Some fish have found a way to avoid predators, by manipulating and reflecting polarized light vibrations, a new study finds.
The new research – published in the journal Science – found that some fish have microscopic structures in their platelets, or skin cells, which they use to scatter polarised light in the water. Fish platelets are not the same thing as mammalian platelets (thrombocytes), which are a component of the blood.
These fish can practically turn invisible by reflecting the light patterns in their surroundings, the researchers said.
Dr. Molly Cummings, primary investigator of the report and an associate professor of the School of Biological Sciences at the University of Texas at Austin, said that even though the ocean may appear to be a uniform environment in our eyes, it is far from being so.
For about five years, Dr. Parrish Brady, a research associate in the Department Of Integrative Biology at the University of Texas at Austin, and Dr. Cummings, as well as other academic collaborators have worked on the project that observes how fish have developed a way to camouflage themselves, using variations of polarised light in their environment.
When light is polarised, the vibrations of the light waves move on the same plane, but when light is unpolarised (which most light is), the vibrations travel on multiple planes.
Above the ocean, sunlight is not polarised. However, once it gets underwater, it usually becomes polarised. Some fish have the ability to mimic polarised vibrations with the help of their skin cells.
Dr. Brady says that fish platelets are nanoscale crystals. Although scientists have long known that some fish user their luminous scales to camouflage themselves, they did not know exactly how fish did that or to what degree.
The platelets are aligned in a specific way to scatter light away from the fish, which gives the platelets their reflective properties, Dr. Brady explained.
The ability of fish to reflect polarised light may also be applied in human camouflage, according to Dr. Cummings. Fish have evolved the means to detect polarised light and probably hide in polarised light as well. Camouflage technology may be improved, using a similar process that fish use.
For the experiment, the researchers built a device called video polarimeter, which is an instrument that they used to record the polarised light around a fish that was positioned near a mirror. The fish was placed on a rotating platform, and the researchers changed the angle of the platform after each 360-degree spin.
After two week of recording five different species of fish, at more than 1,500 angular configurations, the researchers found that two of the fish – the lookdown and the bigeye scad – were really good at camouflaging in polarised light.
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