Biologists identify 16 deep-sea fish species with camouflage that wards off predators

Underwater photographers have noticed for years that dark-colored fish in deep seas are difficult to photograph but a research report published last month provides a better idea of how many of these fish are camouflaged in the deeper regions.

The report, "Ultra-black Camouflage in Deep-Sea Fishes," published in the peer-reviewed journal Current Biology on July 16, documents that at least 16 species of deep-sea fish produce the darker colors that make them hard to spot, certainly for photographers, but mostly for predators.

The species represent seven distantly related orders, according to the report.

"These fishes have a continuous layer of melanosomes in the dermis that are optimized in size and shape to allow them to reflect [less than] 0.5% of light," the report said. "Sighting distance models suggest low reflectance reduces predator sighting distance up to six-fold."

The team of marine biologists from the United States and United Kingdom included lead report contact Alexandria Davis, a  Ph.D. student with the biology department at Duke University in Durham, North Carolina.

To research the ultra-black coloration, unlike black coloration also found in deep sea fish, the team collected specimens up to a mile deep during two cruises, one in the Gulf of Mexico and the other in Monterey Bay, California. The captured fish were kept in chilled seawater as researchers used a spectrometer to measure how much light reflected off the fishes' skin.

The researchers found that the 16 identified species reflected less than 0.5% of light, which made them 20 times darker and less reflective than normally black items.

"This low reflectance puts deep-sea fishes on par with the blackest known animals, with the species exhibiting the lowest reflectance measured here, surpassing the darkness of ultra-black butterflies and equaling the blackest birds of paradise," the report said. "By comparison, man-made materials, such as black paper, reflect ~10% of incident light, and the blackest synthetic materials, manufactured from vertically aligned carbon nanotubes, reflect 0.045% of light."