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Sternoptyx diaphana Hermann, 1781. Longspine Hatchetfish. To 6 cm (2.4 in) SL (Jesperson 1934). Circumglobal; western Pacific Ocean north to Japan (Fujii in Masuda et al. 1984) to Kuril Islands (Parin et al. 1995); Oregon (Matarese et al. 1989) to northern Chile (31��55���S) (Kong and Mel��ndez 1991). Depth: surface to 2,374 m (7,787 ft) (min.: Personal communication: Scripps Institution of Oceanography Fish Collection, La Jolla, California; max.: Porteiro et al. 2017). A maximum record of 4,667 m (15,308 ft) (Personal communication: Los Angeles County Museum of Natural History Fish Collection, Los Angeles, California) was taken in a midwater trawl towed from this depth to the surface and thus the exact depth of capture is unknown., Published as part of Love, Milton S., Bizzarro, Joseph J., Cornthwaite, Maria, Frable, Benjamin W. & Maslenikov, Katherine P., 2021, Checklist of marine and estuarine fishes from the Alaska-Yukon Border, Beaufort Sea, to Cabo San Lucas, Mexico, pp. 1-285 in Zootaxa 5053 (1) on page 57, DOI: 10.11646/zootaxa.5053.1.1, http://zenodo.org/record/5578008, {"references":["Jesperson, P. (1934) Gonostomatidae and Sternoptychidae. International Council for the Exploration of the Sea, Faune Ichthyologique de l'Atlantique Nord, No. 151.","Masuda, H., Amaoka, K., Araga, C., Uyeno, T. & Yoshino, T. (Eds). (1984) The Fishes of the Japanese Archipelago. Tokai University Press, Tokyo.","Parin, N. V., Fedorov, V. V., Borodulina, O. D. & Bekker, V. E. (1995) New records of mesopelagic and epipelagic fishes in Pacific waters off the southern Kuril Islands. Journal of Ichthyology, 35, 193 - 204.","Matarese, A. C., Kendall Jr., A. W., Blood, D. M. & Vintner, B. M. (1989) Laboratory guide to early life history stages of northeast Pacific fishes. NOAA Technical Report NMFS, 80.","Kong, I. & Melendez, C. R. (1991) Estudio taxonomico y sistematico de la ictiofauna de aguas profundas capturada entie Arica e Isla Mocha (18 ° 30 ' - 38 ° 30 ' Lat. S). Estudios Oceanograficos, 10, 1 - 81.","Porteiro, F. M., Sutton, T., Byrkjedal, I., Orlov, A. M. & Heino, M. (2017) Fishes of the northern Mid-Atlantic Ridge collected during the MAR-ECO cruise in June - July 2004: an annotated checklist. Arquipelago, Supplement 10."]}

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.

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.

Comprehensive trophic studies in the vast mid-oceanic regions are rare compared to coastal and fisheries-oriented investigations. Field sampling conducted by the multidisciplinary, international Census of Marine Life project MAR-ECO, namely the 2004 G.O. Sars cruise, has generated one of the largest open ocean deep-pelagic sample collections ever obtained. With the overall goal of understanding carbon flow processes within and through the deep-pelagic nekton associated with the northern Mid-Atlantic Ridge system (N MAR), quantitative trophic analyses were conducted in order to identify the major intraspecific patterns in diet of characteristic members of the midwater fish community. Diets of five abundant species of zooplanktivorous fishes were examined in detail in terms of prey taxonomy and variability in space, ontogeny and diel cycle. Two major patterns of feeding were identified. Pattern 1 included three species preying primarily on copepods, Argyropelecus hemigymnus, Maurolicus muelleri and Vinciguerria attenuata, the former two of which revealed spatial differences in diet with latitude, mostly likely related to latitudinal prey distributions and densities. Maurolicus demonstrated ecological differences in diet that mirrored phenotypic variation North and South of the Subpolar Front, an “oceanic species concept” question that warrants further research. Pattern 2 included two species feeding primarily on amphipods, Argyropelecus aculeatus and Sternoptyx diaphana, both of which showed ontogenetic variability in feeding primarily related to specific amphipod taxon sizes, rather than prey switching to other major prey taxa. This is the first study that highlights the importance of amphipods in the diets of these species. All fish species showed selectivity in prey choice, possibly related to competition with the other major nekton components along the N MAR, namely the Myctophidae and other zooplanktivorous Stomiiformes. Daily ration fell within the expected values for midwater fishes (1–4% of body weight) with the exception of S. diaphana, suggesting that this species is unique among the zooplanktivores – either its ration is three times higher than the other species, or it eats one-third as often (i.e., every 3 days). Given the high percent stomach fullness observed throughout the diel cycle, we believe the former to be the case, which is the first estimate of its kind for a midwater fish. In order to facilitate further quantitative research on mesopelagic carbon cycling, detailed prey length/weight regressions are presented here.

