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Argyropelecus hemigymnus Cocco, 1829. Spurred Hatchetfish. To 4.9 cm (1.9 in) TL or more (Mecklenburg et al. 2018). Circumglobal; western Pacific Ocean north to Japan (Aizawa in Nakabo 2002) and Russian northwestern Pacific (Orlov and Tokranov 2019); Washington (Matarese et al. 1989) to Chile (Baird 1971). Depth: 50���3,065 m (164���10,053 ft) (min.: Mecklenburg et al. 2018; max.: Porteiro et al. 2017)., 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 56, DOI: 10.11646/zootaxa.5053.1.1, http://zenodo.org/record/5578008, {"references":["Mecklenburg, C. W., Lynghammar, A., Johannesen, E., Byrkjedal, I., Christiansen, J. S., Dolgov, A. V., Karamushko, O. V., Mecklenburg, T. A., Moller, P. R., Steinke, D. & Wienerrolther, R. M. (2018) Marine Fishes of the Arctic Region. Conservation of Arctic Flora and Fauna, Akureyrl.","Nakabo, T. (Ed.). (2002) Fishes of Japan with Pictorial Keys to the Species. Tokai University Press, Tokyo.","Orlov, A. M. & Tokranov, A. M. (2019) Checklist of deep-sea fishes of the Russian northwestern Pacific Ocean found at depths below 1000 m. Progress in Oceanography, 176, https: // doi. org / 10.1016 / j. pocean. 2019.102143","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.","Baird, R. C. (1971) The systematics, distribution, and zoogeography of the marine hatchetfishes (family Sternoptychidae). Bulletin of the Museum of Comparative Zoology, 142, 1 - 128.","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."]}

The recent paper by Artüz & Fricke (2019) is focused on the analysis of marine teleost fishes of the Sea of Marmara, where they have tried to correct doubtful species occurrences and presented an annotated checklist. In a few cases, the authors have provided convincing data for the removal of some species from the regional inventory, such as Apogon imberbis (Linnaeus, 1758), Scomberesox saurus (Walbaum, 1792) and Polyprion americanus (Bloch & Schneider, 1801), and pointed out revision-seeking genera (i.e. Alosa spp., Pegusa spp., etc.), which should certainly be taken into consideration. However, the paper also raises several doubts resulting from mistranslations of some previous research, misinterpretation and incomplete examination of certain published biodiversity data related to the Sea of Marmara. Despite the authors presented a number of mistaken first record data (for example Sardinella aurita Valenciennes, 1837, for full account see Bilecenoglu et al. 2002), included some unsubstantiated/questionable species (such as Symphodus melops (Linnaeus, 1758), Gobius vittatus Vinciguerra, 1883, etc.), and unexpectedly neglected the occurrence of some common coastal and deepsea species from the area, such as Arnoglossus kessleri Schmidt, 1915, Gobius bucchichi Steindachner, 1870, Labrus merula Linnaeus, 1758, Parablennius zvonimiri (Kolombatović, 1892) and Argyropelecus hemigymnus Cocco, 1829, I herein concentrate solely on the erroneous/invalid records (totaling 42 fish species) with appropriate explanations.

The presence of nitric oxide synthase (NOS) and nerve fibres in the photophores of seven bioluminescent fish species (Hygophum benoiti, Myctophum punctatum, Electrona risso, Cyclothone braueri, Vinciguerria attenuata, Maurolicus muelleri and Porichthys notatus) with endogenous photocytes, were investigated. Antibodies directed against neuronal and inducible NOS (n and iNOS respectively) and NADPH-diaphorase activity were used to reveal the locations of NOS, while antibodies directed against acetylated tubulin were used to visualize nerve fibres. The nNOS antibody labelled structures in all investigated photophores except in the organs from P. notatus. The photocytes of P. notatus showed NADPH-diaph- orase activity. In the myctophid species, NOS-like immunoreactivity was found in small intracellular structures of the photocytes and in nerve fibres reaching the photocytes. nNOS-positive fibres were also found among lens ⁄ filter cells in V. attenuata, and in M. muelleri the cytoplasm of lens ⁄ filter cells contained NOS- like material. In C. braueri, a cell type located at a collecting chamber for lumi- nous products in the photophore contained NOS-like material. All photophores received an innervation reaching the photocytes, as well as other components including lens ⁄ filter areas. The results of this study comply with an involvement of nitric oxide in the control of bioluminescence in several fish species

