Some fish have legs that can taste prey underfoot

Sea robins are fish with two large, winglike fins and six crablike legs. But their extra limbs do more than just scurry about the seafloor.

Research now suggests that some sea robin legs can sense tastes. The ends of those legs are coated with small bumps called papillae. These sensors work like the taste buds on your tongue. Here, they let the underwater walkers taste prey that are buried under sand.

Researchers shared the new findings October 7. The work appeared in Current Biology.

illustrated text reads "Wild Things: A graphic tale" with animals drawn around the letters
Text: Sea robin legs double as tongues. Written by Andrea Tamayo and Maria Temming, illustrated by JoAnna Wendel. Image: A grayish brown fish with two large fins sticking out of its sides and three crablike legs on either side of its underbelly stands on the seafloor. In its mouth is the fleshy interior of a mussel, which it has just plucked from an open mussel shell. The fish is thinking, “Om nom nom.”
Text (above image): Sea robins are funky fish. They use six crablike limbs to scuttle around the seafloor. Image: A grayish brown fish with two large fins on its sides, smaller fins down its back and six thin legs underneath it scuttles across the ocean floor. The fish is called a sea robin.
Text (above image): Northern sea robins are especially good at finding food buried in the sand. So good that other fish lurk near them, trying to snatch a bite of any leftovers. Image: A sea robin eyes a group of blue and yellow fish following it around as it walks across the seafloor. The three fish surrounding it are all watching the sea robin and thinking, “Food? Food? Food?” Text (below image): That got an international team of scientists curious how these sea robins’ extra limbs help them forage.
Text (above image): In tanks filled with a layer of sand, researchers buried mussels, capsules filled with mussel bits or capsules filled with saltwater. Then they placed the northern sea robins in the tanks. Image: One image shows a cylindrical tank of water with sand at the bottom and a sea robin in the middle. A close-up version of that image shows the sea robin smiling as it walks across the sand at the bottom of the tank. Treats are buried below it in the sand. The sea robin is thinking, “Time for lunch!” Text (below image): Kicking through the sand, the fish homed in on the mussels and treats with mussel pieces. They left the saltwater capsules alone. This hinted that their legs could chemically sense their food.
Text (above image): Another species, striped sea robins, failed to find buried food in their tanks. Image: One image shows a cylindrical tank of water with sand at the bottom and a sea robin in the middle. A close-up version of that image shows a copper-colored sea robin with a stripe running down its side standing on the sand at the bottom of the tank. Treats are buried below it in the sand. But the sea robin looks confused as it kicks around, thinking, “Boop de boop, nothing here…” Text (below image): Their legs, it seemed, lacked the chemical sensing ability of northern sea robins’.
Text (above image): Close-up images of both species’ legs revealed what made northern sea robins’ legs so special. Image: The grayish-brown northern sea robin and the copper-colored striped sea robin drift in a blue background of water. A close-up of one of the northern sea robin’s legs shows that the tip of its leg is covered in little bumps, like those on animal tongues. A close-up of one of the striped sea robin’s legs shows that the tip its leg has no bumps (papillae) like the ones on animal tongues.
Text (above image): Genetic tests revealed genes in northern sea robins that were key to forming the bumps and taste receptors on their legs. A relative of this species also has the genes for legs that taste. Image: A family tree shows how different species of sea robins have branched off from each other over time. Many current species do not have the genes for legs that taste. But two current species do. Those species are the northern sea robin and the leopard sea robin. An illustration below the family tree shows one member of each of these species looking at each other. The leopard sea robin, which is light gray with dark gray spots, says, “You can taste with them, too??” The northern sea robin replies, “Sure can!”
Text (above image): Sea robins aren’t the only sea creatures that can taste with body parts besides their mouths. Image: A gray catfish with long whiskers, a bright red octopus and a northern sea robin drift against a gray water background. Labels show that “some catfish taste with their whiskers and skin” and octopuses “can taste greasy molecules with their arms.” Text (below image): But sea robins’ feat of tasting with their legs is a first for fish.
All panels: JoAnna Wendel
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