Percophids are a family of small marine benthic fishes common over soft bottoms from inshore to the outer slopes

in tropical to temperate regions of the Atlantic and in the Indo-West and southeast Pacific (Reader and Neira, 1998; Okiyama, 2000). Five species belonging to four genera have been recorded around the Salas y Gómez Ridge in the southeast Pacific, all of which are endemic to the area except for Chrionema chryseres, a species which also occurs off the Hawaiian Islands and Japan (Parin, 1985, 1990;

Parin et al., 1997). Of these five species, larval stages have been described only for Osopsaron karlik and Chrionema

pallidum (Belyanina 1989, 1990)

Castro, Leonardo R.

Landaeta, Mauricio F.

Neira, Francisco J.

Aquatic Commons

693
Percophids are a family of small marine 
benthic fi shes common over soft bot-
toms from inshore to the outer slopes 
in tropical to temperate regions of the 
Atlantic and in the Indo-West and 
southeast Pacifi c (Reader and Neira, 
1998; Okiyama, 2000). Five species 
belonging to four genera have been 
recorded around the Salas y Gómez 
Ridge in the southeast Pacifi c, all of 
which are endemic to the area except 
for Chrionema chryseres, a species 
which also occurs off the Hawaiian 
Islands and Japan (Parin, 1985, 1990; 
Parin et al., 1997). Of these fi ve species, 
larval stages have been described only 
for Osopsaron karlik and Chrionema 
pallidum (Belyanina 1989, 1990).
Dactylopsaron dimorphicum (Parin 
and Belyanina, 1990) is a dwarf per-
cophid (29 mm maximum body length) 
previously recorded only at the Cupole 
(26°S; 86°W) and Baral (25°S; 96°W) 
seamounts located to the west of 
the Salas y Gómez Ridge and at the 
junction of this and the Nazca Ridge, 
respectively, at depths of 240−345 m 
(Parin, 1990; Parin et al., 1997). Adults 
Larvae of Dactylopsaron dimorphicum 
(Perciformes: Percophidae) from oceanic islands 
in the southeast Pacifi c 
Mauricio F. Landaeta
Laboratorio de Oceanografía Pesquera y Ecología Larval
Departamento de Oceanografía
Universidad de Concepción 
Casilla 160-C
Concepción, Chile 
Francisco J. Neira
Faculty of Fisheries and Marine Environment 
Australian Maritime College 
PO Box 21
Beaconsfi eld, Tasmania 7270, Australia
Leonardo R. Castro 
Laboratorio de Oceanografía Pesquera y Ecología Larval 
Departamento de Oceanografía, Universidad de Concepción 
Casilla 160-C
Concepción, Chile
E-mail addres (for L. R. Castro, contact author): lecastro@udec.cl
Manuscript approved for publication 
15 January 2003 by Scientifi c Editor.
Manuscript received 4 April 2003 at NMFS 
Scientifi c Publications Offi ce.
Fish Bull. 101:693–697 (2003).
of this monotypic genus differ from 
other percophids in that the fi rst dorsal 
fi n is positioned at the back of the head 
and is in line with the mid-operculum, 
8−10 digitiform processes are present 
on the posterior upper opercular mar-
gin, and expanded lobes are present at 
the distal end of the medial branchio-
stegal rays (Parin, 1990). This species 
is sexually dimorphic, males have a 
thicker and much longer fi rst dorsal-fi n 
spine than females (Parin, 1990). There 
is no information on their reproductive 
biology and eggs are unknown (Watson 
et al., 1984). 
We describe the postfl exion larvae 
of D. dimorphicum using material col-
lected around Salas and Gómez and 
Easter Islands in the southeast Pacifi c. 
We also provide information on the spa-
tial distribution of this species around 
both islands, and on how to distinguish 
the larvae from those of teleosts with 
similar larvae in the area. This note 
constitutes the fi rst record of D. dimor-
phicum off Easter Island, as well as the 
fi rst record of the larvae in nearshore 
waters of both Pacifi c islands. 
Methods
Field work 
Larvae were obtained during an oce an -
ographic expedition (CIMAR-5) to 
Easter Island (27°10′S; 109°20′W) 
and Salas y Gómez Island (26°30′S; 
105°20′W), approximately 3750 km 
west of Chile, in November 1999. Sam-
ples were collected onboard the Chil-
ean navy research vessel AGOR Vidal 
Gormaz by using a bongo sampler 
equipped with two conical nets (0.6-m 
diameter mouth openings, 3 m long, 
350-µm mesh size). The mouth of each 
net was fi tted with an OSK fl owmeter to 
estimate volume of water fi ltered. Tows 
were carried out for 10 min obliquely to 
the surface from either the maximum 
permissible depth in shallow (<200 m) 
stations or from 400 m in deeper sta-
tions. Samples around Easter Island 
were obtained at 10 stations located 
approximately one nautical mile 
(nmi) from the coast both during day 
and night, and along four transects 
(NW−SE and NE−SW) each containing 
four stations located at 3, 7, 12, and 20 
nmi offshore (Fig. 1). Samples around 
