Fish and Camouflage: How Certain Platelets Allow Fish to 'Disappear'

Fish don't need invisibility potions. Certain ones have microscopic platelets in the cells of their skin -- these reflect light waves that take place in a single plane (polarized light) and allow them to befuddle and disappear from the view of their predators in the open ocean.

Researchers at the University of Texas Austin (UT) published a report on this recently in the journal Science. They say that their findings might help in the development of better ocean camouflage by materials scientists and the military.
When you see bright glare from sunlight reflecting off a water surface, that's one form of polarized light. This happens even more often beneath the water surface. A lot of fish--and modern satellites--can pick up variations in underwater polarized light.

Knowing that fish can detect this light, Molly Cummings, professor at UT, said in a release, "Given that, we suggested they've probably evolved the means to hide in polarized light. If we can identify that process, then we can improve upon our own camouflage technology for that environment." (Scroll down to read further...)

Fish and satellites can find targets in the ocean by looking at certain factors in light: color contrast, brightness contrast and polarization contrast. The latter is thought to be the most effective, the release confirmed.

In the study, the scientists used what is called a video polarimeter, which can make recordings in real time of polarized light. In this way, they were able to view polarized light as the fish do, as a statement noted.

In a team composed of City College of New York, Texas A&M University and other institutions, the researchers built a rotating platform to hold fish in place at the same time that the polarimeter made measurements, said the statement.

After taking more than 1,500 measurements, the team noted that the two fish that originate in the open ocean, which are called bigeye scad and the lookdown, possessed better camouflage than a mirror did, in polarized light. They blended in better than three other fish from environments in which polarized light is less of a factor, according to the statement.

Their superior camouflage took place in "chase angles" extending 45 degrees from the tail or head-the directions in which predators would approach the fish. The lab learned that platelet structure made this possible, said the release.

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