Myctophid Research Articles

Plankton community structure and connectivity in the Kimberley-Browse region of NW Australia

We describe the zooplankton and ichthyoplankton communities of coastal waters of the Kimberley coast (North West Australia), sampled in macrotidal Camden Sound during both the wet and dry seasons of 2011, and compare these to six other Kimberley embayments during the wet season of 2013. Zooplankton abundance in Camden Sound was 7038 ± 3913 SD ind. m−3 in the wet season and 1892 ± 708 SD ind. m−3 in the dry season, with copepods accounting for 85% by number. In all, 78 species of copepods were recorded, with the families Paracalanidae and Oithonidae dominant. In Camden Sound, 48 families of larval fish occurred, with ichthyoplankton more abundant in the wet season than the dry season (1.16 ± 0.2ind. m−3 cf 0.76 ± 0.2ind. m−3). Larval gobiids (Subfamily Gobiinae) were most abundant, with other common families associated with either pelagic or soft-bottom habitats as adults. Multivariate analyses of both copepod and ichthyoplankton communities demonstrated strong seasonal contrasts, although an along-shelf gradient in copepod community composition was apparent along the embayments sampled in 2013. There was little spatial variation in plankton communities within Camden Sound as a result of the large tidal range (up to 11.7 m, with 2.5 m−1 velocities), although gradients in abundance and composition on cross-shelf transects occurred in the more northern embayments that had a lower tidal range, such as Napier Broome Bay. Copepod communities of the Kimberley-Browse region were placed in regional perspective by multivariate analyses of similar data collected in the eastern Indian Ocean at Scott Reef, in the Arafura Sea and on the southern North West (NW) shelf. The plankton communities of the NW shelf form a series of along-shore metacommunities linked by advection, with weaker cross-shelf connectivity. The presence of the larvae of mesopelagic fishes of the family Myctophidae in coastal waters confirms seasonal cross-shelf connectivity.

Cryptic variation of mtDNA in lantern fishes (Myctophidae) of the South Atlantic

Causes of cryptic variation of the cox 1 mtDNA gene have been studied in three myctophid species from the South Atlantic: Large-finned lanternfish (Hygophum macrochir), Dofleini’s lantern fish (Lobianchia dofleini), and Noble lampfish (Lampanyctus nobilis). It has been revealed that each species represented by sympatric haplogroups with nucleotide differences from 4.3 to 10%. In H. macrochir, the affinity of one lineage to haplotypes of the closely related species H. taaningi (“taaningi-like” haplogroup) points, most probably, to a single hybridization between them, which took place approximately 2.7 million years ago, during the global climatic and oceanographic transformations of the Late Pliocene. It has been also suggested that L. dofleini and L. nobilis haplotypes migrated from the Indian Ocean.

Fish larvae retention linked to abrupt bathymetry at Mejillones Bay (northern Chile) during coastal upwelling events

The influence of oceanic circulation and bathymetry on the fish larvae retention inside Mejillones Bay, northern Chile, was examined. Fish larvae were collected during two coastal upwelling events in November 1999 and January 2000. An elevated fish larvae accumulation was found near an oceanic front and a zone of low-speed currents. Three groups of fish larvae were identified: the coastal species (Engraulis ringens and Sardinops sagax), associated with high chlorophyll-a levels; larvae from the families Phosichthyidae (Vinciguerria lucetia) and Myctophidae (Diogenichthys laternatus and Triphoturus oculeus), associated with the thermocline (12°C), and finally, larvae of the families Myctophidae (Diogenichthys atlanticus) and Bathylagidae (Bathylagus nigrigenys), associated with high values of temperature and salinity. The presence of a seamount and submarine canyon inside Mejillones Bay appears to play an important role in the circulation during seasonal upwelling events. We propose a conceptual model of circulation and particles retention into Mejillones Bay. The assumption is that during strong upwelling conditions the flows that move along the canyon emerge in the centre of Mejillones Bay, producing a fish larvae retention zone. Understanding the biophysical interactions responsible to trap and/or concentrate particles is essential to protect these fragile upwelling ecosystems.

