1) The study examined growth rates in 5 species of lanternfish (family Myctophidae) larvae from the eastern Gulf of Mexico by measuring their length and weight over time. 2) Larval period length varied between species from 31 days for Ceratoscopelus townsendi to 60 days for Notolychnus valdiviae. 3) Growth rates in length also varied between species, ranging from 0.1 mm/day for N. valdiviae to 0.4 mm/day for C. townsendi.

1. BULLETIN OF MARINE SCIENCE, 84(1): 123–135, 2009
123Bulletin of Marine Science
© 2009 Rosenstiel School of Marine and Atmospheric Science
of the University of Miami
GROWTH AMONG LARVAE OF LANTERNFISHES (TELEOSTEI:
MYCTOPHIDAE) FROM THE EASTERN GULF OF MEXICO
Walter J. Conleyand John V. Gartner, Jr.
ABSTRACT
The larvae of five species of myctophid fishes; Benthosema suborbitale (Gilbert,
1913), Ceratoscopelus townsendi (Eigenmann and Eigenmann, 1889), Hygophum
taaningi Becker, 1965, Myctophum selenops Tåning, 1928, and Notolychnus valdiviae
(Brauer, 1904) from the eastern Gulf of Mexico were examined to measure early
growth in length and weight. Age was determined from examination of sagittal
otoliths. Larval period ranged from 31 d for the rapidly growing C. townsendi to
60 d for the diminutive N. valdiviae. Growth rate ranged from 0.1 mm SL d–1
for
N. valdiviae to 0.4 mm SL d–1
for C. townsendi. Increases in weight were variable
and related to larval morphology. The most rapid increases in weight with length
were observed for the stout larvae of M. selenops, whereas the slender larvae of C.
townsendi and N. valdiviae increased more gradually. The growth rate and age at
transformation were highly variable among the five species, but within the range
displayed by other nearshore tropical-subtropical species from the Gulf of Mexico.
Variations in growth appear to be related to species-specific variations in life history
traits and larval morphology. These are the first data reported on the growth of
larval myctophids from the Atlantic.
Early life history events determine adult population size and structure for verte-
brate species (Stearns, 1976). Effects are particularly noticeable among teleosts where
high fecundity combines with an unpredictable mix of biotic and abiotic factors to
determine larval growth and survival (Hjort, 1914; Miller et al., 1988; Claramunt
and Wahl, 2000). The larval stage is the most vulnerable for fishes. Factors affecting
survival during early life include successful feeding, escape from predation, and rate
of growth. Among the many factors affecting growth-related survival are size at age
(Anderson, 1988; Sogard, 1997), the duration of the larval period (Houde, 1987a), and
rate of growth (Takasuka et al., 2003, 2004). Larger size is related to better swimming
ability and larger mouths thus larvae may find both a refuge from predation (Bailey,
1984; Luecke et al., 1990; Paradis et al., 1996) and a broader array of potential prey
(Sabatés and Saiz, 2000; Conley and Hopkins, 2004). Spending less time in the larval
stage reduces the time an individual or cohort is exposed to mortality factors and
the rate at which larvae grow may be an indicator of their relative health. Larvae that
grow more slowly have been ingested more frequently by predators (Takasuka et al.,
2003), thus there is an adaptive advantage to eating well and growing rapidly (Rosen-
berg and Haugen, 1982; Miller et al., 1988). Many of these factors are likely species
and location specific (Rilling and Houde, 1999; Comyns et al., 2002) and our under-
standing of these processes is dominated by information from commercially impor-
tant coastal species (Hunter, 1972; Arthur, 1976; Warlen, 1988) that exhibit a wide
range in their rate of growth (Houde, 1987b). The adaptive value of rapid growth may
be less in oligotrophic waters (Hillgruber et al., 1997) where the density of predators
and food availability are lower.