□ Sternoptyx diaphana Hermann, 1781 – Diaphanous hatchetfish; ①②, Pai-velho ②③, Published as part of Carneiro, Miguel, Martins, Rogélia, Landi, Monica & Costa, Filipe O., 2014, Updated checklist of marine fishes (Chordata: Craniata) from Portugal and the proposed extension of the Portuguese continental shelf, pp. 1-73 in European Journal of Taxonomy 73 on page 24, DOI: 10.5852/ejt.2014.73, http://zenodo.org/record/3866515

Encounter models were used to simulate the mate location problem in the deep-sea hatchetfish Sternoptyx diaphana and other sparsely distributed meso- and bathypelagic fishes. For S. diaphana the local density of adult males varies considerably with time, depth and geographic location. It is the local density of males and their relative movement that are critical to female reproductive success. Over the range of male densities and mean swimming speeds expected in nature, encounter probabilities between adult males and females are exponentially related to the distance at which a mate is recognized (the perception distance). At the slow swim speeds and sparse population densities considered here, there are strong non-linearities in the relationship of male-female encounter probability to perception distance. In these threshold regions, small changes in perception distance result in relatively larger changes in encounter frequencies. At perception distances of less than 2 m, mean mate location times for females of S. diaphana are predicted by the model to be on the order of days and weeks and considerably longer for more sparsely distributed populations. Perception distances of from 4 to over 10 m are indicated in order to ensure mate location in S. diaphana within a day. Much longer perception distances are required for similar performance for the other populations considered. For sparsely distributed species like S. diaphana , low encounter frequencies can place limitations on net reproduction independent of the per capita resource base. Mechanisms that increase perception distances (e.g., olfaction) in deep sea fishes should be particularly effective in enhancing mate location. Bioluminescence may serve that purpose in S. diaphana. Irrespective of sensory modalities, at least one sex must maintain significant mean swim speed for considerable lengths of time to effect reproduction. The simulations also reveal the importance of scale and non-linearities in determining encounter frequencies among marine organisms. Encounter dynamics are in turn critical to various transfer functions and rates in oceanic ecosystems such as reproduction and predation.