The role of lantern fish (Myctophidae) in the life-cycle of cetacean parasites from western Mediterranean waters

Myctophids (lantern fish) and cephalopods play a key role in trophic webs from the continental slope and oceanic waters linking the zooplankton to top predators. Many cetaceans feed on both lantern fish and cephalopods, and such prey would thus be expected to bridge the trophic gap in the life-cycles of helminths infecting cetaceans. However, information on the life-cycles of most of these helminths is extremely scanty. We examined the parasite fauna of myctophids and cephalopods in two areas from the western Mediterranean where at least 21 helminth taxa from cetaceans have been reported and both cetacean diversity and abundance is high. A total of 1012 individuals of 8 lantern fish species, namely, Ceratoscopelus maderensis, Lampanyctus crocodilus, Notoscopelus elongatus, Benthosema glaciale, Myctophum punctatum, Lobianchia dofleini, Diaphus holti and Hygophum benoiti, and 792 individuals of 2 cephalopod species, Alloteuthis media and Sepietta oweniana, were collected from the Gulf of Valencia and Alboran Sea (Spanish Mediterranean) during 2010–2012 and examined for larval helminths. All these species have been reported as prey for at least some cetacean species in the area. Only five helminth taxa were found. The nematodes Anisakis pegreffii and Anisakis physeteris were detected in N. elongatus and C. maderensis (overall prevalence for Anisakis: 8.1% and 0.5%, respectively). Their prevalence in N. elongatus was significantly higher than that from the other three myctophid species with n>50 individuals. A single individual of Hysterothylacium sp. was found in N. elongatus (prevalence: 0.5%) and Raphidascarididae gen. spp. in N. elongatus and L. crocodilus (prevalence: 20.3% and 0.7%, respectively). Juvenile didymozoid digeneans (Torticaecum type) were detected in N. elongatus and L. crocodilus (prevalence: 18.5% and 4.3%, respectively). Two unidentified cestode plerocercoids were collected from N. elongatus. Our study suggests, for the first time, that myctophids could play a role as paratenic hosts in the oceanic life-cycle of A. pegreffii and A. physeteris in the western Mediterranean. None of the other larvae identified at least to family level infect cetaceans, but some of them can be transmitted to large predatory fish. The extreme scarcity of such cetacean parasites in this, and previous parasitological surveys of mesopelagic fish and cephalopods is at odds with the key role of these preys in the diet of oceanic cetaceans.

Amazon River water in the northeastern Caribbean Sea and its effect on larval reef fish assemblages during April 2009

AbstractDuring April to June 2009, a large bolus of Amazon River water impacted the northeastern Caribbean Sea. Shipboard observations collected near Saba Bank, the U.S. and British Virgin Islands, and the Anegada Passage showed low surface salinity (35.76 ± 0.05 Practical Salinity Unit (PSU)), elevated surface temperature (26.77 ± 0.14°C), high chlorophyll‐a (1.26 ± 0.21 mg m−3) and high dissolved oxygen (4.90 ± 0.06 mL L−1) in a 20‐ to 30‐m thick surface layer in the riverine plume. The water was ~1°C warmer, 1 PSU fresher, 0.3 mL L−1 higher in oxygen and 1.2 mg m−3 higher in chlorophyll‐a than Atlantic Ocean waters to the north, with Caribbean surface waters showing intermediate values. Plankton net tows obtained in the upper 100 m of the water column revealed larval fish assemblages within the plume that were significantly different from those of the surrounding waters and from those encountered in the area in previous years. The plume waters contained higher concentrations of mesopelagic fish larvae from the families Myctophidae and Nomeidae, which as adults typically inhabit offshore, deep water habitats. Concentrations of larvae from inshore and reef‐associated families such as Scaridae, Serranidae, Labridae and Clupeidae were lower than those found outside the plume in similar shallow areas, particularly in near‐surface waters. An event like the one observed in 2009 had not been documented in at least the past 30 yr, and yet it was followed by another similarly extreme event in 2010. The ecological implications, including any long‐term consequences of such recent extreme events, are important and merit further study.

