How Some Fish Can (Kinda) Make Themselves Invisible

Nov 30, 2015

A team of scientists at UT Austin has brought us closer to understanding how some animals turn almost invisible in certain lights by studying fish deep in the ocean.


The research starts with the principle that the more visible an object is, the more it contrasts with its surroundings.  If there’s a lot of contrast it just sticks out more in your vision.  So, a fish in the open ocean should be pretty easy to spot. But many are not; as they swim around, they often seem to turn invisible to predators.

“So, I hate to use the word invisible, because that would suggest absolutely ideal camouflage, and they are doing a pretty darn good camouflage,” says UT biologist Molly Cummings, the author of the study. She and her team have been studying five species of lookdown fish in waters off of the Florida Keys and the island of Curaçao.

A visualization of the lookdown fish's ability to camouflage.
Credit UT Austin

They’ve found the fish have platelets that react to polarized light, a type of light that humans can rarely see but that fish perceive everywhere. These platelets reflect, or mimic, the polarized light that’s bouncing around in the water, making the fish harder to spot.  

“On top of this, we’ve noticed that…there’s not a smoking gun of evolution at play, but there is some good evidence for us to believe that these specific polarized reflective properties have been shaped by natural selection,” Cummings says. 

How’s that? Well, the fish have more of these platelets around their heads and tails. That means they’re harder to see if they’re being chased—like for dinner. And they’re also harder to see if they’re doing the chasing—if they’re looking for dinner. The research could lead to better camouflaged materials underwater, and it’s funded in part by the U.S. Navy, a group that has a great interest in that very thing.