Navy research shows how some fish make themselves ‘invisible’

The combination of specific elements in their silvery skin and a particular type of light are what make some types of fish appear to essentially invisible in the open water, a new study funded by the US Navy and published in the latest edition of the journal Science has discovered.

According to National Geographic, University of Texas, Austin biologists Molly Cummings and Parish Brady constructed a slowly-spinning device similar to a weather vane with four arms. One of the arms was equipped with a high-tech camera that monitored a net used to catch fish on the opposite side—where it took photographs of actual ocean fish.

Experts had already suspected that certain types of fish, including the lookdown and the bigeye scad, could reflect light using their skin. However, by placing their device in the waters near the Florida Keys and Curaçao, the authors of the new study were able to confirm that these fish had tiny structures in their skin known as platelets that could reflect polarized light (light that moves along a single plane), rendering them all but invisible.

Scientists had previously detected these platelets, but had previously been able to confirm if they were used to help the fish hide in polarized light. Not only do they provide camouflage, the study authors found, but they do a better job of it than previously anticipated, particularly in the bigeye scad, which showed less contrast than near-shore fish and mirrors held in the fish nets.

Natural camouflage could be used in next-gen stealth tech

The UT-Austin team’s research was funded by the Navy as part of the military’s effort to learn how some fish are able to hide so well in plain sight underwater, and how this ability might be used in order to develop next-gen stealth technology, according to the Washington Post.

As Brady told the newspaper, the Navy has been searching for ways to hide vessels in the deep open waters for several years. The new research brings them a step closer to achieving that goal, he added, but precisely when and how such technology could come about remains unclear.

“If we can identify that process, then we can improve upon our own camouflage technology for that environment,” Cummings told the Post, calling the research “a great example of how human applications can take advantage of evolutionary solutions and the value of evolutionary biology. It’s important for people to recognize that we take advantage of evolutionary processes and solutions all the time and that even our military does.”

She and Brady studied the fish from more than 1,500 angles, and found that they were hardest to see in what they refer to as “chase angles” of 45 degrees from head or tail, which predators use to pursue their intended victims and which the fish themselves use to hunt prey. The next step, they said, will be to see if the fish can enhance these abilities by intentionally moving platelets.

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