MATARESE ET AL : LARVAL DEVELOPMENT OF PACIFIC TOMCOD 



tion of some spots laterally and in the dorsal and 

 anal fin folds. By 15.0-16.0 mm SL, additional 

 melanophores occur along the dorsolateral and 

 ventrolateral surface, but those in the bars remain 

 enlarged and distinctive (Figure 2 A). After trans- 

 formation, the larval pigment bars are no longer 

 visible and the entire lateral area is pigmented, as 

 are the dorsal and anal fins (Figure 2B). 



Posterior to the second pigment bar, mela- 

 nophores occur in the caudal region along the 

 ventral body margin in the smallest larvae, con- 

 nect with the ventral stripes by 5.7 mm SL (Figure 

 IB), and extend to the notochord tip by 6.2 mm SL. 

 Caudal melanophores are smaller and less den- 

 dritic than those in the bars and appear as a single 

 ventral midline row (Figure ID). Several 

 melanophores are added on the dorsal body mar- 

 gin posterior to the second pigment bar by 10.0 

 mm SL and, eventually, to the caudal fin fold ven- 

 trally and posteriorly by 15.0 mm SL. By 16.0 mm 

 SL the dorsal and ventral midlines are dis- 

 tinctively lined with melanophores, and the 

 lateral midline pigment, both internal and exter- 

 nal, extends to the tail tip (Figure 2A). The pro- 

 ximal portion of the caudal fin is pigmented. After 

 transformation pigment covers most of the fin 

 (Figure 2B). 



Morphology (Tables 3, 4) 



Larvae of M. proximus are moderately elongate 

 with the greatest body depth, about 19% SL, oc- 

 curring at or near the pectoral fin base. The body 

 tapers slightly toward the anus and then narrows 

 abruptly posterior to the anus. The gut is only 

 moderately long. The distance from snout to anus 

 ranges from 41% to 48% SL in larvae and declines 

 to 45% SL in juveniles. In our smallest yolk-sac 

 larva (2.7 mm SL), the vent opens laterally to the 

 right near the ventral fin fold and does not become 

 vertical until the larvae reach about 7.5-8.5 mm 

 SL. This lateral position of the anus in small gadid 

 larvae was reported by Marak ( 1967) and Russell 

 (1976). All yolk is absorbed by 3.0 mm SL. 

 Notochord flexion is protracted, beginning at 

 about 8-10 mm SL and ending at about 15 mm SL. 

 Transformation begins at about 22 mm SL and is 

 completed at about 27-28 mm SL. The largest 

 pelagic specimen collected was 46.6 mm SL. 



Head length as a proportion of standard length 

 increases from 22% SL in preflexion larvae to 32% 

 SL in transforming specimens. It declines to 30% 

 SL in pelagic juveniles. Eye diameter as a propor- 



tion of head length decreases from 35% HL in 

 preflexion larvae to 25% HL in pelagic juveniles, 

 whereas snout length/head length increases from 

 18% HLto29% HL. Upper jaw length/head length 

 and body depth at pectoral fin base/standard 

 length remain relatively constant, increasing only 

 slightly from preflexion larvae to the pelagic 

 juvenile stage. Depth at anus/standard length in- 

 creases from 11% SL in preflexion larvae to 19% 

 SL in juveniles. 



The distance from the snout to the origin of the 

 first dorsal fin as a proportion of standard length 

 decreases slightly during development while the 

 distance from the snout to the second dorsal fin/ 

 standard length remains nearly constant. The 

 length from the snout to the origin of the third 

 dorsal fin/standard length increases slightly dur- 

 ing development. 



Distances from the snout to the origin of the first 

 anal fin/standard length decreases slightly from 

 47% SL in larvae undergoing notochord flexion to 

 45% SL in pelagic juveniles, whereas the snout to 

 second anal fin distance/standard length increases 

 slightly from 63% SL in larvae undergoing 

 notochord flexion to 68% SL in pelagic juveniles. 



Meristic Structures 

 (Tables 5, 6; Figure 3) 



Considerable variation occurs in the develop- 

 ment of meristic structures as the size at which 

 bones ossify varies from specimen to specimen 

 (Table 5). The following discussion approximately 

 parallels the sequence of development of meristic 

 characters in M. proximus. Terminology of bones 

 follows Ahlstrom and Counts (1955) and 

 Ahlstrom.'^ 



Head and Axial Skeleton 



Branchiostegals can be discerned in some 

 specimens as small as 3.9 mm SL. Ossification 

 begins in some larvae at 8.1 mm SL, but the full 

 complement of seven branchiostegals is not consis- 

 tently ossified until the larvae are about 19 mm 

 SL. The sequence of ossification of branchiostegals 

 is from upper to lower. 



Teeth begin ossifying on the dentary in 11.9 mm 

 SL larvae (Table 6). Initially, the number of teeth 



'E. H. Ahlstrom, Southwest Fisheries Center, National Ma- 

 rine Fisheries Service, NOAA, La Jolla, CA 92038, pars, com- 

 mun. Julv 1979. (Deceased.) 



929 



