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Barreleye (Micropinna microstoma)

Macropinna microstoma is the only species in the genus Macropinna. It belongs to the barreleye family, Opisthoproctidae. This fish occurs year-round aroud seamounts and knolls at depths of 16-50,000 m and a temperature range of 1.8-3.5 °C beneath temperate and subarctic waters in the North Pacific. It has been caught by midwater trawl nets in areas with bottom depths of 1600-3600 m.

It is usually @ 15 cm long, but can grow to 44 cm. Adults are dark brown. A transparent, cowl-like shield covers the top of the head. This tough, flexible integument attaches to the dorsal and medial scales behind the head and to the broad, transparent subocular bones that protect the prominent, tubular eyes laterally. Old drawings do not show the transparent dome, which is usually destroyed when brought up from the depths. The fluid-field chamber beneath the shield surrounds and protects the eyes with vivid green lenses. The tubular, barrel-shaped eyes can be rotated to point forward or straight up, looking through the transparent dome (1). Robison and Reisenbichler (3) note that the tubular eyes can look forward as well as upward (with the maximum arc of rotation observed about 75 degrees). The morphology of the eyes apparently allows at least two feeding modes: (1) with the body horizontal and the eyes directed upward, it can spot food against lighted waters above. It pivots its body to bring the mouth up for ingestion while its eyes are locked on target, rotating from dorsal to rostral relative to the body; and (2) with the body horizontal, the eyes rotate dorsal to rostral while tracking the path of descending food until it reaches the level of the mouth. M. microstoma has a tiny mouth and most of its body is covered with large scales. It has 11 dorsal and 14 anal soft rays, but no dorsal or anal spines. There is an adipose fin at the base of the caudal peduncle. This solitary fish makes seasonal migrations of under 200 km. It normally hangs nearly motionless in the water, at a depth of @ 600-800 m (2,000-2,600 ft), using its large fins for stability and with its eyes directed upward. It eats cnidarians and probably also eats crustaceans and other zooplankton. In low light conditions, it is assumed that it detects prey by its silhouette. Bruce Robison and Kim Reisenbichler (3) noted that when the fish sees prey such as small fish and jellyfish, the eyes rotate like binoculars, facing forward as it turns its body from a horizontal to a vertical position to feed. Robison speculates that M. microstoma steals food from siphonophores (2).

the fish is oviparous and has planktonic larvae. It has been known to science since 1939, but is uncommon and is not known to have been photographed alive until 2004. .


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