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Bony fishes are extremely successful in the marine environment, having evolved into nearly every ocean habitat. However, bony fishes do not seem to inhabit the ocean's deepest depths, likely due to constraints of pressure adaptation. How deep do bony fishes live? Relatively few studies have examined the deepest living vertebrates, because sampling in hadal environments, depths 6000-11,000 m, is technologically challenging. Here, we review the literature on records of the deepest living bony fishes. Current depth records are held by the hadal snailfish Pseudoliparis swirei (family Liparidae) in the Mariana Trench, collection depth 7966 m, filmed to 8178 m, and the cusk eel Abyssobrotula galatheae (family Ophidiidae) in the Puerto Rico Trench, collection depth 7965 m. Observations of abyssal and hadal fish communities suggest that hadal snailfishes are endemic to trenches but occasionally cross into abyssal areas. On the other hand, cusk eels dwell on the abyssal plains, but can extend their ranges into the trenches. These habitat differences allow both snailfishes and cusk eels to occupy distinct niches in the greatest ocean depths. We then comment on the ecological and physiological significance of these two major hadal families and present recommendations for future research., Author(s): Mackenzie E. Gerringer [sup.1] , Thomas D. Linley [sup.2] [sup.3] , Jørgen G. Nielsen [sup.4] Author Affiliations: (1) grid.264269.d, 0000 0001 0151 0940, Biology Department, State University of New [...]

After a preceding revision based on 87 specimens, the systematics of the abyssal giant cuskeel genus Spectrunculus Jordan and Thompson, 1914 has been revisited, based on the examination of 34 additional specimens and new otolith shape data of the holotype of S. grandis. From the latter, a clear distinction in otolith ostium width could be found in specimens from the Atlantic, Southern Indian Ocean, and Southwest Pacific, which were formerly identified as S. grandis. Consequently, the new species, S. stenostio, is described, which has a narrower ostium when related to its length or to sulcus length and differs also in the combination of three body shape characters, three meristic characters, and maximum size from the three other congeners, S. crassus (Atlantic, East Pacific), S. grandis (Pacific), and the previously synonymized S. radcliffei (Pacific, Southern Indian Ocean, Southeast Atlantic). The latter species is here resurrected based on a rather short pre-anal length and additional morphometric as well as meristic and maximum size differences. An identification key for the four species of Spectrunculus is provided. [ABSTRACT FROM AUTHOR]

The cuskeel genus Neobythites (Ophidiidae) is recorded for the first time from the Solomon Sea, SW Pacific, and a new species, N. solomonensis n. sp., is described based on five specimens (SL 137-166 mm) caught at 498-839 m depth in the eastern Solomon Sea. The new species is characterized by having two spines on hind margin of preoperculum, a distinct lateral body stripe and dark-brown or grey dorsal-fin margin. The most similar species is N. somaliaensis Nielsen, 1995, of which 14 specimens are compared. Neobythites solomonensis n. sp. differs from the latter in the following characters (N. somaliaensis in brackets): total vertebrae 58-61 (61-64), developed gill rakers 12-14 (9-11), orbit length 4.0-4.9 (5.0-6.1) in % SL, longest gill filament on anterior arch 4.6-5.3 (11.0-14.0) in % head length and presence (absence) of body stripe. The significance of studying colour patterns in the speciose genus Neobythites (55 valid species) is discussed. [ABSTRACT FROM AUTHOR]

Neobythites kenyaensis, a cuskeel (Ophidiidae) with two ocelli on the dorsal fin, is redescribed based on 33 meristic, body shape, colour, and otolith characters obtained from 15 specimens, 12 of which were studied for the first time. Nine of the 12 new specimens were collected during a research cruise off Mozambique together with vouchered colour photographs made on board when the fish were still fresh. Two specimens were collected off Natal, South Africa, one of them only available as a fresh colour photograph and one specimen off Dar es Salaam, Tanzania. Accordingly, while N. kenyaensis was only known from Kenya and northernmost Tanzania (Zanzibar) since its description in 1995, we proved now its continuous distribution along the entire SE African coast from off Ras Ngomeni, Kenya, to off Durban, South Africa, at depths of 238-457 m. Neobythites kenyaensis is rather unique among the 54 species of its genus in possessing an ocellus positioned near the dorsal-fin origin (anterior ocellus) which it shares only with the West-Pacific N. longiventralis and West-Atlantic N. ocellatus. It differs from the latter in the following characteristics: second, central ocellus more posteriorly placed on dorsal fin, more precaudal vertebrae (13 vs. 12), less developed gill rakers (8-10 vs. 14-16), shorter head (19.5- 20.5 vs. 21.5-23.5% SL), and shorter pelvic fins (9.9-12.0 vs. 16.0-21.5% SL ). Both species differ clearly from N. longiventralis in having a much shorter pelvin fin (9.9-21.5 vs. 32.0-34.% SL). The central ocellus-spot size, determined by the number of rays covered by the ocellus spot, varies considerably in N. kenyaensis and reaches the largest size reported for any ocellus-bearing Neobythites species. This character is strongly and positively correlated with both latitude and depth, suggesting gradual differentiation processes among adjacent populations or subpopulations. Another finding reported for the first time in Ophidiidae is the significant correlation of three otolith measurements with fish size (SL) in N. kenyaensis. [ABSTRACT FROM AUTHOR]