Salas y Gomez Island were obtained 
along four transects (N−S and E−W), 
each containing four stations at 1, 3, 
6, and 10 nmi offshore (Fig. 2). Addi-
tionally eight deep stations (>1500 m) 
were also sampled between Easter and 
Salas y Gómez islands. All samples 
were fi xed in 5% formalin and later pre-
served in 70% ethanol. Water volume 
sampled per tow ranged between 112.6 
and 517.7 m3. Larval abundances were 
standardized to 1000 m3 and mapped 
by using SURFER® (Golden Software, 
Golden, CO). Statistical analyses were 
performed using STATISTICA (Star-
Soft, Inc., Tulsa, OK). 
Larval identifi cation and 
processing 
Postfl exion larvae were identifi ed as 
those of Dactylopsaron dimorphicum
by a combination of dorsal and anal-fi n 
meristics (D. IV [III–V] + 22 [20−22] 
694 Fishery Bulletin 101(3)
Longitude (W)
La
tit
ud
e 
(S
)
Figure 1
Spatial distribution of postfl exion larvae of Dactylopsaron dimorphi-
cum (numbers/1000 m3) around Easter Island in November 1999. 
Figure 2
Spatial distribution of postfl exion larvae of Dactylopsaron dimorphi-
cum (numbers/1000 m3) around Salas y Gómez Island in November 
1999. 
Longitude (W)
La
tit
ud
e 
(S
)
and A. 24 [23–25]; Table 1), and by the presence of the 
unique digitiform opercular processes (Parin, 1990; Oki-
yama, 2000). Identifi cation was verifi ed by using fi n meris-
tics from cleared and stained specimens (Potthoff, 1984). 
A total of 55 postflexion larvae of D. dimorphicum
(8.2–15.3 mm standard length) were examined to describe 
morphometrics, meristics, and pigmentation. Three larvae 
(9.1, 13.1 and 13.4 mm SL) were cleared and stained fol-
lowing the method of Potthoff (1984). Terminology 
and morphometric measurements follow Neira et 
al. (1998). Measurements were made to the near-
est 0.01 mm by using a dissecting microscope 
fi tted with an eyepiece micrometer. Body length 
(BL, Neira et al., 1998) in postfl exion larvae cor-
responds to standard length (SL), i.e. tip of snout 
to posterior margin of hypurals. Measurements of 
body depth (BD), head length (HL), and preanal 
length (PAL) were converted to a percentage (%) of 
SL (Table 2). Eye diameter (ED) and snout length 
(SnL) were converted to a percentage (%) of HL. 
Pigment described refers solely to melanin. Illus-
trations were made with the aid of a camera lucida. 
Results
Description of larvae 
Postfl exion larvae of Dactylopsaron dimorphicum
are elongate (BD 13.1–18.3%; Table 2), and have 
a moderate to large head (HL 28.6–36.7%) and 
an elongate snout (Fig. 3). Eyes are round and 
pigmented by 8.2 mm SL. The mouth is large, pro-
trusible, and has a long ascending premaxillary 
process giving a characteristic “duckbill” appear-
ance. Small villiform teeth are present along the 
premaxilla and dentary. There are no head spines. 
The digitiform processes on the upper opercular 
margin are present in larvae >13.2 mm SL; the 
lower, rearward-directed process that reaches the 
end of the pectoral-fi n base in adults was still 
forming in the largest larva examined (15.3 mm 
SL). The branchiostegal membranes are free from 
the ithsmus. The short fi rst dorsal fi n is located at 
the nape and lies in line with the mid-operculum; 
pterygiophores of the fi ve fi rst-dorsal fi n spines in 
two of the cleared and stained larvae (13.1 and 13.4 
mm SL) were located between the neural spines of 
the second and third trunk vertebrae. The 9.1-mm-
SL cleared and stained larva possessed only 15 
of the 17−20 pectoral-fi n rays, and fi rst dorsal-fi n 
spines were developing. The elongate pelvic fi ns 
are thoracic, i.e. inserted in front of the pectoral-
fi n bases. Lateral line scales begin to form at >13 
mm SL. Larvae are unpigmented, although a few 
had a small melanophore at the base of the 17 or 
18th dorsal-fi n ray. There are 31–35 myomeres. The 
number of vertebrae in the cleared and stained 
larvae is 34–35 (11–12 + 22–24). 
Larval distribution
Postfl exion D. dimorphicum larvae were collected 
within 6 nmi off both Easter and Salas and Gómez 
695NOTE Landaeta et al.: Larvae of Dactylopsaron dimorphicum in the southeast Pacifi c
Table 1
Meristic counts of percophid species recorded in submarine ridges of Salas y Gómez Island in the southeastern Pacifi c (from Parin 
[1985, 1990] and Okiyama [2000]). 
Dorsal Anal Pectoral Pelvic Caudal (branched) Vertebrae
Chrionema chryseres VI +16 26 23 I, 5 15 (11) 27–28
Chrionema pallidum VI +14−15 18 20−22 I, 5 15 (11) 27–28
Dactylopsaron dimorphicum IV [III-V] + 22 [20−22] 24 [23−25] 18 [17−20] I, 5 14 (8) 34–351
Enigmapercis acutirostris II +21 25 21 I, 5 15 (8−9) —
Osopsaron karlik V-VI +19−20 22−23 19−20 I, 5 14 32
1 This study.
Table 2
Standard length range (mm), and mean values (±1 SD) of 