Sternoptyx diaphana Hermann 1781 (Fig. 2 F; Table 3) Material examined. 32 specimens (15.7���49.1 mm SL): MNRJ 30124, 3(21.6 ���34.0 mm), D-0382; MNRJ 30129, 1(30.4 mm), D-0502; MNRJ 30130, 1(27.1 mm), D-0503; MNRJ 30133, 9(26.1���39.2 mm), D-0505; MNRJ 30134, 2(16.7���49.1 mm), D-0504; MNRJ 30138, 2(38.8���44.6 mm), E-0501; MNRJ 30143, 1(30.3 mm), E-0509; MNRJ uncat., 1 (27.6 mm), E-0519; MNRJ 30149, 1(25.8 mm), E-0522; MNRJ 30156, 1(25.1 mm), E-0535; MNRJ 30158, 1(18.5 mm), E-0537; MNRJ 30161, 1(25.3 mm), E-0538; MNRJ 30164, 1(28.2 mm), E-0548; MNRJ 30166, 1(27.0 mm), E-0552; MNRJ 30352, 1(15.7 mm), AG 2-9; MNRJ 30355, 2(19.5 ��� 37.0 mm), AG 2 - 1; MNRJ 30361, 1(20.8 mm), AG 1 - 1; MNRJ 30367, 1(29.6 mm), AG 2-3; MNRJ 30369, 1(23.5 mm), AG 1-4. Additional material. 5 specimens (20.3���27.8 mm SL): MZUSP 78245, 4(20.3���23.8 mm), REVIZEE Program, mid-water trawl, 31 ��04��� 25 ������S, 49 �� 15 ���05������W, 29.xi. 1999; USU 0 1387, 1(27.8 mm); MD-55, 21�� 24 ���S, 39 �� 56 ���W, 09.v. 1987. Diagnosis. Sternoptyx diaphana can be differentiated from its congeners by the following combination of characters: dorsal-fin rays 8���11, usually less than 11; vertebrae 27 or 29, rarely 28; pectoral fin without pigmentation; dorsal-fin base usually smaller than 90 % of the dorsal-blade base width; body depth much greater than its length; SAN height greater than three times body height; SL smaller than 50 mm. Meristic description. Fin rays: D 8���11; A 12���15; P 1 9���10; P 2 5. Gill rakers: 7���8 (4���5 + 1 + 2���3). Photophores: BR 5; I 5; AB 10; PAN 3; AN 3; SC 4. Distribution. Worldwide in tropical and subtropical waters. In Brazil, it occurs off northeast and southeast regions, between 14 �� and 22 ��S. Also collected from a single station off southern Brazil at 31 ��S (Figueiredo et al. 2002). S. diaphana S. pseudodiaphana S. pseudobscura Standard length SL (mm) 15.7���49.1 34.0��� 46.1 17.2���51.4 Measurements in % SL Pre-dorsal length 64.4���74.1 67.8���70.7 65.2���80.3 Pre-anal length 54.4���73.1 63.3���66.4 58.7���73.5 Pre-pelvic length 53.5���70.4 61.3���65.2 55.7���71.2 Pre-pectoral length 30.2���42.9 39.2���40.9 31.1���46.4 Body depth 77.5 ��� 77.5 73.5���88.5 77.5���94.1 Caudal peduncle depth 10.7���47.6 11.6���11.7 10.3���13.2 Caudal peduncle length 21.3���35.7 ��� 12.8���26.2 Trunk depth 41.3���52.3 37.7���39.4 34.9���47.3 Trunk length 31.6���42.1 39.1���39.5 14.9���28.6 SAN height 10.7���16.9 14.9���16.1 15.6���22.9 SAN depth 31.9���41.9 25.2���26.5 32.7���38.4 Dorsal fin base 12.9���19.4 17.2 ���19.0 11.3 ���19.0 Anal fin base 48.0��� 58.4 50.8���58.9 43.9���56.3 Pectoral fin length 29.2���38.3 29.8���33.3 27.6���33.5 Head length 25.5���35.2 28.4���30.9 26.1���32.8 continued next page, Published as part of Lima, Adriano T., Costa, Paulo A. S., Braga, Adriana C., Nunan, Gustavo W. A. & Mincarone, Michael M., 2011, Fishes of the family Sternoptychidae (Stomiiformes) collected on the Brazilian continental slope between 11 �� and 23 �� S, pp. 34-48 in Zootaxa 2742 on page 42, DOI: 10.5281/zenodo.206673, {"references":["Figueiredo, J. L., Santos, A. P., Yamaguti, N., Bernardes, R. A. & Rossi-Wongtschowski, C. L. D. B. (2002) Peixes da Zona Economica Exclusiva da regiao sudeste-sul do Brasil: levantamento com rede de meia-agua. Editora da Universidade de Sao Paulo, Sao Paulo, 242 pp."]}

Recent pelagic and benthic trawling activities over the Brazilian continental slope between 11° and 23°S captured nine species representing five genera of the stomiiform family Sternoptychidae. Among these, three species are new records for Brazilian waters: Sternoptyx pseudodiaphana, Argyripnus atlanticus, and Polyipnus sp. The known distributions of Argyropelecus aculeatus and Maurolicus stehmanni along the Brazilian coast are extended northward to 13°S and 16°S, respectively, while that of Sternoptyx diaphana is extended southward to 13°S. Argyropelecus hemigymnus, Argyropelecus sladeni, and Sternoptyx pseudobscura were rarely caught (n=2–16). A key to the western South Atlantic species of Sternoptychidae is provided.

