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How Fish Make Themselves Invisible—Mystery Solved

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Clever blighters.

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.


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


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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