Genetic support for the morphological identification of larvae of Myctophidae, Gonostomatidae, Sternoptychidae and Phosichthyidae (Pisces) from the western Mediterranean

Mesopelagic fishes experience an extreme body transformation from larvae to adults. The identification of the larval stages of fishes from the two orders Myctophiformes and Stomiiformes is currently based on the comparison of morphological, pigmentary and meristic characteristics of different developmental stages. However, no molecular evidence to confirm the identity of the larvae of these mesopelagic species is available so far. Since DNA barcoding emerged as an accurate procedure for species discrimination and larval identification, we have used the cytochrome c oxidase 1 or the mitochondrial 12S ribosomal DNA regions to identify larvae and adults of the most frequent and abundant species of myctophiforms (family Myctophidae) and stomiiforms (families Gonostomatidae, Sternoptychidae and Phosichthyidae) from the Mediterranean Sea. The comparisons of sequences from larval and adult stages corroborated the value of the morphological characters that were used for taxonomic classification. The combination of the sequences obtained in this study and those of related species from GenBank was used to discuss the consistency of monophyletic clades for different genera. Pairwise nucleotide distances were notably higher inter- than intraspecifically, and were useful to discern between congeners such as Cyclothone braueri and C. pygmaea, Hygophum benoiti and H. hygomii, Lampanyctus crocodilus and L. pusillus, and Notoscopelus bolini and N. elongatus .

Report ofMyctophum phengodes(Teleostei: Myctophidae) with Extraneous Photophores

A unique specimen of Myctophum phengodes (family Myctophidae) from the South Atlantic is reported with three extraneous primary photophores along one side of the dorsal profile; all usual photophore series for this species are present. The supracaudal gland is encircled by a silvery band instead of a simple black band, a condition not observed in other species of Myctophum examined. Photophore patterns of myctophids are the primary method of determining species identification. Other myctophids have been found with small positional variations for a single photophore (usually only one side of the body), but are readily identifiable to species. While one specimen with extraneous photophores widely separated from and not part of typical series is not considered taxonomically significant, it is important to determine if this is a single abnormal individual or a unique population identifier.

Seven-locus molecular phylogeny of Myctophiformes (Teleostei; Scopelomorpha) highlights the utility of the order for studies of deep-sea evolution

Fishes of the order Myctophiformes (Teleostei; Scopelomorpha) comprise over half of all deep-sea biomass, and are a critical component of marine ecosystems worldwide. Members of the family Myctophidae, within Myctophiformes, form the majority of species diversity within the order (∼250 species, 33 genera, 2 subfamilies), and are further known for their diverse bioluminescent traits, comprised of distinct cranial, postcranial, and caudal luminous systems that is perhaps the most elaborate among all vertebrates. These features make myctophids particularly compelling from both economic and scientific perspectives, yet no studies have sampled these fishes at a density appropriate for addressing any questions requiring a phylogenetic hypothesis as input. This study therefore presents a seven-locus molecular phylogeny of the order, sampling over 50% of all nominal myctophid species. This taxon sampling triples the representation of the next most comprehensive analysis, and reveals several new and well-supported hypotheses of relationships, in addition to supporting traditional hypotheses based on combined morphological data. This analysis shows that the slendertailed myctophids Gonichthys, Centrobranchus, Loweina, and Tarletonbeania are rendered non-monophyletic by a polyphyletic Myctophum; the enigmatic, monotypic genus Notolychnus valdiviae is nested within tribe Lampanyctini; the genus Diaphus is divided into at least two clades, with the suborbital (So) group recovered as monophyletic with strong support; and the genera Lampanyctus and Nannobrachium are recovered as non-monophyletic. These molecular results highlight the potential of myctophids as a premier model system for the application of modern comparative methods to studies of deep-sea evolution.

Ichthyoplankton Community Associated with Oceanic Fronts in Early Winter on the Continental Shelf of the Southern East China Sea

The study of ichthyoplankton community associated with oceanic features on the continental shelf of southern East China Sea (ECS) was conducted in early winter from 2006 to 2009. The species composition of the ichthyoplankton and its spatial distribution was classified and compared with oceanic front. A total number of 1,809 fish larvae individuals were sampled from 5 field surveys, and represented 76 families and 137 species. Using the Bray-Curtis dissimilarity, the abundance of species found to exceed 0.5% of the total sample from 36 stations were classified into four groups: China Coastal Group, Mixed Shelf Group, Taiwan Strait Group, and Kuroshio Group. The shallow water species Sebastiscus marmoratus dominated the China Coastal Group, while the Mixed Shelf Group was dominated by Saurida spp., Trichiurus lepturus, and Bregmaceros spp. The Taiwan Strait Group was dominated by Engraulis japonicus and Benthosema pterotum. The dominant species in the Kuroshio Group was found to include Sigmops gracile and unidentified Myctophid larvae. The spatial distribution of the ichthyoplankton community groups was superimposed on a thermal front map of the study area. This clearly revealed that the China Coastal Front could be the boundary which separated the China Coastal Group on the west and the Mixed Shelf Group on the east. In addition, ichthyoplankton were found to increase in abundance and diversity in the region close to the Kuroshio Front.