Mesopelagic fishes are prominent members of oligotrophic ecosystems. Mycto-
phids are an abundant vertically migrating mesopelagic fish group (Gjøsaeter and
Kawaguchi, 1980; Gartner et al., 1987), providing forage for a variety of fishes and

2. BULLETIN OF MARINE SCIENCE, VOL. 84, NO. 1, 2009124
other vertebrates (Pereyra et al., 1969; Klages and Bester, 1998). In oceanic surface
waters, myctophid larvae are dominant members of the ichthyoplankton assemblage,
ranging from about 30 to over 70% of fish larvae collected (Ahlstom, 1972; Loeb, 1980;
Sanvicente-Añorve et al., 1998; Muhling et al., 2007), yet we know little about their
early life history. Myctophid larvae are one to several orders of magnitude greater in
abundance than adults and juveniles in the eastern Gulf of Mexico (Gartner et al.,
1989a) suggesting that larval mortality is an important factor in determining adult
population size and structure. Here we report information on the growth in length
and weight of five larval myctophids from the eastern Gulf of Mexico, represent-
ing the second report of myctophid larval age and growth from any ocean (Methot,
1981), and the first from the Atlantic.
Materials and Methods
All larvae were collected in the eastern Gulf of Mexico within 20 km of 27°N, 86°W, an area
known as “Standard Station.” Temperature was determined with expendable bathythermo-
graphs (XBT), and salinity was determined from electrical measurement of conductivity with
depth (CTD). Hydrographic conditions are typical of vertically stratified oligotrophic envi-
ronments and were summarized by Sutton and Hopkins (1996). Three separate collections
were used in these analyses. The range in size of juveniles included 13,369 individuals (Gart-
ner et al., 1987) and the range in size of larvae included 6158 individuals collected during all
seasons in discrete tows of the upper 300 m (Conley, 1993). As these larvae were preserved in
Formalin, they could not be used for analysis of age and growth (Radtke and Waiwood, 1980).
To determine age and growth, net tows were made hourly during four late spring or summer
cruises during August 1984, July 1985, May 1986, and July 1990; representing over 2 mo of
daily sampling. Ichthyoplankton samples were collected in oblique tows of the upper 150 m
using two 505 µm mesh plankton nets suspended side by side within a modified Tucker trawl
frame (Hopkins et al., 1973). These nets had a mouth opening of 0.56 m2
per net, and a length
to mouth ratio of 7:1. Fish larvae were sorted immediately from the catch, identified, mea-
sured to the nearest 0.1 mm standard length (SL), and frozen in individually sealed Nalgene®
capsules. Larvae were separated into three groups; one to determine dry weight, a second for
extraction of otoliths, and a third to determine chemical composition (not included here).
To determine age, the sagittal otoliths were removed from the otic capsules of individual
larvae, mounted in Thermoplast, and examined at 630× magnification. Images were projected
to a phase contrast monitor and microincrements were quantified by two independent observ-
ers. If microincrement counts differed, the otolith was reexamined. If independent counts dif-
fering by more than three microincrements could not be resolved, the otolith was discarded.
Several growth models were explored for best fit to results and selected based upon calculated
regression coefficients and size of 0-age larvae. Dry weight was measured to the nearest 0.001
mg by drying formerly frozen larvae at 60 °C and weighing individuals on a Perkin-Elmer
Autobalance AD-2 in a temperature and humidity controlled chamber.
Results
Little change (< 3 °C) in surface water temperature was observed at Standard Sta-
tion (Fig. 1). A shallow mixed layer was generally present in the upper 25–75 m.
Temperature rapidly decreased between 75 and 400 m, with little change at greater
depths. Maximum salinities were measured at approximately 100 m; gradually de-
creasing from 36.0 to 34.9 at 1000 m.
Sixty-five Benthosema suborbitale (Gilbert, 1913) otoliths were examined from lar-
vae ranging between 4.2 and 10.8 mm SL (Fig. 2). Examination of larval and juvenile

3. conley and gartner, jr.: variation in growth among lanternfish larvae 125
length (Table 1) revealed that transformation to juvenile in this species occurs be-
tween 10.0 and 11.0 mm SL, corresponding to a calculated age at metamorphosis of
48 d (Table 1). Assuming transformation at 10.5 mm SL and hatching at 2.5 mm SL,
the daily increase in SL for this species was 0.2 mm. The smallest larva of B. suborbit-
ale weighed 2.9 × 10–2
mg at 2.8 mm SL and the largest weighed 2.8 mg at 9.7 mm SL.
