FISHERY BULLETIN: VOL. 72. NO. 2 



Ossification 



The sequence of ossification of the skull, axial, 

 and appendicular skeleton is generally similar 

 among the four species in which ossification was 

 observed (Table 12). Without exception, the pre- 

 maxillaries, preopercular spines, and cleithra os- 

 sify in the smallest larvae (2.5-3.8 mm). Next to 

 ossify at 4 to 5 mm are the maxillaries, dentaries, 

 parasphenoid, supraoccipital, articulars, frontals, 

 angulars, and the branchial arches. The entire 

 maxillary arch is ossified before the larvae are 6 

 mm long. Teeth are formed along the entire mar- 

 gin of the premaxillaries and anterior region of 

 the dentaries in the youngest larvae following the 

 ossification of these elements. It is apparent that 

 the bones related to feeding ossify early, and this 

 is consistent with the need of the larvae for food 

 from external sources following the absorption of 

 the yolk. 



Seven branchiostegal rays on each side are pre- 

 sent in 3-mm larvae. Ossification begins with the 

 posterior and longer rays and proceeds anteriad. 

 The ceratohyal and epihyal to which the bran- 

 chiostegal rays are attached ossify simulta- 

 neously with the rays. The rest of the hyoid arch 

 including the glassohyal, urohyal, and hypohyal 

 ossify at metamorphosis. 



Aside from the quadrate and hyomandibular 

 which ossify during the larval period, the rest of 

 the palatine arch is not calcified until metamor- 

 phosis. 



The branchial arches initially ossify in larvae 4 

 to 5 mm long and all arches are calcified at 6 mm. 

 The first branchial arch is the first to ossify start- 

 ing from the center of the ceratobranchial towards 



20.0 

 18.0- 

 16.0 



;i2.o 



c 



-• 10.0 



— I 1 1 1 1 1 1 1 1 1 1 1 I I I I I '" 



2 4 6 8 10 12 It 16 18 20 22 24 26 28 30 32 34 



Dar* Aflar Halchlni 



Figure 9. — Growth of Oligoplites saurus larvae reared in the 

 laboratory at an average temperature of 26.0°C. 



both ends. The epibranchial is the next to ossify 

 beginning from near the angle of the arch out- 

 ward. Ossification of the other arches follows in a 

 similar sequence. 



The gill rakers calcify following the ossification 

 of the elements to which they are attached. The 

 number of gill rakers increase as growth pro- 

 gresses but gill rakers are slow to ossify, and the 

 full complement usually is not completed until the 

 transition and early juvenile stages. The adult 

 count in Seriola zonata is fewer than is formed in 

 the juveniles due to the reduction of the terminal 

 gill rakers into tubercles in the ceratobranchial. 

 Patches of fine teeth are formed on the superior 

 pharyngeals of the third and fourth gill arches 

 while the fifth and shortest gill arch has teeth 

 patches for most of its length. Pharyngeal teeth 

 ossify in larvae 6 to 8 mm long. 



In the cranium, the parasphenoid, frontals, and 

 supraoccipitals ossify in the youngest larvae 

 (2.5-3.8 mm). Except for the parietals which ossify 

 in the midlarval period, the rest of the cranium is 

 not ossified until the late larval and transition 

 periods. 



The cleithra, postcleithra, and posttemporals 

 are ossified in the early and midlarval stages, but 

 the rest of the pectoral girdle calcifies in late and 

 transforming larvae. From 2 to 4 posttemporal 

 spines protrude from the myotomes during the 

 early larval period. These are small and hardly 

 visible in most species except in stained speci- 

 mens. These spines are soon overgrown by the 

 developing muscles. 



The pelvic girdle calcifies following the 

 ossification of the pelvic fins. 



Ossification occurs at 5 to 8 mm in the vertebral 

 column and proceeds in an anteroposterior direc- 

 tion. The neural and hemal spines ossify ahead of 

 the centra of their respective vertebrae. The 

 centra ossify at their anterior margins and 

 ossification proceeds posteriorly. This pattern of 

 ossification in the vertebrae was noted in 

 Trachurus symmetricus (Ahlstrom and Ball, 

 1954). 



Ribs similarly ossify in an anteroposterior di- 

 rection. The pleural ribs are the first to ossify 

 followed by the epipleural ribs. All trunk verte- 

 brae have ossified pleural and epipleural ribs in 

 juveniles 15 to 17 mm long except on the first and 

 second in which pleural ribs are lacking. 



Teeth are initially uniserial but become multi- 

 serial as tooth formation progresses. Following 



440 



