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A fish facing forward on a black background, with large eyes and a mouth shaped like an inverted V.

The prickly lanternfish is the best-known deep pelagic species among the general public.

© IRD - TAPIOCA

Atlantic

Strange and emblematic creatures of the ocean depths

The prickly lanternfish is the best-known deep pelagic species among the general public.
  • Slideshow
  • Author : Louise Hurel
  • photo: IRD - TAPIOCA

Discover ten deep-sea pelagic species, with bodies as distinctive as their unusual behaviours! 

Far from the colourful specimens of coastal ecosystems, deep-sea fish are seen as a strange but relatively homogenous group of creatures. In reality, these animals display great morphological, behavioural and ecological diversity and represent the largest mass of vertebrates on Earth. To gain a better understanding of this fauna, a team of scientists from IRD and their partners carried out the first full overview of the biodiversity of deep-sea pelagic fish on a global scale. The study covered 1,554 species from all over the world, revealing the main fish species and their regional variability. It also revealed different vertical migrations, a daily movement between the deep and shallow zones of the ocean thanks to which these fish play an essential role in carbon sequestration.

Here are a few examples.

 

Ten deep-sea pelagic species to discover.

A fish in profile with a red hue and black eyes.

Rondeletia loricata hides from predators using its red light.

© IRD - TAPIOCA

A fish with eyes so small that they are not distinguishable. It consists of two rounded parts and has a long filament at the tip of its head that serves as a glowing lure.

Rhynchactis leptonema is an extremely rare fish that relies on bioluminescent bacteria to produce its light.

© IRD - TAPIOCA

A long and slender fish, whose morphology is more similar to an eel, with large eyes and a beak-shaped mouth.

The morphology of Nemichthys curvirostris, very different from that of other pelagic fish, allows it to move and hide.

© IRD - TAPIOCA

A fish in profile, in shades of black and red, with a jaw larger than its head.

Malacosteus niger is one of the rare pelagic species that produce red light.

© IRD - TAPIOCA

A fish with white, translucent skin, displaying large eyes and tiny teeth, with what looks like a larva in red tones attached to its side.

Haplophryne mollis is a "two-in-one" fish: the male is permanently attached to the female's side.

© IRD - TAPIOCA

The head of a fish resembling a shark, with very small eyes and a large mouth filled with big teeth.

Gigantactis vanhoeffeni lures its prey with a glowing bait attached to the tip of its head.

© IRD - TAPIOCA

A small fish in profile with eyes that take up the entire size of its head.

Dasyscopelus asper is very abundant and represents an important food source for other pelagic species.

© IRD - TAPIOCA

A black fish in profile, with very small pale blue eyes and a large mouth.

Eustomia sp, known as the Black Dragonfish, is a rare and little-studied species.

© IRD - TAPIOCA

The head of a fish with very small eyes and very large teeth that prevent it from closing its jaw.

Chauliodus sloani is an iconic deep-sea predator, easily recognizable by its long teeth.

© IRD - TAPIOCA

A small grayish fish shaped like a hatchet with large eyes.

Argyropelecus aculeatus is called the Lovely Hatchetfish because of the unique shape of its body.

© IRD - TAPIOCA

  • Argyropelecus aculeatus, aka the Lovely Hatchetfish
    A small grayish fish shaped like a hatchet with large eyes.

    Argyropelecus aculeatus is called the Lovely Hatchetfish because of the unique shape of its body.

    © IRD - TAPIOCA

    Called the Lovely Hatchetfish (or Atlantic Silver Hatchetfish, due to the silvery colouring of its body), this species has very large eyes for capturing light. This allows it to see during its daily vertical migration - the longest in the world - to feed on zooplankton at the ocean surface. It is very abundant and well identified in certain regions, where it is sometimes found washed up on beaches, such as in the Azores, where a postage stamp was even created bearing its effigy!

  • Chauliodus sloani, aka Sloane's Viperfish
    The head of a fish with very small eyes and very large teeth that prevent it from closing its jaw.

    Chauliodus sloani is an iconic deep-sea predator, easily recognizable by its long teeth.

    © IRD - TAPIOCA

    An emblematic predator of the seabed, Sloane's Viperfish is easily recognisable by its long teeth that prevent it from closing its jaw. Very abundant, it lives in cold waters and adjusts its migration according to the region of the globe it is in. In tropical areas, for example, it does not rise as far as the surface because the waters are too warm for it. It plays a significant role in global carbon flows by feeding on large prey that have ingested carbon at the ocean surface.

