Barreleye Fish (Barrel Eye)

The barreleye fish (also known as the spook fish) is a bizarre species that has a transparent head filled with fluid, also known as a forehead shield. Barreleye fish inhabit tropical and cold waters such as the Atlantic, Indian, and Pacific oceans at a depth of around 2,000 to 4,000 feet deep where they can see with their tubular eyes in the mesopelagic to the bathypelagic or twilight zones of the ocean.

This species of fish was first described in 1939 by William Chapman, which was quite recent. The main reason this fish took so long to identify was due to marine biologists having a difficult time studying the barreleye since it lives so deep in the ocean. One of the main characteristics of the barreleye fish is their tubular rotating eyes that are located inside their transparent heads.

5 Fascinating Facts About Barreleye Fish

• The barreleye fish is colorblind because their eyes do not have cone cells that help with the perception of color.
• They live in the twilight zone, which is so deep in the ocean that it does not receive any sunlight.
• The barreleye’s transparent head looks so strange that people thought pictures were photoshopped. The transparent dome-shaped head was only discovered in 2004 when a picture of the fish was taken.
• Barreleye fish have a see-through head with fluid inside that protects their eyes, which look like green tubes. This transparent shield is so delicate that when researchers tried to bring the fish to the surface, they accidentally damaged it.
• The green glowing orbs in their head are eyes that point upwards to capture light, but they can rotate forward to search for prey.

Classification and Scientific Name

Barreleye fish belong to the Opisthoproctidae family, which has only been spotted a few times. This makes the barreleye fish rare, even though there are around 20 different species that are in nine genera from the same family. Scientists know very little about this fish since its discovery because of the deep waters they reside in, which makes it difficult to study.

Barreleye Fish Species

Here are the most popular species of barreleye (spook) fish that experts have been able to study:

Species:  

• Javelin spookfish (Bathylychnops exilis): found in deep waters in the North Pacific Ocean or in the eastern Atlantic Ocean at around 2100 feet deep and reaching a length of 20 inches in size.
• Dolichopteroides binocularis: found in the Pacific Ocean at a depth of 3,100 to 3,900 feet and grows to 13 inches in size.
• Brownsnout spookfish (Dolichopteryx longipes): from the Dolichopteryx genus; it reaches a length of 7 inches and can be found at a sea depth of 4,000 feet or more.
• Opisthoproctus grimaldii: A tropical species found between 984 to 1,300 feet deep in the ocean; it reaches a size of 7 inches.
• Opisthoproctus soleatus: A small species that swims at a depth of 1,600 to 2,300 feet in the ocean.

Barreleye Fish Appearance

The barreleye fish’s appearance depends on its species, but the type from the Macropinna genus has a transparent head shield that contains a protective fluid. The eyes are located inside their transparent head and look like green orbs.

At first glance, the barreleye fish’s eyes resemble a brain, and the nostrils seem to be the eyes. However, the green orbs are indeed eyes, and the two eye-shaped circles are the nostrils or olfactory organs. The fish essentially sees through its forehead, giving the fish a strange appearance. The transparent head looks like a galaxy.

Barreleye fish have large and flat fins that enable them to be motionless in the water and float. Their fins allow them to keep themselves upright without seeming unstable in the water, with the pectoral fins located in a lower area of the fish’s body. The average fish grows to a maximum adult size of 6 to 7 inches and weighs only a few ounces..

The scales along their body are long and V-shaped. Their body coloration seems to be a magenta grey, but the absence of sunlight in the deep depths of the ocean where they reside makes it difficult to determine their true color.

Barreleye fish have small mouths to catch small prey, as they do not eat anything large. The mouth is below their olfactory organs (nostrils), which are below their eyes, which give them three-dimensional vision and allow them to look sideways, forwards, and upwards in the water. They have a lens over their eyes that ensures enough light enters from the surface.

Distribution, Population, and Habitat

Distribution

Barreleye fish live in temperate or tropical waters in the Pacific, Atlantic, and Indian Oceans. They inhabit the mesopelagic to the bathypelagic zones in the ocean and prefer deep depths where very little sunlight reaches. They inhabit a wide range, from the Bering Sea to Japan to Baja California.

Population

Experts do not know much about the barreleye fish population due to the difficulty of studying at such great depths. They may be solitary, as researchers have never seen them in groups. The IUCN red list has not been able to list the barreleye fish’s conservation status yet because their numbers are unknown.

Habitat

Barreleye fish inhabit the midwaters of warm and cold waters in the northeastern Pacific, Indian, and Atlantic oceans, making them marine fish. They live in depths of 2,000 to 4,000 feet, where it is dark. However, some barreleye fish live closer to the surface, at around 1,480 feet deep. Barreleye fish seem to float in the dark waters on the lookout for food and potential predators. There is not much vegetation around them due to the lack of sunlight, so their main habitat consists of deep, dark waters.

Predators and Prey

What Eats Barreleye Fish?

There is not much known about predators in their habitat. They likely fall prey to larger predatory fish that roam the deep waters since the barreleye fish does not have body adaptations to defend itself.

The Barreleye Fish’s Diet

Barreleye fish are ambush predators. They will float motionless in the water with their tubular eyes pointing upwards on the lookout for jellyfish, which are their main prey. Their eyes allow them to detect the glow of jellyfish along with the silhouette of other small crustaceans.

The small mouth of the barreleye fish makes it difficult for them to eat larger prey, and they mainly consume small jellyfish, zooplankton, crustaceans, and mollusks. The small crustaceans that the barreleye fish eat float in the tentacles of siphonophores.

Barreleye Reproduction and Lifespan

Barreleye fish are pelagic spawners, so the eggs and fry sit in oil that makes them float to the surface until they hatch. There is no sexual dimorphism in this fish, and neither the males nor the females care for their offspring.

They are oviparous fish, so the male will fertilize the eggs with sperm after the female barreleye fish lays her eggs. The barreleye fish fry will eat small particles of organic matter along with zooplankton until they are old enough to eat an adult diet.

The average lifespan for a barreleye fish is around 60 years, which is quite a long time for a fish.

Fishing and Cooking

Barreleye fish are rare, and they are not used in fishing or cooking. When researchers tried to bring this species to the surface, the fish’s transparent fluid head was damaged in the process.