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,