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Mesopelagic fishes play a central role in marine food webs linking primary consumers to top predators. In this study, measures of direct calorimetry were used to analyse the energy density (ED) of 34 mesopelagic species collected at 12 stations in the equatorial and tropical Atlantic. Mean ED ranged from 2.7 kJ g−1 wet weight (WW) for the lanterfish Lampanyctus nobilis to 8.7 kJ g−1 WW for the lanterfish Benthosema glaciale. This study includes species of the orders Myctophiformes and Stomiiformes and represents migrants, non‐migrants and partial‐migrants species. The majority of the species were grouped into the medium‐energy quality category (ED from 4 to 6 kJ g−1); Myctophiformes showed higher energetic values than the Stomiiformes. For the different species, the ED values were discussed in relation to spawning period and energy allocation strategies for reproduction and growth and feeding and migratory behaviour, as well as the ecoregion of study. These values will be useful for future assessment of energetic transfer between trophic levels and energetic modelling of Atlantic ecosystems. [ABSTRACT FROM AUTHOR]

Every night the greatest migration on Earth starts in the deep pelagic oceans where organisms move up to the meso‐ and epipelagic to find food and return to the deeper zones during the day. One of the dominant fish taxa undertaking vertical migrations are the dragonfishes (Stomiiformes). However, the functional aspects of locomotion and the architecture of the musculotendinous system (MTS) in these fishes have never been examined. In general, the MTS is organized in segmented blocks of specific three‐dimensional 'W‐shaped' foldings, the myomeres, separated by thin sheets of connective tissue, the myosepta. Within a myoseptum characteristic intermuscular bones or tendons may be developed. Together with the fins, the MTS forms the functional unit for locomotion in fishes. For this study, microdissections of cleared and double stained specimens of seven stomiiform species (Astronesthes sp., Chauliodus sloani, Malacosteus australis, Eustomias simplex, Polymetme sp., Sigmops elongatus, Argyropelecus affinis) were conducted to investigate their MTS. Soft tissue was investigated non‐invasively in E. schmidti using a micro‐CT scan of one specimen stained with iodine. Additionally, classical histological serial sections were consulted. The investigated stomiiforms are characterized by the absence of anterior cones in the anteriormost myosepta. These cones are developed in myosepta at the level of the dorsal fin and elongate gradually in more posterior myosepta. In all but one investigated stomiiform taxon the horizontal septum is reduced. The amount of connective tissue in the myosepta is very low anteriorly, but increases gradually with body length. Red musculature overlies laterally the white musculature and exhibits strong tendons in each myomere within the muscle bundles dorsal and ventral to the horizontal midline. The amount of red musculature increases immensely towards the caudal fin. The elongated lateral tendons of the posterior body segments attach in a highly complex pattern on the caudal‐fin rays, which indicates that the posterior most myosepta are equipped for a multisegmental force transmission towards the caudal fin. This unique anatomical condition might be essential for steady swimming during diel vertical migrations, when prey is rarely available. [ABSTRACT FROM AUTHOR]

Species of the Sternoptychidae teleost family display an impressive morphology, including their extreme reduced size. Here, we report the first mitochondrial genome of the diaphanous hatchet fish Sternoptyx diaphana. By using short-read sequencing Illumina HiSeq, we generated two mitochondrial contigs which were later physically assembled by PCR. The mitochondrial genome of S. diaphana was 17,224 bp in length (excluding the control region) and is composed of 13 PCGs and 2 ribosomal RNA genes. Strikingly, we could not identify the tRNA-Phe and two copies of tRNA-Met were differently positioned. Additionally, the mitogenome displays a completely new gene rearrangement among vertebrates. We expect that the study presented here will pave the way for further molecular studies with this underrepresented group of illusive teleost fish.

Species of the Sternoptychidae teleost family display an impressive morphology, including their extreme reduced size. Here, we report the first mitochondrial genome of the diaphanous hatchet fish Sternoptyx diaphana. By using short-read sequencing Illumina HiSeq, we generated two mitochondrial contigs which were later physically assembled by PCR. The mitochondrial genome of S. diaphana was 17,224 bp in length (excluding the control region) and is composed of 13 PCGs and 2 ribosomal RNA genes. Strikingly, we could not identify the tRNA-Phe and two copies of tRNA-Met were differently positioned. Additionally, the mitogenome displays a completely new gene rearrangement among vertebrates. We expect that the study presented here will pave the way for further molecular studies with this underrepresented group of illusive teleost fish. [ABSTRACT FROM AUTHOR]