Sternoptyx diaphana Hermann is a non-migrating hatchetfish inhabiting the mesopelagic zone between 300 and 1500 m in temperate to tropical oceanic regions. An analysis is presented of the diet of this species, collected from 5 oceanic faunal provinces—the Pacific Subantarctic, and 4 subregions of the North Atlantic Ocean. Stomach analyses of 20 to 40 mm specimens revealed considerable intra-trawl (fish to fish), intraregional (Station to station), and inter-regional variation in size and composition of the diet. Generic composition of stomach contents differed noticeably from region to region, with the highest degree of faunal affinity being only 38%. The dominant food items both in terms of biomass and abundance also varied inter-regionally, with fish, euphausiids, or decapods predominant by weight; and euphaussids, copepods, or amphipods most prevalent by number. Differences in size distribution of food items from region to region were also noted. S. diaphana from regions of cooler overlying water masses fed on fewer but larger prey items, and diet was less diverse than that of fish from warmer waters. The diet consists primarily of omnivorous and carnivorous prey, and there is evidence that larger specimens feed on larger food items. The broad size-distribution and taxonomic spectrum of the prey, features of functional morphology, and low density as inferred from trawl catches, indicate that S. diaphana is a predator of limited pursuit capability. Feeding strategy appears to involve capture of the nearest “available” prey within its immediate vicinity.

INTRODUCTIONThe retinae of deep sea fishes have been studied by optical microscopy by several authors. Brauer's (1908) work is the most important early account, and the major recent work is that of Munk (1966a). In this monograph he reviews previous papers including that of Contino (1939), Franz (1907), Hanyu & Ali (1962), Verrier (1931), Vilter (1953, 1954a,b) and Wunder (1958), and also describes the eyes of a number of species himself. Since then Munk (1966band 1968) has described other species by optical microscopy. Locket (1969, 1970) has used electron microscopic methods of fixation to study two species by optical and electron microscopy. These two fishes,Poromitra nigrofulvusandSternoptyx diaphana, are not closely related and have different retinal structures.Poromitrahas banks of rods in its retina, a condition first described by Vilter (1953) inBathylagus;Sternoptyxhas a single layer of long rods, a condition also found in the present species. The earlier authors worked on material collected during research expeditions and preserved in alcohol or formalin. During the 1966 biological cruise of R.R.S. ‘Discovery’ Locket was able to fix eyes from deep-sea fish with a view to electron microscopy. Though the fixation is not perfect, it does preserve much ultrastructural detail and interspecies variation in retinal structure can be studied in this material.

The retina of Sternoptyx diaphana has been studied by optical and electron microscopy. There is a single layer of long slender rods, whose outer segments are in contact with the pigment epithelium. The inner segments contain abundant mitochondria but have no oil droplet, paraboloid nor myoid region. The outer nuclear layer contains only visual cell nuclei. The sessile synapses are of simple type. A single layer of stellate horizontal cells is present. There are small populations of bipolar and amacrine cells, separated by a lamellar system of radial fibre origin. There are two populations of nuclei in the ganglion cell layer, and a separate nerve fibre layer. The findings are illustrated and discussed.

39. Sternoptyx diaphana, Hermann. Sternoptyx diaphana, Hermann, Naturforscher, XVI. p. 781, p. 8, Taf. I. figs. 1 and 2; XVII. p. 249 ("Copied by Walbaum, Artcdi, III., Vol. I. figs. 1 and 2, and by Schneider,p. 494, PI. XXXV."). Cuvier, Regne Animal, 2d ed., PI. XIII. fig. 1. Cuvier & Valenciennes, Hist. Nat. Poiss., XXII. p. 415. G��nther, Cat. Fish. Brit. Mus., V. p. 387 (no specimens). Specimens were caught at the stations mentioned below., Published as part of Goode, G. B. & Bean, T. H., 1883, Reports on the results of dredging under the supervision of Alexander Agassiz, on the east coast of the United States, during the summer of 1880, by the U. S. coast survey steamer " Blake, " Commander J. R. Bartlett, U. S. N., commanding., pp. 183-226 in Bulletin of the Museum of Comparative Zoology at Harvard College 10 (5) on page 220, DOI: 10.5281/zenodo.28095

A single specimen of the hatchetfish Sternoptyx diaphana Hermann was caught at the surface on the southeast part of the Grand Bank. The most northerly records for the North Atlantic are from locations east of the Grand Bank in the Gulf Stream.