FISHERY BULLETIN: VOL. 70, NO. 3 



Terms used in the description of larval osteology 

 conform largely to those used in recent studies 

 of the osteology of adult teleosts (e.g., Harring- 

 ton, 1955; Weitzman, 1962; Topp and Cole, 

 1968). 



DESCRIPTION OF DEVELOPMENT 



DISTINGUISHING FEATURES 



Early-stage larvae of S. macdonaldi are char- 

 acterized by a low number of melanophores (av- 

 erage of eight) in the series along the ventral 

 midline of the tail. Of the 27 other species 

 illustrated in the literature, only S. paiicispinis 

 larvae, with an average of nine melanophores 

 in this series, approaches the low number of S. 

 macdonaldi. Early larvae of S. macdonaldi are 

 also characterized by their small, densely pig- 

 mented pectoral fins. Melanophores cover com- 

 pletely the blade of the fin, but are restricted 

 to the inner surface of the fin base. Also char- 

 acteristic is the series of melanophores which 

 extends from the nape to the pectoral fin base. 

 Such melanophores are not present on any other 

 of the 27 other eastern Pacific species illustrated 

 to date. 



A fourth character of limited utility is the ab- 

 sence of melanophores on the dorsal surface of 

 the tail. S. macdonaldi is one of the 16 eastern 

 Pacific species illustrated to date which lacks 

 this pigment, and can be immediately separated 

 from the 12 species in which it is present. This 

 character should be used with caution because 

 the dorsal series of melanophores forms later 

 than the ventral series, at about the time of yolk 

 depletion (Moser, 1967; Waldron, 1968). Thus, 

 prolarvae collected prematurely from the ovaries 

 may not have yet developed their dorsal pig- 

 ment series, and illustrations of this stage are 

 not strictly comparable with those of larvae cul- 

 tured to the point of yolk depletion. 



GENERAL MORPHOLOGY 



Larvae of S. macdonaldi are similar in general 

 appearance to those of S. paucisvinis (Moser, 

 1967). Larvae hatch within the ovaries at a 

 length of 4 to 5 mm, and then are extruded from 



the female. Newborn larvae have large heads 

 with well-formed eyes and functional jaws ( Fig- 

 ure lA). The gut is short and bulbous; usually 

 remnants of the yolk and oil globule are visible 

 anteriorally in the region of the liver. 



Relative body depth increases markedly dur- 

 ing early larval stages and less so during later 

 larval stages (Figures 1, 2). Body depth at the 

 base of the pectoral fins averages 23 Sr of the 

 body length before notochord flexion, 33% dur- 

 ing flexion, and 34% after flexion. In pelagic 

 juveniles (Figure 3), relative body depth de- 

 creases slightly to about 30% in individuals 35 

 to 40 mm long. S. paucispinis is more slender 

 throughout the larval and early juvenile stages; 

 body depth averages 20% of the body length be- 

 fore notochord flexion, 24% during flexion, 31% 

 following flexion, and 28% in pelagic juveniles. 



Relative gut length increases gradually 

 throughout the larval period. Accordingly, 

 snout-anus length averages 42% of the body 

 length before notochord flexion, 52% during 

 flexion, 60% after flexion, 64% in pelagic ju- 

 veniles. A similar gradual increase occurs in 

 S. paucispi^ns (41, 44, 56, and 63% in the re- 

 spective stages). 



Relative head length increases slightly during 

 the larval period; head length averages 28% of 

 the body length before notochord flexion and 

 37% during and after flexion, but decreases dur- 

 ing transformation and is 32 '"r in the largest 

 pelagic juveniles. Eye diameter averages 33% 

 of the head length throughout the larval period 

 and shows no trend of relative increase or de- 

 crease. Relative eye diameter decreases slightly 

 to about 28*;/ in transforming individuals, but 

 increases to about 32 ''r in the largest pelagic 

 juveniles. 



Upper jaw length is variable with respect to 

 head length, probably because of the difficul- 

 ty in obtaining uniform measurements from 

 specimens with partially opened jaws. There is, 

 however, a general trend of relative increase; 

 jaw length averages 47% of head length before 

 notochord flexion, 49% during flexion, and 52% 

 in postflexion larvae. In large larvae and in 

 pelagic juveniles the end of the maxillary is lo- 

 cated beneath the middle of the orbit. With 

 continued elongation of the maxillary in demer- 



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