The rate of increase in weight with length was among the lowest of the five species
examined (Fig. 3).
Thirty-two Ceratoscopelus townsendi (Eigenmann and Eigenmann, 1889) otoliths
were examined from larvae ranging in size from 4.4 to 9.8 mm SL (Fig. 2). Transfor-
mation occurred between 14.0–15.0 mm SL at an age of 31 d (Table 1). Within the
larval stage, daily growth was approximately 0.4 mm SL, the highest rate of any of
the species examined (Fig. 2). The smallest larva of C. townsendi weighed 7.7 × 10–2
mg at 3.9 mm SL and the largest weighed 3.0 mg at 10.5 mm SL, with relatively low
increases in weight with size (Fig. 3).
Twenty-eight Hygophum taaningi Becker, 1965 otoliths were examined from indi-
viduals which ranged in size from 5.4 to 7.9 mm SL (Fig. 2). The largest larva recorded
from the eastern Gulf of Mexico was slightly larger than the smallest juvenile (Table 1)
Figure 1. Temperature (XBT) and salinity (CTD) profiles for the eastern Gulf of Mexico within
20 km of 27°N, 86°W.

4. BULLETIN OF MARINE SCIENCE, VOL. 84, NO. 1, 2009126
and estimated size at transformation was 11.0–12.0 mm SL. Assuming a transforma-
tion at 11.0 mm SL, larvae of this species grew approximately 0.2 mm per d, and age
at transition was 50 d. The smallest larva of H. taaningi weighed 7.3 × 10–2
mg at 3.6
mm SL and the largest weighed 1.1 mg at 6.8 mm SL (Fig. 3). The rate of increase in
weight with length was the second highest among the five species examined.
Figure 2. Microincrement counts from sagittal otoliths of larvae of five species of myctophids
from the eastern Gulf of Mexico. L = standard length in mm and t = age in days.

5. conley and gartner, jr.: variation in growth among lanternfish larvae 127
Twenty-two otoliths of Myctophum selenops Tåning, 1928, were examined from
larvae that ranged in size from 4.6 to 7.7 mm SL (Fig. 2). Assuming a transformation
at 9.5 mm SL (Table 1) and a hatch at 2.8 mm SL, larvae of this species grew approxi-
mately 0.2 mm SL daily, with the larval period lasting approximately 31 d. The small-
est larva of M. selenops weighed 5.2 × 10–2
mg at 2.9 mm SL and the largest weighed
2.4 mg at 7.5 mm SL, exhibiting the highest rate of dry weight increase to length of
the five species examined (Fig. 3).
Twenty-nine otoliths of Notolychnus valdiviae (Brauer, 1904) were examined from
larvae that ranged in size from 5.2 to 8.0 mm SL (Fig. 2). The larval period of N.
valdiviae was estimated at 60 d (Table 2). Assuming transformation at 10.0 mm SL
(Table 1), average daily growth was approximately 0.1 mm SL, the lowest among the
five species examined. The weight of N. valdiviae ranged from 4.5 × 10–2
mg at 3.0
mm SL to 1.6 mg at 8.5 mm SL and the rate of increase in weight with size was also
the lowest among the five species examined (Fig. 3).
Discussion
Juveniles and adults of three (B. suborbitale, C. townsendi, and N. valdiviae) of
the five species examined are considered abundant in the eastern Gulf of Mexico
(Gartner et al., 1987). Restricted to tropical and subtropical waters of all three oceans
(Nafpaktitis and Nafpaktitis, 1969; Clarke, 1973; Hulley, 1981), B. suborbitale adults
are vertical migrators, but juveniles remain at depth (Gartner et al., 1987). Analysis
of reproductive patterns indicates sustained year-round spawning (Gartner, 1993).