We updated the distribution and habitat patterns of Maurolicus stehmanni in the Southwest Atlantic Ocean by compiling data obtained from research surveys conducted on the Argentinean continental shelf, as well as from opportunistic records. This paper confirms the presence of M. stehmanni in the Argentinean continental shelf, extending its southernmost distributional limit by ca. 1000 km (from 43.0°S to 52.2°S). Adult specimens of M. stehmanni were collected in various locations from 2004 to 2016. Eggs and larvae of Maurolicus spp. were caught during ichthyoplankton tows carried out from 2003 to 2013. The present paper furthermore extends the habitat type in which this species was recorded: specimens were found in the inner continental shelf (between 46.2°S and 52.2°S) instead of the shelf break and continental slope. Two specimens were found lying dead upon the beach of Puerto Madryn, Nuevo Gulf (42.8°S). The presence of eggs and larvae in coastal embayments (San Matías and San José gulfs), in concomitant occurrence with adults, may suggest the establishment of this species in the region. [ABSTRACT FROM AUTHOR]

The vertical distributions of early developmental stages of oceanic fishes were investigated across the tropical and equatorial Atlantic, from oligotrophic waters close to the Brazilian coast to more productive waters close to the Mauritanian Upwelling Region. Stratification of the water column was observed throughout the study region. Fishes were caught with a MOCNESS-1 net with mouth area of 1 m 2 at 11 stations. Each station was sampled both during the day and at night within a single 24-h period. The investigation covered both larvae and transforming stages from the surface to 800 m depth. Distribution patterns were analysed, and weighted mean depths for the larvae and transforming stages of each species were calculated for day and night conditions. Forty-seven different species were found. The highest number of species occurred in the three stations south of Cape Verde Islands, characterized by a mixture of South Atlantic Central Water (SACW) and Eastern North Atlantic Central Water (ENACW). There was a marked drop in species richness in the three stations closer to the African upwelling, dominated by ENACW. The highest abundances occurred in the families Myctophidae, Sternoptychidae, Gonostomatidae and Phosichthyidae. Day and night vertical distributions of larvae and transforming stages showed contrasting patterns, both in the depths of the main concentration layers in the water column, and in the diel migration patterns (where these were observed). Larvae generally showed a preference for the upper mixed layer (ca. 0–50 m) and upper thermocline (ca. 50–100 m), except for sternoptychids, which were also abundant in the lower thermocline layer (100–200 m) and even extended into the mesopelagic zone (down to 500 m). Transforming stages showed a more widespread distribution, with main concentrations in the mesopelagic zone (200–800 m). Larvae showed peak concentrations in the more illuminated and zooplankton-rich upper mixed layers during the day and a wider distribution through the upper 100 m during the night. For most species, transforming stages were concentrated in the mesopelagic layers both day and night, although in some species ( Diaphus cf. vanhoeffeni and Vinciguerria nimbaria ), the transforming stages displayed vertical migration into the upper 100 m at night, in a manner similar to their adult stages. [ABSTRACT FROM AUTHOR]

The composition of the larval fish assemblage in the sound-scattering layer of the continental shelf waters off the coast of south-eastern Brazil (12 and 22° S), a research project that is part of the Brazilian programme Avaliação do Potencial Sustentável de Recursos Vivos na Zona Econômica Exclusiva (REVIZEE), is described. Samples were collected during daylight hours and at dusk at five oceanographic stations in the winter of 1999 using an Isaacs-Kidd Midwater Trawl (IKMT). The oceanographic stations were chosen based on the detection of plankton layers by acoustic observation. A total of 2192 larval fish were identified, comprising 52 families and 62 species. Maurolicus stehmanni (Sternoptychidae) was the most abundant species found within the study area, comprising 18·5% of all identified larvae, followed by Psilotris celsus (Gobiidae) at 10·9%. [ABSTRACT FROM AUTHOR]

The clupeomorph fishGasteroclupea branisaiSigneux, 1964 from the Late Cretaceous-Paleocene of El Molino Formation, Cayara locality, Bolivia is redescribed in detail. This South American double-armored herring is the sole member of the family Gasteroclupeidae and exhibits a unique combination of features (skull roof ornamented with fine tubercles, beryciform foramen, endopterygoid teeth, about 16–18 supraneurals, a series of 35–38 predorsal and 40 ventral scutes, median fins small and containing 12–14 rays) that clearly supports its assignment to the extinct clupeomorph order Ellimmichthyiformes.G. branisaishares a number of synapomorphies withSorbinichthys elusivoandS. africanus(five hypurals, second hypural autogenous, distal end of the second uroneural not reaching the distal end of the first uroneural) with which it forms a monophyletic assemblage recognized herein for the first time as the new suborder Sorbinichthyoidei. The peculiar morphology ofGasteroclupeathat is characterized by having an extremely deep abdominal profile, hypertrophied coracoid, and elongated pectoral fins, resembles in many aspects the body plan of extant freshwater hatchetfishes of the characiform family Gasteropelecidae, suggesting that the morphological adaptations ofG. branisaican be related, at least in part, to a similar lifestyle. [ABSTRACT FROM AUTHOR]

