larva (table 7). The last two finlets in the 

 23.7-mm. juvenile (Strasburg, 1964: fig. 2) are 

 situated very close together but arc not yet 

 fused. 



Anal fin and finlets. — Ossification of anal fin 

 rays occurs simultaneously with that of the sec- 

 ond dorsal fin. Although subsequent develop- 

 ment of rays and finlets is nearly identical with 

 that of the second dorsal fin and finlets, the 

 adult complement is not attained until the juve- 

 nile has exceeded 10.7 mm. long. All the rays 

 and finlets are completely formed in the 13.2- 

 mm. larva. As in the dorsal finlets, the last two 

 anal finlets on the 23.7-mm. juvenile (Stras- 

 burg. 1964 : fig. 2) are very close together, their 

 bases nearly touching each other. 



First dorsal fin. — As in the anal and second 

 dorsal fins, the base of the first dorsal fin thick- 

 ens when the larvae are about 6.2 mm. long. 

 The first two or three spines develop almost 

 simultaneously and are first seen in the 6.8-mm. 

 larva (fig. 3A). The first spines are short 

 (0.10 mm.), and, unlike the sequence of ray 

 development in the anal and second dorsal 

 fins, subsequent spines are added only posterior- 

 ly. Additional spines develop slowly; the num- 

 ber increases from 2 in the 6.8-mm. larva to 10 

 in the 10.2-mm. larva. In larvae over 10.2 mm. 

 long, however, the spines are added more rapid- 

 ly, so that 27 spines are already evident in the 

 13.2-mm. larva (table?). 



The height and shape of the fin also change 

 with growth of the larvae. Larvae between 8.4 

 and 8.7 mm. long have all six spines of equal 

 height. Shortly thereafter, the anteriormost 

 spine becomes the longest and each succeeding 

 spine is shorter than the one preceding it. A 

 concavity in the fin outline becomes noticeable 

 after the eighth or ninth spine has ossified (i.e., 

 when the larvae are about 9.0 or 10.0 mm. 

 long). All spines after the ninth are about 

 equal in height (fig. 3D). 



Pelvic fins.— The pelvic fins are the last to 

 develop. They appear first, as a protuberance 

 on the ventral contour of the body below the 

 pectoral fin base, in larvae between 6.8 and 9.0 

 mm. Unlike the interradial membranes of other 

 fins, which develop from the larval fin fold, 

 those of the pelvic fins grow out from the fin 

 base. Initially, the spine and one or two rays 



ossify almost simultaneously and are first no- 

 ticed in the 9.2-mm. larva. Both spine and rays 

 are short (0.29 mm.) , but their length increases 

 rapidly, so that in the 17.8-mm. larva (table 3), 

 the longest pelvic fin ray (1.44 mm.) is almost 

 as long as the longest pectoral ray (1.50 mm.). 

 The full complement of one spine and five rays 

 is completely formed in juveniles longer than 

 13.2 mm. 



Vertebral Column 



In the wahoo, as in many other fishes, the 

 vertebral spines ossify before the centra. A 

 vertebra is considered to be developing as soon 

 as any part begins to ossify, as indicated by 

 stain absorption. Because the anterior abdom- 

 inal vertebrae, which develop first, lack haemal 

 spines, the ossification of the neural spines is 

 the first stage of vertebral development. Neural 

 spines first appear in wahoo at 6.7 mm. The 

 number of neural spines increases rapidly from 

 1 in the 6.8-mm. larva to 10 in the 8.4-mm. 

 larva. All the neural and haemal spines are 

 partially or completely ossified in the 13.2-mm. 

 larva, and all the centra in the 17.8-mm. juve- 

 nile. 



The sequence of development of the centra is 

 from anterior to posterior, in the order of their 

 position. As in the Pacific mackerel, ossifica- 

 tion of the centrum starts at the dorsal and 

 ventral portions and progresses laterally until 

 the two ossified portions meet at the midline. 

 The dorsal portion of the first six centra and 

 the ventral portion of the first four ai-e ossified 

 in the 8.4-mm. larva. In the 13.2-mm. larva, 

 the first 10 centra are completely ossified, the 

 11th to 22d centra are partially ossified, and the 

 dorsal and ventral portions of the 23d to 34th 

 centra are beginning to ossify. The ventral 

 portions of the two centra anterior to the last 

 one, which give rise to the urostyle, also begin 

 to ossify in the 13.2-mm. larva. The remaining 

 26 centra become ossified between lengths of 

 13.2 and 23.7 mm. 



The urostyle first develops in larvae about 

 8 mm. long and is completely ossified in larvae 

 larger than 13 mm. In the 13.2-mm. larva, 

 only about half the area of the largest hypural 

 element is ossified. The early development of 

 the urostyle and the last two centra is similar 



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