Ceratoscopelus townsendi, a cosmopolitan species with a number of distinct and
geographically separated populations (Badcock and Araujo, 1988), is a strong verti-
cal migrator but small juveniles remain near daytime depths at night (Gartner et
al., 1987). This species exhibits the highest fecundity among eastern Gulf of Mexico
myctophids, with two relatively restricted spawning periods in the winter and sum-
mer (Gartner, 1993). Notolychnus valdiviae adults are the smallest of the lantern-
fishes with an unusual adult morphology (Nafpaktitis et al., 1977). This species is
also primarily tropical to subtropical, occurring in all three oceans (Nafpaktitis et
al., 1977; Hulley, 1981). Unlike B. suborbitale and C. townsendi, there is no evidence
that juveniles remain at depth (Gartner et al., 1987). A year-round spawning pattern
is evident, but with relatively low fecundity (Gartner, 1993).
Adults and juveniles of H. taaningi are common and M. selenops uncommon to
rare in the eastern Gulf of Mexico (Gartner et al., 1987). The former is also common
in the northern Sargasso Sea (Gartner et al., 1989b). Myctophum selenops has been
Table 1. Size ranges of larval myctophids and juveniles collected from the eastern Gulf of Mexico
compared to smallest larvae as estimated from the analysis of growth. Sizes are from the examina-
tion of 6158 larvae (Conley, 1993) and 13,369 juveniles (Gartner et al., 1987).
Estimated
size at 0-age
(mm SL)
Smallest
larva
(mm SL)
Largest
larva
(mm SL)
Smallest
juvenile
(mm SL)
Size at
transformation
(mm SL)
Benthosema suborbitale 2.5 2.2 10.8 10.0 10.0–11.0
Ceratoscopelus townsendi 3.1 2.1 14.5 14.0 14.0–15.0
Hygophum taaningi 4.2 2.2 11.6 11.0 11.0–12.0
Myctophum selenops 2.8 2.8 8.7 10.0 9.0–10.0
Notolychnus valdiviae 3.0 2.9 10.9 9.0 9.0–11.0

6. BULLETIN OF MARINE SCIENCE, VOL. 84, NO. 1, 2009128
described as an uncommon broadly-tropical myctophid (Hulley, 1981) with largest
collections from the Caribbean Sea (Nafpaktitis et al., 1977). The larvae of M. selen-
ops are the second most abundant lanternfish collected in the Caribbean (Richards,
1984). Houde et al. (1979) reported that larvae are absent from the Gulf of Mexico
north of 28°30΄N and west of 86°W during August and most abundant during spring
Figure 3. Relationship between dry weight and standard length for larvae of five species of mycto-
phids from the eastern Gulf of Mexico. DW = dry weight in mg and L = standard length in mm.

7. conley and gartner, jr.: variation in growth among lanternfish larvae 129
and summer at other locations. In the eastern Gulf of Mexico, larvae of M. selenops
peak in summer with overall abundances ranked 20th
among the most common 25
species (Conley, 1993). No reproductive information is available for H. taaningi or
M. selenops.
Age in days was estimated from sagittal otolith microincrements assumed to be de-
posited daily. Although it is desirable to validate microincrements as daily (Beamish
and McFarlane, 1983), the application of common techniques for the assessment of
daily growth in nearshore fishes was not possible for these midwater fishes. Mycto-
phids are sensitive to the stress of capture and are rarely collected live. Attempts to
maintain fishes for more than brief periods have been unsuccessful (Robison, 1973).
In over a decade of sampling in the eastern Gulf, myctophid larvae have never been
collected alive. Nonetheless, the assumption of microincrements as indicators of age
in days is reasonable for myctophid larvae because: (1) daily deposition of microin-
crements has been confirmed, through marginal increment analysis, for all post-
metamorphic myctophids that have been examined thus far from the Gulf of Mexico
including two of the species examined in this study (Gartner, 1990, 1991a,b; unpubl.
data); (2) there is circumstantial evidence for daily deposition of microincrements
for myctophids from the Mediterranean (Gjøsaeter, 1987) and Tasmania (Young et
al., 1988); (3) microincrements exhibit a strong one-to-one relationship to age in days
for almost all teleost larvae that are not growth limited (Jones, 1986); (4) microincre-
ments exhibited by the larvae examined in this study displayed clearly defined, easily
distinguished microincrements that were regularly spaced, and; (5) calculation from
growth equations resulted in sizes of 0-age individuals matching, or within 2 mm, of
the smallest larvae collected (Table 1).
