It may seem like there’s nowhere to hide in the open ocean, but fish have figured out a way to mask themselves in nothing but water and sunlight, a new study says.
Scientists already suspected that silvery fish like the lookdown and the bigeye scad use their skin as camouflage, reflecting light away to be less conspicuous. But it has been difficult to test these ideas where they really matter.
So in a new study, a team built a slowly spinning device with four outstretched arms like a weather vane. One arm steadied a high-tech camera pointed at a fish-constraining net on the opposite side. The researchers dropped the instrument in the ocean off the Florida Keys and Curaçao, where it took over 1,500 photographs and measurements of live fish as the sun moved across the sky.
The research, led by Parish Brady and Molly Cummings at the University of Texas, Austin, showed that open-water fish hid well in polarized lightor light moving in a single plane. Polarized light is common underwater.
The team also found tiny structures in some fish skin, called platelets, bend polarized light to make the fish almost invisible. Researchers had seen these platelets earlier, but whether open ocean fish used them to hide in polarized light was unknown.
Of the fish they studied, two species called the lookdown and the bigeye scad emerged as camouflage champions. They blended in beautifully, showing less contrast than nearshore fish and human-made mirrors held in the nets behind the fish. Previously, researchers had guessed that the fish skin reflected light like a mirrorin fact, it does a much better job.
Not surprisingly, their camouflage also worked best at 45 degree angles from the front or backangles at which predators strike, according to the study, published November 20 in Science.
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