Barreleye – Howling Pixel


Barreleyes, also known as spook fish (a name also applied to several species of chimaera), are small deep-sea argentiniform fish comprising the family Opisthoproctidae found in tropical-to-temperate waters of the Atlantic, Pacific, and Indian Oceans.[2][3][4]

These fish are named because of their barrel-shaped, tubular eyes, which are generally directed upwards to detect the silhouettes of available prey; however, the fish are capable of directing their eyes forward, as well. The family name Opisthoproctidae is derived from the Greek words opisthe (“behind”) and proktos (“anus“).

Winteria telescopa

The eyes of

Winteria telescopa

differ slightly from those of other opisthoproctids by their more forward-pointing gaze.


The morphology of the Opisthoproctidae varies between three main forms: the stout, deep-bodied barreleyes of the genera Opisthoproctus and Macropinna, the extremely slender and elongated spookfishes of the genera Dolichopteryx and Bathylychnops, and the intermediate fusiform spookfishes of the genera Rhynchohyalus and Winteria.

All species have large, telescoping eyes, which dominate and protrude from the head, but are enclosed within a large transparent dome of soft tissue.[5] These eyes generally gaze upwards, but can also be directed forwards.[6] The opisthoproctid eye has a large lens and a retina with an exceptionally high complement of rod cells and a high density of rhodopsin (the “visual purple” pigment); no cone cells are present. To better serve their vision, barreleyes have large, dome-shaped, transparent heads; this presumably allows the eyes to collect even more incident light and likely protects the sensitive eyes from the nematocysts (stinging cells) of the siphonophores, from which the barreleye is believed to steal food. It may also serve as an accessory lens (modulated by intrinsic or peripheral muscles), or refract light with an index very close to seawater. Dolichopteryx longipes is the only vertebrate known to use a mirror (as well as a lens) in its eyes for focusing images.[7]

The toothless mouth is small and terminal, ending in a pointed snout. As in related families (e.g. Argentinidae), an epibranchial or crumenal organ is present behind the fourth gill arch. This organ—analogous to the gizzard—consists of a small diverticulum wherein the gill rakers insert and interdigitate for the purpose of grinding up ingested material. The living body of most species is a dark brown, covered in large, silvery imbricate scales, but these are absent in Dolichopteryx, leaving the body itself a transparent white. In all species, a variable number of dark melanophores colour the muzzle, ventral surface, and midline.

Also present in Dolichopteryx, Opisthoproctus, and Winteria species are a number of luminous organs; Dolichopteryx has several along the length of its belly, and Opisthoproctus has a single organ in the form of a rectal pouch. These organs glow with a weak light due to the presence of symbiotic bioluminescent bacteria, specifically, Photobacterium phosphoreum (family Vibrionaceae). The ventral surfaces of Opisthoproctus species are characterised by a flattened and projecting ‘sole’; in the mirrorbelly (Opisthoproctus grimaldii) and Opisthoproctus soleatus, this sole may act as a reflector, by directing the emitted light downwards. The strains of P. phosphoreum present in the two Opisthoproctus species have been isolated and cultured in the lab. Through restriction fragment length polymorphism analysis, the two strains have been shown to differ only slightly.[8][9]

In all species, the fins are spineless and fairly small; in Dolichopteryx however, the pectoral fins are greatly elongated and wing-like, extending about half the body’s length, and are apparently used for stationkeeping in the water column. The pectoral fins are inserted low on the body, and in some species, the pelvic fins are inserted ventrolaterally rather than strictly ventrally. Several species also possess either a ventral or dorsal adipose fin, and the caudal fin is forked to emarginated. The anal fin is either present or greatly reduced, and may not be externally visible; it is strongly retrorse in Opisthoproctus. A single dorsal fin originates slightly before or directly over the anal fin. A perceptible hump in the back begins just behind the head. The gas bladder is absent in most species, and the lateral line is uninterrupted. The branchiostegal rays (bony rays supporting the gill membranes behind the lower jaw) number two to four. The javelin spookfish (Bathylychnops exilis) is by far the largest species at 50 centimetres (20 in) standard length; most other species are under 20 centimetres (7.9 in).