The genus Maurolicus comprises extremely abundant vertically-migrating fishes that have considerable biomass in a number of regions worldwide. The genus was generally considered monotypic, with a single species, M. muelleri (Gmelin, 1789), inhabiting all world oceans. Based on differences in combinations of a limited number of morphometric characters, 15 separate species have been proposed, mostly associated with different ocean basins and seamounts. However, due to similarities in external morphology and overlap in ranges of morphometric characteristics, there remains a need for further validation of these species. Here, we present results of a multi-gene analysis, together with morphological data, for five putative Maurolicus species from multiple locations in the northern and southern hemispheres. Sampling encompasses described species from the North and South Atlantic, Mediterranean Sea, south-east Indian Ocean and the western South Pacific. Mitochondrial (16S and COI) and nuclear (ITS-2) gene sequences for 120 specimens were used in Maximum Parsimony and Bayesian Inference analyses as well as creation of haplotype networks. Morphological character analyses were based on data from 279 adult individuals. Several clear groupings emerge, conflicting with previously recognised species: (1) a ‘northern’ clade comprising Maurolicus muelleri and M. amethystinopunctatus , (2) a ‘southern’ clade comprising M. australis , M. walvisensis (also M. japonicus ) and (3) eastern Equatorial and western North Atlantic M. weitzmani . The southern clade taxa are genetically indistinguishable and not well defined morphologically and present a clear case for synonymisation as M. australis . Synonymisation is also proposed for M. muelleri and M. amethystinopunctatus , with limited morphological variation likely to reflect physical and biological differences experienced north / south of the sub-polar front. Maurolicus weitzmani is clearly differentiated from all other Maurolicus species on both a molecular and morphological basis. Studies of genetic and morphological diversity in Maurolicus will further contribute to the question of ‘what constitutes a species in the open ocean?’, where a complex picture is emerging of both unexpected variation, as well as the unexpectantly absent genetic variation, in cosmopolitan taxa. [ABSTRACT FROM AUTHOR]

The first ecological survey in the tropical part of the northern Mid-Atlantic Ridge (MAR) was conducted between 17°14′N and 16°40′N in February–March 2015 during the 37th cruise of the RV Professor Logachev . Significant effort of the survey was aimed at studies of benthic non-vent soft sediment fauna at depths from 2270 m to 3900 m. Samples of this fauna at seven stations revealed ~780 specimens and at least 136 species. The most common species was the hermit crab Parapagurus cf. nudus . Also common were the ophiuroids Ophiotypa simplex and Ophiomusium cf. lymani . Most benthic organisms were <3 cm in size. Collection of fish taken in the depth range from 0 to 3850 m included 1128 specimens represented by 48 species from 16 families. The highest number of species was in the families Myctophidae (18), Gonostomatidae (9) and Sternoptychidae (5). In the course of the cruise, two new fields of massive sulphide deposits were discovered on the south-western slope of the seamount on the eastern flank of the rift valley, one at 17°08.7′N and second at 17°07.45′N. During video profiling in this area indications of modern hydrothermal activity were recorded. Extensive fields of shells of Bathymodiolus puteoserpentis and Thyasira sp. were discovered and samples of bivalves were taken using the TV-grab and geological square corer. Surprisingly high concentration of drowned pelagic algae Sargassum sp. (Phaeophyceae, Fucales) in different state of degradation was observed at TV transects at the seafloor both on soft and hard substrates. Thalli of Sargassum fluitans appeared in trawl catches. Massive aggregations of Sargassum also were abundant at the sea surface in the area from December 2014 to April 2015. [ABSTRACT FROM AUTHOR]

We present the results of application of geometric morphometrics for studies of variability in populations of the members of two families of South Atlantic mesopelagic fishes, Sternoptyx diaphana (Sternoptychidae) and Ceratoscopelus warmingii (Myctophidae), in which an almost complete genetic isolation was previously discovered within the borders of hydrographic regions. A system of landmark points is developed, describing both anatomical features and configuration of luminescent organs, photophores, which allows to consider not only the influence of external physical and ecological conditions but also the existence of population-specific signaling system as a potential cause of genetic isolation. Morphological similarities are demonstrated for S. diaphana throughout the whole studied portion of the distribution area, while certain differences affecting the head shape and position of individual photophores on the body are discovered between C. warmingii populations. [ABSTRACT FROM AUTHOR]