Linear growth models have been used to estimate larval growth for other Gulf of
Mexico species (Cowan, 1988; Peebles and Tolley, 1988), as well as some temperate
small-bodied fish (Rilling and Houde, 1999). A linear model resulted in regression
coefficients that were higher overall than most common power functions, but the
linear function underestimated the size of the smallest myctophid larvae; with all
but one < 2.0 mm SL. An exponential growth model produced regression coefficients
that were equivalent to the linear model, but better estimated the size of the smallest
larvae (Table 1). Other fishes, such as Atlantic gadoids, exhibited concave up curvi-
Table 2. Growth rate and age of transformation for larval clupeids and sciaenids from the Gulf of
Mexico compared to myctophid larvae.
Species Growth equation
Age in days at
transformation Reference
Brevoortia patronus Loge
= 0.005(t) + 2.7 88–103 DeeganandThompson(1987)
Brevoortia patronus L(t) = 2.355e2.212(1–e0.0608t)
65 Warlen (1988)
Cynoscion nebulosus L = 0.405(t) + 0.116 __ Peebles and Tolley (1988)
Micropogonias undulatus L = 0.189(t) + 0.634 > 80 Cowan (1988)
Benthosema suborbitale L = 2.5e0.03t
48 This study
Ceratoscopelus townsendi L = 3.1e0.05t
31 This study
Hygophum taaningi L = 4.2e0.02t
50 This study
Myctophum selenops L = 2.8e0.04t
31 This study
Notolychnus valdiviae L = 3.0e0.02t
60 This study

8. BULLETIN OF MARINE SCIENCE, VOL. 84, NO. 1, 2009130
linear growth (Campana and Hurley, 1989). Larvae grew slowly in the first week or
two of life but growth rate accelerated as larvae approached transformation. This
pattern was also observed in the examination of the width of microincrements in
the larval zone of three postmetmorphic myctophids, which suggested larval growth
rate increased with increasing age prior to transformation (Gartner, 1991b). The only
other examination of otoliths removed from larval myctophids was an examination
of growth pattern of the Pacific lampfish, Stenobrachius leucopsarus (Eigenmann
and Eigenmann, 1890). The larvae of this species exhibited a growth pattern similar
to that of Atlantic myctophid and gadoid fishes.
Fish larvae are the smallest nutritionally independent vertebrates (Wieser, 1995)
with weight gains of five to seven orders of magnitude common (Houde, 1987a).
Many factors, both abiotic and biotic, affect growth and survival, but no one factor
can adequately explain the complex dynamics of fish populations (Anderson, 1988;
Miller et al., 1988). The growth mortality hypothesis (see Anderson, 1988; Takasuka
et al., 2004) predicts that increasing size increases survival through a reduction in
exposure to predators and other mortality factors, thus there should be selection for
rapid growth. But the larval period is highly variable among tropical-subtropical spe-
cies, ranging from a few days to months (Brothers et al., 1983; Searcy and Sponaugle,
2000). Many Gulf of Mexico fish larvae are recruited to the juvenile stage between 31
to > 100 d at lengths ranging from 9 to 22 mm SL (Tables 1 and 2). Average growth
rates of myctophid species ranged from 0.1 mm SL d–1
to 0.4 mm SL d–1
, but growth
rates as high as 0.85 mm d–1
have been reported for round herring Etrumeus teres
(DeKay, 1842) from the Gulf of Mexico (Chen et al., 1992).
Hillgruber et al. (1997) compared the feeding of the larvae of the coastal Atlantic
mackerel (Scomber scombrus Linnaeus, 1758) with the mesopelagic blue whiting Mi-
cromesistius poutassou (Risso, 1827). While recognizing species-specific variation,
the authors suggested that the rapid growth of mackerel was an adaptation to reduce
their exposure to predators as they develop in a rich feeding environment. Slower
growth, but more efficient foraging, of the midwater blue whiting was interpreted
as an adaptation to life in a relatively stable, if food-poor, environment. Myctophid
larvae are often the most abundant fish group in this stable, food-poor environment
(Ahlstom, 1972; Loeb, 1980; Sanvicente-Añorve et al., 1998; Muhling et al., 2007)
and also appear to be efficient foragers (Conley and Hopkins, 2004). Compared to
round herring (Chen et al., 1992), myctophids do grow slowly; but the slowest grow-
ing myctophids were similar in daily growth and age at transformation (Table 2)
to nearshore tropical-subtropical clupeids (Deegan and Thompson, 1987; Warlen,
1988) and sciaenids (Cowan, 1988; Peebles and Tolley, 1988). Instead, this group of
myctophids exhibits a variety of growth rates, with the fastest growing species (C.
townsendi) increasing in length more than three times the slowest growing species
(N. valdiviae).