Opisthoproctus grimaldii

Barreleyes inhabit moderate depths, from the mesopelagic to bathypelagic zone, circa 400–2,500 m deep. They are presumably solitary and do not undergo diel vertical migrations; instead, barreleyes remain just below the limit of light penetration and use their sensitive, upward-pointing tubular eyes—adapted for enhanced binocular vision at the expense of lateral vision—to survey the waters above. The high number of rods in their eyes’ retinae allows barreleyes to resolve the silhouettes of objects overhead in the faintest of ambient light (and to accurately distinguish bioluminescent light from ambient light), and their binocular vision allows the fish to accurately track and home in on small zooplankton such as hydroids, copepods, and other pelagic crustaceans. The distribution of some species coincides with the isohaline and isotherm layers of the ocean; for example, in Opisthoproctus soleatus, upper distribution limits coincide with the 400-m isotherm for 8 °C (46 °F).

What little is known of barreleye reproduction indicates they are pelagic spawners; that is, eggs and sperm are released en masse directly into the water. The fertilized eggs are buoyant and planktonic; the larvae and juveniles drift with the currents—likely at much shallower depths than the adults—and upon metamorphosis into adult form, they descend to deeper waters. Dolichopteryx species are noted for their paedomorphic features, the result of neoteny (the retention of larval characteristics).

The bioluminescent organs of Dolichopteryx and Opisthoproctus, together with the reflective soles of the latter, may serve as camouflage in the form of counterillumination. This predator avoidance strategy involves the use of ventral light to break up the fishes’ silhouettes, so that (when viewed from below) they blend in with the ambient light from above. Counterillumination is also seen in several other unrelated deep-sea families, which include the marine hatchetfish (Sternoptychidae). Also found in marine hatchetfish and other unrelated families are tubular eyes, such as telescopefish and tube-eye.


  1. ^ Poulsen, J.Y., Sado, T., Hahn, C., Byrkjedal, I., Moku, M. & Miya, M. (2016): Preservation Obscures Pelagic Deep-Sea Fish Diversity: Doubling the Number of Sole-Bearing Opisthoproctids and Resurrection of the Genus Monacoa (Opisthoproctidae, Argentiniformes). PLoS ONE, 11 (8): e0159762.
  2. ^ Froese, Rainer, and Daniel Pauly, eds. (2012). “Opisthoproctidae” in FishBase. February 2012 version.
  3. ^ A. G. V. Salvanes and J. B. Kristofersen (2001). “Mesopelagic fishes” (PDF). Encyclopedia of ocean sciences, Vol. 3.
  4. ^ Peter B. Moyle and Joseph J. Cech, Jr (2004). Fishes: An introduction to ichthyology. Prentice-Hall, Inc; Upper Saddle River, NJ. p. 320. ISBN 978-0-13-100847-2.
  5. ^ Weird Fish With Transparent Head National Geographic News. February 26, 2009 Photograph courtesy Monterey Bay Aquarium Research Institute
  6. ^ “Fish with transparent head”. Boing Boing.
  7. ^ Griggs, J. (2008-12-24). “First vertebrate eye to use mirror instead of lens”. New Scientist. Archived from the original on 26 December 2008. Retrieved 2008-12-27.
  8. ^ Connie J. Wolfe and Margo G. Haygood (August 1991). “Restriction Fragment Length Polymorphism Analysis Reveals High Levels of Genetic Divergence Among the Light Organ Symbionts of Flashlight Fish” (PDF). The Biological Bulletin. 181 (1): 135–143. doi:10.2307/1542496. JSTOR 1542496. PMID 29303659.
  9. ^ Peter J. Herring (2000). “Bioluminescent signals and the role of reflectors” (abstract). Journal of Optics A: Pure and Applied Optics. 2 (6): R29–R38. doi:10.1088/1464-4258/2/6/202.

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Bathylychnops exilis

Bathylychnops exilis, the Javelin spookfish, is a species of barreleye found in the northern Pacific and in the eastern Atlantic Ocean near the Azores where it is found at depths of around 640 metres (2,100 ft). This species grows to a length of 50 centimetres (20 in) SL.The species is notable for unusual protuberances that grow from its eyes, which each have “a well developed lens” and a retina, and which have led to the species being called a “four-eyed” fish. It has been suggested that the purpose of these extra eyes is detection of threats from below, since these eyes point downwards.

