Overview
The Barreleye (Macropinna microstoma), colloquially known as the ‘spookfish,’ is one of the most breathtakingly unusual organisms inhabiting the deep ocean. Swimming in the perpetually dim twilight of the mesopelagic zone across the North Pacific, this small bathypelagic fish is famous worldwide for its completely transparent, fluid-filled dome that encloses its glowing emerald-green tubular eyes. Representing a triumph of deep-sea optical engineering, the barreleye navigates the pitch-black abyss with visual capabilities that defy traditional vertebrate anatomy.
Biology and Physical Characteristics
The defining biological feature of Macropinna microstoma is its transparent cranial shield—a delicate, fluid-filled gelatinous canopy that covers the entire upper surface of its head. Protected within this clear dome are two immense, vivid green tubular eyes that can rotate from pointing vertically upward (to spot silhouettes of siphonophores and small fish against downwelling surface light) to pointing directly forward to track prey into its small mouth. The green pigments in its large lenses filter out downwelling surface sunlight while accentuating the bioluminescent glow of deep-sea organisms. The two small depressions on the front of its face, often mistaken for eyes, are actually specialized olfactory nares.
Behavior and Ecology
Barreleyes are solitary, lethargic drift predators that maintain near-neutral buoyancy in deep oceanic currents. Using broad, flat pectoral and pelvic fins, the fish hovers virtually motionless in the water column, scanning overhead for drifting food. Marine biologists utilizing remotely operated vehicles (ROVs) have observed that barreleyes often steal food from colonial siphonophores; when a siphonophore traps crustaceans in its stinging tentacles, the barreleye maneuvers carefully around the tentacles, protected from stings by its transparent dome, to pick off captured prey.
Conservation and Human Impact
The barreleye is currently classified as Least Concern on the IUCN Red List due to its expansive North Pacific distribution and residence in deep bathyal waters far below industrial fishing depths. Because it lives between 2,000 and 2,600 feet below the surface, it rarely interacts with human activity. However, emerging threats to deep-sea ecosystems—including ocean acidification, climate-induced deoxygenation, and deep-sea mining exploration—have spurred deep-sea marine researchers to monitor the delicate bathypelagic food webs upon which the barreleye relies.
Interesting Factoid
The Barreleye’s entire forehead is a completely clear, fluid-filled transparent canopy, allowing its glowing green barrel eyes to rotate 90 degrees inside its skull to look straight up or straight forward.
Last updated: October 2026