Open-ocean fish reveal an omnidirectional solution to camouflage in polarized environments

Science  20 Nov 2015:
Vol. 350, Issue 6263, pp. 965-969
DOI: 10.1126/science.aad5284

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Disappearing act

Unlike coastal regions and reefs, the open ocean is mostly empty. Many fish species, nonetheless, spend most of their lives there. Such emptiness makes camouflage exceedingly difficult, so how does an organism hide in water filled with bouncing and reflected light? Brady et al. show that some families of fish have evolved skin that reflects and polarizes light, allowing them to blend into their mirrorlike conditions more easily. These results help to explain the silvery coloration found in sea-living fish across the world's oceans.

Science, this issue p. 965


Despite appearing featureless to our eyes, the open ocean is a highly variable environment for polarization-sensitive viewers. Dynamic visual backgrounds coupled with predator encounters from all possible directions make this habitat one of the most challenging for camouflage. We tested open-ocean crypsis in nature by collecting more than 1500 videopolarimetry measurements from live fish from distinct habitats under a variety of viewing conditions. Open-ocean fish species exhibited camouflage that was superior to that of both nearshore fish and mirrorlike surfaces, with significantly higher crypsis at angles associated with predator detection and pursuit. Histological measurements revealed that specific arrangements of reflective guanine platelets in the fish’s skin produce angle-dependent polarization modifications for polarocrypsis in the open ocean, suggesting a mechanism for natural selection to shape reflectance properties in this complex environment.

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