Pacific Blackdragon

FishPacific Ocean

Aug 5

Written By Alexander Julius Jensen

Idiacanthus antrostomus

A female Pacific blackdragon is ~60 cm (2 ft) long and uses a bioluminescent lure on her chin to attract prey. Her skin is 'ultra-black', among the darkest in nature, and her teeth are anti-reflective, so as not to reflect light from her lure and alert her prey. The male is only ~8 cm (3 in) long.

Here There Be Monsters!

A 1598 map of Iceland by Abraham Ortelius showcases a sea of monsters.

Many maps of old feature absurd, behemoth monsters living in their waters. Sea serpents ravage ships, bloated whales spout water from twin blowholes, giant man-eating lobsters terrorise sailors, and off-putting chimaeras, with fishy bodies, hog heads, and human eyes along their torsos, float oddly atop the waves. Most of these maps come from Europe, between the 15th and 17th centuries; the Age of Exploration. This era opened up much of the world to Europeans, as explorers set out by sea to find new wealth and knowledge. New trade routes were found, new coastlines mapped, and entire new oceans were discovered (by the Europeans, at least) — the Pacific among them. It is estimated that during the 16th century, the mortality rate of sailors was around 50%. Half of those who took to sea never returned. And so the distant oceans became, equally, a place of glory, opportunity, and mystery as well as a place of danger and death — 'Here there be monsters!', the mapmakers warn.

The Pacific blackdragon is not a winged beast that rises from the ocean's dark abyss. It doesn't scour the coasts for livestock like a medieval drake. It doesn't strangle ships and scarf down sailors like a sea serpent. It's certainly no Leviathan. The largest the blackdragon grows is around 60 cm (2 ft) long — and that is the female, the heftier sex. The puny male is only about 8 cm (3 in) long. This "dragon", both male and female, is considered entirely harmless to humans. Once you set eyes on it, however, such an affirmation may seem hard to believe, for, in her appearance, a female blackdragon is more frightening, more nightmarish, than any monster found on a map.

The body of a female Pacific blackdragon is long and serpentine — eel-like, although there is no close relation ¹ — tapering from a large head to a skinny, whip-like tail. Frilly gills mark the border between her body and head. Her jaws make up most of her face, the bottom one protruding slightly. Her mouth contains an asymmetrical scattering of needle-pointed teeth. From her chin trails a long whisker, tipped with a light-producing organ. She is an ambush predator and this light is her lure.

The Blackest of Dragons

The ultra-black skin of a Pacific blackdragon is covered in a continuous layer of tightly packed melanosomes.

The Pacific blackdragon, not unexpectedly, is a monster of the deep, residing in the Pacific Ocean's mesopelagic zone — the oceanic layer between 200 metres (660 ft) and 1,000 metres (3,300 ft) deep. Sunlight just barely manages to trickle to these depths and so the large eyes of a blackdragon — although appearing pale and dead — are well-developed to snatch as much light as possible. But, come night, no celestial light reaches even the upper ranges of the deep. This is when the female blackdragon rises to feed. Her lure glows bluish with bioluminescence; possibly the only light for miles, like a lighthouse beacon in the night.

Curious fish, attracted by her glow, see only a bobbing wisp. This "dragon" is called black for a reason. None of her bioluminescent light falls on her own body, or rather, her body is so dark that it soaks up any light that hits it. Her skin, especially on her belly, is 'ultra-black'.² This is thanks to a layer of structures called melanosomes; structures that are circular, closely packed together, and contain melanin — the same biomolecule that gives your hair and skin pigment. We, and many other creatures, also have melanosomes, but they're typically found deeper in the skin and are scattered throughout. Those of the blackdragon form a continuous layer over the surface of its skin. It seems that this particular arrangement of melanosomes serves to direct light that wasn't caught by one melanosome to another in the layer, essentially reflecting the light between melanosomes until there is very little light left which can escape. This unique structure is capable of soaking up around 99.95% of the light that hits it — particularly wavelengths similar to ambient sunlight or the light from bioluminescent animals. For the Pacific blackdragon, this means complete invisibility in the dark depths, even in the presence of her own glowing lure.

An eel-like female Pacific blackdragon — like a serpent of the deep.

And so she sets the bait to attract unwitting victims. Her prey approaches and floats entranced by the luminance of her lure; blind and completely oblivious of the black nightmare floating above. She moves in closer. Her gaping maw splits her head; her mouth is a lightless cavern, lined with organic, razor-sharp stalactites and -mites. Her teeth are transparent and anti-reflective, so as not to give away her presence. She bites down like a jagged guillotine, skewering her prey's body. Her victim never even saw the killer.