Brownsnout spookfish

The brownsnout spookfish (Dolichopteryx longipes) is a species of barreleye in the family Opisthoproctidae. It and the glasshead barreleye fish are the only vertebrates known to employ a mirror, in addition to a lens, to focus an image in its eyes. This species probably has a worldwide tropical and temperate distribution; in the Atlantic Ocean it is known from Bermuda, the Bahamas, the Greater Antilles, and the Gulf of Mexico, and in the Pacific Ocean it is known from the California Current region and the South China Sea. It is found in the mesopelagic and bathypelagic zones at a depth of 500–2,400 meters (1,600–7,900 ft), but usually occurs below 1,000 meters (3,280 feet 10 inches). In the Gulf of Mexico it is found shallower, at 310–460 meters (1,020–1,510 ft).

Deep sea fish

Deep-sea fish are fish that live in the darkness below the sunlit surface waters, that is below the epipelagic or photic zone of the sea. The lanternfish is, by far, the most common deep-sea fish. Other deep sea fishes include the flashlight fish, cookiecutter shark, bristlemouths, anglerfish, viperfish, and some species of eelpout.

Only about 2% of known marine species inhabit the pelagic environment. This means that they live in the water column as opposed to the benthic organisms that live in or on the sea floor. Deep-sea organisms generally inhabit bathypelagic (1000–4000m deep) and abyssopelagic (4000–6000m deep) zones. However, characteristics of deep-sea organisms, such as bioluminescence can be seen in the mesopelagic (200–1000m deep) zone as well. The mesopelagic zone is the disphotic zone, meaning light there is minimal but still measurable. The oxygen minimum layer exists somewhere between a depth of 700m and 1000m deep depending on the place in the ocean. This area is also where nutrients are most abundant. The bathypelagic and abyssopelagic zones are aphotic, meaning that no light penetrates this area of the ocean. These zones make up about 75% of the inhabitable ocean space.The epipelagic zone (0–200m) is the area where light penetrates the water and photosynthesis occurs. This is also known as the photic zone. Because this typically extends only a few hundred meters below the water, the deep sea, about 90% of the ocean volume, is in darkness. The deep sea is also an extremely hostile environment, with temperatures that rarely exceed 3 °C (37.4 °F) and fall as low as −1.8 °C (28.76 °F) (with the exception of hydrothermal vent ecosystems that can exceed 350 °C, or 662 °F), low oxygen levels, and pressures between 20 and 1,000 atmospheres (between 2 and 100 megapascals).

Diversity of fish

Fish are very diverse animals and can be categorised in many ways. This article is an overview of some of ways in which fish are categorised. Although most fish species have probably been discovered and described, about 250 new ones are still discovered every year. According to FishBase, 33,100 species of fish had been described by April 2015. That is more than the combined total of all other vertebrate species: mammals, amphibians, reptiles and birds.

Fish species diversity is roughly divided equally between marine (oceanic) and freshwater ecosystems. Coral reefs in the Indo-Pacific constitute the centre of diversity for marine fishes, whereas continental freshwater fishes are most diverse in large river basins of tropical rainforests, especially the Amazon, Congo, and Mekong basins. More than 5,600 fish species inhabit Neotropical freshwaters alone, such that Neotropical fishes represent about 10% of all vertebrate species on the Earth. Exceptionally rich sites in the Amazon basin, such as Cantão State Park, can contain more freshwater fish species than occur in all of Europe.

Dolichopteroides binocularis

Dolichopteroides binocularis is a species of barreleye found in oceanic waters at depths of from 960 to 1,200 metres (3,150 to 3,940 ft). This species grows to a length of 24.2 centimetres (9.5 in) SL. It was placed in its own genus Dolichopteroides in 2009.

Ioichthys kashkini

Ioichthys kashkini is a species of barreleye known only from the Arabian Sea where it has been recovered from a depth of 700 metres (2,300 ft).

