barreleye

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Transparent-Headed Fish

First described in 1939, the unusual Pacific barreleye (Macropinna microstoma) is instantly recognisable by the transparent, fluid-filled dome that curves over its head like the cockpit of a fighter jet. The two green spheres within are actually the fish’s tubular eyes, while the dark capsules in front are the fish’s olfactory organs, responsible for smell. The barreleye lives in inky depths of over 600 metres, where sunlight fades to darkness, and its eyes have adapted remarkably. They’re so sensitive that they can detect faint silhouettes of prey passing overhead, and their green pigments are thought to filter out sunlight, allowing the barreleye to focus on its preys’ bioluminescent glow. It’s long been thought that these eyes are fixed, so the fish only has a tunnel-vision view of whatever is above its head, but researchers at the Monterey Bay Aquarium Research Institute have shown that the eyes can rotate around 75 degrees, from a vertical to a horizontal position. Along with its large flat fins, this amazing vision allows the 15 cm fish maneuver precisely and capture prey with its small pointed mouth. Interestingly, the barreleye shares its deep-sea habitat with many kinds of jellies, including the siphonophore, which grows to over 10 metres and trails out thousands of stinging tentacles like drift nets to capture prey. Researchers think that one of the barreleye’s feeding methods is to carefully manoeuvre among the siphonophore’s tentacles to steal its prey, and the transparent dome shields the fish’s eyes from the stinging tentacles.

(Image Credit)

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Barreleye
Macropinna microstoma

February 23, 2009–With a head like a fighter-plane cockpit, a Pacific barreleye fish shows off its highly sensitive, barrel-like eyes–topped by green, orblike lenses–in a picture released today but taken in 2004.  The fish, discovered alive in the deep water off California’s central coast by the Monterey Bay Aquarium Research Institute (MBARI), is the first specimen of its kind to be found with its soft transparent dome intact.   The 6-inch (15-centimeter) barreleye (Macropinna microstoma) had been known since 1939–but only from mangled specimens dragged to the surface by nets. 

Photos © Monterey Bay Aquarium Research Institute

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Barreleye (Opisthoproctidae)

Barreleyes are small deep-sea argentiniform fish comprising the family Opisthoproctidae found in tropical-to-temperate waters of the Atlantic, Pacific, and Indian Oceans. All species have large, telescoping eyes, which dominate and protrude from the head, but are enclosed within a large transparent dome of soft tissue. These eyes generally gaze upwards to detect the silhouettes of available prey, but can also be directed forwards. The toothless mouth is small and terminal, ending in a pointed snout. photo credits: mekarjayabocary, wikipedia

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Yesterday, researchers on the Western Flyer were treated to this rare sighting.

The barreleye (Macropinna microstoma) has only been observed with MBARI ROVs 5 times in 27 years!

Most of the time, the fish hangs motionless in the water, with its body in a horizontal position and its eyes looking upward. The green pigments in its eyes may filter out sunlight coming directly from the sea surface, helping the barreleye spot the bioluminescent glow of jellies or other animals directly overhead. When it spots prey (such as a drifting jelly), the fish rotates its eyes forward and swims upward, in feeding mode.

Stay updated on the expedition here.

More about the barreleye fish, including video.

(via: Monterey Bay Aquarium Research Institute)

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Brownsnout Spookfish (Dolichopteryx longipes)

…a species of opisthoproctid barreleye that likely has a worldwide tropical and temperate distribution, but is known from Bermuda, the Bahamas, the Greater Antilles, the Gulf of Mexico and the South China Sea/ California Current Region. D. longipes inhabits the mesopelagic and bathypelagic zones and likely feeds on copepods and other small crustaceans

Dolichopteryx longipes is currently the only known vertebrate to employ a mirror to focus an image in its eyes. D. longipes utilizes both refractive and reflective optics in sight, with its eyes being split into two parts. A swelling called a “diverticulum”  and the main eye. The main eye uses a lens “like most eyes” to focus an image. However, when sent to the diverticulum the light is reflected and focused onto the retina by a curved mirror. This structure allows the fish to see both up and down at the same time. The mirror system is also superior in gathering light. It is hypothesized that the main eye helps detect objects against sunlight and the diverticulum helps detect bioluminesent flashes from other directions. 

