693 



Larvae of Dactylopsaron dimorphicum 

 (Perciformes: Percophidae) from oceanic islands 

 in the southeast Pacific 



Mauricio F. Landaeta 



Laboratorio de Oceanografia Pesquera y Ecologia Larval 

 Departamento de Oceanografia 

 Universidad de Concepcion 

 Casilla 160-C 

 Concepcion, Chile 



Francisco J. Neira 



Faculty of Fisfienes and Marine Environment 



Australian Mantime College 



PO Box 21 



Beaconsfield, Tasmania 7270, Australia 



Leonardo R. Castro 



Laboratorio de Oceanografia Pesquera y Ecologia Larval 



Departamento de Oceanografia, Universidad de Concepcion 



Casilla 160-C 



Concepcion, Cfiile 



E-mail addres (for L R Castro, contact author): lecastro@udec.cl 



Percophids are a family of small marine 

 benthic fishes common over soft bot- 

 toms from inshore to the outer slopes 

 in tropical to teinperate 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 Gomez 

 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). 



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 Gomez Ridge and at the 

 junction of this and the Nazca Ridge, 

 respectively, at depths of 240-345 m 

 (Parin, 1990; Parin et al., 1997 ). Aduhs 



of this monotypic genus differ from 

 other percophids in that the first dorsal 

 fin 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 first dorsal-fin 

 spine than females (Parin, 1990). There 

 is no information on their reproductive 

 biology and eggs are unknown (Watson 

 etal., 1984). 



We describe the postflexion larvae 

 of D. dimorphicum using material col- 

 lected around Salas and Gomez and 

 Easter Islands in the southeast Pacific. 

 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 first record of D. dimor- 

 phicum off Easter Island, as well as the 

 first record of the larvae in nearshore 

 waters of both Pacific islands. 



Methods 



Field work 



Larvae were obtained during an ocean- 

 ographic expedition (CIMAR-5) to 

 Easter Island (27°10'S; 109°20'W) 

 and Salas y Gomez 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-nm mesh size). The mouth of each 

 net was fitted with an OSK flowmeter to 

 estimate volume of water filtered. 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 Gomez islands. All samples 

 were fixed in 5% formalin and later pre- 

 served in 70% ethanol. Water volume 

 sampled per tow ranged between 112.6 

 and 517.7 m-'. Larval abundances were 

 standardized to 1000 m-^ and mapped 

 by using SURFER® (Golden Software, 

 Golden, CO). Statistical analyses were 

 performed using STATISTICA (Star- 

 Soft, Inc., Tulsa, OK). 



Larval identification and 

 processing 



Postflexion larvae were identified as 

 those of Dactylopsaron dimorphicum 

 by a combination of dorsal and anal-fin 

 meristics (D. IV [III-V] + 22 [20-22] 



Manuscript approved for publication 

 15 January 2003 by Scientific Editor. 



Manuscript received 4 April 2003 at NMFS 

 Scientific Publications Office. 

 Fish Bull. 101:693-697 (2003). 



