Camouflaged fish found hiding in plain sight

Last year, I spent a week fossil hunting on the southwest coast of England. In between sifting through piles of rock and stone searching for bits of ammonite and other extinct creatures, my friend and I spent some time exploring tide pools along the shore, a popular activity in the region. Obsessed at the time with fossils, we probably missed a lot of interesting organisms — including fish that change color to match their background.

Rock gobies, which can reach about 12 centimeters long, are found in pools along the intertidal zone in parts of Europe and North Africa. People thought that the fish might be able to change color, but the definitive proof comes from a study published October 15 in PLOS ONE. And not only can the fish camouflage themselves, the study finds, but they can do it in less than a minute.

Martin Stevens and colleagues at the University of Exeter in Penryn, England, collected rock gobies from rock pools in nearby Falmouth. They brought the fish back into the lab, keeping them in a gray bucket — a neutral background. In their first experiment, the researchers moved the fish into water-filled trays with either a white or black background and watched what happened. They then placed the fish in trays with red or blue backgrounds.

Within a minute of being placed in a tray, the gobies altered their skin. They became darker when placed on the black tray, and lighter on the white one. The gobies were even better at color matching: Placed onto a blue tray, the fish quickly became more gray. On the red tray, they became redder. The red color may be the most important to match up, the researchers say, because red algae and brown stones and seaweed are common in the rock pools where the fish live.

When a fish sees that there is a new background, pigment-containing cells in the skin, called chromatophores, change the goby’s look. The camouflage probably helps protect the fish from being seen by predators, such as birds and bigger fish, the researchers say, as well as scientists, children and fossil hunters exploring the rocky shores.