Argyropelecus hemigymnus Cocco, 1829 Argyropelecus hemigymnus Cocco, 1829: 146. Type locality: Messina, Sicily, Italy. Argyropelecus hemigymnus, Galil & Goren, 1994: 49; Goren & Galil, 1997: 201, 2002: 151. Distribution. Circumglobal; depth range 0���2400 m., Published as part of Goren, Menachem & Galil, Bella S., 2015, A checklist of the deep sea fishes of the Levant Sea, Mediterranean Sea, pp. 507-530 in Zootaxa 3994 (4) on page 520, DOI: 10.11646/zootaxa.3994.4.2, http://zenodo.org/record/244394, {"references":["Galil, B. S. & Goren, M. (1994) The deep sea Levantine Fauna. New records and rare occurrences. Senckenbergiana Maritima, 25, 41 - 52.","Goren, M. & Galil, B. S. (1997) New records of deep-sea fishes from the Levant Basin and a note on the deep-sea fishes of the Mediterranean. Israel Journal of Zoology, 43, 197 - 203."]}

13 pages, 7 figures, 4 tables The present study analysed the trophic ecology of the early developmental stages of four species of mesopelagic fish, the myctophids Ceratoscopelus maderensis, Hygophum benoiti and Benthosema glaciale and the sternoptychid Argyropelecus hemigymnus. These species display different morphological traits and a segregated vertical distribution throughout the water column. The study was conducted off Mallorca Island (39° N, 3° E) in the western Mediterranean, during the summer stratification period. The results indicated that feeding patterns of myctophid larvae were strictly diurnal, while in A. hemigymnus larvae, day and night feeding occurred. In the transformation stage of C. maderensis, B. glaciale and A. hemigymnus, day and night feeding was evidenced. The feeding incidence during the larval stages was low, increasing in the transformation stages, and being particularly high for A. hemigymnus. Although an increasing tendency in size and number of ingested prey was observed, the trophic niche breadth did not indicate a trophic specialization in any of the species analysed. Gut content analysis determined that diet composition was very similar among the four species, with the different developmental stages of copepods being the dominant prey throughout the early larval development. Nevertheless, in transformation stages of C. maderensis and H. benoiti, other preys, like ostracods, become important contributors to the diet. Despite the important physical and biological structuring of the water column, no differences in feeding success were observed for larvae occurring in the layers of higher biological production This research was funded by project CTM2008-04489-C03

Special issue The wrapping up of the IDEADOS project: International Workshop on Environment, Ecosystems and Demersal Resources, and Fisheries.-- 12 pages, 12 figures, 2 tables, The diel vertical distribution of fish larvae off the Balearic Islands during late autumn and summer was analysed in relation to the environmental conditions. Four fixed sampling stations, located in the outer shelf and slope zones, were sampled during both the day and night by means of oblique hauls at different water depths. In autumn the first 60. m were characterised by vertical mixing and relatively higher fluorescence values, while summer was characterised by strong near-surface stratification and the presence of a Deep Fluorescence Maximum (DFM). The fish larval community was dominated by mesopelagic species, myctophiforms and stomiiforms, with some differences in species composition and their relative contribution between periods. A higher number of species was observed to reproduce in summer. The diel vertical distribution patterns differed among species and, within species, some differences were detected between the day and night. Although their relative depth preferences were similar between surveys, seasonal comparisons for the most abundant species showed that in autumn larvae presented both a shallower distribution during the day and a deeper distribution during the night than in the summer period. The larvae of all species, except for Argyropelecus hemigymnus, were absent from layers below 200. m. In these deeper layers, only A. hemigymnus larvae and juvenile stages of myctophiforms and stomiiforms were found. Another group of species, including Hygophum benoiti, Ceratoscopelus maderensis, Cyclothone braueri and Lampanyctus crocodilus, characterised the surface assemblage, mainly appearing in the first 50. m during the day, while at night their distribution was wider, extending to deeper layers. Benthosema glaciale, Symbolophorus veranyi and Myctophum punctatum were located at intermediate levels (mostly 50-100. m). Larval size stratification was evident for the most abundant species, with younger stages being found at shallower depths in the water column, while postflexion stages presented a wide distribution at night, undergoing vertical displacement to the near-surface layers during the day. The roles of the position of the thermocline, the availability of food and light intensity as factors modulating these differences are discussed. © 2013 Elsevier B.V., This research was funded by project CTM2008-04489-C03

