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Holtbyrnia anomala is a bathypelagic platytroctid widely distributed in the Atlantic Ocean. In this contribution, we report, for the first time, the occurrence of this species in the tropical southwest Atlantic. A single specimen was collected in 2000 on the continental slope off Rio de Janeiro, Brazil, at an average depth of 1158 m. This report also represents the first record of Holtbyrnia anomala in the Brazilian Economic Exclusive Zone.

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Barathronus is a genus of blind cusk eels comprising 11 valid species. In this paper, we report the second specimen ever documented of Barathronus roulei (Bythitidae) obtained from the Porcupine Bank by R.V. Vizconde de Eza using a bottom trawl at a depth of 1349 m. Morphological description and illustrations, including a radiograph, are provided. In addition, three new sequences corresponding to three different genes, cytochrome c oxidase subunit I (COI)-DNA barcoding, 16S ribosomal RNA (16S), and recombination activating protein 1 (RAG1), have been added to the molecular repositories, representing the first sequences for the species.

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If similar evolutionary forces maintain intra- and interspecific diversity, patterns of diversity at both levels of biological organization can be expected to covary across space. Although this prediction of a positive species-genetic diversity correlation (SGDC) has been tested for several taxa in natural landscapes, no study has yet evaluated the influence of the community delineation on these SGDCs. In this study, we focused on tropical fishes of the Indo-Pacific Ocean, using range-wide single nucleotide polymorphism data for a deep-sea fish (Etelis coruscans) and species presence data of 4878 Teleostei species. We investigated whether a diversity continuum occurred, for different community delineations (subfamily, family, order and class) and spatial extents, and which processes explained these diversity patterns. We found no association between genetic diversity and species richness (α-SGDC), regardless of the community and spatial extent. In contrast, we evidenced a positive relationship between genetic and species dissimilarities (ß-SGDC) when the community was defined at the subfamily or family level of the species of interest, and when the Western Indian Ocean was excluded. This relationship was related to the imprint of dispersal processes across levels of biological organization in Lutjanidae. However, this positive ß-SGDC was lost when considering higher taxonomic communities and at the scale of the entire Indo-Pacific, suggesting different responses of populations and communities to evolutionary processes at these scales. This study provides evidence that the taxonomic scale at which communities are defined and the spatial extent are pivotal to better understand the processes shaping diversity across levels of biological organization.

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A macrourid, Coryphaenoides yaquinae sp. inc., was observed to be attracted to bait and exhibiting normal foraging behaviour during a period of 80 min within view of a baited video camera on the sea floor at 7259 m - the deepest ever observation of a fish species with a swim bladder. The buoyancy provided by an oxygen-filled swim bladder at 74.4 MPa pressure was estimated to be 0.164 N, at a theoretical energy cost of 20 kJ, 200 times less than the cost of equivalent lipid buoyancy. During normal metabolism, 192 days would be required to fill the swimbladder. At these depths, oxygen is very incompressible, so changes in volume during ascent or descent are small. However, swimbladder function is crucially dependent on a very low rate of diffusion of oxygen across the swimbladder wall. The oxygen in the swimbladder could theoretically sustain aerobic metabolism for over 1 year but is unlikely to be used as a reserve.

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Mitogenomes are defined as compact and structurally stable over aeons. This perception results from a vertebrate-centric vision, where few types of mtDNA rearrangements are described. Here, we bring a new light to the involvement of mitochondrial replication in the strand asymmetry of the vertebrate mtDNA. Using several species of deep-sea hatchetfish (Sternoptychidae) displaying distinct mtDNA structural arrangements, we unravel the inversion of the coding direction of protein-coding genes (PCGs). This unexpected change is coupled with a strand asymmetry nucleotide composition reversal and is shown to be directly related to the strand location of the Control Region (CR). An analysis of the fourfold redundant sites of the PCGs (greater than 6000 vertebrates), revealed the rarity of this phenomenon, found in nine fish species (five deep-sea hatchetfish). Curiously, in Antarctic notothenioid fishes (Trematominae), where a single PCG inversion (the only other record in fish) is coupled with the inversion of the CR, the standard asymmetry is disrupted for the remaining PCGs but not yet reversed, suggesting a transitory state. Our results hint that a relaxation of the classic vertebrate mitochondrial structural stasis promotes disruption of the natural balance of asymmetry of the mtDNA. These findings support the long-lasting hypothesis that replication is the main molecular mechanism promoting the strand-specific compositional bias of this unique and indispensable molecule.

