Seeing With Your ... Skin?
The hogfish is the chameleon of the sea: it is really good at camouflaging itself. An American biologist discovered that the fish does this in an unusual way. It not only sees with its eyes, it sees with its skin as well.
In the ocean, where danger is always lurking, the hogfish protects itself by changing colour. It can quickly take on the colour of sand or coral. But how does it know it has blended in well and made itself "invisible"? According to an American biologist, the fish uses its skin to do this.
Dead fish
Biologist Lorian Schweikert of the University of North Carolina Wilmington became curious about the hogfish's camouflage technique when she hooked one several years ago. When she went to put the dead fish in a cooler, she saw that its scales had taken on the same colour as the deck of the boat. Apparently this fish did not need to be alive to adapt to its surroundings. A dead fish can no longer see (there has to be an eye-brain connection for that to happen), so Schweikert suspected that it was able to "see" with its skin.
Photosensitive
Schweikert went on to research this "skin vision" in the subsequent years. She started looking for light-sensitive proteins – which are necessary for vision. She discovered that these proteins were not only present in the fish's eyes, but in their skin as well. There is a whole layer of these light-sensitive proteins underneath the pigment cells that give the skin its colour.
Internal photo
What happens when the fish is exposed to light? It arrives at the pigment cells first, and then reaches the light-sensitive layer. The fish therefore takes a kind of "picture" of itself, from the inside out. This allows the fish to view its own skin from the inside as it changes colour.
That is useful, since it can't twist its neck round to check on its body!