 sailfish larvae have consumed istiophorid larvae half 

 as long as their own body length. It is believed that 

 the larvae of striped marlin, like the sailfish, begin to 

 feed on fish larvae after reaching a size of about 7 mm. 



Table 3.— Comparison of numbers (and percentage) of tows 

 from which istiophorid larvae were captured, showing the var- 

 ious depths and times of towing, in the western Pacific area. 

 (From Ueyanagi, 1964.) 



3.23 Adolescent phase 



Nakamura (1968) described the juveniles of striped 

 marlin based on two specimens collected from the 

 South Pacific and the western Indian Ocean (see 

 2.21). His drawing has been reproduced as Figure 4. In 

 the juvenile stage the snout is very elongate and, in 

 fact, is longest at this stage relative to body length. 

 The shape of the first dorsal fin still differs from the 

 adult configuration, being highest anteriorly and 

 decreasing gradually in height posteriorly. The 

 arrangement of the viscera is similar to that of the 

 adult. Nakamura also mentioned that the juvenile of 

 striped marlin is similar to that of the white marlin in 

 many respects except that the former has no ocelli on 

 the first dorsal fin. 



It is believed that large, powerful pelagic fishes such 

 as tunas, billfishes, dolphins, etc., are the principal 

 predators of juvenile striped marlin. 



Little is known about parasites in juvenile striped 

 marlin. 



Immature striped marlin (80-100 cm eye-fork 



Figure 4.— Juvenile striped marlin (121.5 mm body length) collected from the southwestern Indian Ocean. (From 



Nakamura, 1968.) 



143 