Summary: This study provides the length‐weight relationship for eleven mesopelagic fishes from oceanic islands of the Southwestern Tropical Atlantic: Bonapartia pedaliota, Sigmops elongatus (Gonostomatidae), Argyropelecus aculeatus, Argyropelecus affinis, Argyropelecus sladeni, Sternoptyx diaphana, Sternoptyx pseudobscura (Sternoptychidae), Malacosteus niger,Thysanactis dentex (Stomiidae), Melanonus zugmayeri (Melanonidae), and Ectreposebastes imus (Setarchidae). Data were collected during a scientific survey (2017) around Rocas Atoll, Fernando de Noronha Archipelago and adjacent seamounts, using a micronekton trawl (side
length of body mesh: 40 mm, side
length of cod‐end mesh: 10 mm) at 35 stations from 0 to 1,113 m depth. A new maximum standard length for Bonapartia pedaliota and Ectreposebastes imus are also provided. [ABSTRACT FROM AUTHOR]

Between 1999 and 2006, the Department of Fisheries and Oceans performed deep-water sampling and discovered new range records for many species of fishes. Here we report 3 species new to British Columbia: Idiacanthus antrostomus, Benthalbella linguidens and Scopelengys tristis, and update the known ranges of 7 additional species ( Argyropelecus sladeni, Sternoptyx pseudobscura, Aristostomias scintillans, Opostomias mitsuii, Bathophilus flemingi, Scopelosaurus adleri, and Magnisudis atlantica) in British Columbia waters. [ABSTRACT FROM AUTHOR]

Seasonal study of the diet and food consumption of juvenile hake has been carried out in the Central Mediterranean Sea (Southern Tyrrhenian Sea). Fish were the most important food resource in terms of weight (ca. 70%). Among the fish, Myctophidae and Sternoptychidae, which are usually distributed deeper than juvenile hake, are most important. During summer, Ceratoscopelus maderensis constituted up to 21% of weight of all prey, and Maurolicus muelleri represented almost 10%. During autumn M. muelleri became the most important food resource. The way in which these more deeply distributed prey enter shallower food webs relates to the daily vertical migrations of lanternfish. In upper water column strata at night or near dawn they become prey of the juvenile hake. Considering that trophic energy flows primarily downward, in the direction of the productivity gradient, the observed flow of energy from deep strata into epipelagic layers could be considered an inverse energy transfer. Daily food consumption of juvenile hake ranged between 4.11 and 4.72% of the body wet-weight (BWW). The application of a square-root model allowed calculation of the fraction of this consumption derived by ingestion of the more deeply distributed mesopelagic fish. Between 11.6% and 17.8% of food consumption was sustained by this energy flow. Such information is useful for understanding the interaction between communities distributed in different depth ranges and to reinforce the idea that marine communities are open systems in which migratory movements can dramatically change the assumptions and results of mass-balance models. [ABSTRACT FROM AUTHOR]

Mesopelagic fishes play an important role in the transfer of organic material in the photic zone to depth although the trophodynamic partitioning amongst co-existing and presumably competing species is unclear. This study employs combined carbon and nitrogen stable isotope analyses ( δ 13 C and δ 15 N) of the 18 most abundant western Mediterranean mesopelagic fishes to explore niche partitioning in this group. Sampling was conducted along the water column from the shelf and slope grounds of the Balearic Islands in two contrasting periods (late autumn and summer). Trophodynamics were explored at assemblage level and at inter- and intra-species resolutions respectively using Bayesian diet mixing models and size specific behaviour respectively. Seasonal δ 13 C differences in near basal particulate organic matter (POM) and zooplankton fractions were almost directly replicated in higher fauna suggesting strong isotopic coupling between mesopelagic fishes and planktonic production. Despite reliance on similar basal production, species were segregated by trophic position with a graduation from 2.9 for the small Gonostomatidae Cyclothone braueri to 4.0 for the Myctophidae Lobianchia dofleini . Mixing model data reflected basic trophic position estimates with higher contributions of small fish and zooplankton/POM in higher and lower trophic level species respectively. Species could be categorized as showing preference for i) mesozooplankton/POM as for C. braueri , (in the lower TrL), ii) euphausiids and fish prey as for L. dofleini and the near bottom Lampanyctus crocodilus (in the upper TrL) and iii) mesozooplankton/euphausiids as Ceratoscopelus maderensis , Lampanyctus pusillus or the migrating L. crocodilus . There was little evidence of size based inter-population trophodynamics, with size-isotope trends explained by co-varying lipid content. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] We measured the radius, focal length, and point spread function of the lenses of pelagic fishes, cephalopods, and a gastropod. [•] Two hatchetfish species and a barrel-eye were found to have the best lenses. [•] The heteropod lens had unidirectional aberrations that matched its ribbon- shaped retina. [•] Lens angular resolution increased with depth. [•] The perceived visual contrast at the retinal cutoff frequency of the fish was constant with depth. [ABSTRACT FROM AUTHOR]

