JOHNSON and LOESCH: MORPHOLOGY AND DEVELOPMENT OF AMERICAN SHAD 





^y y m 



K^'^'Ji 





Figure 13.— Postflexion A losa sapidissima. A, 23.4 mm SL larva; B, 28.5 mm SL larva. 



The pigment pattern associated with the area pos- 

 terior to the fleshy orbit of the eye, and anterior to the 

 opercular, is variable. The density and number of 

 melanophores around the eye increased to ~22 mm 

 SL. Larvae in the 15-18 mm SL range exhibited most 

 of this pigment just posterior to the fleshy orbit of the 

 eyes, with no melanophores over the opercular bone 

 (Fig. 1 1). Larvae >20 mm (Fig. 13) exhibited distinct 

 melanophores extending from the fleshy orbit onto 

 the opercular bone. A substantial number of the 

 specimens examined >20 mm SL showed no in- 

 crease in the actual number of melanophores. In- 

 stead, this pigment appeared to migrate, and in some 

 cases contract, from the fleshy orbit of the eye onto 

 the opercular bone. Field-sampled specimens >28 mm 

 showed a reduced number and density of pigment 

 just posterior to the fleshy orbit of the eye and a more 

 concentrated number just anterior to the tip of the 

 opercular bone. 



Preflexion A. sapidissima have a series of very 

 small, distinct melanophores along the dorsal surface 

 of the gut. These melanophores remained distinct on 

 the larvae to about 18 mm SL (Figs. 10-12). About 2 d 

 after hatch, pigmentation was evident on the ventral 

 surface of the gut. This pigment was in a dense pat- 

 tern of short dash-shaped melanophores that gave 

 the appearance of a solid line by 15 mm SL (Fig. 11). 

 After 15 mm SL, ventral gut pigmentation contracted 

 from a solid line pattern to a series of spaced 

 melanophores (Figs. 11, 12). 



As larvae developed into the postflexion stage, gut 

 pigmentation became increasingly difficult to detect 

 because of the added body tissue and weight. Short- 

 ening of the gut, with increasing SL, is seen in con- 



junction with the formation of larger, distinct, stellate 

 melanophores along the dorsal gut surface (Fig. 12). 

 There is also a dense concentration of stellate 

 melanophores at the anus in postflexion and juvenile 

 A. sapidissima. 



Pigment developed along the anal fin base at 1 5 mm 

 SL where one to three stellate melanophores were 

 found in a series of specimens 15-18 mm SL (Fig. 11). 

 The number of anal fin base melanophores increased 

 to between 14 and 20 for 18-20 mm SL larvae (Fig. 

 12). Postflexion A. sapidissima (Fig. 13) had ~22-26 

 stellate melanophores in a straight-line pattern over 

 the radials of the anal fin. This line of pigmentation 

 was continuous from the anus, where a dense concen- 

 tration of melanophores was found, to the caudal 

 peduncle, where pigmentation associated with the 

 caudal fin was evident. 



Pigment is found at the base of the dorsal fin over 

 the developing radials in 12 mm SL larvae. From zero 

 to five small dorsal fin melanophores were counted 

 on a series of 1 1 .8- 1 3 mm SL specimens. The number 

 and density of melanophores associated with the dor- 

 sal fin increased as the fish grew and the dorsal fin 

 migrated forward. Larvae in the 15-18 mm SL range 

 have 10-19 stellate melanophores over the radials of 

 the dorsal fin (Figs. 11, 12). Larvae >20 mm SL have 

 a stellate melanophore directly over each radial of 

 the dorsal fin (Fig. 13); there are 20 radials with at 

 least one melanophore (more than one in most 

 specimens examined) at the base of the fin. 



There is a continuous pair of pigmentation stripes 

 from the eye to the caudal peduncle along the dorsal 

 midline. The paired melanophores anterior to the 

 dorsal fin are distinct, appearing as two lines, while 



335 



