How fish can turn invisible in the open sea

A team of scientists led by Molly Cummings and Parrish Brady from the University of Texas had been conducting a study on how fish adjust to the fluctuating polarized lights underwater for five years.

The team is comprised by researchers from the University of Texas in Austin and has discovered that two species of fish have developed through the evolutionary process the capability of reading and reflecting polarized light.

The researchers said that waves of polarized light have vibrations that travel on the same level. And many fish happen to have the ability to detect and mimic the polarized vibrations because of the platelets in their skin.

In the open ocean, visibility depends on three main light patterns: brightness contrast, color contrast and polarization contrast. Fish have evolved the means to detect polarised light and probably hide in polarised light as well.

With an automated rotating platform to hold the fish in place, they measured it with the polarimeter. Fish species with skin cells embedded with microscopic structures called platelets can identify and imitate vibrations caused by polarized lights.

By knowing exactly how fish can camouflage through the use of light, more specifically polarized light, the military application of these findings is almost priceless. It seems that the fish managed to overcome this obstacle, and after years of evolution and refinement, they came up with this quaint camouflage that offers them and edge when it comes to eluding predators.

The crew was left with more than 1,500 distinct angular shapes, with two weeks worth of data that was recorded packed into each amount, for five distinct species of fish. The results showed that both fish from the open sea, the bigeye as well as the lookdown scad, had better camouflage in polarized light compared to a mirror had. But this camouflage approach works well only if the surrounding water appears uniform. Each fish was confined to a platform that also had a mirror. Camouflage technology may be improved, using a similar process that fish use. To make their findings, the researchers built a video polarimeter that can record polarized light in real time.

The Navy recently funded a study in order to find out how can two types of fish, the lookdown and the big-eyed scad, hide in the light from the ones who prey on them. After every 360 degrees, the researchers adjusted the polarimeter's angle by increments. But when rocks, algae and other marine nooks and crannies are nowhere to be found, fish turn to manipulate the physical interactions of light to balance the scale.

Using mirrors for camouflage in such an atmosphere can actually backfire and make it simpler to stick out in the open ocean. The fish were hardest to see when all directions were positioned 45 degrees from the head or tail. However, once it gets underwater, it usually becomes polarised.

Scientists have long known that fish can seemingly disappear in open waters, but they have never been able to figure out how or why. The U.S. Navy, for obvious reasons, has strictly been on the lookout for ways to hide in open water, and it was among the supporters of the research.

"I think it's a great example of how human applications can take advantage of evolutionary solutions and the value of evolutionary biology". It's an important aspect to understand the evolutionary solutions animals take against predators.

 

The researchers' next line of inquiry will be to see if the fish are able to actively use the ability - perhaps by adjusting the platelets on the fly (or the swim) or by changing to the "correct" swimming angle for hiding whenever predators lurk.