MOSER: DEVELOPMENT OF ROCKFISH 



In large adults the lateral melanistic patches 

 and bands coalesce to form a solid black zone 

 above the horizontal septa with a crimson zone 

 below. At least the posterior half of the lateral 

 line remains bordered by crimson. The spinous 

 and soft dorsal fins become black. The caudal 

 fin is black except for a vertical crimson zone 

 at the base. The anal and ventral fins remain 

 crimson with black between the rays. The pec- 

 toral fins become black except for a red zone at 

 the proximal third of each fin. 



SEQUENCE OF OSSIFICATION 



The sequence of calcification of bones in larvae 

 of S. macdonaldi is similar to that described for 

 larvae of Myctophidae (Moser and Ahlstrom, 

 1970). As in myctophids, the maxillaries and 

 cleithra are the first elements to ossify. In fact, 

 the maxillaries, cleithra, and opercles are begin- 

 ning to ossify in full-term intraovarian larvae. 

 The sequence of ossification of other head, ap- 

 pendicular, and axial elements in a stained series 

 of S. macdonaldi is shown in Table 3. For each 

 element, the larval length at initial ossifi.cation 

 and the larval length at which the element 

 achieves its adult form are given. Selection of 

 the point at which an element achieves its adult 

 form, admittedly, is somewhat subjective since 

 bone formation is a gradual process that contin- 

 ues throughout the life of the fish. In rockfish, 

 as in most other teleosts, most of the skeletal 

 elements become ossified during the larval period 

 and assume a shape which, except for minor sur- 

 face irregularities and processes, closely resem- 

 bles that found in juveniles and adults. The 

 branchial arches and cranial spines ossify grad- 

 ually and generally have not achieved their adult 

 form before the end of the larval period. For 

 this reason these are listed in separate tables 

 (Tables 4, 5), which give only the sequence of 

 initial ossification. 



Although the neurocranium is unossified in 

 unborn larvae, the frontals, pterotics, and para- 

 sphenoid form soon after birth, in larvae 5.1 to 

 5.2 mm. These are followed by the parietals, 

 exoccipital, bosioccipital, and supraoccipital, and 

 later the circumorbital bones and the more in- 

 terior neurocranial elements. 



In the upper jaw the maxillaries begin to ossi- 

 fy before birth. These are followed by the main 

 elements of the lower jaw, the dentaries and ar- 

 ticulars, which begin to ossify at 5.1 to 5.2 mm. 

 Other elements of the jaws, the premaxillaries 

 and angulars, are beginning to ossify in a 6.3-mm 

 stained larva. All elements of the mandibular 

 arch achieve their adult form early in the larval 

 period, between 7.0 and 8.5 mm. The elements 

 of the palatine series are slower to ossify. The 

 quadrates begin to ossify at about 6.3 mm and 

 the others follow gradually; the last elements 

 to initiate ossification, the palatines and metapt- 

 erygoids, achieve their adult form in 12.0-mm 

 and 15.9-mm larvae respectively. 



The bones of the hyoid arch and opercular 

 series initiate ossification gradually, beginning 

 with the opercle in unborn larvae. The other 

 bones of the opercular series have started to os- 

 sify before the larvae reach 6.3 mm, and all have 

 achieved their adult form at 7.9 to 8.2 mm. Ele- 

 ments of the hyoid arch, particularly the cera- 

 tohyals and interhyals, are slower to initiate and 

 complete ossification. 



In the appendicular skeleton, the cleithra are 

 the first bones to become ossified. They are heav- 

 ily stained in unborn larvae and are the first 

 skeletal elements to ossify. Following birth, 

 the other bones of the pectoral girdle gradually 

 initiate ossification. Among the last to appear 

 are the four proximal radial elements, which os- 

 sify in a dorsal-to-ventral sequence. The cora- 

 coids and the single pair of extrascapulars ini- 

 tiate calcification at about 12.0 mm and are 

 formed in the 15.9-mm specimen. The pelvic 

 bones appear initially in a 9.2-mm stained spe- 

 cimen; through gradual ossification the pelvics 

 become fused along their medial surfaces. 



The paired neural arch elements are the first 

 bones of the axial skeleton to ossify. At first 

 only the most anterior pair is visible in a 7.0-mm 

 larva, but gradually others are added in a pos- 

 teriad sequence. When the larvae are about 8.0 

 mm long, the distal ends of each pair begin to 

 fuse in the midline to complete the neural arch. 

 This fusion and the resultant formation of a 

 neural spine on each arch also occurs in an an- 

 terior to posterior sequence. The full comple- 

 ment of neural spines, including a shortened one 



951 