selected body proportions (given as a percentage of body 
length) of postfl exion larvae of Dactylopsaron dimorphi-
cum from Easter and Salas y Gomez islands in the south-
eastern Pacifi c Ocean (n=55).
Standard length (mm)  8.2−15.3
Head length (%SL) 28.6−36.7 (32.3 ±3.3)
Eye diameter (%HL) 18.2−24.7 (22.0 ±3.1)
Snout length (%HL) 25.6−36.2 (31.0 ±5.5)
Body depth (%SL) 13.1−18.3 (15.3 ±2.2)
Preanal length (%SL) 45.4–56.9 (49.5 ±4.0)
Figure 4
Combined body length (SL, mm) frequency distribution of 
postfl exion larvae of Dactylopsaron dimorphicum around 
Easter Island and Salas y Gómez Island in November 1999. 
Body length (mm)
Fr
eq
ue
nc
y 
(%
)
Islands (Figs 1 and 2). Around Easter Island, larvae were 
caught only in nearshore stations (<2 nmi) over the narrow 
shelf and were more abundant along the southern edge. 
A
B
Figure 3
Postfl exion larvae of Dactylopsaron dimorphicum collected around Easter Island in 
November 1999. (A) 8.5 mm SL; (B) 14.8 mm SL. Illustrated by F. J. Neira. 
696 Fishery Bulletin 101(3)
The highest larval concentrations (>100 larvae/1000 m3) 
occurred at the southeastern tip of the island and averaged 
27 ±46 larvae/1000 m3 (Fig. 1). No signifi cant differences 
were found between day and night larval concentrations 
(Kruskal-Wallis test=0.047; P>0.05). Around Salas and 
Gómez Island, larvae were caught only at two stations 
6 nmi west and south of the island, and in mean concentra-
tions <10 larvae 1000/m3 (Fig. 2). No larvae were caught in 
any of the eight stations sampled between the two islands. 
Body lengths of larvae caught in both islands ranged from 
8 to 16 mm SL, and over 30% of the larvae were around 12 
mm SL (Fig. 4).
Discussion
Postflexion larvae of D. dimorphicum are likely to be 
confused with those of four other co-occurring percophid 
species (see Table 1), and those of the creediid Crystallo-
dytes pauciradiatus that occur in the same region (Castro 
and Landaeta, 2002) and have similar bodies with little or 
no pigment. In the case of the percophids, the digitiform 
opercular processes exclusive to D. dimorphicum, together 
with dorsal and anal-fi n meristics, should be suffi cient 
to distinguish between postfl exion larvae of all species. 
Larval C. pauciradiatus can be identifi ed by using myo-
mere counts (56−58 vs. 31−35 in D. dimorphicum) and their 
small, early forming posterior preopercular spines (Reader 
et al., 2000).
Our collection of D. dimorphicum larvae at Easter Island, 
some 453 km to the southwest of Salas y Gomez Island 
where it was fi rst described (Parin, 1990), constitutes the 
fi rst record for Easter Island, thereby extending the known 
range of this species over the South Pacifi c plate. Despite 
numerous past fi sh surveys around Easter Island (i.e. Ran-
dall and Cea-Egaña, 1984; Mujica, 1993), adults of this dwarf 
percophid had not been reported there, a fact that could be 
attributed to factors such as collection methods, depth of 
surveys, and the very small size of these larvae. However, the 
presence and abundance of larval D. dimorphicum reported 
in this study, and the fact that they were among the fi ve most 
abundant larval taxa caught around Easter Island (Castro 
and Landaeta, 2002), implies the existence of a well-estab-
lished breeding population. Biogeographically, this fi nding 
also suggests that larval drift could play an important role in 
the expansion of this and other fi sh species that have pelagic 
larvae in this region of the southeast Pacifi c. In this context, 
it is perhaps relevant that expansions of fi sh ranges are not 
uncommon in this region, even though both Easter and Sa-
las y Gomez Islands lie in different biogeographic provinces 
(Parin et al., 1997). A good example is the pentacerotid Pen-
taceros decacanthus, which was regarded as endemic of the 
Nazca and Salas y Gómez Ridges until it was recorded in 
Easter Island (Parin and Kotlyar, 1988). 
Acknowledgments
We would like to thank Paula Rosenberg and all the crew 
from the AGOR Vidal Gormaz for their help with sampling. 
We also thank Muneo Okiyama for his comments on iden-
tifi cation of percophid larvae. This research was funded 
by the Comité Oceanográfi co Nacional (CONA), Chile, and 
forms part of a study on distribution patterns and larval 
accumulation around oceanic islands headed by Leonardo 
Castro. 
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Larvae of Dactylopsaron dimorphicum (Perciformes: Percophidae) from oceanic islands in the southeast Pacific

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Larvae of Dactylopsaron dimorphicum (Perciformes: Percophidae) from oceanic islands in the southeast Pacific

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