FISHERY BULLETIN: VOL. 72. NO. 



YOLK SAC LARVAE 



The newly hatched omaka larvae measured 

 1.32 mm to 1.70 mm SL live, with a mean of 

 1.46 ± 0.12 mm for 47 larvae. Following preser- 

 vation in 2.5% formaldehyde, a different group 

 often larvae ranged from 0.87 mm to 1.03 mm 

 with a mean of 0.98 ± 0.05 mm. The difference 

 between means (0.48 mm) indicates a shrinkage 

 of 33%. 



Pigmentation 



Live Larvae at Hatching 



Newly hatched omaka larvae resembled ad- 

 vanced embryos in pigmentation pattern. Melano- 

 phore pigment was heaviest on the dorso-lateral 

 surfaces of the body with melanophores usually 

 forming a loop posterior to the head. Additional 

 small clusters of melanophores were observed on 

 the top of the head and at the anterior and 

 posterior margins of the eye vesicles. A broad 

 band of small melanophores encircled the body 

 about 6 myomeres posterior to the anal papilla. 

 Ventral body pigment was not apparent in the 

 newly hatched larvae but was found in older yolk 

 sac larvae, perhaps due to the migration of some 

 dorso-lateral melanophores and those in the band 

 region (see Orton, 1953). Dendritic melanophores 

 (Figure 2A) lined the posterior margin of the yolk 

 sac. The oil globule displayed heavier pigmenta- 

 tion than in the late egg stage, with melanophores 

 present on both its anterior and posterior surfaces. 



Preserved Larvae at Hatching 



The remaining pigmentation following preser- 

 vation in 2.5% formaldehyde for at least 24 h 

 were the melanophores on the head and dorso- 

 lateral region of the body. The band of pigment 

 around the body posterior to the anal papilla 

 was lost except for a few scattered melanophores. 

 The yolk sac and oil globule had contracted and 

 obscured any pigment which may have remained. 



Live Larvae One to Three Days Old 



The pigmentation pattern of the yolk sac larvae 

 changed markedly during the first few days after 

 hatching. Owing to the rapid change, larvae 

 (preserved) at any time exhibited various stages 



of pigment development. Therefore the descrip- 

 tions presented are "average" patterns observed. 

 Had the larvae come from simultaneously fer- 

 tilized eggs, the differences would probably have 

 been less pronounced. As the pigment pattern 

 stabilized with age, variations among larvae 

 were correspondingly reduced. 



There was a loss of lateral pigmentation 

 coinciding with a coalescense of the small dorsal 

 melanophores to form fewer, large melanophores 

 on the dorsal edge of the body, and also with the 

 appearance of pigment on the ventral edge of the 

 hypomeres. These cjianges were apparent in most 

 of the day-old larvae. 



By the end of the second day, the larvae pos- 

 sessed discrete melanophores on the dorsal and 

 ventral edges of the body in a single discon- 

 tinuous line. The dorsal body melanophores 

 showed branches or "dendrites" which projected 

 up into the fin fold. These were most pro- 

 nounced in the region of the dorsal fin opposite 

 the divergence of the posterior end of the gut 

 from the body. A network of dendritic melano- 

 phores developed about midway along the dorsal 

 and ventral fin folds (Figure 2B). These networks 

 were gradually lost within the next five days of 

 growth. 



Also evident on the second day was the cluster of 

 melanophores on the top of the head and over the 

 snout region (present in the advanced embryo). 

 The first indication of eye pigmentation appeared 

 with faintly pigmented melanophores over the 

 iris, but concentrated along its posterior margin. 



The caudal region usually possessed a single 

 minute melanophore dorsal and two or three 

 ventral to the end of the notochord (Figure 2A). 

 The dorsal melanophore was lost in the older 

 larvae, but the ventral melanophores persisted 

 and were situated over the early caudal actino- 

 trichia at about the sixth day. 



Three-day-old larvae were similar in pigmen- 

 tation to the two-day-old larvae except in their 

 heavier eye pigmentation and fewer melano- 

 phores on the dorsal body edge. 



Preserved Larvae One to Three Days Old 



Following preservation in 2.5% formaldehyde 

 for 48 h, virtually all pigmentation, except for 

 the dorsal and ventral body, eye, and head 

 melanophores, were lost. In a few specimens, 



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