* Argyropelecus hemigymnus Cocco, 1829 – Hatchetfish; Pai-velho ①②③, 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

Coelenterazine, a luciferine, and luciferase activity specific to coelenterazine were detected and assayed in various tissues of mid-water fishes, Argyropelecus hemigymnus, Chauliodus sloani, Myctophum punctatum, Vinciguerria attenuata and Cyclothone braueri. Coelenterazine was found mainly in digestive systems and photophores of these fishes, A large species to species variation was found: extremely high levels of coelenterazine and luciferase were found in the M. punctatum digestive system whereas only a very low level of coelenterazine was detected in C., braueri. Coelenterazine was detected in A. hemigymnus eggs supporting the hypothesis of a maternal transfer of luminous capabilities. Luciferase activity specific to coelenterazine was found in photophores as well as in various other tissues suggesting another (besides light emission) biological function for this enzymatic activity, Distribution of coelenterazine in all tissues of the individuals supports the hypothesis of the dietary acquisition of coelenterazine by these fishes.

Argyropelecus hemigymnus Cocco 1829 (Fig. 2 D; Table 2) Material examined. 5 specimens (20.2 ���29.0 mm SL): MNRJ 30141, 1(20.2 mm), E-0507; MNRJ 30351, 2(25.2 ���29.0 mm), AG 1-7.2; MNRJ 30358, 1(24.1 mm), AG 1-12; MNRJ 30360, 1(28.5 mm), AG 2-9. Additional material. 5 specimens (17.1���27.6 mm SL; REVIZEE Program, mid-water trawl): MZUSP 78223, 4(20.0��� 27.6 mm), 31 ��04��� 25 ������S, 49 �� 15 ���05������W, 29.xi. 1999; MZUSP 80523, 1(17.1 mm), 26 �� 16 ��� 29 ������S, 45 �� 46 ��� 35 ������W, 07.x. 1999. Diagnosis. Argyropelecus hemigymnus can be differentiated from its congeners by the following combination of characters: small size, rarely larger than 38 mm SL; trunk long and narrow; a single well developed post-abdominal spine, directed posteriorly, with both margins serrated. Meristic description. Fin rays: D 8; A 10���11; P 1 10. Gill rakers: 19���21 (7���9 + 1���2 + 10���11). Photophores: BR 6; I 6; AB 12; SAB 6; PAN 4; AN 6; SC 4; SP 2. Distribution. Worldwide in tropical, subtropical, and subpolar waters. This species occurs along the entire Brazilian coast., 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 40, DOI: 10.5281/zenodo.206673

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.

We develop a model for mate location by olfaction and apply it to reproductive behavior in the deep-sea hetchetfish Argyropelecus hemigymnus. The model includes diffusion theory to model the geometry of the region of detectable pheromone around the female, kinetic theory to medel the motion of the males prior to detection of a pheromone field, and a Monte Carlo search routine to estimate the time to locate the female after detection. The model yields results that are consistent with our present understanding of the biology of A. hemigymnus. The success of olfactory communication systems is strongly dependent on diffusion velocity, which is a function of depth in the ocean. The receiving organism must have low detection thresholds and high dynamic sensitivity to changes in odor concentration to use olfaction effectively for long-range detection and location of advertising females. Olfaction appears to be critical to reproductive success and therefore viability for many dispersed and sparse populations livi...

