However, more than 650 feet deep in the ocean, in the lower mesopelagic and bathypelagic zones, there is little sunlight. So in these areas, evolutionary adaptations like transparency and mirrored surfaces aren’t all that helpful in keeping dinner raiders away. This is because the fish that use these defense strategies reflect at least 0.4% of bioluminescence from other deep-sea animals, which describes the production and emission of light by a living organism.
Pigmentation is another method of being incognito at sea; it allows animals to absorb light from bioluminescent sources and thus be visually undetectable rather than reflecting that light on their own.
Karen Osborn, a research zoologist at the Smithsonian’s National Museum of Natural History, thought about taking a closer look at the fish’s skin when she tried to photograph black fish that she and her colleagues caught in Tucker’s trawls in the Gulf of Mexico. and in Monterey Bay, California. Tucker trawls allow scientists to catch fish from mid-water levels, where ultra-black fish can be found. Regardless of the quality and layout of her camera and lighting, Osborn was unable to capture any detail in the shots.
Knowing the ineffectiveness of common camouflage tactics, the researchers hypothesized that pressure to limit reflected light could have led to the evolution of pigmented body surfaces with near-zero reflectance in ultra black fish. Reflectance is the measure of the proportion of light that hits a surface and is reflected on that surface.
Using different tests, models, and comparisons with other cold-blooded animals, the scientists found that black fish absorbed more than 99.5% of the light hitting their skin; in other words, they had a reflectance of less than 0.5%.
How ultra black fish disappear
To test the fish’s ultra-black coloration, the researchers collected 18 species from the waters of the Gulf of Mexico and Monterey Bay, California, during two research cruises.
They measured the reflectance of the fish with a three-part rear reflectance probe, said Alexander Davis, co-author of the study and a biology PhD student at Duke University in North Carolina: a light source, a detector that It counts the number of photons (light particles) that return and a fiber optic cable. The fiber optic cable collects the light that shines on the subjects and sends it back to the detector, allowing the scientist to know how much light is reflected.
Oneirodes, a genus of fish known as monkfish, had the lowest measured reflectance.
The coloration of ultra-black fish is even darker than some man-made materials, such as black paper and freshly paved asphalt, Davis said, which reflect about 0.04% to 10% or more light.
The underlying structure that made the ultra black coloration possible was tight melanosomes just under the skin of the fish. Melanosomes are pigment particles that provide color to animal tissues and help your skin absorb light rather than reflect it.
Ultra-black fish can be both predators and prey, so the researchers thought the fish may have faced pressure to develop a dark coloration to avoid other predators.
“When things are as dark as the bottom of the sea, if you reflect even a handful of photons, something can detect you,” Davis said. “And here, these animals are covering everything [bodies] in this ultra black leather to absorb basically all the light and combine with the blackness of the deep sea. ”
According to the study, the findings rank ultra-black fish at the same level and beyond some of the blackest animals known: ultra-black butterflies have a reflectance of 0.06% to 0.5%, and blackest birds show a reflectance. from 0.05% to 0.31%.
The researchers also found that by reducing their reflectance, ultrablack fish can reduce their chances of being seen by predators six times more than fish with 2% reflectance.
The researchers suggested that the biology of ultra-black fish could advance the development of less expensive, flexible, and more durable ultra-black materials for optical technology, including cameras and telescopes, and for camouflage.
“One of the main uses of ultra-black materials is to coat the interior of the optical equipment to prevent stray light from bouncing off it,” Davis said. “As long as you can create a random matrix of these nanoparticles that are highly absorbent and are the correct size and shape, then you should be able to cover anything with it. So you don’t need to create a detailed structure for it to work.” .
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