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The deep-sea spiny eels of the genus Notacanthus Bloch 1788 are currently represented by six valid species, of which only one, Notacanthus indicus, has been described so far from the Arabian Sea, part of the Western Indian Ocean. This paper reports the discovery of a new species, described herein as Notacanthus laccadiviensis, from the outer reef drop-off, off the Kavaratti Island, Lakshadweep Archipelago, Arabian Sea. The new species differs from its congeners in the shape of the head; morphology of dorsal, pectoral and anal fins; number of gill rakers; number of vertebrae; and body colour, and specifically from N. indicus (the only known congener from the Indian Ocean) in the unusual morphology of the dorsal fin, and number of rays in the dorsal and pectoral fins.

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A new species of the hagfish genus Eptatretus (Myxinidae) is described based on two specimens (407-433 mm total length) collected off the northern Bahamas, between depths of 910 and 1153 m. The new species is distinguished from its congeners by having seven pairs of gill apertures well-spaced and arranged in a near straight line, a 3/2 multicusp pattern of teeth, 10-11 anterior unicusps, 50-51 total cusps, 12-14 prebranchial pores, 48-52 trunk pores, 79-84 total pores, and no nasal-sinus papillae. An identification key for the species of Eptatretus from the western Atlantic Ocean is also provided.

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Persistent organic pollutants, including polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and other brominated flame retardants, were detected in the liver, muscle, and ovary tissues of the Indonesian coelacanth (Latimeria menadoensis) incidentally caught around Gangga Island, North Sulawesi Province, Indonesia, on November 5, 2014. Concentrations of total PCBs (209 congeners, 300-2600 ng g-1 lipid weight) in all tissues showed higher than those of PBDEs (41 congeners, 3.9-6.3 ng g-1 lw) and BTBPE (1.1-3.6 ng g-1 lw). The tissue-specific PCB and PBDE profiles were likely due to differences in the lipid composition. Toxic equivalent (TEQ) values of dioxin-like PCBs in coelacanth tissues were lower than the benchmark values for early-life fish. However, compared with the data reported for deep-sea fishes in the Pacific and Indian Oceans, the relatively high concentrations of PCBs detected in this study raise concerns regarding Indonesian coelacanth conservation and habitat conditions.

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Although parasite community studies are growing in numbers, our understanding of which macro-ecological and evolutionary processes have shaped parasite communities is still based on a narrow range of host­parasite systems. The present study assessed the diversity and endoparasite species composition in New Zealand deep-sea fish (grenadiers, family Macrouridae), and tested the effects of host phylogeny and geography on the structure of endoparasite communities using a distance decay framework. We found that grenadiers from the Chatham Rise harboured a surprisingly high diversity of digeneans, cestodes and nematodes, with different species of grenadiers having different parasite assemblages. Our results demonstrate that community similarity based on the presence/absence of parasites was only affected by the phylogenetic relatedness among grenadier species. In contrast, both phylogenetic distance among grenadiers (measured as the number of base-pair differences of DNA sequences) and geographic distance between sample locations influenced the similarity of parasite communities based on the parasites' prevalence and mean abundance. Our key findings highlight the significant effect of deep-sea host phylogeny in shaping their parasite assemblages, a factor previously neglected in studies of parasite communities in deep-sea systems.

