larvae. Teeth in the upper jaw are formed only 

 T.\BLE s. — Sequence of ossification of bones of wahoo larmi- on the premaxillary, when the larvae are about 



4.1 mm. long. The first few teeth appear al- 

 most simultaneously as small protuberances. 

 In the lower jaw, teeth develop on the dentary 

 when the larvae are about 4.2 mm. long. About 

 seven widely spaced teeth of uniform size are 

 present in each jaw when the larvae are about 

 4.4 mm. long. In larvae above 5.8 mm., smaller 

 teeth are added near the bases of the larger 

 ones; at 13.2 mm., one or two small teeth are 

 usually present between two adjacent long 

 teeth (fig. 3D). Initially, when the jaws are 

 of equal length, the number of teeth in each 

 is about equal. As the upper jaw protrudes be- 

 yond the tip of the lower jaw, three to four 

 additional teeth appear on the protruded section 

 of the upper jaw (figs. 2D and 3A-D). The 

 three or four anteriormost teeth in the upper 

 jaw become slightly recurved ; the teeth pos- 

 terior to these appear straight and more nearly 

 maxillary ossifies first in larvae about 3.1 mm. vertical to the longitudinal axis of the jaw. 

 long. The premaxillary begins to ossify at When the juveniles attain a length of 13.2 mm., 

 about 3.8 mm., but the development is restricted about half the number of teeth found in the 

 to the anterior half of the jaw. Ossification adults are already ossified; however, the coni- 

 proceeds posteriad until the full length is de- cal shape of the teeth of the larvae differs from 

 veloped in larvae about 4.5 mm. long. The pre- the compressed and triangular teeth of the 

 maxillary essentially excludes the maxillary adults. 



from the gape (i.e., from the functional biting ^he palatine bone begins to ossify in larvae 



surface of the jaw) by its position ventral to ^bout 4.3 mm. long, and ossification is com- 

 the maxillary. pj^^ ^^^ ^^^^^ g 4 ^^ -pj^^ ^^.^^ palatine tooth 



The lower jaw also has two bones, the dent- develops when the larvae are about 4.6 mm. 

 ary and articular. The dentary first develops i^^g ^he number of teeth increases slowly and 

 in larvae about 3.1 mm. long and is completely ^^aches a maximum of nine in the 13.2-mm. 

 ossified in larvae over 3.8 mm. Ossification of larva 



the articular begins in larvae about 4.2 mm. mi. i. • x -j? 1 j. j.t. ^i. 



, , . 1 A . u i .1 r The vomer begins to ossify later than the 



long and is complete at about 4.5 mm. , , . , ,, . , ^ a r- 



palatine, when the larvae are about 4.5 mm. 



Gill Arches , long, but completes ossification at the same time 



The gill arches do not absorb stain until the as the palatine. The first vomerine tooth is de- 

 larvae are about 3.4 mm. long. After the first veloped in larvae about 8.4 mm. long; two are 

 arch has ossified, however, subsequent arches present at about 10.7 mm., and this number 

 develop in quick succession and all are com- remains constant through the 23.7-mm. stage, 

 pletely ossified in larvae about 6.8 mm. long. 

 As in the adults, the larvae and juveniles have 

 no gill rakers. 



Teeth 



The teeth in both jaws develop at a smaller 

 size in wahoo larvae than in yellowfin tuna 

 larvae, but slightly later than in skipjack tuna 



Preopercular Spines, Preopercle, and Opercle 



Unlike the preopercular spines of skipjack 

 tuna, which appear when the larvae are about 

 3.7 to 3.9 mm. total length (Matsumoto, 1958), 

 the preopercular spines of the wahoo appear 

 when the larvae are longer than 4.1 mm., SL. 

 At this stage only a single spine is ossified at 



MORPHOLOGY AND DISTRIBUTION OF LARVAL WAHOO 



313 



