Silvery Fish Can Become Invisible To Predation
October 22, 2012

Silvery Fish Can Become Invisible To Predation

Michael Harper for — Your Universe Online

After all the research we´ve been doing for centuries, nature continues to surprise us from time to time, forcing us to reconsider long-held theories or showing us something totally new.

Take, for instance, the reflective properties of silver fish, such as herring or sardines. It´s long been observed that these resplendent fish have the ability to deflect light, making it tricky for a predator to focus and snatch them up. After taking the time to observe and study these fish, however, 2 researchers have found that this isn´t the end to the story. These fish aren´t just able to reflect light, they´re able to become nearly invisible to their foes.

Dr. Nicholas Roberts, along with research assistants Tom Jordan and Julian Partridge from Bristol University performed this research which involves the matter of polarization and reflective surfaces.

As a brief refresher, polarization is what happens when light is reflected in one plane of direction. Think, for example, the glare that comes off the surface of a lake. Polarized sunglasses optimize a layer which only lets certain wavelengths of light through, reducing the overall haze and glare seen by the wearer.

It´s long been understood that these herring and sardines have reflective guanine crystals in their skin which can fully polarize light when reflected. When this light becomes polarized, reflectivity drops.

After researching these fish, Jordan and Partridge have discovered that there´s more to the story. In fact, they found that these fish have not just one reflective layer of guanine crystals, but two, and these crystals work together to not only polarize light, but maintain high reflectivity. This combination of polarization and reflection creates a sort of optical illusion which could make these fish appear invisible under the right light.

"We believe these species of fish have evolved this particular multilayer structure to help conceal them from predators, such as dolphin and tuna," said Roberts, explaining the research in a press release.

"These fish have found a way to maximize their reflectivity over all angles they are viewed from. This helps the fish best match the light environment of the open ocean, making them less likely to be seen," Roberts added.

Of course, we wouldn´t be this far along as a society without noting this behavior and then trying to apply it to modern technology. As it stands, polarizing technology is already present in all sorts of lenses from sunglasses to cameras.

Jordan explained how these modern devices use polarization to reduce glare and cut out specific wavelengths.

"Many modern day optical devices such as LED lights and low loss optical fibers use these non-polarizing types of reflectors to improve efficiency. However, these man-made reflectors currently require the use of materials with specific optical properties that are not always ideal," he said.

By observing and studying these fish, said Jordan, there may be an insurgence in these kinds of polarizing devices. "The mechanism that has evolved in fish overcomes this current design limitation and provides a new way to manufacture these non-polarizing reflectors."

The study was recently published in the journal Nature Photonics.