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Despite their remoteness, deep-sea species bioaccumulate mercury, mostly in the form of the neurotoxin methylmercury (MeHg). Although the concentration of MeHg in the water column is known to increase with depth down to a maximum found at the base of the permanent thermocline, the knowledge of the relationship between MeHg content in marine species and their depth of occurrence is limited. We analyzed total mercury (THg) and MeHg concentrations in 25 species of fish inhabiting the Avilés Submarine Canyon and its adjacent shelf (Cantabrian Sea, North-East Atlantic) between 50 and 1868 m depth. THg concentrations ranged from 0.03 µg g-1 in wet weight (ww) in Chauliodus sloani and 4.0 µg g-1 ww in Coryphaenoides guentheri. 65% of the species analyzed exceeded 0.5 µg g-1 ww of MeHg, the maximum level for safe consumption recommended by FAO/WHO. THg and MeHg contents in muscle tissue increased with the depth of occurrence of fish and was influenced by their habitat so that demersal species had higher THg content than pelagic species inhabiting the same depth. MeHg accounted for an average 76 ± 3.9% of THg (mean ± SD), which is lower than that reported for other fish communities and can be explained by the high concentration of Hg present in sediments of the Nalón estuary, which discharges right off the Avilés Canyon head. The % of THg as MeHg was also strongly correlated with δ15N values, confirming that MeHg can be an indicator of the trophic identity of a species within the food web.

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Oarfish (Regalecus russelii Cuvier) are mesopelagic fish with little known about their life history. Oarfish live in deep water, making it difficult for researchers to collect specimens; thus, records of their parasitic helminths are limited. Two plerocercoids were found for the first time in an oarfish stranded on the coast of Akita Prefecture, Japan. These plerocercoids were identified as Clistobothrium sp. RR-1 using morphological and molecular analyses. It was revealed that oarfish represent one of the intermediate hosts of the genus Clistobothrium, and large sharks are the definitive hosts for these parasites.

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The seas of the North Pacific Ocean are characterized by a large variety of fish fauna, including endemic species. Molecular genetic methods, often based on DNA barcoding approaches, have been recently used to determine species boundaries and identify cryptic diversity within these species. This study complements the DNA barcode library of fish from the Northeast Pacific area. A library based on 154 sequences of the mitochondrial COI gene from 44 species was assembled and analyzed. It was found that 39 species (89%) can be unambiguously identified by the clear thresholds forming a barcoding gap. Deviations from the standard 2% threshold value resulted in detection of the species Enophrys lucasi in the sample, which is not typical for the eastern part of the Bering Sea. This barcoding gap also made it possible to identify naturally occurring low values of interspecific divergence of eulittoral taxa Aspidophoroides and the deep-sea genus Coryphaenoides. Synonymy of the genus Albatrossia in favor of the genus Coryphaenoides is suggested based on both the original and previously published data.

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BACKGROUND: Little is known about the life history of oarfish of the genus Regalecus, although it is a famous deep-sea fish and an apparent origin of sea serpent legends. We successfully performed artificial insemination using a recently dead pair of sexually mature individuals. We report for the first time development from fertilized eggs to early larvae in the Lampridiformes. RESULTS: Eggs required 18 days of development from fertilization to hatching under 20.5-22.5 °C conditions. Oarfish larvae had similar morphological features as other lampridiform larvae hatched in the ocean. Larvae typically faced downward and swam using pectoral fins; they frequently opened their mouths. This mouth-opening behavior and swimming ability were both consistent with osteological development. The larvae did not eat and died four days after hatching. CONCLUSIONS: This is the first successful instance of artificial insemination and hatching in the oarfish, as well as the first reliable morphological and behavioral description of lampridiform larvae.

