Preanal Trunk Pigmentation 



The preanal trunk region is free of dermal 

 pigmentation in larvae smaller than 10.7 mm. ; 

 the only pigmentation present is internal, along 

 the dorsal part of the abdominal cavity. The 

 pigmentation here consists of 7 to 10 large 

 pigment spots, each composed of either a single 

 melanophore or several small melanophores 

 which are contiguous. These melanophores can 

 be seen through the thin abdominal muscula- 

 ture in larvae smaller than 8.4 mm. (fig. 2A-D) . 

 The number of abdominal melanophores in- 

 creases and they spread out ventrally over the 

 peritoneum when the larvae are about 6.8 mm. 

 long, but not in all larvae — see, for example, the 

 8.4-mm. larva of figure 3B. Evidently this 

 spreading of melanophores varies among in- 

 dividuals. The abdominal melanophores of the 

 10.7-mm. larva have spread ventrally over the 

 dorsal one-third of the digestive tract, and a 

 few dermal melanophores have developed on 

 the surface of the body over the dorsal part of 

 the abdominal region (fig. 3C). Subsequently, 

 only these dermal melanophores are noticeable, 

 owing to a thickening of the abdominal mus- 

 culature. Dermal pigmentation is lacking along 

 the ventral surface of the body in the abdominal 

 region. The 17.8-mm. larva has about 14 small 

 dermal melanophores on the dorsal part of the 

 first few myomeres, and a wide band of dermal 

 melanophores over the lower half of the body 

 posterior to the pectoral fin. This band extends 

 to the level of the posterior end of the base of 

 the anal fin. 



Orton (1953) has shown that in certain 

 teleost larvae, including two scombroids, Pneu- 

 matophorus diego and Sarda, lineolatiis, the 

 pigment cells along the dorsal region of the 

 body migrate ventrally and that in all pelagic 

 species that she examined the first "wave" of 

 pigment migration is typically completed in 2 

 days after hatching. In all except one wahoo 

 larvae that I examined, the pigment spots were 

 in a ventral position. One larva had a pigment 

 spot at the nape (fig. 2B) ; possibly this was a 

 melanophore that had not yet migrated 

 ventrally. 



Postanal Trunk Pigmentation 



Two stages of pigment formation are evident 



in the postanal trunk area. The first is seen in 

 larvae less than 4.4 mm. long, which usually 

 have one but sometimes two or three melano- 

 phores on the ventral midline of the body near 

 the caudal peduncle, and, in most specimens, 

 a very small melanophore is near and ventral to 

 the posterior end of the notochord (fig. 2A-D) . 

 These pigment spots resemble those in larvae 

 of skipjack tuna. The second stage is seen in 

 larvae 5.8 to 6.2 mm. long (fig. 2D) ; the 

 melanophore at the caudal peduncle region has 

 migrated anteriorly to the base of the anal fin 

 and has increased in size. The 6.8-mm. larva 

 has a group of fine granules of pigment that 

 extend along the base of the anal fin (fig. 3A) 

 in place of the enlarged melanophore; this pat> 

 tern prevails until the larvae are more than 10.7 

 mm. long. In the 13.2-mm. larva, the granules 

 of pigment are replaced by a series of evenly 

 spaced melanophores that extend from about 

 the middle of the anal fin to the base of about 

 the eighth anal finlet (fig. 3D) . 



Fin Pigmentation 



Fin pigmentation is not extensive, except on 

 the first dorsal fin. Some fins, the pectoral, 

 pelvic, and caudal, are unpigmented throughout 

 the larval and early juvenile stages. Pigmenta- 

 tion on the first dorsal fin develops when the 

 larvae are 10.7 to 13.2 mm. long. At 13.2 mm., 

 at least the first five interspinous membranes 

 of the first dorsal fin are pigmented with scat- 

 tered melanophores of various sizes (fig. 3D), 

 and at 17.8 mm., the first eight interspinous 

 membranes are pigmented. In the 17.8-mm. 

 larva, melanophores are also developed on the 

 basal portion of nearly all dorsal and ventral 

 finlets. When the juveniles are about 23.7 mm. 

 long (see Strasburg, 1964: fig. 2), the basal 

 half of the entire first dorsal fin and of all 

 dorsal and ventral finlets is darkly pigmented. 



CHANGES IN BODY PARTS 



To study the growth of body parts, measure- 

 ments (table 3) were made as described pre- 

 viously. Measurements of the larger body 

 dimensions, such as standard length, head 

 length, and distance from snout to anus and 

 snout to second dorsal fin, were made to the 



306 



MORPHOLOGY AND DISTRIBUTION OF LARVAL WAHOO 



