FISHERY BULLETIN: VOL. 78, NO. 2 



other flatfiish larvae of similar form in the area 

 have three such bands. The only other three- 

 banded flatfish larva is deepsea sole, Emhas- 

 sichthys bathybius, but it hatches at about 9 mm, 

 has over 60 myomeres, and a different elongate 

 form (Richardson in press). The most similar ap- 

 pearing banded larval flatfish is the flathead sole, 

 Hippoglossoides elassodon, which has four pig- 

 ment bands. 



Before the three pigment bands become obvious, 

 i.e., in larvae <4 mm SL, larvae of/, isolepis are 

 similar to those of P. vetulus. They usually are 

 separable by the size and distribution of postanal 

 ventral midline melanophores. Those of/, isolepis 

 are small and appear more or less as a double row 

 when viewed from the ventral surface; those of P. 

 vetulus are enlarged and stellate and appear as a 

 single row when viewed ventrally. 



Newly transformed /. isolepis juveniles are also 

 similar to P. vetulus. Before development of adult 

 characters such as scales on the fins of/, isolepis, 

 which will easily separate the two, /. isolepis can 

 usually be distinguished by remnants of the larval 

 pigment bands on the blind side. The number of 

 gill rakers on the lower limb (Miller and Lea 1972) 

 also will separate the two species (7-8 for/, isolepis 

 and 10-13 for P. vetulus). 



DEVELOPMENT OF EGGS 



(Figure 1) 



Isopsetta isolepis eggs are spherical and trans- 

 parent, with a narrow perivitelline space, a 

 homogeneous yolk, and no oil globule. Although 

 the eggs apparently sink at salinities s;26.61%o 

 (Levings 1968), they are taken in our plankton 

 samples, and live eggs floated in the rearing exper- 

 iments (salinity ~26.9%o). Diameters of 80 reared 

 eggs averaged 0.93 mm (0.90-0.99 mm), while yolk 

 diameters averaged 0.76 mm (0.60-0.95 mm). 



Embryonic development is typical of most tele- 

 osts with planktonic eggs. The stages of egg de- 

 velopment we use correspond to the basic divisions 

 of embryonic development used by Ahlstrom and 

 Counts (1955), with detailed subdivisions of each 

 stage (Naplin and Obenchain in press). 



Pigmentation 



Pigment first appears during the middle stage of 

 embryonic development. At this time, distinct 

 melanophores are scattered unevenly from the 

 middle of the eyes posteriorly over the trunk. The 



Figure l. — isopsetta isolepis eggs, late stage from plankton 



collections. 



melanophores become more organized into two 

 dorsolateral lines on the anterior somites, and di- 

 minish in size and frequency posteriorly. The dor- 

 solateral lines are the site of melanophore forma- 

 tion, and pigment is present farther posteriorly as 

 development continues. 



The development of this species is unusual in 

 that the anteriormost melanophores become in- 

 creasingly dendritic and so fine that they gradu- 

 ally become less visible. By the time the embryos 

 have reached the late stage (tail five-eighths of the 

 way around the yolk), less head pigment is visible 

 and the trunk is covered with very small but dis- 

 tinctly visible dendritic melanophores. Several 

 distinct ventral melanophores lie at the juncture 

 of the trunk and the yolk sac, and one or two 

 isolated spots are on the yolk sac nearby. Most of 

 the tail pigment is scattered dorsally in no obvious 

 pattern, and several lateral melanophores are now 

 in the ventral tail area. 



When the tail is three-fourths of the way around 

 the yolk, the head and trunk generally appear to 

 be pigmented, although less distinctly than in the 

 middle stage. Ventral trunk pigment is present, 

 and some embryos may have one to three yolk-sac 

 melanophores nearby. Scattered melanophores 

 appear dorsally on the posterior trunk and on all 

 surfaces of the tail. More lateral melanophores are 

 present toward the tail tip. 



From the time the tail is seven-eighths of the way 

 around the yolk through hatching, little change in 

 the pigment pattern occurs; however, the lateral 

 tail melanophores have moved to become ventral. 

 Dorsal and ventral tail pigment melanophores are 



404 



