RICHARDSON ET AL.: EGGS AND LARVAE OF BUTTER SOLE 



spread into thin lines between the margin of the 

 body and finfold. The ventral melanophores are 

 variable, ranging from no melanophores to many, 

 and are separated at irregular intervals over the 

 length of the tail, while the dorsal pigment can 

 appear almost continuous. Near the tail tip the 

 dorsal and ventral melanophores align, as in the 

 early larvae, to form the precursor of the pos- 

 teriormost band of pigment noted in the larvae. 



The reared embryos appear more lightly pig- 

 mented than wild-caught embryos. In the latter, it 

 is possible that the marked fading of the head 

 pigment may not occur until after hatching. 



Morphology 



Physical development of /. isolepis embryos 

 progresses as in other fishes. At the time of initial 

 pigment formation, the blastopore has closed and 

 the embryonic body is gradually thickening on top 

 of the yolk sac. During this stage, the eyecups are 

 forming, but no lens tissue is discernible. About 

 12 somites have formed, and Kupffer's vesicle is 

 still visible just anterior to the tail bud. 



When the tail is five-eighths of the way around 

 the yolk, the eyecups are well-formed and lenses 

 are present. The brain has differentiated into a 

 forebrain and a larger midbrain. The auditory ves- 

 icles are forming but are not yet hollow. About 27 

 somites are present, Kupffer's vesicle is no longer 

 visible, and the small tail has a definite finfold. 



By the time the tail has reached three-fourths of 

 the way around the yolk, the auditory vesicles are 

 well-formed and immediately apparent. The em- 

 bryo now has about 37 somites. Hatching can 

 occur when the embryo's tail has reached seven- 

 eighths of the way around the yolk to full circle. At 

 this point, the embryo has the full complement of 

 somites or myomeres (39-42) and is morphologi- 

 cally similar to a newly hatched larva. 



DEVELOPMENT OF LARVAE 



(Figures 2-5) 



Pigmentation 



Pigment on newly hatched larvae is scattered 

 lightly on the head and snout, and appears on the 

 dorsal, lateral, and ventral body surface above the 

 abdominal cavity and also in the tail region. No 

 pattern is obvious. The eyes are unpigmented. 



In the head region, the eyes begin to darken by 4 

 d (about 3.8-4.0 mm) after hatching and are fully 



pigmented by 7 d (3.9-4.1 mm) in the reared lar- 

 vae. Eyes in the smallest plankton specimen (2.9 

 mm) are pigmented. During early development, 

 pigment over the head and snout disappears (by 

 about 4 mm in reared larvae, 2.9 mm in plank- 

 tonic larvae) except for a few internal melano- 

 phores above the otic capsule. Pigment appears on 

 the lower jar and throat region by 4 or 5 mm and 

 persists through the larval period. By about 6 or 7 

 mm several melanophores are present at the ven- 

 tral angle of the preopercle. Later in development, 

 scattered melanophores are added on the head 

 (>10 mm) and on the upper jaw ( >14 mm). Addi- 

 tional pigment is added to the entire head region 

 on the eyed side during transformation (> 17 mm). 



In the abdominal region, melanophores disap- 

 pear from the dorsal and lateral body surfaces 

 above the gut cavity by the time larvae are about 4 

 mm long. Pigment is added again in this region 

 during the transformation period when larvae are 

 about 17 mm long. It is added first in two patches 

 on the dorsal pterygiophores. More melanophores 

 are then added laterally as well as on the dorsal 

 pterygiophores, mainly along the myosepta, 

 obscuring the original patches. A series of internal 

 melanophores develops dorsal to the notochord 

 above the abdominal cavity in larvae >10 mm. 

 Melanophores are added along the ventral margin 

 of the gut cavity by the time larvae are about 4 mm 

 long. With development, additional melanophores 

 extend over the ventral and posterior portions of 

 the abdominal cavity appearing in a half-moon 

 shape on most larvae >8 mm long. This pattern 

 persists until transformation when the increase in 

 body pigment on the eyed side obscures it. 



In the tail region, three characteristic bands of 

 pigment become obvious in reared larvae 4 d (3.9- 

 4.1 mm) after hatching and are visible on the 2.9 

 mm plankton caught larvae. These are located on 

 the body at positions roughly 50, 67, and 90^^ SL. 

 In larvae <10 mm, these bands generally extend 

 from dorsal to ventral body margins. With de- 

 velopment the middle band becomes the most pro- 

 nounced of the three. This middle band remains 

 visible on the eyed side of some newly transformed 

 benthic juveniles, and remnants of it persist on the 

 blind side of juveniles as long as 35 mm. After 

 notochord flexion (>14 mm), the posterior band is 

 seen as a line of pigment at the base of the caudal 

 fin. The anterior band becomes less pronounced 

 and often does not extend above the lateral mid- 

 line in larvae >14 mm. Along the notochord, a se- 

 ries of internal melanophores develops dorsal to 



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