Overview
The Barreleye Fish (Macropinna microstoma), also known as the Pacific barreleye or spookfish, is one of the most structurally bizarre teleost fishes swimming in Earth’s oceans. Residing in the dimly lit mesopelagic twilight zone of the northern Pacific, this deep-sea fish is famous for its completely transparent, fluid-filled cranial dome, inside which two emerald-green tubular eyes rotate freely to hunt prey silhouetted against the surface.
Biology and Physical Characteristics
The anatomy of Macropinna microstoma long perplexed marine biologists because fragile specimens pulled up in historic trawling nets invariably suffered ruptured domes. In 2008, live submersible ROV observations confirmed that in life, its skull is capped by an intact, crystal-clear gelatinous shield. Inside this chamber reside large, barrel-shaped tubular eyes capped with vibrant green photosynthetic accessory pigments that filter out downwelling surface sunlight, isolating the subtle bioluminescent glows of siphonophores and small jellyfish overhead.
Behavior and Ecology
Barreleyes are precision hover hunters that maintain neutral buoyancy using broad, fan-like pectoral and pelvic fins, remaining suspended almost motionlessly in the water column. While their eyes normally point directly upward to scan for food drifting overhead, the fish can rotate its tubular eyes forward toward its small, toothless mouth when maneuvering to snatch food. Its clear dome shields its sensitive eyes from the stinging tentacles of siphonophores, from which it frequently plucks captured crustaceans.
Conservation and Human Impact
Assessed as Least Concern on the IUCN Red List due to a vast geographic range spanning the North Pacific rim and low susceptibility to commercial fishing gear, Macropinna microstoma remains ecologically stable. Remote exploration via deep-diving robotic submersibles continues to reveal vital insights into its distribution, reproductive behavior, and sensory physiology.
Interesting Factoid
The two small indentation holes on the front of the barreleye’s face that look like normal fish eyes are actually nares (nostrils)—its real eyes are the glowing green glowing spheres inside its see-through forehead!
Last updated: October 2026