Watson: Early life history stages of Cheihpogon xenopterus 



1039 



<10-12 mm, except that melanophores tend to be 

 more concentrated near distal margin between up- 

 per 5-7 rays and in patch about midway along up- 

 per rays. After about 12 mm concentration midway 

 along upper rays commonly persists, but may dimin- 

 ish or disappear, and distal patch expands to form 

 distinct blotch along upper 6-8 rays, bordered by 

 unpigmented (or sparsely pigmented) margin (Fig. 

 4C). Distal blotch expands into elongate oval band 

 over much of width of pectoral fin in juveniles (Fig. 

 3B). Upper 4-6 pectoral rays also may remain 

 sparsely to moderately pigmented, especially proxi- 

 mally and in the blotch midway along upper rays, in 

 larger larvae and juveniles. Apart from upper rays 

 and distal blotch or band, remainder of fin has little 

 pigment after ca. 15 mm. 



Pelvic-fin pigment may form before hatching; al- 

 ways present after hatching. Sparse initially, com- 

 monly sparse to moderate throughout larval devel- 

 opment (Fig. 4). Pattern variable: melanophores tend 

 to be more concentrated near distal margin of most 

 or all of fin, in distal patch at innermost ray or be- 

 tween two or three middle rays, or in two distal 

 patches at innermost and outermost rays. Occasion- 

 ally melanophores more concentrated distally and mid- 

 way along rays. Distal patch near middle of fin is most 

 common pattern in larger larvae and juveniles. 



Caudal-fin pigmentation forms in late embryos, 

 initially proximally, mostly or entirely on lower rays. 

 Pigment increases and spreads to about three-quar- 

 ters of length of lower principal rays by ca. 8 mm. 

 Melanophores consistently present on upper part of 

 fin by about 8 mm but pigment here is sparse in lar- 

 vae and sparse to moderate in juveniles. 



Diagonal band forms on dorsal fin, originating dis- 

 tally between anterior 2-3 rays just after 8 mm (Fig. 

 2C) and reaching base of rays 6-7 between 18 and 

 22 mm. Pigmentation may be sparse in lower (=pos- 

 terior) part of band and in larger juveniles band ap- 

 pears more like elongate oval patch along first 5-6 

 rays. Distal blotch forms at last 2-3 rays beginning 

 at about 12-13 mm. Melanophores form on membranes 

 between (primarily adjacent to) first 5-6 rays after 18 

 mm. Anal fin unpigmented in larvae, but distal blotch 

 forms at last 2-3 rays in juveniles (Fig. 3B). 



Comparisons 

 Eggs 



Most exocoetids have spherical eggs that are about 

 J. 5-3 mm in diameter, lack oil globules, and have 

 filaments on the chorion (Collette et al., 1984). 

 Cheilopogon eggs are typical exocoetids in these char- 



acters. For most of the Cheilopogon species the fila- 

 ments are evenly distributed as in C. xenopterus. 

 Only C. heteriiriis and C. unicolor have been de- 

 scribed as having a different arrangement, with fila- 

 ments grouped in bipolar clusters (Barnhart, 1932; 

 Miller, 1952; Imai, 1959; Gorbunova and Parin, 1963; 

 Watson, 1996). Among the species with uniform fila- 

 ment distribution, the number of filaments ranges 

 from about 10 to 90; the range in C. xenopterus (about 

 40-60) apparently is typical (e.g. Collette et al., 1984). 

 Filament length in these species ranges from less 

 than 1 mm to just over 10 mm; most commonly the 

 filaments are long, a character shared with Cypselurus 

 (e.g. Collette et al., 1984). The short filaments of 

 Cheilopogon xenopterus (about 1 mm) are a character 

 shared with Prognichthys (Kovalevskaya, 1982) and 

 with at least some of the members of the C. nigricans 

 species group (Parin and Belyanina, 1996), which 

 includes C. dorsomaculata and C. xenopterus in the 

 eastern tropical Pacific. Eggs have not been described 

 for C. dorsomaculata or the two Prognichthys spe- 

 cies in the eastern tropical Pacific (Parin, 1995) and 

 it is unknown how they might be distinguished from 

 the eggs of C. xenopterus except that late stage 

 Prognichthys embryos should be more densely pig- 

 mented. An unidentified type of exocoetid egg (2.2 

 mm diameter with ca. 150 short filaments ) occasion- 

 ally co-occurs with C. xenopterus in plankton 

 samples; it might be one of these species (larval 

 Prognichthys are relatively common in the samples). 

 Collette et al. ( 1984) noted that some flyingfishes 

 apparently have a preanal finfold during early de- 

 velopment and suggested that it is an embryonic fea- 

 ture that is lost soon after hatching. There is no prea- 

 nal finfold in C. xenopterus. 



Larvae and juveniles 



Larval Cheilopogon range between about 4 and 6 mm 

 (e.g. Collette et al., 1984) and are well developed at 

 hatching. Cheilopogon xenopterus may be a bit 

 smaller than usual, but otherwise is typical of the 

 genus at hatching. Cheilopogon larvae develop a pair 

 of mandibular barbels that persist into the juvenile 

 stage and remain separate or fuse mesially — the 

 membrane joining the barbels either remaining low 

 and simple or becoming broad and fimbriate. Among 

 the Cheilopogon species in the eastern Pacific, C 

 furcatus, C. heterurus hubbsi, and C. papilio retain 

 separate barbels in the juvenile stage. The barbels 

 become fused basally by means of a low, sparsely pig- 

 mented or unpigmented membrane in C. atrisignis 

 and C. spilonotopterus, whereas in C. dorsomaculata 

 and C. xenopterus the basal membrane is somewhat 

 broader and densely pigmented along its margin. 



