Ashland Marine Biology: Barreleye Fish


In our last class lecture, we discussed much about the adaptations of deep sea animals. This fascinated me because the mystery behind these creatures is worth looking more into. While scrolling through an article discussing the 25 most terrifying deep sea creatures, number 8 struck me as truly interesting. This organism is known as the barreleye fish. In the family 


 it is scientifically known as 

Macropinna microstoma,

and more commonly known as the spook fish. The reasoning behind its common name can clearly be seen below through the obvious observation that they have a transparent dome head, which indeed looks strange and spooky.  The barreleye fish have two upward facing eyes that allows them to specifically search for potential predators around them. What we would think would be eyes on this species (which are the two spots on its mouth) are actually nasal organs (equivalent to the nose in humans). I found that fact interesting because it definitely made me think that the two spots on its face were its eyes, when actually its eyes are the two green glands in the transparent portion of its head. The history of its existence has been described since 1939 but it wasn’t until about 2008 that the true understanding of this species had been further discovered.

Originally thought to have eyes that are fixed in place to only look up above, it was believed by marine biologists for quite some time that this was their disadvantage to not see what what in front of them. According to an article by Bruce Robison and Kim Reisenbichler, there is now a complete understanding that these fish eyes are tubular. Not only that, but the eyes are meant to peer through their transparent membrane to look straight above in search of potential predators. According to Robison and Reisenbichler, they used machinery known as remotely operated vehicles to study these deep sea fish off the coasts of central California. They reportedly caught one and examined its physiology. Their flat fins allow them to take advantage of being nearly motionless in the water and to maneuver efficiently. This is interesting because it allows them to save their energy. 

      Figure 1. The barreleye fish with its transparent head and tubular eyes (as green glands) shown above.

In addition to their strange physiology of their eyes, the fact remains that their eyes show green pigments when the remotely operated vehicles (ROVs). These pigments are speculated to filter out all the sunlight above them and allow them to detect prey through bio-luminescence. This is a very interesting adaptation because it allows this species to stay protected by seeming quiet and vulnerable. Its small mouth makes it a predator who relies on getting energy/food effectively. The barreleye fish feed on jellyfish, which is effective and a positive thing considering they live within the same habitat as the jelly fish at these deep depths (2,000-2,600 feet). According to this article, Apolemia colonial jellyfish have stinging tentacles that can extend as long as thirty-three feet long, which can be deadly to other organisms within that area. As means to have a defense mechanism, the barreleye fish have adapted in protecting its eyes with a the ability to avoid the tentacles and also to rotate its overhead eyes. The fact that they can protect themselves in this way shows their ability to have adapted to the challenges of the deep ocean. The fact that it was the Monterey Bay Aquarium who discovered this species fully intact for the first time in its dome shaped head. I think what really was interesting to learning about this species was the fact that there are so many more organisms in the deep ocean that I hope to learn more in the future. 

B.H. Robison and K. R. Reisenbichler. Macropinna microstoma and the paradox of its tubular eyes.


. 2008, No. 4, December 18, 2008.

Monterey Bay Aquarium Research Institute. Researchers solve mystery of dep-sea fish with tubular eyes and transparent head. February 23, 2009. 


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