Biology:Macropinna microstoma

Short description: Species of fish

Introduction

Discovered in 1939, by marine biologist Chapman, found in deep temperate waters off of the Pacific, Indian, and Atlantic Ocean. The Macropinna Microstoma (barreleye fish) is located in deep oceanic water due to their light-sensitive tubular eyes. The eyes are capped with bright green lenses, and surrounded by a fluid-filled shield. Mostly unknown until 2004.

Environment

Macropinna Microstoma is a deep-sea fish, living 1015 meters below the water surface. Barreleye are found mostly off of California's coast and the North Pacific ocean. Living in such deep, dark waters results in the light sensitivity Macropinna Microstoma experience. Due to this the barreleye fish has upwards ocular viewing. To be able to see prey the barreleye looks upwards towards the surface light.

Biology

Macropinna microstoma
File:Macropinna microstoma.jpg
Conservation status
Not evaluated (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Argentiniformes
Family:	Opisthoproctidae
Genus:	Macropinna W. M. Chapman, 1939
Species:	M. microstoma
Binomial name
Macropinna microstoma W. M. Chapman, 1939

Macropinna Microstoma weight can range from 440-800 lbs and they can get as long as 10 to 13". They have large, dome-shaped, transparent heads. This protects their sensitive eyes from the nematocysts (stinging cells) of the siphonophores, from which the barreleye (Macropinna microstoma) is believed to steal food. You can see the entire inner part through it, that is, their eyes, brain and all the nerve endings that make up their head. At first glance it seems that their eyes are at the front of their head in the form of two black holes; this is their olfactory organs. The characteristic green pigment of their eyes and glasses is what allows them to filter the sunlight coming directly from the water's surface. Most  marine biologists use to believe that Barreleye’s eyes were fixed in their heads, which would allow them to only look upward. Their large, flat fins allow them to remain nearly motionless in the water, and to maneuver very precisely. Most of the time, the fish hangs motionless in the water, with its body in a horizontal position and its eyes looking upward. The green pigments in its eyes may filter out sunlight coming directly from the sea surface, helping the Barreleye spot the bioluminescent glow of jellies or other animals directly overhead.

Diet

Barreleyes share their deep-sea environment with many different types of jellies. Some of the most common are siphonophores (length of 30 feet). The Barreleye fish have a strong digestive system and they usually feed on jellies and small drifting animals. The small marine creatures trapped on the tentacles of the jellies are also targeted by the Barreleye fish.

Reproduction

Macropinna microstoma are thought to be pelagic (they are coated with a drop of oil that allows them to float on the closest surface of the sea until they hatch) spawners, females will lay eggs in water and males will release sperms in water. After hatching they begin to descend to the depths as they grow, until they are located in the ideal habitat to live. During this time they feed on zooplankton and small particles of organic material that floats in the water. It’s believed that there is no sexual dimorphism between the male and the female and they don’t care for their young.

Macropinna microstoma is the only species of fish in the genus Macropinna, belonging to the Opisthoproctidae, the barreleye family. It is recognized for a highly unusual transparent, fluid-filled shield on its head, through which the lenses of its eyes can be seen. It was originally believed that the tubular eyes of these fish were fixed in place and, therefore, only provided a tunnel vision view of what was seen above their head. However, in 2008, scientists discovered that their eyes were able to rotate both up and forward in their transparent shield (Robison & Reisenbichler, 2008).

M. microstoma has a tiny mouth and most of its body is covered with large scales. The fish normally hangs nearly motionless in the water, at a depth of about 600 metres (2,000 ft) to 800 metres (2,600 ft), using its large fins for stability and with its eyes directed upward. In the low light conditions it is assumed the fish detects 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.

M. microstoma has been known to science since 1939, but is not known to have been photographed alive until 2004. Old drawings do not show the transparent dome, as it is usually destroyed when brought up from the depths. It is broadly distributed across the northern Pacific Ocean, from the Bering Sea to Japan and Baja California.

Further reading

• Froese, Rainer and Pauly, Daniel, eds. (2012). "Macropinna microstoma" in FishBase. February 2012 version.
• Robison, Bruce H.; Reisenbichler, Kim R. (2008). "Macropinna microstoma and the Paradox of Its Tubular Eyes". Copeia 2008 (4): 780–4. doi:10.1643/CG-07-082. 
• McFall-Ngai, Margaret; Ding, Lin; Childress, James; Horwitz, Joseph (1988). "Biochemical Characteristics of the Pigmentation of Mesopelagic Fish Lenses". Biological Bulletin 175 (3): 397–402. doi:10.2307/1541731. http://biostor.org/reference/10229. 
• Crescitelli, Frederick; McFall-Ngai, Margaret; Horwitz, Joseph (1985). "The visual pigment sensitivity hypothesis: Further evidence from fishes of varying habitats". Journal of Comparative Physiology A 157 (3): 323–33. doi:10.1007/BF00618122. PMID 3837092. 
• Schwab, Ivan R.; Ho, Viet; Roth, Alan; Blankenship, Thomas N.; Fitzgerald, Paul G. (2001). "Evolutionary attempts at 4 eyes in vertebrates". Transactions of the American Ophthalmological Society 99: 145–56; discussion 156–7. PMID 11797302. 
• Schwab, Ivan R. (2011). "Barreleye, Macropinna microstoma". Evolution's Witness: How Eyes Evolved. Oxford University Press. pp. 101–2. ISBN 978-0-19-536974-8. https://books.google.com/books?id=ftpQB_GjtJgC&pg=PA101. 

External links

• Photos (archived from the original)
• MBARI Article with ROV Video footage
• ROV Video footage from above article

Wikidata ☰ Q131722 entry