Fish Fins Can Sense Touch Like Human Fingertips, Study Shows

Some fish may have surprisingly sensitive fins, able to sense touch and collect information about the surrounding environment like human fingertips, according to a new study from the University of Chicago.

"It was a surprise to us that, similar to mammalian skin, fish fins are able to sense light pressure and subtle motion," Adam Hardy, one of the study authors and a graduate student in the Department of Organismal Biology and Anatomy, said in a news release. "This information seems to be conveyed by a type of cell important for touch in mammals, which suggests that the underlying sensory morphology may be evolutionarily conserved."

Located just behind the gills, pectoral fins are a pair of distinctive appendages that correspond to forelimbs in four-legged animals, helping fish stay balanced and swim forward. It turns out that the pectoral fins of a pictus catfish -- a small, bottom-dwelling species native to the muddy waters of the Amazon River -- possess neurons and cells that are very sensitive to touch.

Studying touch in fish is particularly difficult, as their fins are almost always in motion. However, pictus catfish don't appear to use their pectoral fins for locomotion, so researchers were able to isolate and study neural activity in response to touch, without conflicting signals from fin movement. As a result, they discovered neurons not only responded when contact was made, but also transmitted information about the degree of pressure and the motion of the brush as well.

"Like us, fish are able to feel the environment around them with their fins. Touch sensation may allow fish to live in dim environments, using touch to navigate when vision is limited," graduate mentor Melina Hale explained. "It raises a lot of exciting questions on how sensory cells shape the brain's perception of environmental features, and may provide insight into the evolution of sensation in vertebrates."

Next, researchers plan to study touch sensitivity in the fins of other species of fish, such as flounders.

"One of big questions were trying to answer is whether this applies to all fish," Hardy added. "We predicted that touch sensitive fins would be very useful for bottom-dwelling fish, but you can imagine its utility in nocturnal or deep-sea environments as well."

Their findings, recently published in the Proceedings of the Royal Society B, not only shed light on the evolution of touch, but may one day inspire new advances in the design of underwater robotics.

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