Primary Growth Increments in Otoliths of Six Tropical Myctophid Species

AbstractThe otoliths of six species of myctophids belonging to the genera Benthosema, Diaphus, Myctophum, Lampanyctus, and Symbolophorus were collected in the western Arabian Sea in 1979 and revealed primary growth increments; the readability of the otoliths, however, varied considerably among the six species. The hypothesis of a daily deposition rate of the increments could not be verified, but strong circumstantial evidence for this was put forward. Under this hypothesis, power curves were fitted to the length at age data, yielding length = 0.59 Age0.77 and length = 0.69 Age0.79 for B. pterotum in the Gulf of Oman and the Gulf of Aden respectively, and length = 2.65 Age0.53 for B. fibulatum. A prominent check in the otoliths is suggested to be caused by metamorphosis.

Biology of Myctophid Fishes (Family Myctophidae) in the Rockall Trough, Northeastern Atlantic Ocean

AbstractAspects of the biology of myctophid fishes, Myctophidae, in the Rockall Trough off northwestern Ireland were studied in a series of consecutive seasonal samples taken from July 1973 to March 1974 and from March 1975 to February 1976. Of the nine species that occurred, the three dominant species, Benthosema glaciale, Lampanyctus macdonaldi, and Protomyctophum arcticum, were concluded to have regular life cycles. Seasonal abundance of larvae at each developmental stage, duration of larval development, vertical distribution pattern of larvae, life span, growth pattern, spawning season, age at maturity, and diet were studied in these three species and their life history strategies, segregation of habitat, spawning season, and diet discussed.Of the remaining six species, two species, Myctophum punctatum and Notoscopelus elongatus, are at the northern geographical limit of their breeding population in the Rockall Trough because of the rare occurrence of their larvae. The other four species, Notolychnus ...

Aspects of the trophic ecology of the mesopelagic fish Lampanyctus alatus (family Myctophidae) in the eastern Gulf of Mexico

AbstractLampanyctus alatus is an abundant myctophid in subtropical waters of the eastern Gulf of Mexico. The population has been estimated at 85–140 × 103 fish per km2 of sea surface, with most of the population biomass (>60%) in individuals larger than 35 mm. This species concentrates in the 80175 m zone at night and at 550–750 m during the day. The diet is essentially crustacean (>98%), with over 60 prey species having been identified. Seventy-three percent of the number and 44% of the biomass of the diet are copepods. Euphausiids rank first in biomass and are particularly important in the diet of larger fishes. Lampanyctus alatus is selective for prey >1 mm and for the copepod genus Pleuromamma.A diel feeding cycle is apparent, stomachs being fullest in the period 0100–0500 h. Daily ration is estimated at 2–4% of body weight and decreases proportionately with increasing fish size. It is estimated that one-fifth of respiration and less than one-tenth of the daily ration is utilized in diel vertical migr...

Genetic divergence in the tribe Electronini (Myctophidae)

To reveal evolutionary relationships and the rate of divergence of lanternfishes in the tribe Electronini (Myctophidae), analysis of sequence of cox 1 mtDNA fragment in three genera (12 species) of the tribe and in a closely related genus Myctophum (9 species) was performed. The results support the tribe monophyly; however, the divergence within it appeared to be not profound: genetic distances between genera and subgenera are smaller than between species within Myctophum and other genera of myctophids. In subgenera of Protomyctophum, species formation has obviously not completed since interspecies distances in them (0.5–4.7%) are comparable to estimates of intraspecific variation in other lanternfishes. Minimal genetic differences were found between species P. (Hierops) arcticum and P. (H.) subparallelum, whose ranges at the present time are isolated in the northern and southern hemispheres. After calibration of the molecular clock, the time of isolation of these two species can be dated to the Middle Pleistocene. Weak tribe diversification indicates its evolutionary youth, which can be related to the absence of efficient hydrographic barriers for isolation. The data obtained do not permit to consider tribe members as the most primitive in the family Myctophidae.