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Methylmercury (MeHg) poses health risks to humans worldwide. The investigation of a longer chain of biogeochemical MeHg transport from production to consumption than that addressed in previous studies could provide additional scientific foundation for the reduction of risks. The main objective of this study is to identify the impacts of the interregional food trade along with the age, gender and socioeconomic status of people on human MeHg exposure in a developing megacity. Based on a field investigation, sampling and measurements, we provide experimental evidence regarding the substantial displacement of human MeHg exposure from production areas to consumption areas induced by the food trade. In 2018, 20% and 64% of the exposure in Beijing originated from the international and interprovincial food trade, respectively. Meanwhile, the ingestion of fish contributed 79% to the total exposure, followed by rice (4.4%), crab (3.8%) and shrimp (2.7%), and the exposure risk in urban districts was higher than that in rural areas by a factor of 2.2. A significantly higher contribution of imported deep-sea species to exposure among young people than among older people was observed (P < 0.01**), and a larger contribution of the international food trade to the MeHg exposure risk for women of childbearing age (average: 27%) than that among other groups (average: 10%) was found. Overall, our efforts demonstrate the dramatic impact of the food trade on MeHg exposure in a developing megacity, and we suggest that MeHg-susceptible populations in China should choose indigenous fish species (e.g., hairtail, yellow croaker and carp species) rather than imported deep-sea species as their dietary protein source.

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Two new species of deep-sea anglerfishes are described on the basis of specimens collected from off northeastern Taiwan. Oneirodes formosanus sp. nov., based on one adult female, differs from its congeners in having a deep caudal peduncle (15.4% SL) and esca with a single simple, elongate, unbranched, internally pigmented, anterior escal appendage; a simple, elongate, posterior escal appendage; an elongate terminal escal papilla; and no medial and lateral escal appendages. Gigantactis cheni sp. nov., based on three adult females, differs from its congeners in having a series of unpigmented filaments at base of illicium; a black terminal elongated esca bearing numerous dermal spinules; relatively more jaws teeth with the outtermost ones relatively short. A synopsis of Taiwanese species of the suborder Ceratioidei is provided.

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This study reports on the first record of the intermediate scabbardfish Aphanopus intermedius in the western South Atlantic Ocean, based on a single specimen 725 mm standard length collected between 0 and 610 m depth around Rocas Atoll off north-eastern Brazil. Measurements and counts are provided and compared with those available in the literature.

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Deep-sea demersal fish surveys using baited cameras were undertaken in the West African oil provinces between 1297 m and 2453 m depth in 2002, 2005 and 2008. A total of 29 deployments amounting to 16,175 images encountered 31 species of bait attending deep-sea fish from 17 families. The extrapolated species richness was 34, indicating that the survey encountered over 90% of bait attending fish species in this area. The dominant species in the area were the morid Antimora rostrata, the synaphobranchids Synaphobranchus cf. kaupii and Simenchelys parasitica, the somniosid Centroscymnus coelolepis and the zoarcid Pachycara crassiceps. An unusually high diversity of bait attending macrourids was observed in addition to patchy aggregations of zoarcids. This study serves as baseline survey data on which to base future long-term environmental monitoring of fish populations in the vicinity of the West African oil provinces.

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Little is known of the diversity of the monogenean parasites infesting deep-sea groupers, and there is even less information available about their geographic distributions within the ranges of their hosts. To improve our understanding of these host-parasite relationships we conducted parasitological evaluations of the deep-water Haifa grouper Hyporthodus haifensis from the southern Mediterranean off Tunisia and Libya. We collected more than one species of diplectanid monogeneans from this host, but among these only one dominant species was abundant. This proved to be morphologically very similar to Pseudorhabdosynochus sulamericanus Santos, Buchmann & Gibson, 2000, a species originally described from the congeneric host H. niveatus off Brazil and also recorded from H. niveatus and H. nigritus off Florida. Here, we conducted a morphological comparison between newly collected specimens and those previously deposited in museum collections by other authors. Further, we used COI barcoding to ascertain the specific identity of the three host species to better elucidate the circumstances that might explain the unexpectedly broad distribution of P. sulamericanus. We assigned our specimens from H. haifensis to P. sulamericanus primarily on the basis of morphological characteristics of the sclerotized vagina. We also noted morphological characteristics of eastern and western Atlantic specimens that are not clearly described or not given in previous descriptions and so prepared a redescription of the species. We confirmed, by COI barcoding, that no sister-species relationships were evident among the three hosts of P. sulamericanus. Our observation that P. sulamericanus infects unrelated host species with putatively allopatric distributions was unexpected given the very limited dispersive capabilities and the high degree of host specificity common to members of Pseudorhabdosynochus. This transatlantic distribution raises questions with regard to phylogeography and assumptions about the allopatry of Atlantic grouper species from the Americas and Afro-Eurasia. Here, we propose some hypothetical explanations for our findings.