Life That Glows

Life That Glows is a 2016 British nature documentary programme made for BBC Television, first shown in the UK on BBC Two on 9 May 2016. The programme is presented and narrated by Sir David Attenborough.

Life That Glows films the biology and ecology of bioluminescent organisms, that is, capable of creating light. The programme features fireflies, who use light as a means of sexual attraction, luminous fungi, luminous marine bacteria responsible for the Milky seas effect, the flashlight fish, the aposematism of the Sierra luminous millipede, earthworms, the bioluminescent tides created by blooms of dinoflagellates in Tasmania, as well as dolphins swimming in the bloom in the Sea of Cortez, the defensive flashes of brittle stars and ostracods, sexual attraction in ostracods, prey attraction by luminous click beetles in Cerrado,Brazil and the Arachnocampa gnats in New Zealand.

The programme then introduces many luminous deep sea animals, including the vampire squid, the polychaete worm Tomopteris that generates yellow light, the jellyfish Atolla, the comb jelly Beroe, the viper fish, pyrosomes, a dragonfish, and the polychaete worm Flota. Then, the programme discusses specialised adaptations in the eyes of particular animals to see bioluminescence, such as the barreleye fish and the cock-eyed squid. Lastly, they feature the mass spawning event of the firefly squid in Japan.

List of fish common names

This is a list of common fish names. While some common names refer to a single species or family, others have been used for a confusing variety of types; the articles listed here should explain the possibilities if the name is ambiguous.

Macropinna microstoma

Macropinna microstoma is the only species of fish in the genus Macropinna, belonging to the Opisthoproctidae, the barreleye family. It is recognized for a highly unusual transparent, fluid-filled dome on its head, through which the lenses of its eyes can be seen. The eyes have a barrel shape and can be rotated to point either forward or straight up, looking through the fish’s transparent dome. M. microstoma has a tiny mouth and most of its body is covered with large scales. The fish normally hangs nearly motionless in the water, at a depth of about 600 metres (2,000 ft) to 800 metres (2,600 ft), using its large fins for stability and with its eyes directed upward. In the low light conditions it is assumed the fish detects prey by its silhouette. MBARI researchers Bruce Robison and Kim Reisenbichler observed that when prey such as small fish and jellyfish are spotted, the eyes rotate like binoculars, facing forward as it turns its body from a horizontal to a vertical position to feed. Robison speculates that M. microstoma steals food from siphonophores.M. microstoma has been known to science since 1939, but is not known to have been photographed alive until 2004. Old drawings do not show the transparent dome, as it is usually destroyed when brought up from the depths.

Monterey Bay Aquarium Research Institute

The Monterey Bay Aquarium Research Institute (MBARI) is a private, non-profit oceanographic research center in Moss Landing, California. MBARI was founded in 1987 by David Packard, and is primarily funded by the David and Lucile Packard Foundation. Christopher Scholin serves as the institute’s president and chief executive officer, managing a work force of approximately 220 scientists, engineers, and operations and administrative staff.

At MBARI, scientists and engineers work together to develop new tools and methods for studying the ocean. Long-term funding from the David and Lucile Packard Foundation allows the institute to take on studies that traditional granting institutions may be reluctant to sponsor. Part of David Packard’s charge for MBARI was to “Take risks. Ask big questions. Don’t be afraid to make mistakes; if you don’t make mistakes, you’re not reaching far enough.”

MBARI’s campus in Moss Landing is located near the center of Monterey Bay, at the head of the Monterey Canyon. Monterey Bay is one of the most biologically diverse bodies of waters in the world, and the underlying submarine canyon is one of the deepest underwater canyons along the continental United States. With this 4,000-meter-deep submarine canyon only a few ship-hours from their base of operations, institute scientists enjoy an advantageous proximity to this natural, deep-sea “laboratory”.

MBARI is not open to the general public, but it has an open house once a year. Although MBARI is a sister institution to the Monterey Bay Aquarium, the two organizations have entirely separate management and funding.


