Toronto Star

U.S. navy fishing for new technology

Ability of some fish to hide from predators may be a skill military could use

- DARRYL FEARS THE WASHINGTON POST

Harry Potter’s invisibili­ty cloak is real. Well, for some fish at least. Astudy released Thursday says that two ocean fish — the big-eyed scad and the lookdown — have fine-tuned a method of avoiding predators by hiding in light. Elements in their silvery skin render them nearly impossible to see. The U.S. navy funded the study as part of an effort to understand how fish do this, and how it could be used to the navy’s advantage.

Although the study focused mostly on just two types of fish, the scad and lookdown are members of a family called the Carangidae, a bountiful clan that includes the white ulua, bluefin trevally, mackerel scad and rainbow runner.

The University of Texas study, published in the journal Science, said the fish use their skin as camouflage to blend in with light waves. They’ve evolved a microscopi­c element on the surface of their skin called guanine platelets. It manipulate­s the way the fish reflect in polarized light, said the study’s author, Parrish Brady, a research associate at the university.

For years, the navy has searched for ways to hide vessels in deep open water. The study’s findings brings the military branch one step closer to understand­ing a new type of camouflage.

Polarized light comprises light waves moving on a single plane. Beneath the water’s surface, fish in the Carangidae clan have found a way to detect variations in polarized light waves and use it to conceal themselves in plain sight. In the open ocean where there’s hardly anyplace to hide from sharks and other predators, it’s a significan­t advantage.

Hiding in light doesn’t always work, but it increases life expectancy, allowing fish with the capability to live longer and breed. The big-eyed scad and lookdown were chosen for the study because of their silvery skin, flat and mirrorlike, with colour reflective cells and sharp angles that make hiding easier.

“If we can identify that process, then we can improve upon our own camouflage technology for that environmen­t,” said Molly Cummings, professor of integrativ­e biology in the College of Natural Sciences and a co-author for the study.

For the study, the open ocean, so deep the bottom can’t be seen, was used as a laboratory off the Florida Keys and Curacao. “We put the fish in a restrainin­g device and measured them with video,” Cummings said.

The fish were held against a mirror as video rolled. A platform supporting the fish spun 360 degrees in three-minute cycles while a polarimete­r — a device that measures how polarized light behaves as it passes through angles — recorded. After every revolution, researcher­s would make an adjustment, then restart the apparatus.

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