Many fish have metallic-looking reflective scales due to plates of guanine, and it had been thought that the mirror-like finish was all there was to their camouflage, but it turns out that they work more subtly. Parrish C Brady of the University of Texas at Austin and colleagues studied more than 1500 video-polarimetry measurements from live fish in distinct habitats and under different viewing conditions, and the researchers have shown that the fish adjust the reflection to take into account the highly variable degree of light polarisation in the open ocean, with optimal camouflage at angles associated with predator detection and pursuit.