The genus Sciadonus Garman, 1899 belongs to the aphyonid clade within the Bythitidae. The present revision is based on 304 specimens all trawled at great depths (1169-5610 m), 19 of which have not been examined earlier. As a consequence, the generic diagnosis from Nielsen et al. (1999) is here modified. The enlarged material resulted in synonymizing of S. galatheae (Nielsen, 1969) and S. pedicellaris Garman, 1899 and in the description of two new species, S. robinsi and S. longiventralis. The new species differ from the other Sciadonus species by lack of pigmentation, fewer dorsal fin rays and position of origin of anal fin. S. longiventralis differs from S. robinsi by shorter predorsal length (28.5 vs 42.5% SL) and length of pelvic fin rays (3.5% SL vs no pelvic rays). [ABSTRACT FROM AUTHOR]

Fishes are widely diverse in shape and body size and can quite rapidly undergo these changes. Consequently, some relationships are not clearly resolved with morphological analyses. In the case of fishes of small body size, informative characteristics can be absent due to simplification of body structures. The Parabrotulidae, a small family of diminutive body size consisting of two genera and three species has most recently been classified as either a perciform within the suborder Zoarcoidei or an ophidiiform. Classification of parabrotulids as ophidiiforms has become predominant; however the Parabrotulidae has not yet been investigated in a molecular phylogenetic framework. We examine molecular data from ten genetic loci to more specifically place the Parabrotulidae within the fish tree of life. In a hypothesis testing framework, the Parabrotulidae as a zoarcoid taxon is rejected. Previous identity with zoarcoids due to the one fin ray for each vertebra being present, a characteristic for the Zoarcidae, appears to be an example of convergence. Our results indicate that parabrotulids are viviparous ophidiiforms within the family Bythitidae. [ABSTRACT FROM AUTHOR]

A revision is presented of the rare, abyssal-living former aphyonid now bythitid genera, Meteoria Nielsen, 1969 and Parasciadonus Nielsen, 1984. The type species of Meteoria, M. erythrops Nielsen, 1969 was based on a female and a juvenile specimen. Additionally, a ripe male of M. erythrops have been caught and furthermore two Meteoria specimens that vary so much from the type species that they are here described as a new species, M. longidorsalis n. sp. It differs from the type species i.a. by the short predorsal length, higher number of dorsal fin rays, smaller interorbital width and head profile. Furthermore, Parasciadonus pauciradiatus Nielsen, 1997 is reassigned to Meteoria leaving Parasciadonus with one species only, P. brevibrachium Nielsen, 1984. This makes it necessary to modify the generic diagnoses from Nielsen et al. (1999: 139). [ABSTRACT FROM AUTHOR]

Currently, three of the seven described species of Sirembo Bleeker, 1858 and both species of Spottobrotula Cohen & Nielsen, 1978 are considered valid. The present revision is based on 73 specimens of Sirembo known from the Red Sea to Japan and southwards to off northwestern Australia and northern New South Wales and 19 specimens of Spottobrotula known from the Persian Gulf to the Mozambique Channel and from the Andaman Sea. The main characters separating the two genera are the number of long rakers on the anterior gill arch and the form of the sagittal otolith. Based on this distinction Spottobrotula amaculata Cohen & Nielsen, 1982 is transferred to Sirembo. While newly caught specimens can easily be identified by their colour pattern, preserved material requires identification based on meristic and morphometric characters. Three new species are herein described, Sirembo wami, Spottobrotula mossambica and Spottobrotula persica, while Sirembo jerdoni is reported for the first time from Vietnam. These and all other species of the two genera can be identified by combining number of long gill rakers, number of pseudobranchial filaments, number of pectoral fin rays, number and size of scales between dorsal fin origin and lateral line, and prepelvic and pelvic fin length in per cent of SL. The distinction from other genera is discussed. http://zoobank.org/urn:lsid:zoobank.org:pub:5C523099-D826-495E-B880-98B99B1D1714 [ABSTRACT FROM AUTHOR]

Two specimens from the Koko Seamount (Koko Guyot), in the Hawaiian-Emperor seamount chain, Central North Pacific, caught in 2009 and 2010 are here described as a new species, Bidenichthys okamotoi. The taxonomy of the species in the genera Bidenichthys Barnard, 1934, and Fiordichthys Paulin, 1995, has been confusing due to the lost type of B. consorbrinus (Hutton, 1876) and the rarity of some of the species. Following the synonymization of Fiordichthys Paulin, 1995, with Bidenichthys by Møller and Nielsen 2015 and of Bidenichthys beeblebroxi Paulin, 1995, with Bidenichthys consobrinus Hutton, 1876, the genus Bidenichthys now comprises five species: B. capensis, B. consobrinus, B. okamotoi, B. paxtoni and B. slartibartfasti. Bidenichthys okamotoi differs from its congeners in, e.g., the fewer precaudal vertebrae (12 vs. 13), more palatine teeth rows (4–6 vs. 2–3), shorter pelvic fins (12.1–13.4% vs. 14.4–21.0% SL), max size (187 vs. 147 mm SL) and the shape of the sulcus of the otolith. We here present an updated diagnosis of the genus. A computed tomography (CT) scan of the holotype of B. okamotoi provides for additional anatomical details. The disjunctive occurrence of Bidenichthys okamotoi on the Emperor Seamount chain about 7500 km from the nearest congeneric taxon in New Zealand is discussed. The fossil otolith-based record of the genus Bidenichthys and its systematic implications is briefly discussed. [ABSTRACT FROM AUTHOR]

