Triplefin Fish is Able to Reflect Light From Around Its Eyes

Researchers at the University of Tübingen found that a type of fish known as a triplefin is able to control light reflected from special organs next to its pupils, according to a new paper published in the journal Royal Society Open Science.

This unique process is a never before seen form of photolocation, which acts much like echolocation except it uses light instead of sound.

Many animals employ sound or light to navigate through their environment. In fact, a range of sea creatures uses light reflecting off their organs to see better in murky or dark water. However, the triplefin is different because it can control and manipulate those organs in a way no other species can, Phys.org reports.

The small fish — which measures just two to three inches long — is native to both the eastern Atlantic Ocean and the western Mediterranean Sea. They almost always live in shallows areas, but can travel to down to much deeper depths. There, the fish hunt by waiting near the sea floor until prey swims by. Though many fish employ that technique, the triplefin is unique because of the glowing red and blue light that surrounds its eyes.

Study of the fish showed that the animals’ eye color changes as they stalk prey. However, the light does not come directly from the eyes. Rather, it is reflected from any available light shining down from above. As a result, in order to alter the light, the fish would need to be able to move their organs in a way that refracted different parts of the spectrum.

Scientists tested this by analyzing reflective eye regions in the iris. That showed simple eye movements could allow the species to adjust color on-demand. In addition, they also added different colored backgrounds to a water-filled tank and found that fish tended to reflect whatever light was available to them. As a result, the study sheds light on a brand new process and gives researchers new insight into photo location.