FISHERY BULLETIN: VOL. 72. NO. 2 



above the midline of the hypural plate, eight 

 below) were completed in larvae by 6.0 mm (day 

 16). (Secondary rays were added anteriad along 

 the dorsal and ventral margins of the caudal 

 peduncle with as many as nine formed on each 

 edge in the largest larvae.) 



The rounded caudal fin fold was confluent with 

 the dorsal and anal fin folds in the young larvae, 

 but an indentation of the fin fold occurred in the 

 region of the future caudal peduncle in the older 

 larvae. The caudal fin was separated from the 

 dorsal and anal fin membranes in larvae between 

 5.3 mm and 6.0 mm (day 14-16). At this stage 

 of development the caudal fin possessed a straight 

 margin, rather than rounded, along its posterior 

 edge and subsequently attained a bilobate shape 

 in larvae of ca. 10.5 mm (day 24). 



Pectoral 



The pectoral fin developed early during the yolk 

 sac stage (see earlier sections). However, rays did 

 not form until the larvae were ca. 5.4 mm (day 14) 

 when six or more rays could be counted in the 

 upper region of the fin. Addition of rays pro- 

 ceeded ventrally with the rays decreasing in 

 length ventrally to give the pectoral fin an obovate 

 shape in the older larvae compared to the earlier, 

 more rounded, membranous larval fin. 



The adult complement of 21 to 22 rays was 

 attained in larvae of 9.3 mm. A short, inconspicu- 

 ous spine at the extreme dorsal margin of the 

 pectoral was evident upon close examination of 

 our cleared and stained specimens of minimal 

 length 8.4 mm and larger cleared and stained 

 juveniles from our field-collected samples. 



Anal 



Formation of the anal fin was first evidenced 

 by the appearance of the anal anlage in larvae 

 as small as 3.75 mm. (See section on ventrum 

 pigmentation.) Following the formation of the 

 dorsal and anal anlagen, it appeared that the 

 separation of the fin fold into dorsal, anal, and 

 caudal sections coincided with the development 

 of incipient rays and first few spines of the dorsal 

 and anal fins in larvae from 5.4 mm to 5.5 

 mm (day 14). 



One anal spine formed concurrently with six 

 or more incipient rays in larvae of 5.4 mm or 

 larger; the two remaining spines developed 



anteriad to the first formed spine in larvae 

 between 7.0 and 9.0 mm which had at least 15 

 rays formed posteriorly. 



Generally by 9.0 mm, the two most anterior 

 anal spines had separated from the third which 

 remained associated with the soft rays. However,, 

 a well-defined separation of the fin membrane did 

 not occur until the larvae were 16.0-17.0 mm in 

 length. The adult complement of II-I, 17-19 for 

 the anal fin was completed in larvae by 9.0 mm, 

 although three smaller specimens (8.13, 8.63 and 

 8.88 mm SL) had complete anal fins. 



An inconspicuous flap of tissue could be 

 observed developing over the bases of the spines 

 and first few rays of the anal fin in most of 

 the larvae by 11 mm. The flap was not completely 

 formed along the basal margin of the anal fin 

 in our largest larva (18 mm) but had covered 

 only about three-fourths of the length of the 

 fin base. This was the precursor to the flap of 

 tissue which overlies the entire length of the 

 dorsal and anal fin bases in adult omaka. 



Dorsal 



The dorsal anlage appeared at approximately 

 the same size as the anal anlage. Development of 

 the soft dorsal occurred prior to formation of the 

 spiny dorsal. There was no clear difference in 

 the rate of development of the soft dorsal fin 

 and anal fin in contrast to the jack mackerel 

 (Ahlstrom and Ball, 1954). 



Distal pterygiophores of the soft rays were 

 evident in larvae of 5.0 to 5.4 mm, with incipient 

 rays becoming differentiated in 5.55 mm (and 

 larger) larvae. Subsequent fin development was 

 rapid. Four to six spines had developed with as 

 many as 16 rays in larvae of 5.8-6.0 mm. Spines 

 were added anteriad and rays posteriad. Most of 

 the larvae of 7.3 to 8.0 mm length had attained 

 a dorsal fin complement of IX-20 to IX-22. In 

 larvae larger than 9.0 mm, the ninth spine had 

 separated from the preceding eight to separate 

 the two dorsal fins. The fourth dorsal spine 

 remained the longest in the larger larvae, with 

 the others progressively decreasing in length. 

 Larvae from 9.0 to 18.0 mm possessed the adult 

 fin complement of VIII-I, 20-23. 



By 9.25 mm, only cleared and stained specimens, 

 showed a small, embedded, forwardly projecting 

 spine arising from the pterygiophore of the first 

 external spine. We did not count this spine 



508 



