The Incredible Vision of Dragonfish
Fish of the deep seas are not just the things that haunt your nightmares, they are also pretty amazing in their ability to just exist in such extreme darkness.
Discord of the Deep
The slow-moving, toothy, lamplighters of the deep are indeed beings that make us think twice about whether aliens have already inhabited Earth. Of the many weird and wonderful critters roaming our depths, dragonfish are by far the most advanced and adapted to the sheer surrounding dark. Aside from their seriously crazy appendages and facial resemblance to Edward’s scissor-hands, deep-sea dragonfish are also the only deep-sea fish capable of creating their own light source through red light waves. Specifically, dragonfish have adapted to both generate and see red light, which is essentially absent from the deep ocean as red light waves are easily filtered through water. Because red light is not typically visible at depth, many deep-sea animals have evolved to be red in color. In this way they outsmart predators by presenting black in appearance, making them much less visible and less likely to fall prey to larger animals.
In this twilight zone of the deep, animals that are black absorb all available color wavelengths, while red reflects as black because of a lack in red wavelengths at depth to reflect off of them. In this way, black and red creatures are the dominant species of the deep seas.
Also called the scaleless dragonfish, our deep-sea not-at-all resembling a dragon, dragonfish (Grammatostomias flagellibarba) friends wonder the bottom-most zones of tropical oceans, with their optimum range resting at between 1,500 m and 2,000 m below the surface. They are quite small considering their advanced adaptability and infamy for being ferocious predators. Clocking in at just under 15 cm, they have extremely large and oversized fang-like teeth in comparison to their body size, which certainly helps with their terrifying and gruesome aesthetic. To top off their gory exterior, they have a long protrusion that extends from their chin. This protrusion is referred to as a barbel, which is tipped with a specialized photophore organ that is responsible for generating light. Through a process known as bioluminescence, dragonfish generate a flashing light used to attract and disorient prey as well as signal to potential mates. Not yet satisfied of their awesomeness? Dragonfish have further evolved photophores along the sides of their body, only switched on during mating to alert others of what is going down. They also quickly learned to use their barbel as a cheeky fishing lure, igniting their photophore and waving it back and forth. Once an unsuspecting fish gets close enough, it is made quick work of by the powerful teeth of the dragonfish. Since many of the smaller fish and crustaceans that they feed on have their own means for capturing light, dragonfish have even adapted their internal stomach lining to reflect black so as not to reveal the concealed prey within.
The unique ability of dragonfish species to create and see their own red light is what has attracted attention to them over the years. Generally, bioluminescence in deep-sea fish means being able to produce and detect blue light, which is a superior light source in dark areas that are entirely absent of natural light. On its own, bioluminescence is an advanced trait for communication, navigation, and hunting; but with the additional layer of shifting to the other end of the color spectrum, dragonfish ability is unparalleled. Because they are the only group of marine animals with this ability, they have well-positioned themselves as prime predators of the deep.
“It doesn’t change. It is always dark. There is something else down there that is driving the evolution of the visual system.”
Comparative Biologist, Harvard University
The deep ocean is not the sort of environment that we associate with rapid evolution and adaptation. Rather, it is the sort of place we think of as withholding secrets of lost eras, treasure troves, ancient relics, and above all else, dinosaurs. Deep-sea beings are some of the oldest living fauna and flora, with studies finding genes and behavioral traits linked to centuries past. So what in these waters is promoting evolution? Many scientists have hypothesized that it is the bioluminescence itself that drives these changes.
Out of almost 60 dragonfish species variants, only 9 have adapted their bioluminescence ability to red light. This novel ability was first discovered just two decades ago and has since been studied with vigor. Scientists now believe that photophores developed as specialized light-emitting cells below the eyes. Instead of using enzymes to emit photons that filter out red light, they flipped it to filter out the more traditional blue. This evolution alone, however, was not enough to give dragonfish the advantage over their deep-sea relatives. They also had to evolve means to be able to see the red light now that they could create it. In response, their eyes enlarged over time so that it could house the red end-of-the-spectrum pigments to boost their vision. The end result is the only marine creature capable of producing and detecting their own light source.
If dragonfish were not yet cool enough for you, this might just tip the scale. Even though at this point they have done centuries of evolutionary work over a fraction of the time, they did not stop there. Producing red light at such depths still has its limitations: red light just does not travel well when encased in dark water masses. This means that dragonfish need to get seriously close to their prey for them to effectively see all of their created red light before they can strike. And to carry this out properly, they have made it so that they are completely invisible to all other creatures.
Dragonfish have adjusted their skin color to be incredibly dark in nature. Some species, like the pacific blackdragon, are classified as ‘ultra-black’. The skin color adjustments help them absorb 99.5% of all light aimed at their skin. Together with camouflaging their skin, they too enhanced their teeth, making them transparent and allowing them to easily encase prey from all sides before the prey even realizes what is upon them. Other dragonfish species hold on to their blue-light photons and so can opt to alternate between flashes of red and blue to simulate a dance for their prey, luring them in right up close before engulfing them whole.
Regardless of the technique a particular dragonfish uses, it is widely understood that they are truly masters of the deep. They have set themselves up to be almost untouchable with their invisibility, light creation, mating wavelength signals, as well as their own personal night vision.