or 3). Larvae of Opisthonema oglinum and 

 Harengula jaguana always had 5 or more post- 

 dorsal-preanus myomeres during all developmen- 

 tal stages (Richards et al. 1974; Houde et al. 1974). 



Fin Development 



A finfold surrounded the trunk and caudal area 

 of newly hatched yellowfin menhaden larvae. 

 Some parts of it remained along the ventral body 

 margin until larvae were approximately 16.0 mm. 

 Pectoral fin buds were already present when lar- 

 vae hatched (Figure 2A), but the pelvic and 

 median fins were not formed. Rays first appeared 

 in fins in the following sequence: dorsal, caudal, 

 anal, pelvics, and pectorals. Because rays first 

 develop as cartilaginous structures, the size at 

 which full complements were present was not 

 necessarily the size at which all rays were ossified 

 (Tables 2, 5). Although the beginning and comple- 

 tion of fin ray development were best correlated 

 with length of larvae, age was also a factor, 

 especially for anal fin development (Table 2). 



Median fins had full complements of rays when 

 larvae were 17.0 mm (Table 5). Dorsal rays first 

 appeared at 7.3 mm, although an opaque area was 

 present in the dorsal finfold, near the future dorsal 

 fin, in some larvae as small as 6.4 mm. Full 

 complements of 20 or 21 dorsal rays usually were 

 attained when larvae were 15.5 to 17.0 mm. Prin- 

 cipal caudal rays first appeared at 7.5 to 8.6 mm 

 and the full complement of 19 principal rays was 

 present when larvae were 9.6 to 10.3 mm. The no- 

 tochord began to flex while principal caudal rays 

 and other caudal fin structures were developing. 

 Procurrent caudal rays began to develop at 11.2 

 mm, and full complements of 8 or 9 dorsal and 6 or 

 7 ventral rays were present at 16.2 to 17.8 mm. 

 Anal rays first developed at 8.8 to 10.3 mm. A full 

 complement of 20 or 21 rays was present on all 

 larvae 16.2 mm or longer, although one specimen 



only 12.6 mm had 20 anal rays. Hildebrand (1963) 

 and Miller and Jorgenson (1973) reported from 21 

 to 24 anal rays in yellowfin menhaden specimens 

 longer than 72 mm that they examined. We 

 examined six juveniles from our rearing 

 experiment that were 40-50 mm in length. Two of 

 these specimens had 22 anal rays, two had 21 rays, 

 and two had 20 rays. 



Rays in paired fins began to develop later than 

 in median fins. Pectoral fins without rays were 

 present soon after hatching, but no rays developed 

 until larvae had attained approximately 15.5 mm. 

 A full complement of 14 to 16 pectoral rays was 

 present on larvae 16.9 mm and longer. Pelvic fins 

 appeared as tiny buds when larvae were 10.9 to 

 11.3 mm, but rays did not develop until larvae were 

 about 13.0 mm. A full complement of 7 pelvic rays 

 was attained at 15.5 to 16.2 mm. 



Scales and Scutes 



Scales and ventral scutes were observed in 

 specimens 17.8 mm and longer. Scales first 

 developed anterior to the dorsal fin and in the 

 region of the caudal peduncle. Specimens 22.7 mm 

 or longer were fully scaled. Ventral scutes first 

 developed anterior to the pelvic fins when larvae 

 were 16.9 mm. Full complements of 30 to 32 (18 to 

 20 anterior to the pelvic fins and 11 to 13 posterior 

 to the pelvic fins) were present on specimens 22.7 

 mm and longer. These counts are the same as those 

 given for adult B. smithi by Dahlberg (1970). 



Osteology 



Ten specimens of yellowfin menhaden were 

 cleared and stained to determine sequence of 

 development of skeletal structures. Ossification 

 was similar to that described for larvae of Atlantic 

 thread herring (Richards et al. 1974) and of scaled 

 sardine (Houde et al. 1974). Consequently, 



Table 5.-Suminary of fin development sequence in larvae of Brevoortia smithi. 



'Rays were present at the tabulated lengths, but not necessarily ossified at those sizes. 



667 



