FISHERY BULLETIN VOL 



. NO 1 



pigment on the finfolds of P. ritteri, a smaller oil 

 globule (average 0.10 vs. 0.14 mm), lack of pig- 

 ment on the oil globule, and presence of pigment 

 ventrally near the tip of the notochord. Distinctive 

 characters of preflexion and flexion larvae of P. 

 ritteri include the lack of pterotic spines on the 

 head which is more rounded than on preflexion H. 

 guttulata, the lack of pigment from the top of the 

 head posteriorly to the nape, a more robust head 

 and trunk (compare Figure 15D with Figure 19D), 

 and the presence of small pigment spots on the 

 pectoral fin blade along its margin or base. Post- 

 flexion and early transforming specimens can be 

 distinguished by a deeper and shorter caudal 

 peduncle, a more robust body, and the origin of the 

 dorsal fin on the future blind side of the head 

 instead of on the medial line of the head as found in 

 H. guttulata. 



Pigmentation. — Yolk-sac larvae are heavily pig- 

 mented with the exception of the last 8 or 9 myo- 

 meres. Pigment is also scattered on the remnant of 

 the yolk sac, on the dorsal and ventral finfolds, and 

 ventrally on the tail near the tip of the notochord 

 (Figure 15A). Except for the appearance of pig- 

 ment along the margins of the pectoral fin blade, 

 no significant changes in pigmentation occur in 

 early preflexion larvae of ca. 3.0 mm NL (Figure 

 15B). 



By 4.0 mm NL, pigment found earlier along the 

 top of the head posterior to the nape is lost, leaving 

 an unpigmented streak which persists until flex- 

 ion of the notochord is complete at 5.5 mm NL 

 (Figures 15C, D; 16A, B). Ventral pigment is simi- 

 larly lost on the abdominal region, resulting in an 

 unpigmented lower abdomen in late preflexion 

 and flexion specimens. Marginal pectoral fin pig- 

 ment present on larvae to about 3.3 mm NL, 

 changes to small, discrete spots on the fin mem- 

 brane along its base. These melanophores persist 

 through postflexion larvae until the pectoral fin 

 differentiates into a small, rayed fin by ca. 10.0 

 mm SL (Figures 16C, 17). 



Pigment on the tail extends posteriad the same 

 distance in flexion larvae as in preflexion larvae, 

 but in postflexion larvae the tail pigment fills in 

 posteriorly to the terminal dorsal and anal fin 

 rays. In later postflexion and transformation 

 stages, the head, trunk, and tail, except the caudal 

 peduncle, are completely covered with pigment 

 which extends over the dorsal and anal fin 

 pterygiophores (Figures 16C, 17). 



At 10.0 mm SL, a dark circular blotch of pig- 

 ment develops on the middle section of the body, 

 with a heavy band of pigment at the posterior 

 extreme of body pigment. Several triangular 

 patches are clustered on the dorsal and anal fin 

 rays above the pterygiophores. The caudal pedun- 

 cle area remains unpigmented (Figure 17). 



Morphology. — Larvae of P. ritteri are the smallest 

 among species of Pleuronichthys in comparable 

 stages of development. Our smallest .specimen has 

 a large yolk sac and is 2.1 mm NL (Figure 15A). 

 The oil globule is positioned posteriorly in the yolk 

 mass and measures 0.11 mm in diameter. The left 

 eye begins to migrate at about 6.0 mm SL and 

 migration of the eye is completed before 10.0 mm 

 SL (Table 14). The smallest available juvenile was 

 12.7 mm SL. 



The gut develops as in other Pleuronichthyti but 

 coiling begins earlier, at about 3.0 mm NL, and the 

 terminal section of the gut is in a vertical position 

 in most specimens >4.0 mm NL. 



The head is relatively larger in preflexion lar- 

 vae of P. ritteri than in the other species (Table 5). 

 Relative head length increases throughout the 

 larval period, then is moderately reduced at trans- 

 formation. Mean relative snout length increases 

 in P. ritteri larvae undergoing notochord flexion 

 and decreases during subsequent .stages, but in 

 other species ofPleuronichthys it decreases during 

 all major phases of larval development. Relative 

 eye size is largest in preflexion larvae, becomes 

 reduced in later larval stages, and increases at 

 transformation. 



The early larvae of P. ritteri are the deepest 

 bodied species of Pleuronichthys. Mean relative 

 body depth measured at the base of the pectoral fin 

 is greater during preflexion and flexion stages of 

 the notochord than in any other species. In post- 

 flexion larvae, however, mean relative body depth 

 is markedly less than in P. decurrens and about 

 equal to that in P. coenosu.'i and P. vertieali.s (Table 

 5). 



Fm and axial skeleton formation. — Early caudal 

 formation involving thickening in the hypural 

 area of the developing caudal fin occurs on 

 larvae 4.3-5.1 mm NL (Table 15). Caudal rays are 

 forming on larvae as small as 4.5 mm NL, with a 

 simultaneous initiation of flexion of the notochord. 

 Specimens between 4.5 and 5.6 mm NL undergo 

 notochord flexion. Our smallest specimen with a 

 fully flexed notochord is 5.3 mm SL. The full 



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