319 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
@ established in 1881 << 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Abstract—Postflexion and transfor- 
mation stages of the Diaphus ostenfeldi 
in the southwestern Pacific Ocean are 
described for the first time. Identifica- 
tion to the species level was based on 
tracing characters from fully formed, 
large metamorphic specimens back- 
ward to smaller specimens. It was 
found that larval D. ostenfeldi =9.5 mm 
standard body length (SL) can be char- 
acterized by a unique character within 
the genus Diaphus, namely the pres- 
ence of melanophores at the dorsal fin 
base and between branchiostegal rays. 
Metamorphosis in larvae of this species 
occurs at a much longer body length 
(~20 mm SL) than in larvae of other 
species of this genus. 
Manuscript submitted 13 April 2020. 
Manuscript accepted 5 October 2020. 
Fish. Bull. 118:319-323 (2020). 
Online publication date: 21 October 2020. 
doi: 10.7755/FB.118.4.1 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
A description of late and transformation stages 
of larvae of the Diaphus ostenfeldi in the western 
periphery of the South Pacific Gyre 
Sergei A. Evseenko (deceased) 
Yana Yu. Bolshakova (contact author) 
Email address for contact author: yanusrunaa@mail.ru 
Shirshov Institute of Oceanology 
Russian Academy of Sciences 
36 Nakhimovskyi Prospekt 
Moscow 117997, Russia 
Diaphus is the most speciose genus of 
the mesopelagic family Myctophidae 
and plays a key role in oceanic food 
webs. Larvae of Diaphus are poorly 
known. Of the 80 species in this genus 
(Fricke et al., 2020), the early stages of 
development are known for only 10 spe- 
cies. These species are the D. agas- 
sizit (Pertseva-Ostroumova, 1975), 
Garman’s lanterfish (D. garmani) (Sassa 
et al., 2003), D. hudsoni (Olivar, 1987), 
short-headed lantern fish (D. brachy- 
cephalus or D. richardsoni) (Olivar 
and Beckley, 1995), D. diadematus 
(Olivar and Beckley, 1995), D. mollis 
(Olivar and Beckley, 1995), D. meto- 
poclampus (Sparta, 1952), D. pacificus 
(Moser and Ahlstrom, 1974), Califor- 
nia headlightfish (D. theta) (Moser and 
Ahlstrom, 1996), and Malayan lantern- 
fish (D. malayanus) (Tsokur, 1975). 
The early stages of development are 
known in only 2 species of the 9 species 
of Diaphus that have been observed 
in the southwestern Pacific Ocean: 
D. hudsoni and D. mollis (McGinnis, 
1982; Bekker and Evseenko, 1986). 
Diaphus ostenfeldi is circumglobal, 
is distributed in the Subtropical Con- 
vergence, a frontal zone between sub- 
antarctic and tropical water masses, 
and is considered to be a convergence 
(Krefft, 1974), notal or subantarctic 
(Parin et al., 1974), or transitional 
(McGinnis, 1982; Bekker and Evseenko, 
1986) species. This species has been 
observed in the central eastern Pacific 
Ocean (McGinnis, 1982) and in the 
southwestern Pacific Ocean (Bekker 
and Evseenko, 1986), and its range is 
known to extend to about 23-24°S in 
the region of the Benguela Current 
(Trunov, 1968; Hulley, 1972). It has been 
found at depths as great as about 120 m 
below the sea surface (Bekker, 1983). 
Juveniles have been taken at depths 
less than 100 m; larger specimens have 
been found at depths 160 m below the 
sea surface (Hulley, 1981; McGinnis, 
1982). Little is known of the ecology 
of this species. Specimens caught in 
the South Atlantic Ocean were limited 
between the 10°C and 15°C isotherms 
at a depth of 200 m; however, it has 
been assumed that the species can live 
at shallower depths, in suitable tem- 
peratures (Krefft, 1974; Hulley, 1981). 
Herein, we present larval descriptions 
for D. ostenfeldi from the southwestern 
Pacific Ocean based on a developmen- 
tal series of larvae from the postflexion 
stage to the transformation stage. 
Materials and methods 
Larvae of D. ostenfeldi were caught at 
4 stations (stations [st.] 3049, 3052, 