Modifications in oxygen consumption and luminescence of isolated luminescent organs of the mesopelagic fish Argyropelecus hemigymnus following glucose and pyruvate administration were studied before and during light emission triggered by adrenaline. Isolated photophores (mean fresh weight 13.5 ± 0.9 mg) at rest, i.e., in the absence of light emission, in saline (20 °C) exhibit a respiration rate of 1.045 ± 0.082 (SE) nmol O2/min (n = 35). A significant decrease (p = 0.05) in oxygen consumption was observed after the addition of 5.5 mM glucose. Instead of the oxygen decrease usually observed as a result of control stimulations using adrenaline, photophores pretreated with glucose increased their oxygen uptake in response to adrenaline, and maximal light emission was reduced by 85% (p = 0.01). The addition of 5.5 mM pyruvate induced a significant transient increase (p = 0.05) in oxygen uptake of isolated photophores, though this treatment did not statistically modify the mean time course of oxygen consumption and light emission in response to adrenaline. The hypothesis of a hypometabolic state of the isolated photophores of A. hemigymnus during light emission is discussed.

Argyropelecus hemigymnus Cocco, 1829 Aegean Sea: 5000-90 (1 spc.), 24.01.1969, G��kova Bay, 430 m, M. Demir., Published as part of Nurettin Meri��, L��tfiye Eryilmaz & M��fit ��zulug, 2007, A catalogue of the fishes held in the Istanbul University, Science Faculty, Hydrobiology Museum., pp. 29-54 in Zootaxa 1472 on page 37

Argyropelecus hemigymnus Cocco, 1829 Aegean Sea: 5000-90 (1 spc.), 24.01.1969, Gökova Bay, 430 m, M. Demir.

SUMMARYNitric 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.

Osservazioni sulla biologia di Argyropelecus hemigymnus, COCCO (1829) (Osteichthyes, Sternoptychidae) in VII Convegno Associazione Alessandro Ghigi per la biologia e la conservazione dei vertebrati - Bologna, 15 - 16 gennaio 1993. Ed. Istituto Nazionale per la Fauna Selvatica, Ozzano dell'Emilia (BO)

o 1. Isolated photophores of the living bathypelagic fish Argyropelecus hemigymnus respond to a strong (25–80 V) and long (4–15 msec) electrical stimulus by a brief flash emission (F response). 2. Weaker and shorter stimuli are subthreshold, but when repeated at a frequency equal to or higher than one per second, the photophores respond by a slow light emission (S response); it is characterized by a long emission latency time, at least 2 sec duration and by a progressive increase in the rate of light production during the stimulation period. The maximal amplitude of the response is more than 300 times lower than the response of the photophore of the epipelagic luminescent fish Porichthys. 3. A train of strong (35V) and long stimuli (4 msec) applied at high frequency (100/sec) quench temporarily the luminescence of spontaneous luminescent photophores. The inhibitory response is reversible: after the end of stimulation, the light production returns to the level recorded before the stimulation. 4. The inhibitory response to electrical stimulation is tentatively explained either by the presence of an inhibitory nervous system or by the liberation of an excess of adrenalin, the possible natural neuromediator that inhibits luminescence of isolated photophores at high concentration.

Based on analysis of videotape records, species of the genusArgyropelecusare capable of swimming diagonally downwards at considerable speeds without altering their body postures. Morphological evidence strongly suggests that they are able to swim diagonally upwards in a similar way. Their distinctive hatchetlike profile presents a streamlined airfoil in both diagonal and horizontal movements, even though the body is not tilted. Modifications of the caudal musculature probably enable all hatchetfishes (including members of the other two genera,PolyipnusandSternoptyx) to use the tail for propulsion for both diagonal and horizontal movements. The dorsal fin probably aids in diagonally downward movements and the pelvic and anal fins in diagonally upward movements, whilst the pectoral fins serve as stabilizers for these movements, and as an axis of rotation for striking at prey. The seemingly ungainly shape of the hatchetfish is the result of achieving a streamlined, fish-like shape for horizontal and diagonal movements without tilting of the body, presumably in order to maintain an effective camouflage in midwater.

