JOHNSON and LOESCH: MORPHOLOGY AND DEVELOPMENT OF AMERICAN SHAD 



Ns EP].2 U*. 



FIGURE 9. — Caudal fin osteology of a postflexion (juve- 

 nile) Alosa sapidissima, 29.6 mm SL. Hy(l-6) = hypural 

 plates; Ep(l-2) = epurals; U(l-2) = ural vertebra; Pu(l-4) 

 = preural vertebra; Hs = haemal spine; Ur(l-2) = 

 uroneurals; Ns = neural spine; Na = neural arch; Ph = 

 parhypural. Clear areas indicate uptake of Alizarin Red S, 

 while stippled areas indicate uptake of Alcian Blue. 



tips of the structures, with Alizarin Red S absorption 

 in the middle. 



Pectoral fin development is evident at hatch in the 

 form of a pectoral fin fold and cartilaginous support 

 structures. Incipient pectoral fin rays are also evident 

 in yolk-sac larvae; however, these rays were outlined 

 under light microscopy (25X). Development of the 

 pectoral fin appears to be slow when compared with 

 the other fin development characteristics (Table 5). 

 There is a 5.6 mm range of SL over which cartilagi- 

 nous pectoral fin rays first absorb Alcian Blue stain. 



The pelvic fin is the last of the five median and 

 paired fins to start and complete development (Ta- 

 ble 5). Pelvic fin development is first evident at the 

 transformation from flexion to postflexion larvae. 

 The pelvic fin basipterygium first appeared during 

 this size interval. 



Pigmentation 



The distribution of melanophores on A. sapidissima 

 appears to be similar to that of other clupeid larvae 

 found in Chesapeake Bay tributaries and the western 

 North Atlantic. There is some variability in the 

 pigmentation patterns among individuals in any 

 given size interval; however, this variation is due in 



part to individual chromatophores and melano- 

 phores existing in a contracted or expanded state. 

 The specimens illustrated in Figures 10-13 indicate 

 the general pattern of pigmentation typical of the A. 

 sapidissima specimens cultured for this study. 



Newly hatched A. sapidissima have very few 

 melanophores on the snout and over the brain. A 

 newly hatched specimen, 8.2 mm SL, had one stellate 

 melanophore on the tip of the snout and two others in 

 a straight line, spaced at equal intervals, toward the 

 anterior end of the eye. The eyes in this specimen and 

 all the specimens sampled were fully pigmented by 

 9.5 mm SL (Fig. 10A). Three to five melanophores 

 were present over the brain of a specimen 10.4 mm 

 SL (2 d after hatch). A small but distinct line of 

 melanophores is present above the yolk sac, over the 

 pectoral symphysis and heart, in specimens 9.3-10.5 

 mm SL (Fig. 10A). 



The number of melanophores on the snout and 

 brain increases with increasing SL. A 10.9 mm SL 

 specimen (Fig. 10B) showed an increased number 

 and density of melanophores on the snout. A line pat- 

 tern of stellate melanophores is developed dorsally 

 from the snout up the midline of the skull and over the 

 top of the brain in larvae 10.9-28.5 mm SL (Figs. 

 10B-13). 



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