In the dark depths of our oceans their are a whole host of incredible, scary and downright crazy organisms and none fit that last description more so than the elusive Barreleye.  Scientifically named Opisthoproctus soleatus this unusual fish has the surprising adaptation whereby the top front portion of its head is completely clear.

This animal is so odd that even when looking at the photo above your eyes struggle to process that what you are seeing is even real.


The Barreleye gets its name due to the large “eyes” that reside within the centre of its clear head. The word eyes isn’t quite an apt description because although officially that is what they are they are not eyes in the same way that we would think. Instead these tubular masses are almost entirely composed of rod cells, similar to those found in the peripheries of our own eyes; And the same as in our own eyes they are incapable of seeing colour instead allowing for greater detail between dark and light. The eyes are probably this way as they point straight up and are used to watch for silhouettes of predators and prey.

The head although clear is not hard and is instead composed of a soft jelly-like substance much like that found in the eyes of other organisms and is not used to protect the brain but instead only used to protect the eyes from then nematocysts (stinging cells) of the Siphonophores from which it is believed to steal the vast majority of its food. It is also theorised that the clear head could act as a lens pulled via muscular structures inside the body to focus and direct images.

The mouth resides at the front of the organism below two mounds which seemingly resemble fake eyes, the mouth is small terminal and toothless. They are also believed to have light emitting bacteria running completely across the stomach of the fish. Next to the the Illuminated stomach the Barreleye also possesses relatively large pectoral fins, we say relatively because despite the picture making this organism look quite large it is in fact only around 4 inches or 10 centimetres and they have only been known to grow to around six inches, so still pretty small.

Where is it found?

The Barreleye is evolved for darkness, as a result it is typically found in the bathypelagic zone around 2,500m deep, although not a lot else is known about this incredibly illusive species. They have only been seen to be a solitary species and although typically found very deep they have been known to appear at only around 400m with many presuming the organism uses temperature or salinity as a way of navigating its way around the ocean. With eyes that only put up it  is very difficult to see where you are going.

Diet of the deep:

When looking at they barreleye you wouldn’t think stealthy ambush predator but that is exactly what it is. Using its incredible eyes as a sort of night vision to see silhouettes of anything that happens to swim above it it then looks out for most types of planktonic organisms as well as cnidarians and waits until they come close enough to strike. Its stomach and throat are very well adapted to this job as well with both not only able to resist the stings of jellyfish but within its throat are a set of jaw like structures that grind up any and all things that go through it so that it is able to get as much nutrition out of each meal as possible. Something that is very useful when hunting in the open ocean.

Final Thoughts:

Many animals have unique and incredible adaptations that make us marvel at the extreme variety that evolution can produce, and how the day to day lives of such an organism could lead to such incredible things in the future. But what is normal for the spider is chaos for the fly and although we cannot fathom how this organism lives and consider it extreme in its ability to survive in the pressures and darkness this is itself a unique perspective from a group over slightly intelligent primates. To many other species survining in the darkness isn’t extreme it is just life.


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