In contrast to her ultra-black skin, her length is lined with specialized light cells called photophores, which can flash with bioluminesce, likely used to attract mates in the deep dark. Her amore is hardly more than a larvae, less than 15% of her length. He has no barbel lure on his chin, no teeth, and no stomach. With no way to attract prey, grab it, or digest it, he obviously doesn't eat — he receives all the energy he'll ever get from his egg yolk at birth. His short lifespan is devoted entirely to mating with a female.³

An Abyssal Age of Exploration

Sailors during the Age of Exploration were unlikely to have encountered the Pacific blackdragon, for the depths at which it lives were as unreachable to them as the moon in the sky. Even today, the deep oceans are largely unknown, with 80% still uncharted and unseen. But, with our rapidly developing technology, this dark realm of crushing depths and nightmare creatures is slowly opening up to us — perhaps that is where the next Age of Exploration lies.

A diagram of the jaw function of a black dragon fish (*Malacosteus niger*), looking like some Lovecraftian monster.

¹ The Pacific blackdragon is a member of the barbeled dragonfish family (Stomiidae). These fish range from the bathypelagic depths to the surface and are usually quite small — typically under 30 cm (12 in) in length. Some have jaws that can open at an angle of more than 100 degrees. None of the blackdragon's relatives are particularly pretty and some are downright horrific (see left).

Clockwise from right; a common fangtooth (*Anoplogaster cornuta*), a crested bigscale (*Poromitra crassiceps*), and a bulbous dreamer (*Oneirodes eschrichtii*).

² The Pacific blackdragon isn't the only 'ultra-black' fish. This unique type of skin was noticed by Karen Osborn, a marine biologist at the Smithsonian Museum, who often takes photos of interesting creatures caught in her trawl net. In her attempts to take their photos, a few deep-sea fish she captured appeared as nothing but black silhouettes. This was the first discovery of ultra-black colouration in aquatic animals, prompting a further investigation, a study, and a published paper with several collaborators.

The study inspected the structure and arrangement of melanosomes in 18 species, 16 of which had a reflectance below 0.5% — for comparison, black construction paper has a reflectance of 10%. The common fangtooth, a big-headed deep-sea fish with curved, needle-like fangs, was one of the studied fish. Only growing to around 17 cm (6.7 in) long, its ultra-black skin serves as camouflage from larger predators, who themselves use bioluminescence to hunt in the deep. The threadfin dragonfish only has ultra-black skin as a juvenile, growing out of it's "dark phase" as it becomes an apex predator adult. The crested bigscale is named such because of the few, but large, scales that cover its body — which are overlaid by ultra-black skin. If attacked by a predator, its large scales slide off easily, taking the skin with them, allowing the bigscale to escape but leaving an exposed bit of "light" skin where the scales were removed. On the benttooth bristlemouth, ultra-black skin was only found along its gut, possibly to conceal recently eaten bioluminescent prey.

Out of all the species studied, the Pacific blackdragon was the second darkest. The darkest was a species from the Oneirodes genus of dreamer anglerfish, with a reflectance of only 0.044%. Ultra-black animals also exist aobve the deep sea abyss, out of the water. There are species of ultra-black butterflies (although the fish are darker) and ultra-black male birds-of-paradise (only matched by the darkest of fish).

A female humpback anglerfish (Melanocetus johnsonii) with a parasitic male attached to her underside.

³ Some anglerfish species take this a step further; the tiny male becomes a permanent parasite on the larger female's body. He fuses to her body, losing much of his features, including his eyes, as the female's body now caters to his nourishment needs — even their bloodstreams eventually connest. A tiny, sightless, amorphous lump on the female's body; his only role is to provide her with a constant supply of sperm.

**Where Does It Live?**

⛰️ In the mesopelagic zone — the oceanic layer between 200 metres (660 ft) and 1,000 metres (3,300 ft) deep.
📍 The Pacific Ocean. ¹

Size // Medium (female) and Tiny (male)
Length // ~60 cm (2 ft) female and ~8 cm (3 in) male
Weight // N/A
Activity: N/A
Lifestyle: Solitary 👤
Lifespan: N/A
Diet: Carnivore
Favorite Food: Other deep-sea fish 🐟
Class: Actinopterygii
Order: Stomiiformes
Family: Stomiidae
Genus: Idiacanthus
Species: I. antrostomus

A male Pacific blackdragon is less than 15% of the female's length. He has no barbel lure on his chin, no teeth, and no stomach — he doesn't eat, having received all the energy he'll ever get from his egg yolk at birth. In his short life, his only goal is to mate with a female.

The Pacific blackdragon lives in the Pacific Ocean's mesopelagic zone — the oceanic layer between 200 metres (660 ft) and 1,000 metres (3,300 ft) deep.

The female blackdragon's body is lined with photophores; specialised cells that are able to create light. This bioluminescence is likely used to attract mates in the abyssal dark.

The Pacific blackdragon achieves its ultra-black colouration via a unique layer covering its skin. Circular, melanin-containing structures, called melanosomes, are numerous and tightly packed along the surface of its skin. This arrangement bounces any light between the melanosomes, causing very little light to be reflected back — less than 99.95% in some cases.

The female Pacific blackdragon's underside skin is especially dark, to hide her body from the light of her own lure.

The Pacific blackdragon is a member of the barbeled dragonfish family (Stomiidae). This family of fish is most closely related to other bony, deep-sea fish such as marine hatchetfish and viperfish.