Picture
   
      Barrel-eye Fish


Mystery Of The Barreleye Fish Solved

​Researchers at the Monterey Bay Aquarium Research Institute recently solved the half-century-old mystery of a fish with tubular eyes and a transparent head. Ever since the "barreleye" fish Macropinna microstoma was first described in 1939, marine biologists have known that its tubular eyes are very good at collecting light.
However, the eyes were believed to be fixed in place and seemed to provide only a "tunnel-vision" view of whatever was directly above the fish's head. These unusual eyes can rotate within a transparent shield that covers the fish's head. This allows the barreleye to peer up at potential prey or focus forward to see what it is eating.
Deep-sea fish have adapted to their pitch-black environment in a variety of amazing ways. Several species of deep-water fishes in the family Opisthoproctidae are called "barreleyes" because their eyes are tubular in shape. Barreleyes typically live near the depth where sunlight from the surface fades to complete blackness. They use their ultra-sensitive tubular eyes to search for the faint silhouettes of prey overhead.
Although such tubular eyes are very good at collecting light, they have a very narrow field of view. Furthermore, until now, most marine biologists believed that barreleye's eyes were fixed in their heads, which would allow them to only look upward. This would make it impossible for the fishes to see what was directly in front of them, and very difficult for them to capture prey with their small, pointed mouths.
Recent Studies show that:
  • its eyes are surrounded by a transparent, fluid-filled shield that covers the top of the fish's head.
  • the fish rotates its tubular eyes as it turns its body from a horizontal to a vertical position.
  • In addition to their amazing "headgear," barreleyes have a variety of other interesting adaptations to deep-sea life. Their large, flat fins allow them to remain nearly motionless in the water, and to maneuver very precisely 
  • Their small mouths suggest that they can be very precise and selective in capturing small prey. On the other hand, their digestive systems are very large, which suggests that they can eat a variety of small drifting animals as well as jellies. In fact, the stomachs of the two net-caught fish contained fragments of jellies.
  • 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.
  • Researchers speculate that barreleyes may manoeuvre carefully among the siphonophore's tentacles, picking off the captured organisms. The fish's eyes would rotate to help the fish keep its "eyes on the prize," while its transparent shield would protect the fish's eyes from the siphonophore's stinging cells.
  • MBARI researchers speculate that Macropinna microstoma may eat animals that have been captured in the tentacles of jellies, such as this siphonophore in the genus Apolemia. 
The bizarre physiological adaptations of the barreleyes have puzzled oceanographers for generations. It is only with the advent of modern underwater robots that scientists have been able to observe such animals in their native environment, and thus to fully understand how these physical adaptations help them survive.

Resources

barreleye_fish_characteristics.docx
File Size: 300 kb
File Type: docx
Download File
from_the_deep.docx
File Size: 1283 kb
File Type: docx
Download File
light-controlling_organ.docx
File Size: 49 kb
File Type: docx
Download File
strange_fish_has_see.docx
File Size: 26 kb
File Type: docx
Download File
the_fish_with_four_eyes.docx
File Size: 252 kb
File Type: docx
Download File
unique_glow.docx
File Size: 70 kb
File Type: docx
Download File
strange_fish_has_see.docx
File Size: 26 kb
File Type: docx
Download File

Scientific studies

macropinna_microstoma_and_the_paradox_of_its_tubul.pdf
File Size: 3059 kb
File Type: pdf
Download File
partridge-2014.pdf
File Size: 1813 kb
File Type: pdf
Download File
rspb.2013.3223.pdf
File Size: 1709 kb
File Type: pdf
Download File

More Resources

Videos
​

Barreleye Fish Images