Barreleyes

Barreleyes are a family of deep-sea fish belonging to the order Stephanoberyci. They are notable for their distinctive, upward-pointing tubular eyes, which resemble barrels. These eyes are highly adapted for detecting the faint silhouettes of prey against the dim light filtering down from the surface. The most striking feature is the transparent, fluid-filled dome that covers the eyes, allowing them to rotate their vision to look directly ahead or straight up. Barreleyes are typically small, rarely exceeding 15 centimeters in length. They inhabit the mesopelagic and bathyal zones of oceans worldwide, at depths ranging from 200 to 1,000 meters. Their diet consists mainly of small crustaceans and plankton. The family contains a few genera, with the most well-known being Macropinna. The barreleye fish Macropinna microstoma has a particularly unique adaptation where its ocular lens is green. Their scarcity and the extreme depths at which they live make them infrequently observed and studied by scientists.