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Marine fish are threatened by anthropogenic chemical discharges. However, knowledge on adverse effects on deep-sea fish or their detoxification capabilities is limited. Herein, we compared the basal activities of selected hepatic detoxification enzymes in several species (Solea solea, Dicentrarchus labrax, Trachyrhynchus scabrus, Mora moro, Cataetix laticeps and Alepocehalus rostratus) collected from the coast, middle and lower slopes of the Blanes Canyon region (Catalan continental margin, NW Mediterranean Sea). The xenobiotic-detoxifying enzymes analysed were the phase-I carboxylesterases (CbEs), and the phase-II conjugation activities uridine diphosphate glucuronyltransferase (UDPGT) and glutathione S-transferase (GST). Moreover, some antioxidant enzyme activities, i.e., catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GR), were also included in this comparative study. Because CbE activity is represented by multiple isoforms, the substrates α-naphthyl acetate (αNA) and ρ-nitrophenyl acetate (ρNPA) were used in the enzyme assays, and in vitro inhibition kinetics with dichlorvos were performed to compare interspecific CbE sensitivity. Activity of xenobiotic detoxification enzymes varied among the species, following a trend with habitat depth and body size. Thus, UDPGT and some antioxidant enzyme activities decreased in fish inhabiting lower slopes of deep-sea, whereas UDPGT and αNA-CbE activities were negatively related to fish size. A trend between CbE activities and the IC50 values for dichlorvos suggested S. solea and M. moro as potentially more sensitive to anticholinesterasic pesticides, and T. scabrus as the most resistant one. A principal component analysis considering all enzyme activities clearly identified the species but this grouping was not related to habitat depth or phylogeny. Although these results can be taken as baseline levels of the main xenobiotic detoxification enzymes in Mediterranean fish, further research is needed to evaluate their response to environmental contaminant exposure.

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The deep-sea environment is a sink for a wide variety of contaminants including heavy metals and organic compounds of anthropogenic origin. Life history traits of many deep-water fish species including longevity and high trophic position may predispose them to contaminant exposure and subsequent induction of pathological changes, including tumour formation. The lack of evidence for this hypothesis prompted this investigation in order to provide data on the presence of pathological changes in the liver and gonads of several deep-water fish species. Fish were obtained from the north east region of the Bay of Biscay (north east Atlantic Ocean) by trawling at depths between 700 and 1400 m. Liver and gonad samples were collected on board ship and fixed for histological processing and subsequent examination by light microscopy. Hepatocellular and nuclear pleomorphism and individual cases of ovotestis and foci of cellular alteration (FCA) were detected in black scabbardfish (Aphanopus carbo). Six cases of FCA were observed in orange roughy (Hoplostethus atlanticus) (n = 50) together with a single case of hepatocellular adenoma. A wide variety of inflammatory and degenerative lesions were found in all species examined. Deep-water fish display a range of pathologies similar to those seen in shelf-sea species used for international monitoring programmes including biological effects of contaminants. This study has confirmed the utility of health screening in deep-water fish for detecting evidence of prior exposure to contaminants and has also gained evidence of pathology potentially associated with exposure to algal toxins.

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