FISHERY BULLETIN: VOL. 81, NO. 2 



Fin Development 



Median and paired fin development is indicated in 

 Tables 3 and 4 for both hatchery- cultured and field- 

 sampled specimens. A summary of the fin develop- 

 ment of cultured specimens is presented in Table 5. 

 Development of the median fins (dorsal, anal, and 

 caudal), including ossification of rays, is first evident 

 between 9.0 and 12.5 mm SL. Median fin develop- 

 ment is completed between 17 and 21 mm SL. Paired 

 fin development is not truly evident until larvae are in 

 the late flexion or early postflexion stages. Develop- 

 ment of the paired fins was complete when larvae 

 were between 23 and 27 mm SL (Table 5). 



The dorsal fin exhibits the earliest development of 

 all fins. Dorsal fin radials first appear in larvae 8.0-9.0 

 mm SL (Table 5). Radials appear as buds and are not 

 fully developed at this stage. 



The developmental sequence for the various com- 

 ponents of the caudal complex is described from the 



first appearance of cartilaginous structures to a 

 gradual ossification and fusion of bones in the caudal 

 complex. The criteria used to place larvae into one of 

 the three larval stages of development are similar to 

 that described by Tucker (1978). Description of the 

 sequence of caudal complex development is based 

 on 19 selected counterstained specimens (Figs. 8, 

 9). 



Larvae between hatch and 9.5 mm SL had a straight 

 notochord (no flexure) and showed no evidence of 

 any support structure development (hypurals, uro- 

 neurals, neural, or haemal spines) (Fig. 8A). Early 

 caudal fin development is evident in the late preflex- 

 ion stage in larvae 9.8-1 1.3 mm SL. The notochord is 

 straight, and one incipient parhypural and one to 

 three incipient hypurals have begun to develop (Fig. 

 8B). The hypurals and parhypural first appear 

 stained with Alcian Blue. There is some incipient 

 caudal fin ray development (Table 3). 



Notochord flexure starts between 1 1.5 and 12.6 mm 



Table 3. — Some fin meristics for \arva\Alosa sapidissima cultured at USFWS Harrison Lake 



National Fish Hatchery, Va. 



330 



