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Ultra-Black is the New Black

A digital illustration of a pure black anglerfish silhouette overlaid on a white spotlight. The text "ultra-black is the new black" is written across the background.

Written by Sabrina Zaidi
Illustrated by Cheryl Nong

Life is bright here on the surface of the Earth – the sun shines, the moon glows, and the stars glimmer. With plants being at the bottom of most food chains, it’s reasonable to believe that animals would only live in areas touched by the light of the sun. Yet, over 200 metres under the sea lives a completely different world, beyond the reach of the sunlight that travels millions of miles to shine upon our planet.1 Whether it’s day or night, it’s all the same darkness – that is, until you’re graced by the light of a jellyfish floating by. Down here, all light is produced by bioluminescence (the process that allows animals to generate their own light), making for a seemingly alien landscape in the deep sea.1 However, some fish have taken a different route to adapt to life in the deep by fully embracing the darkness. Only a few other species in the animal kingdom exhibit these features, but no one does it as well as ultra-black deep-sea fish. 

With a colour reminiscent to vantablack which is one of the darkest synthetic substances, the specific pigmentation of ultra-black deep-sea fish can absorb any light that reaches them from the bioluminescence of other organisms nearby.1 This makes them nearly invisible against the pitch-black background of the sunless deep sea as they reflect less than only 0.5% of all light.1 A black sheet of paper, in comparison, reflects around 10% of light, and other dark-coloured fish have a reflectance of 2%.1 Currently 16 species of fish have been found to have ultra-black pigmentation, including the dreamer anglerfish, which is the blackest animal on the planet with a light reflectance of only 0.044%!1 The researchers who discovered this phenomenon found that their blackness acts as a sort of invisibility cloak, allowing the fish to go undetected by visual predators.2 Reducing skin reflectance from 2% to 1% prevented predators from seeing the fish by 29%, and going down to 0.05% reflectance reduced sightings from predators by as much as 84%.1 While there are other animals with ultra-black pigmentation, its function for camouflage had never before been documented. Other animals that exhibit this feature, like some species of birds of paradise, jumping spiders, and butterflies, use it to enhance the appearance of colourful markings to make them look bolder for better colour signaling. 1 

digital illustration of a cluster of black fish swimming upwards across the page. Behind them are a spread of radioactive waste barrels, droplets of mercury, and a submarine.

Ultra-black fish possess highly unique biological characteristics that make them so black. In the same study, the researchers found that these fish uniquely have very densely packed melanosomes on the outer layer of their skin, which are organelles that store and produce melanin pigments. 1,3 In the melanosomes, melanin is what gives pigmentation to the skin, hair, and eyes in animals.3 Their ability to reflect such low levels of light is the result of a specially optimized configuration of these melanosomes such that the surface of their body lacks unpigmented cells that would normally be present on a standard dark-coloured fish. 1 Additionally, the melanosomes scatter light so that the melanin is able to absorb light more easily. 1 However, the trade-off for having this unique cellular composition is that the skin of ultra-black fish is very fragile as it doesn’t have collagen, which usually offers protection in other fish.1,4

As we appreciate these fish for being the masters of camouflage that they are, we can learn a lot from their cells for the development of our own synthetic ultra-black materials. Melanin has properties that allow it to absorb hazards like radiation, heavy metals, and x-rays which can have potential applications for personal protective equipment and other uses.2 The ultra-black colouration itself piqued the interest of Naval researchers who could use the pigment as a basis for developing a coating for ships and submarines.2 With this fascinating new discovery, there’s no telling what else we can find down in the depths of the ocean that can further our understanding of biology, and even build upon current advancements.

Sources:
  1. Davis AL, Thomas KN, Goetz FE, Robison BH, Johnsen S, Osborn KJ. Ultra-black camouflage in deep-sea fishes. Current Biology. 2020;30(17). doi:10.1016/j.cub.2020.06.044 
  2. Sexton C. Elusive, ultra-black fish are cloaked to survive in the Deep Ocean. Smithsonian Magazine. 2020 Jul 21 [accessed 2023 Nov 24]. https://www.smithsonianmag.com/smithsonian-institution/Elusive-Ultra-black-Fishes-Are-Cloaked-to-Survive-the-Deep-Ocean-180975367/ 
  3. Raposo G, Marks MS. Melanosomes — dark organelles enlighten endosomal membrane transport. Nature Reviews Molecular Cell Biology. 2007;8(10):786–797. doi:10.1038/nrm2258 
  4. Metcalfe T. Meet the “ultra-black” fish of the ocean’s depths. NBC News. 2020 Jul 20.

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