Weird Wildlife Wednesday: What the Fish?!
Meet Macropinna microstoma or the barreleye fish.
Species: M. microstoma
The clear bubble is like a built-in scuba mask; the glowing green orbs are the barreleye’s eyes which point upward. The two spots above the mouth (that your brain is telling you are eyes) are nares, or the fishy olfactory nerves that are rather like nostrils. The fish is smaller than it may seem in the videos, only about 140mm long.
An inhabitant of the zone where sunlight transitions into blackness 600-800 meters below the surface of the water, this fish, like many deep-sea species, has several elegant adaptations allowing it to survive. Large, flat fins allow the fish to maintain an almost motionless position in the water as the large green eyes filter out certain pigments of sunlight, making the bioluminescent glow of siphonophores above more apparent. After spotting prey, the eyes rotate forward as the fish swims up to feed. The protective shield then keeps the eyes safe from siphonophore stinging cells as the barreleye feeds. The small mouth allows the fish to very precisely eat and catch smaller prey.
Discovered in 1939, early documentation of the barreleye does not include details of the invisible shield because it always broke before the fish reached the surface in a net. Researchers Bruce Robison and Kim Reisenbichler at the Monterey Bay Aquarium Research Institute obtained the footage above with an ROV and discovered the shield over the eyes. Biologists initially also thought that the eyes of this fish remained in a fixed position. Robinson and Reisenbichler were also able to capture a live, in-tact specimen and determine in controlled tests that the domed eyes of this fish rotate when it assumes the vertical feeding position in the water.
Source: MBARI Press Release