Figure 5.— Development of the larva of the Pacific mackerel. Scomber japonicus ( = Pneumatophorus diego ): 

 a, larva 4.0 mm. long; b, larva 5.0 mm. long; c, larva 7.8 mm. long; d, larva 10.5 mm. long (adapted from 

 drawing by Mattson, fig. 3 of Kramer, 1960). 



Figure 6. — Late larva of the Pacific maclcerei, acomoer japonicus ( = Pneumatophorus diego ). 16.5 

 mm. long (adapted from drawing by Mattson, fig. 4 of Kramer, 1960). 



dorsal and second dorsal fins. The body depth 

 in early-stage larvae increases at a rate twice 

 that of later stage larvae. 



In Pacific mackerel, the order of first ap- 

 pearance of the fins is as follows: larval 

 pectorals (without rays), caudal, pectorals 

 (with rays), anal and second dorsal fins 

 simultaneously, anal and dorsal finlets simul- 

 taneously, first dorsal, and ventrals. The de- 

 velopment and appearance of the caudal keels 

 were discussed in detail because of the oc- 

 casional mis concept ion that they are pseudofins 

 with rays; each keel is made up of a series of 

 scales assembled linearly on a complex curve. 



Kramer (1960) further described the ossifica- 

 tion and formation of the vertebral column and 

 its parts for centra, urostyle, hypurals and 

 epurals, vertebral arches and spines, ribs, 

 epipleurals, zygapophyses, and parapophyses. 

 Development of the fin and finlet interspinal 

 systems were described with particular em- 

 phasis on the individual parts of the interspinal 

 bones; especially the continuity of the inter- 

 neural system between the first and second 

 dorsal fins and the complex structures forming 

 the dorsal slot of the first dorsal fin. 



For Pacific mackerel larvae collected from 

 1953-57, the change in abundance from 3.00 to 