This paper is based on 760 Atlantic specimens of pelican eels caught from off Iceland to 48°S in depths between 2750 and c. 500 m. Stomach contents from 120 specimens show a varied diet dominated by crustaceans, fish and squid. The frequent occurrence of Sargasso weed consumed by Eurypharynx indicates a lack of prey-item discrimination. The forward directed eyes appear to enable stereoscopic prey localization, possibly aided by the well developed lateral line. The huge gape is unsuitable for suction feeding. It is proposed that prey engulfing is accomplished by a forward thrust of the head by which the produced water pressure will expand the buccal cavity to a volume several times that of the fish itself. When ripening, males especially show morphological changes in some characters, indicating that the pelican eel breeds only once, a condition which seems to be the rule among eels. [ABSTRACT FROM AUTHOR]

En 2010, un spécimen d'Ophidiidae du genre Neobythites a été récolté par 295 m de profondeur au cours de l'expédition française "Atimo Vatae" dans le sud de Madagascar. Ce spécimen appartient à une espèce différente des 12 autres espèces connues de la partie la plus occidentale de l'océan Indien. Néanmoins, cet individu correspond à la diagnose de N. bimarginatus Fourmanoir & Rivaton, 1979, l'une des 30 espèces de Neobythites connues de l'océan Indien oriental et du Pacifique ouest. N. bimarginatus possède un caractère unique : la coloration de ses nageoires dorsale et anale, dont les extrémités discales et proximales sont claires, alors que la partie médiane est noire. L'espèce est connue par 13 spécimens de Nouvelle-Calédonie et de quelques îles voisines, ce qui représente une distance de plus de 10 000 km de Madagascar. Des récoltes complémentaires sont nécessaires sur la partie supérieure de la pente continentale pour déterminer la distribution exacte et la structure de la population de N. bimarginatus. [ABSTRACT FROM AUTHOR]

Aphyonids are poorly-known, live-bearing brotulas (Ophidiiformes, Bythitidae) that until recently were considered to be in a distinct family, Aphyonidae. A single, ca. 9.3 cm total length aphyonid observed during a remotely-operated vehicle survey in the Mariana Archipelago at 2504.2 m on Explorer Ridge (20.68152°N, 145.08750°E) is the first seen alive in its natural habitat. Collection to verify its identification was not possible, but based on observations it was a species of either Barathronus or Nybelinella. The fish swam 1–10 cm over sediment between rocks and small boulders on a 45° talus slope. Swimming speeds were consistently slow, 0.33 ± 0.15 body lengths per second, and the fish appeared to be neutrally buoyant. Although there are few other records of aphyonid-clade fishes in the Pacific away from continental margins, this observation suggests that they will be found elsewhere in the basin when appropriate methods are used to detect these small fishes in the high-relief, rugose habitats of central Pacific oceanic islands and seamounts. [ABSTRACT FROM AUTHOR]

The order Ophidiiformes is a large but not very well known group of fishes, unique among teleosts for showing high diversity in both deep sea and shallow reef habitats. The current classification includes more than 500 species, 115 genera and four families, based primarily on mode of reproduction: viviparous Aphyonidae and Bythitidae vs oviparous Carapidae and Ophidiidae. Since 2004 we revised the bythitid tribe Dinematichthyini, described more than 100 new species and noticed that this group has unique morphological characters, perhaps supporting a higher level of classification than the current status. Here we study the viviparous families phylogenetically with partial mitochondrial ( nd4 , 16s ) and nuclear ( Rag1 ) DNA sequences (2194 bp). We use a fossil calibration of otolith-based taxa to calibrate the age of the clade comprising bythitid and dinematicththyid representatives, together with fossil calibrations adopted from previous phylogenetic studies. The separation of the order into two major lineages, the viviparous Bythitoidei and the oviparous Ophidioidei is confirmed. At the familial level, however, a new classification is presented for the viviparous clades, placing Aphyonidae as a derived, pedomorphic member of Bythitidae (new diagnosis provided, 33 genera and 118 species). The current subfamily Brosmophycinae is considered polyphyletic and we propose family status for Dinematichthyidae (25 genera, 114 species), supported by unique, morphological synapomorphic characters in the male copulatory apparatus. Previous use of the caudal fin separation or fusion with vertical fins is ambiguous. Age estimates based on calibrated molecular phylogeny agrees with fossil data, giving an origin within the Cretaceous (between 84 and 104 mya) for a common ancestor to Ophidiiformes. [ABSTRACT FROM AUTHOR]