Here’s a picture to visualize it

Classification

Animalia-Chordata-Actinopterygii-Argentiniformes-Opisthoproctidae-Dolichopteryx-D. longipes

Images: T.Frank and Richard Young

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Glasshead Barreleye (Rhynchohyalus natalensis)

Barreleyes are deep sea fish from the family Opisthoproctida. All species have large telescopic eyes which protrude fro the skull and are enclosed in a transparent dome of soft tissue. 

In this species, the whitish translucent structure at the top is the fish’s primary eye. The silvery structure at the bottom is a ‘second eye’, which acts as a mirror to bounce light into the primary eye. They can also detect and interpret light themselves.

Having upwards facing eyes means that the fish can detect the silhouette of prey swimming above.

Image © President and Fellows of Harvard College

(Source of photo/info here)

With a head like a fighter-plane cockpit, a Pacific barreleye fish (Macropinna microstoma) shows off its highly sensitive, barrel-like eyes–topped by green, orblike lenses. This particular fish, discovered alive in the deep water off California’s central coast by the Monterey Bay Aquarium Research Institute (MBARI), is the first specimen of its kind to be found with its soft transparent dome intact. The 6-inch (15-centimeter) barreleye had been known since 1939–but only from mangled specimens dragged to the surface by nets (until this picture was taken in 2004). It is the only species of fish in the genus Macropinna, belonging to 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.

(Other source)

Barreleye (Macropinna microstoma)

Macropinna microstoma is a species of barreleye that is unusual for its transparent fluid filled dome structure on top of its head. The fish has specialised eyes and other features which aid it in life in the deep sea.

The fish’s tubular eyes, capped by green lenses, are large and extremely sensitive to light. They can be rotated to face forward or upwards. Since they live in conditions where light does not penetrate well, they face their sensitive eyes upwards to search for the faint silhouette of prey swimming overhead.

The green pigment in the lens filters out sunlight, helping the fish spot faint bioluminescent glows of their prey. This may also help discern silhouettes, as several species of deep sea organisms use counter illumination to match the incoming surface light. If the surface light is filtered off, then the counter illumination becomes apparent.

When feeding, they will rotate their eyes forward. The eyes give them binocular vision and depth perception, which makes it easier for the fish to capture prey with their small pointed mouths.

The fish has other adaptations, such as the transparent dome. This allows they eyes to collect for incident light than it would if they were embedded into the head. It may also served to protect the eyes from the stinging cells of siphonophores, which the fish is believed to prey on.

The large flat fins of the fish allow it to drift motionless in the water column, where it spends most of its time searching for prey above it.

Images and Info: Monterey Bay Aquarium Research Institute

The Barreleye Fish:

I’d like to introduce you to this little deep sea beauty known as the Barreleye fish (also known as the spook fish). These creatures are normally found around the tropical or temperature waters of the Atlantic, Pacific, and Indian oceans. Typically, they grow to around 15cm (about 6 inches). Although it’s dome-like head looks like a mini biosphere, it’s actually the casing for its upward facing eyes.

To learn all about these fantastic creatures, see:
http://www.fromquarkstoquasars.com/the-barreleye-fish/

Image sources:
http://www.mbari.org/news/news_releases/2009/barreleye/barreleye.html

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“With a head like a fighter-plane cockpit, a Pacific barreleye fish shows off its highly sensitive, barrel-like eyes–topped by green, orblike lenses–in a picture released today but taken in 2004.
The fish, discovered alive in the deep water off California’s central coast by the Monterey Bay Aquarium Research Institute (MBARI), is the first specimen of its kind to be found with its soft transparent dome intact. The 6-inch (15-centimeter) barreleye (Macropinna microstoma) had been known since 1939–but only from mangled specimens dragged to the surface by nets.”

Pacific Barreleye Macropinna microstoma

The large green eyes of the Pacific Barreleye are encased in a clear protective shield. These eyes generally face upwards and are very sensitive to light. Unlike most other fish they have binocular vision (meaning that their eyes are orientated the same way - like humans) which greatly enhances their depth perception and ability to spot faint objects. This adaptation helps it find food in the pitch black ocean floor, where food its scarce and opportunistic.