  • Dasyscopelus asper, aka the Prickly Lanternfish
    A small fish in profile with eyes that take up the entire size of its head.

    Dasyscopelus asper is very abundant and represents an important food source for other pelagic species.

    © IRD - TAPIOCA

    This species belongs to the group of deep-sea pelagic fish that is best known to the general public. It is small and owes its name to its bioluminescent head, which it uses to illuminate its surroundings to locate the zooplankton it feeds on. It is a great vertical migrator and is the first link in the descent of carbon to the depths. Very abundant, it is an important source of food for other pelagic species and is currently of interest to major fishing companies, who want to use it to produce fishmeal. 

  • Eustomia sp, aka Black Dragonfish
    A black fish in profile, with very small pale blue eyes and a large mouth.

    Eustomia sp, known as the Black Dragonfish, is a rare and little-studied species.

    © IRD - TAPIOCA

    The little-known Black Dragon Fish is part of a group of rare and little-studied species, of which a number of new species were recently described. Unlike the Lanternfish, which uses bioluminescence to light its way, the Black Dragonfish uses its light to attract its prey. As the smallness of its eyes suggest, this rare specimen stays in deep water, where it does not need to see to feed. It waits for migrating fish to arrive and thus captures the carbon they transport from the surface.

  • Gigantactis vanhoeffeni
    The head of a fish resembling a shark, with very small eyes and a large mouth filled with big teeth.

    Gigantactis vanhoeffeni lures its prey with a glowing bait attached to the tip of its head.

    © IRD - TAPIOCA

    Gigantactis vanhoeffeni is a member of the anglerfish family. Although very rare, its very unusual appearance makes it an emblematic deep-sea fish. It is particularly slow and has small eyes and lies in wait for its prey, which it attracts with the luminescent lure attached to its head. 

  • Haplophryne mollis
    A fish with white, translucent skin, displaying large eyes and tiny teeth, with what looks like a larva in red tones attached to its side.

    Haplophryne mollis is a "two-in-one" fish: the male is permanently attached to the female's side.

    © IRD - TAPIOCA

    Haplophryne mollis is a unique “two-in-one” fish. Once the male has found a female, it remains latched to her side for life and is fully fused to her vascular system. This highly unusual parasitic mode of reproduction is of great interest to scientists, who hope to draw inspiration from it to improve organ transplantation. These fish have very little capacity and stay at the bottom of the ocean, where they attract prey with their luminous filament.  

  • Malacosteus niger
    A fish in profile, in shades of black and red, with a jaw larger than its head.

    Malacosteus niger is one of the rare pelagic species that produce red light.

    © IRD - TAPIOCA

    Malacosteus niger can feed on large prey thanks to its sizeable jaws. This predatory species is one of the few to produce red bioluminescence, which enables it to locate crustaceans, even at great depths.

  • Nemichthys curvirostris
    A long and slender fish, whose morphology is more similar to an eel, with large eyes and a beak-shaped mouth.

    The morphology of Nemichthys curvirostris, very different from that of other pelagic fish, allows it to move and hide.

    © IRD - TAPIOCA

    Unlike other pelagic fish, this serpentine species has a very unusual morphology, which enables it to move around and hide. It is a migratory species that feeds on zooplankton which it catches in the upper waters at night before descending to the depths to avoid predators during the day.

  • Rhynchactis leptonema
    A fish with eyes so small that they are not distinguishable. It consists of two rounded parts and has a long filament at the tip of its head that serves as a glowing lure.

    Rhynchactis leptonema is an extremely rare fish that relies on bioluminescent bacteria to produce its light.

    © IRD - TAPIOCA

    Rhynchactis leptonema is an extremely rare fish, of which only a few specimens have been caught around the world, mainly off Brazil and Japan. It is a member of the anglerfish family and swims very little. It does not migrate and uses light to attract its prey. Unlike some other fish in this family, it does not produce its own light through bioluminescence, but depends on bioluminescent bacteria present in marine snow. Little is known about this phenomenon, which scientists are seeking to understand better. 

  • Rondeletia loricata
    A fish in profile with a red hue and black eyes.

    Rondeletia loricata hides from predators using its red light.

    © IRD - TAPIOCA

    The red colour of Rondeletia loricata allows it to hide from predators, as this wavelength is difficult to see at the ocean floor. Not very abundant, it lives at depths of between 100 and 3,500 metres and does not migrate. It hunts small fish and crustaceans for food.

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