FISHERY BULLETIN; VOL. 72, NO. 4 



SSSSISSiSlSSMa^r: 



Figure 6. — Opisthonema oglinum larva 19.7 mm standard length. 



spaces between ossified segments equal, the seg- 

 ments ossify in a wedgelike shape.) By 17.1 mm, 

 the three rings had widened appreciably and 

 the spaces had narrowed. 



Neural and hemal spines ossify in a posterior 

 to anterior direction. Neural spines are well 

 formed over the last three centra, which precede 

 the first preural well before ossification on the 

 centra is completed. By 17.1 mm, ossification of 

 these elements is just complete to below the dorsal 

 fin, and by 22 mm they are all ossified. 



Fin Development 



The earliest fin development was of the caudal 

 and dorsal fins, more-or-less as lobes, at about 

 4 mm TL. This early development may be due 

 to a rearing abnormality since fin development 

 is seldom seen in field-caught larvae less than 

 7 mm SL. Increasing numbers of caudal and 

 dorsal rays were defined at lengths from 6 to 

 8.4 mm, but were not clear enough to count 

 until our 8.4-mm specimen (17 caudal and 11 

 dorsal rays, Table 1 and Figure 3). Between 8.4 

 and 10.0 mm, the final two caudal rays were 



differentiated to complete the adult complement 

 of 19 principal cartilaginous rays (10 superior 

 and 9 inferior). 



Rays continued to be added to the dorsal fin: 

 16 were present at 12.5 mm and 18 to 20 were 

 present from 15 to 20 mm (Table 1, Figures 4 

 through 7). As growth proceeded, one or two more 

 rays were added to complete the adult comple- 

 ment of 21 or 22 dorsal rays (Figure 8). In adult 

 Opisthonema , the last ray of the dorsal fin is 

 elongate — more than twice as long as the next 

 longest ray. Until about larval size of 20 mm, the 

 last ray was half as long as the longest ray, 

 but from then on it began to elongate. From 

 about 27 mm, the last ray grew longer than the 

 prior longest ray (Table 1). 



The anal fin formed later than the dorsal, 

 from a thickening of the ventral finfold in the 

 relatively short space between the anus and the 

 caudal fin (Figure 3). At 10.5 mm, the fin rays 

 had begun to differentiate and nine rays could 

 be counted. Ossified rays increased rapidly to 

 14, 15, or 16 at about 14 mm, after which rays 

 were added more slowly to sizes from 15 to 20 mm. 

 Between 14 and 20 mm, counts of 17 to 20 rays 



1130 