Among myctophid larvae, variation in the increase of length and weight reflects
known life history and morphological characteristics. Ceratoscopelus townsendi
adults are the largest of the abundant myctophids in the eastern Gulf of Mexico
(Gartner et al., 1987) and their larvae exhibited the fastest increase in length with
age. Increase in dry weight with length for this species, however, was among the low-
est of the five species examined. Larvae are slender and remain so throughout the
larval period. Conversely, M. selenops had the highest rate of increase in weight with
length. These are stout larvae throughout the larval period (Moser and Ahlstrom,

9. conley and gartner, jr.: variation in growth among lanternfish larvae 131
1974; Olivar et al., 1999) with large heads and mouths relative to body length (Conley
and Hopkins, 2004). Larvae of H. taaningi also exhibited a high rate of increase in
weight with length. These larvae, while not as robust as M. selenops, are not slender,
but broad along the dorso-ventral axis (Moser and Watson, 2001). Larvae of B. subor-
bitale exhibited an unusual pattern of growth. At < 4 mm SL it is a relatively slender
larva, but between 4 and 8 mm SL, the larvae add girth with relatively little increase
in body length (Badcock and Merrett, 1976). This is reflected in the relatively large
amount of scatter in age within this size range (Fig. 2). Notolychnus valdiviae adults
are the smallest of the myctophids (Nafpaktitis et al., 1977) and the slowest grow-
ing larvae in both length and weight. This species also exhibited the longest larval
period, transforming in about 60 d.
Thus, the examination of the biology of myctophid larvae suggests that this group
has adapted in multiple ways to survive in a stable oligotrophic environment. These
adaptations include dramatic variation in larval morphology (Moser, 1981; Moser
et al., 1984), variation in the depth at which individual species reside (Loeb, 1980;
Conley, 1993; Sassa et al., 2002; Sabatés et al., 2003), variation in eye morphology
(Weihs and Moser, 1981) and retinal histology (Pankhurst, 1987; Sabatés et al., 2003),
variation in the type and size of food preferred (Sabatés and Saiz, 2000; Conley and
Hopkins, 2004), gape (Conley and Hopkins, 2004), and growth in length and weight.
There does not, therefore, appear to be consistently slower pelagic growth rate. In-
stead, myctophid larvae display a notable diversity in many of the parameters that
likely influence survival through the larval period.
Acknowledgments
Many individuals assisted in the collection of zooplankton. Our thanks go to J. Donnelly,
M. Flock, S. Kinsey, K. Passarella, J. Rast, and T. Sutton who assisted with net collections.
Comments and suggestions from three anonymous reviewers served to improve the quality
of this manuscript, for which we are grateful. We especially wish to express our gratitude to
C. Obordo for her assistance with library searches. The cruises were supported by the State of
Florida and NSF OCE #841787 grant to T. L. Hopkins, The Houston Underwater Club Seas-
pace Scholarship, John Lake Foundation, and Gulf Coast Charitable Trust.
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13. CONLEY AND GARTNER, JR.: VARIATION IN GROWTH AMONG LANTERNFISH LARVAE 135
Date SuBmitted: 28 December, 2007.
Date AccePted: 9 October, 2008.
AVailaBle Online: 26 November, 2008.
Addresses: (W.J.C.) Biology Department, State University of New York, 44 Pierrepont Avenue,
Potsdam, New York 13676. (J.V.G.) Department of Natural Science, St. Petersburg College,
6605- 5th Avenue North, St. Petersburg, Florida 33710. CorresPonding Author: (W.J.C.)
E-mail: <conleywj@potsdam.edu>.