The OpenBMC project is a Linux Foundation collaborative open-source project whose goal is to produce an open source implementation of the Baseboard Management Controllers (BMC) Firmware Stack. OpenBMC is a Linux distribution for BMCs meant to work across heterogeneous systems that include enterprise, high-performance computing (HPC), telecommunications, and cloud-scale data centers.


POWER8 is a family of superscalar symmetric multiprocessors based on the Power ISA, announced in August 2013 at the Hot Chips conference. The designs are available for licensing under the OpenPOWER Foundation, which is the first time for such availability of IBM’s highest-end processors.Systems based on POWER8 became available from IBM in June 2014. Systems and POWER8 processor designs made by other OpenPOWER members was available in early 2015.


POWER9 is a family of superscalar, multithreading, symmetric multiprocessors based on the Power ISA announced in August 2016 at the Hot Chips conference.

The POWER9-based processors are being manufactured using a 14 nm FinFET process, in 12- and 24-core versions, for scale out and scale up applications, and possibly other variations, since the POWER9 architecture is open for licensing and modification by the OpenPOWER Foundation members.The current fastest supercomputer in the world, Summit, is based on POWER9, while also using Nvidia’s Volta GPUs as accelerators.

Pelagic fish

Pelagic fish live in the pelagic zone of ocean or lake waters – being neither close to the bottom nor near the shore – in contrast with demersal fish, which do live on or near the bottom, and reef fish, which are associated with coral reefs.The marine pelagic environment is the largest aquatic habitat on Earth, occupying 1,370 million cubic kilometres (330 million cubic miles), and is the habitat for 11% of known fish species. The oceans have a mean depth of 4000 metres. About 98% of the total water volume is below 100 metres (330 ft), and 75% is below 1,000 metres (3,300 ft).Marine pelagic fish can be divided into pelagic coastal fish and oceanic pelagic fish. Coastal fish inhabit the relatively shallow and sunlit waters above the continental shelf, while oceanic fish (which may well also swim inshore) inhabit the vast and deep waters beyond the continental shelf.Pelagic fish range in size from small coastal forage fish, such as herrings and sardines, to large apex predator oceanic fishes, such as bluefin tuna and oceanic sharks. They are usually agile swimmers with streamlined bodies, capable of sustained cruising on long-distance migrations. Many pelagic fish swim in schools weighing hundreds of tonnes. Others are solitary, like the large ocean sunfish weighing over 500 kilograms, which sometimes drift passively with ocean currents, eating jellyfish.

Rhynchohyalus natalensis

Rhynchohyalus natalensis, the glasshead barreleye, is a species of barreleye found in oceans around the world at depths from 247 to 549 metres (810 to 1,801 ft). This species grows to a length of 16 centimetres (6.3 in) SL. It and the brownsnout spookfish are the only vertebrates known to employ mirrors, in addition to lenses, to focus the images in its eyes.


Spookfish may refer to:

Barreleye, a family of fish

Brownsnout spookfish Dolichopteryx longipes, a fish species that uses mirrors in its eyes, the only known animal to have this function.

Javelin spookfish Bathylychnops exilis

several species of Chimaera

Vision in fishes

Vision is an important sensory system for most species of fish. Fish eyes are similar to the eyes of terrestrial vertebrates like birds and mammals, but have a more spherical lens. Birds and mammals (including humans) normally adjust focus by changing the shape of their lens, but fish normally adjust focus by moving the lens closer to or further from the retina. Fish retinas generally have both rod cells and cone cells (for scotopic and photopic vision), and most species have colour vision. Some fish can see ultraviolet and some are sensitive to polarized light.

Among jawless fishes, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. The ancestors of modern hagfish, thought to be the protovertebrate were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. Fish vision shows evolutionary adaptation to their visual environment, for example deep sea fish have eyes suited to the dark environment.


Winteria may refer to:

Winteria, a synonym of the genus Cleistocactus of cactuses.

Winteria, a genus of barreleye fishes containing only the species Winteria telescopa.

Winteria telescopa

Winteria telescopa, the binocular fish, is a species of barreleye found in oceans around the world at depths from 400 to 2,500 metres (1,300 to 8,200 ft). This species grows to a length of 15 centimetres (5.9 in) SL.

This fish was featured in the documentary series The Blue Planet.


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