Studies on the vertical distribution of larval fish in water masses along the Brazilian coast are very rare. The present study aimed to identify larval fish occurring in the surface (1 m) layer and at depth in four water masses of the Campos Basin, southeastern Brazil: South Atlantic Central Water (SACW) (250 m), Antarctic Intermediate Water (AAIW) (800 m), Upper Circumpolar Deep Water (UCDW) (1,200 m) and North Atlantic Deep Water (NADW) (2,300 m). Material used in this study was obtained in 2009 through nocturnal horizontal stratified hauls using a Multinet (500 μm mesh size) during both rainy (February to April) and dry periods (August to September). A total of 10,978 fish larvae comprising 169 taxa were identified during the rainy (n = 6,015) and dry (n = 4,963) periods. The number of taxa decreased as the sampling depth increased. Larvae of Clupeidae, Engraulidae and Scombridae dominated in samples collected in the surface layer, while Sternoptychidae and Myctophidae were the most representative families in SACW. The other three water masses were dominated by Gonostomatidae larvae. [ABSTRACT FROM AUTHOR]

Abstract: Anatomical and functional studies of the autonomic innervation of the photophores of luminescent fishes are scarce. The present immunohistochemical study demonstrated the presence of nerve fibers in the luminous epithelium and lens epithelium of the photophores of the hatchet fish, Argyropelecus hemigymnus and identified the immunoreactive elements of this innervation. Phenylethanolanine N-methyltransferase (PNMT) and catecholamine (CA)-synthesizing enzymes were detected in nerve varicosities inside the two epithelia. Neuropeptides were localized in neuropeptide Y (NPY) and substance P (SP)- and its NK11 receptor-immunopositive nerves in the lens epithelium. Neuropeptides were also localized in non-neural cell types such as the lens cells, which displayed immunoreactivities for pituitary adenylate cyclase activating peptide (PACAP) and their receptors R-12 and 93093-3. This reflects the ability of the neuropeptide-containing nerves and lens cells to turn on and off the expression of selected messengers. It appears that the neuropeptide-containing nerves demonstrated in this study may be sensory. Furthermore, neuronal nitric oxide synthase-immunopositive axons associated with photocytes in the luminous epithelium have previously been described in this species. Whereas it is clear that the photophores receive efferent (motor) fibers of spinal sympathetic origin, the origin of the neuropeptide sensory innervation remains to be determined. The functional roles of the above neuropeptides or their effects on the bioluminescence or the chemical nature of the terminals, either sensory or postganglionic neurons innervating the photophores, are still not known. [Copyright &y& Elsevier]

