SUMIDA ET AL EARLY DEVELOPMENT OF SEVEN FLATFISHES 



period and then increases sharply in juveniles (Ta- 

 ble 5). Relative eye height is consistently less 

 than eye width; this is the usual pattern among all 

 species being dealt with in this report. 



The spine on each pterotic bone first appears on 

 larvae about 6.0 mm NL and achieves maximum 

 development in flexion larvae. It begins to regress 

 near the end of the larval period and is a rugose 

 bump in newly transformed juveniles. No other 

 species of Plciironichthys develops pterotic spines 

 during the larval period, although they are pres- 

 ent on larvae of H. guttulata. 



Another distinctive feature of P. decurrens lar- 

 vae is body depth. As in other species of 

 Pleurontchthys. early larvae are slender. Relative 

 body depth increases markedly during the post- 

 flexion stage with the result that larvae of this 

 species become strikingly deeper bodied than 

 those of the other six flatfishes with heavily pig- 

 mented larvae (Table 5). 



Fin and axicd skeleton formation. — Because this 

 species is larger at corresponding stages of de- 

 velopment than the other six flatfishes considered, 

 fin formation occurs at comparatively larger lar- 

 val sizes. Caudal fin development occurs between 

 7.9 and 11.0 mm NL; the smallest postflexion 

 specimen, 10.2 mm SL, has the full count of 19 

 caudal rays (Table 6). The dorsal and anal fins 

 begin forming simultaneously with the caudal, 

 but obtain their full complement of rays later, by 



14.5 mm SL. Pelvic buds are evident on most 

 specimens undergoing flexion, but the full count of 

 fin rays was first obtained on a 15.4-mm SL speci- 

 men. The axial skelton is ossified on specimens as 

 small as 11.2 mm SL, as determined by radio- 

 graphs. Counts of 14 precaudal and 24-27 caudal 

 vertebrae were recorded on five postflexion speci- 

 mens. 



Transformation. — Flatfish larvae are normally 

 symmetrical larvae with eyes opposite each other 

 on either side of the head during their preflexion to 

 flexion stages and into the postflexion stage. Some 

 flatfish larvae remain symmetrical with regard to 

 eye placement until attaining quite large sizes, 

 i.e., 50-120 mm (Hubbs and Chu 19.34; Bruun 

 1937; Nielsen 1963; Amaoka 1970, 1971, 1972, 

 1973). However, in the flatfishes being studied the 

 migration of one eye (left in dextral flounders, 

 right in sinistral flounders) begins early in the 

 postflexion stage. It can require some time to move 

 completely over. Thus, the left eye was migrating 

 on a 10.5-mm larva of P. decurrens, but was not 

 completely over on a 21.0-mm specimen. Ossified 

 rays are not formed in the pectoral fin until after 

 eye migration is completed. On first formation the 

 rays are spaced some distance apart in the blade of 

 the pectoral fin. The pectoral fin rapidly changes 

 form with the structure of the larval pectoral (base 

 and blade) disappearing, to be replaced by a group 

 of ossified, closely spaced rays. Metamorphosis is 



Table 6. — Meristics of larvae and a juvenile of Pleuronuhthys decurrens. 

 (Specimens between dashed lines are undergoing notochord flexion.) 



Station 



Fin rays 



Precaudal Caudal 



Source 

 Total of count 



5401-90 60 

 5704-87 50 

 6501-63 52 

 5206-70 65 

 6501-60 70 

 5003-87 35 

 6606-60 65 

 6605-80 80 



5009-47 60 

 5407-60 70 

 5805-70 80 

 7505-90 70 

 4903-82 57 

 6609-80 60 

 5308-73 60 

 5004-97 32 

 Off Santa Cruz Island, Calif 



10.2 SL Postfl 



105 



11 2 

 145 

 154 

 170 

 192 

 21 

 29 4 



Postfl 

 Postfl 

 Postfl 

 PosttI 

 Posttl 

 Postfl 

 Postfl 

 Juv 



50 

 ca 64 

 71 

 74 

 72 

 77 

 75 

 74 

 78 



46 

 45 

 46 

 52 

 48 

 48 

 52 

 48 

 52 



19 

 19 

 19 

 19 

 19 

 19 

 19 



Bud 

 5/5 

 5/5 

 5/5 

 6/6 

 6/6 

 6/6 

 6/6 

 6/6 



LP' 

 LP' 

 LP' 

 LP' 

 LP' 

 LP' 

 LP' 

 LP' 

 11/11 



X-ray 



'Prefl - pretlexion, E fl - early flexion; Midfl - midflexion; L fl - late flexion. Postfl 

 ^LP refers to functional larval pectoral fins whicfi fiave no ossified rays 



postflexion, Juv - juvenile 



115 



