Barreleye fish: Macropinna Microstoma

The term Barreleye encompasses all fish under the Opisthoproctidaeumbrella. The name actually originates from the Greek words for ‘behind’ and ‘anus’ which begins to portray its strangeness. The species Macropinna Microstoma is what we will be looking at today, a creature some what a scientific anomaly for over half a century.

Discovery and features

Wilbert McLeod Chapman, an American ichthyologist, researching fish science, first discovered Macropinna in 1939 when working for the Washington State Department of Fisheries. When the deep sea residing fish was caught in nets and pulled to the surface its main feature of a transparent head was destroyed or mutilated due to its fragility. It was not to be until sixty-nine years later, in 2008, after huge strides in technological fields that a living Macropinna was captured and seen in all its glory.

In 2008 a study was published by Bruce H. Robison and Kim R. Reisenbichler, both working at the Monterey Bay Aquarium Research Institute. The paper, titled Macropinna microstoma and the paradox of its tubular eyeschanged the natural landscape surrounding the species. Marine biologists had mostly assumed that the impressive eyes of Macropinna were fixed in a stationary, rigid position focusing on the space directly above the fishes head but nobody had yet seen said eyes. The pair proved, with meticulous research, that the eyes can indeed rotate under the guidance and protection of a ‘shield’ coating allowing Macropinna to indeed look up but also to look straight ahead.

The Macropinna looking up and looking forward. Source:

Before Robison and Reisenbichler’s research nobody knew of the transparent ‘bubble’ head, and the drastic discovery enthralled the science world. Macropinna reside near the depths of the ocean where sunlight begins to fade into total nothingness in terms of light hence the adaptation of the eyes to look upwards in search of silhouettes of both prey and predator.

Robison and Reisenbichler initally sent down remotely operated vehicles in an area off of the Californian coastline known for being a Macropinna habitat. With the vehicles in position at around 600-800 metres below the surface the pair could only sit and observe as the fish stayed motionless in the water; the head of the species coming into view for the first time must have been an astonishing sight. The pair did not rest on their laurels, managing to catch a Macropinna sample and study it for hours onboard their research vessel. Most of what is known about Macropinna was discovered here.

The duo observed Macropinna in a small aquarium in which they noticed it remanining virtually motionless yet again, due to its flat, large fins on either side. Macropinna have been described as an ambush predator due to such lack of movement, using their specially trained and adapted eyes to search for prey before swimming upwards with its small, toothless mouth wide open. The small size of the mouth stops them consuming large prey and suggests to researchers that they can be picky with what they consume although scientists have shown that the diet is usually broad, containing crustaceans, tentacles, small fish, and more. The main source of food currently known by researchers surrounds Siphonophores, or jellyfish, that share the habitat with Macropinna. Macropinna, using its large fins to manuevere very precisely, drifts through the potentially harmful tentacles of their neighbours, scavenging captured prey whilst using their transparent fluid shield to protect their eyes.

Macropinna Microstoma. Source: MBARI

Not much is known about these average sized beings and some of what is is based on educated assumptions. Macropinna are thought to be solitary and thought to be pelagic breeders, meaning they rely on wave currents to disperse egg and sperm cells. No known predator is as yet known. Just as it took over half a century to first discover and log the awe inspiring adaptations of the Macropinna, it will once again take time and technological effort to uncover more about this mightily creative species.

Further information and links

Chapman was the author of Fishing in Troubled Waters describing his story “fishing off the Solomon Islands during WWII”. The below video from MBARI is narrated by Bruce Robison himself and shows fascinating video from the remotely operated vehicles of Macropinna in its natural habitat:

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