Abstract: Midwater fish faunas over three cold seep habitats >1000m (AC601, GC852, AT340) and over a cold-water coral bank (VK826, <1000m) in the north-central Gulf of Mexico (GOM) are described and compared. Day and night discrete-depth sampling was accomplished at each study site, 9–29 August 2007, using an opening–closing Tucker trawl towed at depth for 30min. The 159 Tucker trawl stations yielded 9802 individuals and at least 126 species (30 families) of juvenile and adult midwater fishes. Myctophidae (38 species, 28% of the total catch), Stomiidae (17 species, 1.4%), Gonostomatidae (12 species, 56%), Sternoptychidae (10 species, 6%), and Phosichthyidae (5 species, 6%) dominated catches at all sites. Thirty-one species (8 families) comprised about 90% of the overall abundance of fishes across the four sites. Despite the wide separation of study sites and some differences in physical oceanography, geographic and temporal patterns in mesopelagic fish assemblages were not evident (ANOSIM, Global R=0.20, p=0.1%, pairwise R values <0.3). However, station groupings were related mostly to similarities in sampled depths (SIMPROF, p<1.5%). Upper water-column station groups (<400m) were typified by Lepidophanes guentheri, Diaphus dumerilii, Vinciguerria nimbaria, Vinciguerria poweriae, Valenciennellus tripunctulatus, Argyropelecus aculeatus, Notolychnus valdiviae, Benthosema suborbitale, Gonostoma elongatum, and Hygophum taaningi. Deeper station groups (mean depth=609m) were typified by Cyclothone alba, Cyclothone acclinidens, Cyclothone braueri, Cyclothone obscura, Cyclothone pallida, Cyclothone pseudopallida, V. tripunctulatus, and Hygophum benoiti. Depth, diel, and size distributions were also analyzed for abundant species. For example, Cyclothone spp., abundant at all sites except VK826, usually occurred in deeper waters (>130m), especially during daylight hours (>335m). Most Cyclothone individuals were captured at night at GC852, whereas catches were more evenly distributed across times at AT340 and VK826. Cyclothone spp. individuals occurred in the deeper parts of the sampled depth range at AT340 and VK826 at all times compared with GC852, where they appeared to undergo a diel migration. The two most abundant Cyclothone spp., C. pallida and C. pseudopallida, had the broadest depth ranges (150–1377m) and exhibited a trend for larger specimens to occur deeper at GC852. Most V. tripunctulatus were captured at night and tended to have larger mean sizes in deeper waters. This species did not exhibit strong diel patterns of vertical distribution. Shallower depths were occupied at night by some individuals at all sites, but most individuals remained somewhat deeper at night at VK826 (350–450m at night and 200–350m by day) and AT340 (200–600m at night and 300–500m by day) compared with GC852 (150–450m at night and 750 and 1000m by day). Nearly all Vinciguerria poweriae were caught at night, and no clear trend of size with depth was apparent. This species occupied a wider depth range at night, with most in the upper 200m. Most myctophids, the strongest diel migrators, were captured at night at the offshore stations. The dominant myctophid, N. valdiviae, was most abundant at GC852 (550–1050m by day and 50–750m at night), but diel movement was more distinct at AT340 (<200m at night and 350–500m by day). No size-related trends with depth were apparent at any site for N. valdiviae, and size distributions were similar among sites. This study and others support the hypothesis that there is a geographically similar mesopelagic fish fauna throughout the GOM. However, the fauna does vary by depth, with some species remaining in deep waters at all times (e.g., Cyclothone spp.) and others occurring at mid-depths and exhibiting varying degrees of diel migration (e.g., many myctophids). Even though faunal composition is similar across the GOM, some species exhibit different movement behaviors at different locations. Such variances could be related to differences in physical or chemical factors, food resources, lunar phase, or bottom depth. [Copyright &y& Elsevier]

The objective of this experiment was to test the efficacy of a probiotic (Efinol®L) during transportation of marbled hatchetfish, Carnegiella strigata. Wild specimens were captured from a small stream and transported for 24 h in plastic fish boxes with a probiotic (10 mg L−1) and probiotic-free water. The boxes were sampled at 3, 12 and 24 h of transport. At the end of the experiment, the survival rate was close to 100% in both treatments. Dissolved oxygen diminished with time in both treatments, but the probiotic group had significantly higher levels. Conductivity, pH and ammonia increased significantly during the transport, demonstrating higher levels in the probiotic-free group. Fish from both treatments presented very high net Na+ and K+ effluxes after 3 h of transport. At 24 h, net K+ effluxes in fish of the probiotic treatment reached values close to zero and a significantly lower Na+ efflux was observed. Cortisol levels in both treatments at 3 and 12 h were significantly higher than that in control samples. Higher body cortisol levels were observed in the probiotic-free group than that in the probiotic group at 3 and 12 h. The results demonstrate that addition of a probiotic during fish transport improves water quality and leads to fish presenting a lower stress response intensity. [ABSTRACT FROM AUTHOR]

An analysis of the 524 nucleotide long segment in the 16SrDNA mitochondrial gene of Maurolicus japonicus revealed that there are two major haplotypes (E and H) and two minor haplotypes (I and J), which comprise 63·6, 27·2, 4·6 and 4·6% of the population, respectively. The nucleotide sequence of the major haplotype E is identical to that of the most common haplotype in Maurolicus walvisensis (63·6% of the population). The other haplotypes of M. japonicus are almost identical to that of the haplotype E with only a single (haplotypes I and J) or three nucleotide differences (haplotype H). Phylogenetic trees of all the 16SrDNA haplotypes found thus far in the Maurolicus taxa show that the relationships among the haplotypes of M. japonicus and M. walvisensis are indistinguishable but that they are clearly distinctive from those of Maurolicus muelleri. Examination of the morphometric characteristics of specimens reveals similarities among the individuals of different haplotypes of M. japonicus and also between M. japonicus and M. walvisensis in almost all characteristics. The results suggest that despite the current ocean-wide allopatric distribution between M. japonicus and M. walvisensis, the two taxa are conspecific as M. japonicus. [ABSTRACT FROM AUTHOR]

