Macropinna is a genus of ray-finned fish belonging to Opisthoproctidae, the barreleyes family. It contains one species, M. microstoma. It is recognized by a very unusual transparent, fluid-filled shield on its head, through which the lenses of its eyes can be seen.
Characteristics
At first it was believed that this fish’s tubular eyes were fixed in place and therefore only provided tunnel vision of what was seen above its head. However, in 2008, scientists discovered that its eyes could rotate both upward and forward in its transparent shield
M. microstoma has a tiny mouth and most of its body is covered with large scales. The fish normally hangs almost motionless in the water, at a depth of about 600 meters (2,000 feet) to 800 meters (2,600 feet), using its large fins for stability and with its eyes directed upward
In low light conditions, the fish is supposed to detect prey by its silhouette. MBARI researchers Bruce Robison and Kim Reisenbichler observed that when prey such as small fish and jellyfish are spotted, 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.
The species was discovered in 1939 by marine biologist W. M. Chapman, and is found in deep temperate waters of the Pacific, Indian and Atlantic oceans. Macropinna microstoma is found in deep oceanic waters because of its light-sensitive tubular eyes. The eyes are covered by bright green lenses and surrounded by a fluid-filled shield. The presence of this fish was almost unknown until 2004.
Habitat, diet and reproduction of Macropinna microstoma
The Macropinna microstoma is a deep-sea fish that lives at a depth of about 1015 meters. It is found mainly off the coast of California and in the North Pacific Ocean. Living in such deep, dark water, the Macropinna microstoma is very sensitive to light. Because of this, the barreleye has upward eye vision. In order to see its prey, the barreleye looks upward toward the surface light.
Macropinna microstoma can grow up to 15 cm long. It has a large, dome-shaped, transparent head. This protects its sensitive eyes from the nematocysts (stinging cells) of the siphonophores, from which it is believed to steal food. Through the dome you can see the entire inside of the head, i.e. its eyes, its brain and all the nerve endings that compose it
At first glance it appears that its eyes are at the front of the head in the form of two black holes; these are its olfactory organs. Marine biologists used to believe that the barreleye’s eyes were fixed in its head, allowing it to look upwards only. Its large flat fins allow it to remain almost motionless in the water and to maneuver with great precision.
Most of the time, the fish remains motionless in the water, with its body horizontal and its eyes looking upwards. Green pigments in its eyes can filter sunlight coming directly from the sea surface, which helps the barreleye detect the bioluminescent glow of jellyfish or other animals directly overhead.
M. Microstoma shares its deep-water environment with many different types of jellyfish. Some of the most common are siphonophores (with a length of 30 feet). The barreleye has a strong digestive system and usually feeds on jellyfish and small drifting animals. Small sea creatures caught in the tentacles of jellyfish are also targeted by the barreleye.
Macropinna microstoma is believed to be a pelagic spawner (the eggs are coated with a layer of oil that allows them to float on the nearest surface of the sea until they hatch). The female lays the eggs in the water and the male releases the sperm into the water
After hatching, the larvae begin to descend to the depths as they grow, until they are in the ideal habitat to live in. During this time they feed on zooplankton and small particles of organic matter floating in the water. It is believed that there is no sexual dimorphism between the male and female and that they do not care for their young.
M. microstoma has been known to science since 1939, but is not known to have been photographed alive until 2004. Older drawings do not show the transparent dome, as it is usually destroyed when removed from the deep. It is widely distributed in the northern Pacific Ocean, from the Bering Sea to Japan and Baja California.