Seasonal occurrence of mesopelagic fish larvae on the onshore side of the Kuroshio off southern Japan

Information on the annual reproductive cycle of mesopelagic fishes has been limited in the western North Pacific, despite their ecological importance. The Kuroshio region is an important spawning ground for various mesopelagic fishes. To describe the reproductive seasonality, we examined the seasonal occurrence patterns of mesopelagic fish larvae at a fixed station (33°12′N, 133°48′E) on the continental slope in Tosa Bay which is strongly influenced by the Kuroshio, based on monthly samples collected from January 2001 to December 2004. In total, 2558 mesopelagic fish larvae were sampled, with a peak abundance during May to June. Larvae of the dominant families Myctophidae, Sternoptychidae, Gonostomatidae, Bathylagidae, and Phosichthyidae were represented by 26 species (or types) belonging to 18 genera. The 12 most abundant species accounted for 96.9% of the total catch. The seasonal occurrence patterns of these larvae were categorized into five groups in accordance with the physical properties of the water column: Winter (Notoscopelus japonicus and Lipolagus ochotensis); Spring (Symbolophorus evermanni and Maurolicus japonicus); Early summer (Myctophum asperum and Diaphus stubby type); Autumn (Lampanyctus sp. A, Cyclothone spp., and Sigmops gracile); and -round (Vinciguerria nimbaria, Diaphus slender type, and Diogenichthys atlanticus) groups. No significant difference was observed in the months of peak abundances of these larvae during the 4 years, suggesting that each species has a fixed seasonal pattern of reproduction. The various patterns of seasonal occurrence would result in seasonal habitat segregation of the larvae among species, potentially enabling the reduction of intraspecific competition for food resources in the oligotrophic waters of the Kuroshio.

Unravelling the mysteries of a mesopelagic diet: a large apex predator specializes on small prey

Summary To gain insight into the foraging behaviour of deep diving seals, we developed a long‐term jaw‐motion recorder, which successfully measured the feeding attempts of four post‐breeding female northern elephant seals for 55–68 days during migration in the north‐east Pacific Ocean. Using the jaw‐motion recorders in conjunction with satellite tracking data, we first reveal the three‐dimensional fine‐scale distribution of deep foraging activity in the north‐east Pacific Ocean. A large number of jaw‐motion events (23 817–58 766 during 2925–4178 dives, per seal) were observed with diel patterns suggesting their dependency on small mesopelagic prey. Calculations using at‐sea field metabolic‐rate and the photographs concurrently obtained by the head‐mounted camera indicated feeding on small mesopelagic prey (10–20 g) including lantern fish (F. Myctophidae). The foraging behaviour of the northern elephant seal contrasts with echolocating toothed whales, which make fewer feeding attempts, suggesting the whales forage more selectively. We hypothesize that the continuous diving mode exhibited by this seal could be attributed to their reliance on small prey and their less efficient ‘passive sensors’ for prey search, that is, their vision or whiskers to detect prey.

Global Trophic Position Comparison of Two Dominant Mesopelagic Fish Families (Myctophidae, Stomiidae) Using Amino Acid Nitrogen Isotopic Analyses

The δ15N values of organisms are commonly used across diverse ecosystems to estimate trophic position and infer trophic connectivity. We undertook a novel cross-basin comparison of trophic position in two ecologically well-characterized and different groups of dominant mid-water fish consumers using amino acid nitrogen isotope compositions. We found that trophic positions estimated from the δ15N values of individual amino acids are nearly uniform within both families of these fishes across five global regions despite great variability in bulk tissue δ15N values. Regional differences in the δ15N values of phenylalanine confirmed that bulk tissue δ15N values reflect region-specific water mass biogeochemistry controlling δ15N values at the base of the food web. Trophic positions calculated from amino acid isotopic analyses (AA-TP) for lanternfishes (family Myctophidae) (AA-TP ∼2.9) largely align with expectations from stomach content studies (TP ∼3.2), while AA-TPs for dragonfishes (family Stomiidae) (AA-TP ∼3.2) were lower than TPs derived from stomach content studies (TP∼4.1). We demonstrate that amino acid nitrogen isotope analysis can overcome shortcomings of bulk tissue isotope analysis across biogeochemically distinct systems to provide globally comparative information regarding marine food web structure.