A new genus and species of deep-sea hatchetfish, Discosternon federicae gen. et sp. nov., is described from the Middle Miocene (Serravallian) calciturbititic deposits of the Tufillo Unit exposed near the town of Gessopalena, central Italy. It is based on a single, very small, well-preserved and nearly complete specimen that exhibits a discoid physiognomy and a unique combination of features, many of which are reductive (loss of dorsal blade, loss of anal-fin hiatus, loss of abdominal keel-like structure, reduction of number of supraneurals, reduction of number of caudal vertebrae, presence of slender neural and haemal spines, external surface of cleithrum smooth). The comparative morphological analysis indicates that Discosternon is probably related to the derived genera Horbatshia and Sternoptyx. The highly reduced body size and the possession of many reductive characters indicate that Discosternon can be presumed to be a miniature fish. Anatomical and morphofunctional considerations suggest that Discosternon possibly was a midwater plankton feeder characterized by a reduced locomotory ability. [ABSTRACT FROM AUTHOR]

The article presents an experimental study which examines the positive effects of exposure to increased water velocity on the growth of newly hatched Arctic charr also known as Salvelinus alpinus L. The experiment used 1224 newly hatched fish with the aid of water velocity treatment which has an effect on growth in terms of length and weight. It was found out the use of a higher water velocity immediately after hatching is associated with a significant increase in growth. The study also suggests that environmental growth advantages achieved early in the life history of cod.

We examined larval mesopelagic fish assemblages, their distribution, and seasonal occurrence patterns in the Kuroshio–Oyashio transition region of the western North Pacific where complex hydrographic structures are observed due to the confluence of the Kuroshio Extension and Oyashio current. Larvae of the dominant families Myctophidae, Gonostomatidae, Bathylagidae, Sternoptychidae, and Phosichthyidae were represented by 31 species or types belonging to 24 genera. Based on species composition analysis using the Morishita–Horn similarity index, five assemblages were recognized: Oyashio, Spring Transition, Summer Transition, Kuroshio, and Slope Water assemblages. The distribution patterns of these assemblages corresponded closely with hydrographic structures such as position of the Oyashio and Kuroshio Extension fronts, warm core rings and streamers. Spring Transition (April) and Summer Transition (July–October) assemblages were the most important larval assemblages in the transition region. Larval abundances were low during late autumn and winter. The Spring Transition and Summer Transition assemblages were composed of subtropical, transitional, subarctic, and slope-water species, suggesting the importance of the transition region as nursery grounds of mesopelagic fishes of various origins from subarctic to subtropical waters. Larval fish transport by the Kuroshio, Oyashio, and Tsugaru Warm currents into the transition region is discussed. [ABSTRACT FROM AUTHOR]

Nitric oxide synthase-like immunoreactivity (NOS-LI IR) was detected by immunohistochemistry in ventral light organs of the mesopelagic fish, Argyropelecus hemigymnus. Strong NOS-LI IR was present in nerve fibres and in other cells central for production or modulation of light: immunoreactive fibres surrounded the photophores, and were also present in the filter area. Filter cells, particularly in the outer layers, showed strong IR throughout the cytoplasm. Pharmacological studies suggested that nitric oxide (NO) modulates adrenaline-stimulated light emission, and that the modulation is correlated to the ability of the light organ to respond to adrenaline. Adrenaline is known to produce two different types of light response in isolated photophores from Argyropelecus: a slow, long-lasting, high intensity response, or a fast and weak response of short duration. Incubation of photophores in the NO donors sodium nitroprusside or S-nitroso-N-acetylpenicillamine prior to adrenaline stimulation reduced the intensity of the strong and long-lasting type of response, but had little or even a potentiating effect on the weakly responding photophores. Hydroxylamine, which is converted to NO if catalase activity is present in the tissue, reduced the duration and the intensity of the adrenaline response in all tested organs. The NOS-inhibitor L-thiocitrulline potentiated the adrenaline response in the weakly responding organs; the weaker the adrenaline effect, the stronger the potentiation caused by L-thiocitrulline. The strongly responding organs were instead inhibited by L-thiocitrulline. The results suggest that NO has an important role in the control of light emission from Argyropelecus hemigymnus photophores. The cGMP analogue dibutyryl cGMP, the guanylate cyclase inhibitor ODQ and the phosphodiesterase inhibitor pentoxiphylline had no effect, indicating that the NO effect does not involve cGMP. [ABSTRACT FROM AUTHOR]

