Hogfish are coral reef-loving fish that are famous for their ability to change colour to match their surroundings. Much like how chameleons do!
They are able to make these changes happen thanks to remarkable cells that are located within their skin. These cells, called chromatophores, can change their colour in a second by rearranging their pigments—a little like mixing different paints to get new shades.
But there has always been a question about them. How does the fish know that it has nailed the colour change when it can't actually see its own skin? It's not as though there are mirrors down there for it use either. So what gives?
A new study done by a team from Duke University and the University of North Carolina Wilmington seems to have cracked the code. According to these researchers, the hogfish has a layer of light-sensing cells underneath its chromatophores that allow it to "watch" its own skin change colour from the inside!
Watch it happen
The light-sensing cells are called opsins. They are a type of protein that is sensitive to blue light. Most of sunlight is blue light, while it is also given off by many computer and TV screens.
No mirror and can't bend your neck? 🐠Our study shows that light receptors underlie color change cells in a 1:1 ratio, perhaps to monitor the status of dynamic skin color change. #sciTwitter #colSci @laura_bagge @lyd_love_laugh @BrackenGrissom @sonkelab https://t.co/yofzziHgNv pic.twitter.com/XeoDoLa7kE
— Lorian Schweikert (@LoriSchweikert) August 22, 2023
So it sees its skin from the inside? Kind of, but also not exactly.
Essentially, it captures changes in the light as it passes through its skin. If its skin changes colour, then the light reaching its skin will also change colour. By monitoring those changes and comparing it to what the animals sees of its surroundings with its eyes, it can do a quick and effective job of matching colours.
As Duke's Sonke Johnsen puts it in their report, "In a way they can tell the animal what its skin looks like, since it can't really bend over to look."
And presto! You've got a fish that can blend in with the coral reef around it. Nature is amazing!