Cross-basin heterogeneity in lanternfish (family Myctophidae) assemblages and isotopic niches (δ13C and δ15N) in the southern Tasman Sea abyssal basin

A cross-basin (longitudinal) study of lanternfishes in the southern Tasman Sea abyssal basin during the austral winter of 2008 and 2009 found that mean biomass in the Western sector was higher than that in the Eastern sector, corresponding with cross-basin patterns in oceanographic heterogeneity and productivity. Dominant species over the abyssal basin differed from those previously recorded over the neighbouring continental slope. Vertical biomass profiles indicated diffuse night-time distributions in the Central sector and extensive diel vertical migrations in the Eastern sector. In the Western sector, macrocrustacean δ13C values were significantly higher, and δ15N significantly lower, than those in the Eastern sector. The results indicate a cross-basin difference in the primary productivity environment and 15N enrichment at the base of the foodweb. The cross-basin pattern in lanternfish δ15N values mirrored that for macrocrustaceans and was not correlated with standard length. Lanternfish δ13C values did not differ between sectors, but there were depth-wise differences, with values in the shallowest stratum (0–200m) significantly higher than those in the deepest stratum (800–1000m). Calculated trophic levels (TLs) of lanternfishes spanned the third trophic level and marked niche segregation was evident in the Eastern (mean TL 3.0–3.9) and Central (mean TL 2.5–3.6) sectors. Together, the results suggest that the Eastern and Western sectors are distinct sub-basin scale pelagic habitats, with implications for ecosystem modelling and future monitoring.

Spawning aggregation of the lanternfish Diaphus danae (family Myctophidae) in the north-western Coral Sea and associations with tuna aggregations

A spawning aggregation of the lanternfish Diaphus danae in the Coral Sea, that is fed on by spawning aggregations of yellowfin and bigeye tuna, has been sampled by mid-water trawling for the first time. Males and females in the aggregation occurred at a ratio of 23 to 1 and occupied two non-overlapping size classes (males 71.2–95.1-mm standard length (SL), females 99.0–121.4-mm SL). Hydrated oocytes with single oil droplets, which indicated imminent spawning, were in higher proportion in the first trawl (2134 hours to 2234 hours) than in the final trawl (0324 hours to 0424 hours) through the aggregation. Maximum estimated female D. danae fecundity (25 803) and gonadosomatic index (34.01) were higher than for any other lanternfish species recorded. Bigeye tuna (Thunnus obesus) individuals collected from aggregations were estimated to have 81–319 D. danae specimens in their stomachs. The annual Coral Sea D. danae aggregation is the only confirmed lanternfish spawning aggregation in Australian waters. The D. danae spawning aggregation provides a rich, transient foraging resource for spawning bigeye and yellowfin tuna in the Coral Sea, these being the only known tuna spawning aggregations in the Eastern Tuna and Billfish Fishery.

Distribution of myctophid resources in the Indian Ocean

Mesopelagics are one of the largest under-exploited marine resources with wide distribution in the world oceans. Lanternfishes are the key members of mesopelagic communities and the total resource in the world oceans is estimated at 600 million tons. Lanternfishes belong to the family Myctophidae which comprises of about 250 species in 35 genera. Myctophids account for about 75% of total global catch of small mesopelagic fishes. They are known to exhibit diel vertical migration, concentrating during the day time between 400 and 1,000 m, and between 5 and 100 m, during the night. In this paper, an attempt is made to review the existing information on the occurrence and distribution of myctophid resources in the Indian Ocean. 137 myctophid species have been reported from the entire Indian Ocean. Studies in the Arabian Sea have indicated that the area is rich in the midwater fish stocks dominated by myctophids with an estimated potential of 100 million tons.

Size distribution of meso- and bathypelagic fish in the Dumont d’Urville Sea (East Antarctica) during the CEAMARC surveys

The pelagic fish community of the Dumont d’Urville Sea (East Antarctica) was investigated during the 2008 austral-summer using IYGPT (International Young Gadoid Pelagic Trawl) samples taken in different depth layers from the surface to 1000 m. The aim of this paper is to describe the mesopelagic fish community and its size distribution. The family Myctophidae dominated the mesopelagic ichthyofauna, while bathylagids were abundant in deeper hauls. Bathylagids , Cyclothone spp. , Gymnoscopelus opisthopterus, Electrona antarctica, Protomyctophum bolini, and Krefftichthys anderssoni were the most abundant taxa in the samples and showed size stratification with depth. Community and size structuring appear to be influenced by the hydrology and by the proximity of the continental margin, as well as a relationship to the circulation of the Modified Circumpolar Deep Water.