Scientists Solve The Mystery Of Why This Fish Is So Freakin’ Crazy

The barreleye (Macropinna microstoma) has extremely light-sensitive eyes that can rotate within a transparent, fluid-filled shield on its head. The fish’s tubular eyes are capped by bright green lenses. The eyes point upward (as shown here) when the fish is looking for food overhead. They point forward when the fish is feeding. The two spots above the fish’s mouth are are olfactory organs called nares, which are analogous to human nostrils. In the second image, you can see that, although the barreleye is facing downward, its eyes are still looking straight up. This close-up “frame grab” from video shows a barreleye that is about 140 mm (six inches) long. Image: © 2004 MBARI

Crazy doesn’t even come close to how freakin’ wierd this fish is.  At my old stomping grounds, MBARI, Bruce Robison and Kim Reisenbichler now know why. Desribed in 1939, Macropinna microstoma, the barreleye fish, isn’t exactly new to science.  All the species in the Opisthoproctidae family are known for having ultra-sensitive tubular eyes that face upward, well adapted for collecting light.  Slight problem.  If the eyes constantly face upward, looking forward to capture prey with their wee little mouths is impossible.

Using MBARI’s remote operate vehicles Robison and Reisenbichler were able to view the barreleyes in the ocean between 600 and 800m.  The found that the eyes of Macropinna can rotate within transparent shield that covers the fish’s head, allowing it to look at whatever it wants.  This transparent, fluid-filled shield that covers the top of the fish’s head was unknown to science, i.e. existing descriptions and illustrations do no show it.  Likely, when previous specimens were caught in deep-sea trawls there were damaged or lost.

But the craziness of this fish doesn’t stop with the clear skull or pivoting eyeballs…

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 (much like MBARI’s ROVs). 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.

And now for the video…

Bruce H. Robison, Kim R. Reisenbichler (2008). Macropinna microstoma and the Paradox of Its Tubular Eyes Copeia, 2008 (4), 780-784 DOI: 10.1643/CG-07-082

25 Replies to “Scientists Solve The Mystery Of Why This Fish Is So Freakin’ Crazy”

  1. Considering how much that transparent head makes it look like an Alvin-style submersible, is this another piece of corroborating evidence for Oscar Wilde’s claim about life imitating art?

  2. I…I…

    I just really don’t know how to respond to this.

    Perhaps…”It’s all CGI – photoshopped!”


    Seriously, the developmental biology of this seems astonishing to me. I would love to see sections through the larval eyes of these guys. Do they initially form like most eyes, through inductive interactions of the surface ectoderm with neural tube outpockets, only to then become grown over by the freaky shield? Is that shield the actual skull (or is it some cartilaginous permutation thereof)? How is it so transparent? Do they not have skull eye sockets? How did those lenses form? What are they made of (is it still pretty much various crystallin proteins)?

    I’m not a specialist in eye development, but I know enough about the process to know that this seems just plain crazy.

    I want more pictures, videos and studies!

  3. Yep, my first thought at seeing the image was “CGI” – but couldn’t believe my eyes when I watched the video.

  4. how big is it really? the mentioned “140 cm (six inches)” does not make sense, 6 inches would be 14.0 cm.


  5. In answer to Irradiatus’ comment, the fish’s skull is actually well underneath the eyes, with a slight bony ridge between the eyes. In fact, that’s all you see in the textbook illustrations of this fish (e.g. What’s really interesting to me is that the fish has scales behind its eeyes, so the cowling somehow develops over the main scales of the fish. All this work just to steal prey from the tentacles of a siphonophore. but I guess it beats chasing food for a living…

  6. So. Many. Questions!
    Has anyone been fortunate enough to observe it feeding?
    Do the scales help with light attenuation/gathering, what is the fluid within the shield? Eye structure? FOV? IOR of the shield? IOR of the fluid? IOR of the eye lens? Is it lensed? Argghhhh!

  7. was the light coming from the fish itself? it looked way too perfect for it to have been shone on the fishes head so perfectly the whole time without moving out of context with the fishes head even the slightest bit, even when the fish quickly escaped the collection tube.

  8. Burton: this 6″ fish was in the intense lightfield of the ROV. From specular highlights on the fish in the photo’s it looks like this ROV has 4 to 6 front illuminating lights. Probably each 400 to 500watts of light so 1600 to 3000 watts of light to cut through the inky dark.

    Hm…couldn’t the specular highlights be analyzed to determine properties of the headshield?

  9. “specular highlights”

    Your CGI background is shining through, Eric. :)

  10. Yeah, it makes it fun trying to explain to the professors here why as a future biologist I’m such a nut with a love for optical physics. Then my video and tech geek love which helps a lot with ROV stuff(Yeah! Going down to Ft. Lauderdale next week to help with a cruise!! Boo..I don’t get to go on the cruise just set up equipment and train someone else on it’s use. (Darn school getting in the way of education!))

  11. Holy Cow….it was on Colbert…did you see it?? I was talking about this in my intro oceans class and one of my students told me he had already seen it…on Colbert!?!?

    Go to and search for the video of the barreleye.

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