We have examined the morphology and photopigments of the pineal organs from a number of mesopelagic fish, including representatives of the hatchet fish (Sternoptychidae), scaly dragon-fish (Chauliodontidae) and bristlemouths (Gonostomidae). Although these fish were caught at depths of between 500 and 1000 m, the morphological organisation of their pineal organs is remarkably similar to that of surface-dwelling fish. Photoreceptor inner and outer segments protrude into the lumen of the pineal vesicle, and the outer segment is composed of a stack of up to 20 curved disks that form a cap-like cover over the inner segment. In all species, the pineal photopigment was spectrally distinct from the retinal rod pigment, with λmax displaced to longer wavelengths, between ∼485 and 503 nm. We also investigated the pineal organ of the deep demersal eel, Synaphobranchus kaupi, caught at depths below 2000 m, which possesses a rod visual pigment with λmax at 478 nm, but the pineal pigment has λmax at ∼515 nm. In one species of hatchet fish, Argyropelecus affinis, two spectral classes of pinealocyte were identified, both spectrally distinct from the retinal rod photopigment. [ABSTRACT FROM AUTHOR]

Benthic and pelagic fishes were sampled east of Maria Island, Tasmania, at two-monthly intervals from April 1984 to June 1985, from the surface to the bottom (500 m depth), using commercial-sized trawls. Biomass was calculated by the 'area swept/volume filtered' method and divided by estimated catchability coefficients so that catches from the two sampling gears could be combined. Of the 54 families caught, three (Myctophidae, Squalidae, Sternoptychidae) contributed 25% of the 115 species. Most benthic and dispersed species were caught regularly, whereas most pelagic species occurred only occasionally and in low numbers, although a core group was always present. Total fish biomass was high (range=77 to 532 g m; x= 390 g m), due almost entirely to the myctophid Lampanyctodes hectoris (over 90% of the biomass). Benthic biomass was relatively low and stable, but derived from many species. Pelagic biomass was high, fluctuated widely and was composed of a few species. Biomass was highest in summer: Maurolicus muelleri increased by a factor of 200, Diaphus danae by 50, and L. hectoris, Macruronus novaezelandiae and Lepidorhynchus denticulatus by almost 10. Peaks in biomass may correlate with the interactions of the subtropical convergence and the East Australian Current and the resultant marked seasonal cycle in water temperature, nutrients and primary productivity. [ABSTRACT FROM AUTHOR]

The vertical distribution of seven sternoptychid species was examined from RMT 1+8 samples collected aboard R. V. 'Meteor' in March-April 1979 and from Royal Research Ship R.R.S. 'Discovery' in July 1974 in the central equatorial Atlantic. During daytime sternoptychids occupied depths between 200 and 1250 m, with Sternoptyx pseudobscura living deepest, centering between 800 and 900 m, and Argyropelecus sladeni most shallow, aggregating predominantly at 300 and 400 m. They are all considered limited or partial migrants, ascending only some 100 and 200 m towards the surface at night. Only A. sladeni was observed to enter the epipelagic zone (0 and 200 m).-Feeding patterns were investigated from stomach content analyses of Sternoptyx diaphana, S. pseudobscura, Argyropelecus sladeni and A. affinis. Additional stomach contents were analysed from samples of S. diaphana, A. hemigymnus and A. olfersi collected in June 1985 from F.R.V. 'Walther Herwig' in the temperate NE Atlantic at 46°N, 17°W by means of the Engel Trawl. The food spectrum of the six species is generally described, and additional dietary evidence regarding calanoid copepod prey is provided for four of these taxa. All sternoptychid species investigated were planktivorous, feeding predominantly on copepods and ostracods, except for the largest size class, which preyed heavily on euphausiids and amphipods. The relationship of predator size towards prey type and prey size is analysed for both Sternoptyx species. Of these, S. pseudobscura in particular exhibits taxonomic selectivity towards polychaete prey. The diet of both species of Sternoptyx included a number of epipelagic or even neustonic calanoid copepod species which contributed more than 50% of the total copepod population by numbers. So far it is not known how the predators find access to prey organisms of the upper 200 m, as netfeeding is considered unlikely. Cyclopoid copepods of the genus Sapphirina were observed as dietary component particular of S. diaphana. [ABSTRACT FROM AUTHOR]

Species of the Sternoptychidae teleost family display an impressive morphology, including their extreme reduced size. Here, we report the first mitochondrial genome of the diaphanous hatchet fish Sternoptyx diaphana . By using short-read sequencing Illumina HiSeq, we generated two mitochondrial contigs which were later physically assembled by PCR. The mitochondrial genome of S. diaphana was 17,224 bp in length (excluding the control region) and is composed of 13 PCGs and 2 ribosomal RNA genes. Strikingly, we could not identify the tRNA-Phe and two copies of tRNA-Met were differently positioned. Additionally, the mitogenome displays a completely new gene rearrangement among vertebrates. We expect that the study presented here will pave the way for further molecular studies with this underrepresented group of illusive teleost fish., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)