The trophic interactions of species of fish of the continental slopes have not been investigated previously in detail. The present study examines the diets of the clupeoid, stomiatoid and salmonoid species occurring demersally and pelagically in the Rockall Trough to the west of Scotland and Ireland. Pelagic fish were collected between the surface and about 2 500-m depth between 1973 and 1978. Demersal fish were sampled at 250-m intervals of depths between 500- and 2 900-m depth during the years 1975 and 1981. Of the 28 species caught, 18 were strictly pelagic and dominated by the stomiatoids while five were strictly demersal. The remaining five species occurred in both the pelagic and demersal environment. The commonest clupeoid was Alepocephalus bairdii, which is a dominant species within the demersal fish associations at depths of 750 to 1 250m. This species, along with the deeper-living A. agassizi, and 3 other alepocephalid species feed primarily on benthopelagic prey but also exploit the epibenthos. The stomiatoid species, such as Cyclothone microdon, C. braueri, Maurolicus muelleri and Argyropelecus hemigymnus, dominate the associations of pelagic fish in the Trough. They feed on different proportions of ostracods, copepods and amphipods. Of the salmonoids, only Argentina silus and Bathylagus euryops occurred commonly and both feed on benthopelagic fauna, the latter at much greater depths than the former. The principal factor acting to prevent direct competition between species is the modal centres of bathymetric distribution of the species. Other contributing factors are briefly discussed.

1. Isolated photophores from Porichthys, Argyropelecus and Maurolicus consume oxygen at a rate of 0.10 ± 0.01, 0.85 ± 0.11 and 0.89 ± 0.17 nmol min−1 respectively in saline at 20°C. 2. Ouabain 10−4mol l−1 reduces the resting oxygen consumption of isolated photophore of Porichthys by 38% and by 30% for Argyropelecus without inducing luminescence. 3. Photophores of Maurolicus produce light in the presence of ouabain 10−4 mol l−1 without any significant decrease of their oxygen consumption. 4. Luminescence induced by ouabain is not due to a neurotransmitter release from nerve endings of isolated photophores of Maurolicus.

1. 1. Photophores isolated from the ventral region of the bathypelagic fish Argyropelecus hemigymnus respond to epinephrine and norepinephrine by a long-lasting luminescence: the maximal light emission occurring at 10 −6 M for epinephrine and 10 −5 M for norepinephrine, is estimated at 8 × 10 6 quanta/sec per photophore. 2. 2. The LD 50 value of the light response calculated from the dose-response curves to both neuromediators, is 2 × 10 −7 M for epinephrine and 2 × 10 −6 M for norepinephrine. 3. 3. The light response to epinephrine is depressed by propranol and phentolamine 10 −5 M, and the maximum is shifted to concentration higher than 10 −6 M. Phentolamine completely blocks the light evoked by norepinephrine at a concentration lower than 10 −5 M and shifts the light maximum to 10 −3 M. 4. 4. Photophores show a greenish fluorescence when excited with 365 nm u.v. light; the fluorescence intensity, is largely decreased after the light emission.

Quantitative measurements have been made on the ultra-structure and capillary supply to the axial muscles of the mesopelagic hatchet fish Argyropelecus hemigymnus (Cocco, 1829). Fish were collected at Eastern North Atlantic Ocean Station 10244, 32°48′N; 31°15′W during November 1980, from a depth of 480 to 550 m. Mitochondria with densely packed cristae occupy 44.3% of slow-fibre volume. Each myofibril is in direct contact with a mitochondrion. Compared with other fishes studied, the capillary supply to A. hemigymnus slow fibres is poorly developed. The average number of capillaries per fibre is 0.9, such that each μm of capillary contact supplies 0.011 μm2 of fibre cross-sectional area. The capillary surface area (μm2) supplying 1 μm3 of slow-fibre mitochondria is 0.17 in anchovy (Engraulis encrasicolus), 0.14 in rat-fish (Chimaera monstrosa), 0.14 in tench (Tinca tinca), 0.16 in catfish (Clarias mossambica), and only 0.025 for A. hemigymnus. It is suggested that, relative to the former species, some modifications in factors determining tissue oxygenation (e.g. myoglobin concentrations, blood flow, perfusion distribution or haemoglobin) and/or mitochondrial respiration rate are required in order to match oxygen supply and demand to the slow muscle in A. hemigymnus.

