The fish are named for the shape of their eyes, which look like tubes or barrels. They are directed upwards in order to allow the fish to detect prey more easily. Their strange eyes are also capable of seeing in total darkness. These fish are incredibly rare. There have only been a handful of sightings in recent years. The fish was first described in 1939 but little was known about it until recent years. 

Barreleye fish are incredibly interesting marine animals that are rarely spotted by human beings. They are also, as all deep-dwelling fish are, difficult to keep in captivity. Below, readers can explore the features of the barreleye fish and what makes it so unusual. You can watch a video of the Barreleye fish here.


Appearance 

These are small fish that grow to around six inches in length. They are named for their barrel-shaped eyes. They look like tubes and have the ability to look straight up through their clear heads to keep an eye on the silhouettes of prey and predators above. They can also direct their eyes forward to see the food it’s eating. It’s only recently that scientists discovered the fish have this capability. The fish are fascinating looking and share few commonalities with other marine creatures, according to New Scientist.

Barreleye Fish

Their telescoping eyes are found in all species of barreleye fish. But, the species are not all identical. Their eyes appear as two glowing green orbs, seen through their clear heads. These take the place of where another fish’s normal eyes would be. 

The fish have no teeth, a pointed snout, and a dark brown body. Most species are covered in scales. The Dolichopteryx is an exception. Without scales, it is a transparent white color. The Dolichopteryx, Opisthoproctus, and Winteria species all have some luminous organs. These parts of their body, mostly along their bellies, glow, according to the Journal of Optics A: Pure and Applied Optics.

The fish are finless, except for the Dolichopteryx, which has pectoral fins that take on a wing-like appearance. The largest barreleye fish is the javelin spook fish that grows to twenty inches in length. Most species are under eight inches long.

Opisthoproctus Grimaldi barreleye fish
Opisthoproctus Grimaldi barreleye fish


Habitat 

These fish are solitary and live at moderate depths, around 2,000 and 2,600 feet 600-800 meters deep. They remain below the limit of where light from the sun can penetrate. They can be found in tropical-to-temperate Atlantic, Pacific, and Indian Oceans, according to the Encyclopedia of Ocean Sciences. 

Recently, according to The Hill,  a barreleye fish was spotted off the coast of California by a team searching for deep-sea jellyfish. It was seen on December 1st, 2021 by senior aquarist Thomas Knowles, who works for the Monterey Bay Aquarium. He is quoted as saying that he and the team, “We all knew that this was likely a once-in-a-lifetime experience.” It was the first time they had seen the fish. 

Diet 

These unusual fish eat crustaceans, small jellies, siphonophores, and zooplankton. Their eyes are uniquely capable of filtering and interpreting light and spotting their prey from below. 

Scientists have suggested that the fish may sometimes find food by hovering underneath a siphonophore’s tentacles to take the discarded food.

A siphonophore - the Portuguese Man of War
A siphonophore – the Portuguese Man of War


Threats 

Although the fish are rare, they are not considered endangered. They are at threat, as all marine creatures are, from climate change, pollution, coastal erosion, and environmental encroachment. The fish are not hunted commercially and are therefore not a threat from the issues of overfishing, plus they are not caught as bycatch due to the depths they travel at. 

Reproduction

Little is known about the fish’s reproductive habits. But, scientists believe they are pelagic spawners. This means that the eggs and sperm are released directly into the water. The former is buoyant, and the larvae and the juvenile fish float along with the currents. 

Barreleye Fish Facts

  • The barreleye fish is also sometimes known as spook fish.
  • Little is known about the fish’s reproductive habits.
  • A barreleye fish was spotted off the coast of California in December 2021. 
  • The fish are finless, except for the species Dolichopteryx.
  • These are small fish that grow to around six inches in length. 
  • They have telescoping eyes and a clear head. 


FAQs 

Why does the barreleye fish have a transparent head?

The fish has a transparent head in order to better serve their vision. Their telescoping eyes can move up, allowing them to see straight up through their heads.

What does the barreleye fish eat?

The barreleye fish eats small jellyfish and other small drifting marine creatures like zooplankton. 

Is the barreleye fish endangered?

At this moment, no, the barreleye fish is not endangered. Although the fish is rare, scientists do not believe it’s in immediate threat from any source. The fish live at moderate depths, meaning that sightings are uncommon. Plus, the fish are solitary, making them harder to find. 

What is so weird about the barreleye fish?

The fish is “weird” because it has tubular, telescoping eyes and a clear head. Their eyes move upward and forward in order to spot prey. It can also see straight through its own head.