Light irradiance was measured at 430, 470 and 500 nm aboard the mesoscaph “Forel” in the Strait of Messina from the surface to 550 m depth in May 1979. The underwater light regime is partly due to the downwelling residual sunlight and partly to bioluminescence. An intense bioluminescence is localized at about 450 m at midday and moves upwards in the evening to reach an area extending from 100 m depth to the surface late in the evening. Two types of luminescence were observed: one associated with luminescent organisms and another diffuse, probably due to bacteria. Three types of luminescent fish were recognized, namely Argyropelecus hemigymnus, myctophids and Cyclothone braueri, and their time and space distribution were studied. While myctophids were encountered from the surface (21:00 hrs) to 550 m depth (16:00 hrs), A. hemigymnus were only observed between 180 m (19:45 hrs) and 500 m (12:15 hrs), and C. braueri between 330 m (16:00 hrs) and 500 m (19:00 hrs). The results do not show a significant relation between the absolute ambient light intensity and the time or the depth where the fish were observed.

The first records of Cyclothone alba, Lampanyctus macdonaldi, and Protomyctophum arcticum from Norwegian waters are reviewed together with some records of the rare Argyropelecus hemigymnus, Argyropelecus olfersi, and Notolepis rissoi. The specimens originate partly from stomach contents of Atlantic salmon, Salmo salar, long-line caught in 1969–72, and partly from pelagic trawl hauls in 1980, off Vesteralen, N. Norway. Environmental conditions of the Norwegian slope mesopelagial are briefly discussed, and it is pointed out that diversity of smaller luminous fishes here may be larger than previously assumed. The presence of ripe Argyropelecus females is suggested to indicate existing spawning populations in these waters.

The relationship between the vertical distributions of euphausiids and fish and light intensity has been studied directly by using a photometer in conjunction with an acoustically controlled rectangular midwater trawl. Samples were taken at a position centered on 47°N; 17°W on 15 and 16 May 1978. Five species of euphausiid and six species of fish have been analysed, both groups contained migrant and non-migrant species. The population of each of these species occurred throughout a light regime spanning at least three orders of magnitude of intensity; none of them was restricted to, or followed, and isolume. There were no sexual or size differences in the distributions of the euphausiids, but the population of Argyropelecus hemigymnus was probably stratified during the day, with smaller individuals occurring shallower than large ones. The results are discussed in relation to previous observations and to the theories of photic regulation of distributions and migrations.

Isolated ventral photophores of Argyropelecus hemigymnus and abdominal photophores of Maurolicus muelleri, respond to adrenaline 10-4M by a light emission which magnitude is proportional to the weight of photophores. The amplitude of the light response is four times as high in Maurolicus with regard to Argyropelecus photophores. According to the counter-lighting hypothesis, this difference suggests that those fishes might live in waters of a different ambiant light level.

40. Argyropelecus hemigymnus, Cocco. Argyropelecus hemigymnus, Cocco, Giorn. Sc. Sic. 1829, fasc. 77, p. 146.Bonaparte, Faun. Ital. Pesc.Cuv. & Val., Ilist. Nat. Poiss., XXII. p. 398. G��nther, Cat. Fish. Brit. Mus., V. p. 385. Sternoptyx hemigymnus, Valenciennes, in Cuvier, Regne Animal, 111. Poiss., PI. 103, fig. 3.? Sternoptyx mediterr��neo., Cocco, Giorni il Faro, 1838, IV. p. 7, fig. 2.Bonaparte, Faun. Ital. Pesc., Fig. This species was obtained at Station 315, at a depth of 225 fathoms. It was also obtained by the steamer " Fish Hawk," August 18, 1882, at Station 1112 (Lat. 39�� 5(3' N., Long. 70�� 35' W., 245 fathoms), and was seen by Dr. Bean on the same vessel in 18S0., 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