Fish Can Sense Touch with Their Fins
A bottom-dwelling fish species demonstrates touch-sensitivity to both pressure and motion.
A species of fish has been found to have touch-sensitive fins, along with cellular structures resembling those that are key to the sense of touch in mammals.
University of Chicago (UC) scientists, in a paper published Feb. 10 in the journal Proceedings of the Royal Society B, have found that the pictus catfish, a bottom-dweller from the Amazon River, has neurons and cells in its pectoral fins (the ones just behind the gills) that are extremely sensitive to touch.
"It was a surprise to us that, similar to mammalian skin, fish fins are able to sense light pressure and subtle motion," said UC graduate student Adam Hardy, an author of the study.
Using the flat end of a pin, and a brush, Hardy and his team stimulated the fish's pectoral fins and then measured the resulting neural activity.
They found that the fish's neurons responded to more than just the touch itself: They also conveyed information about the pressure being applied as well as the motion of the brush.
Meanwhile, cell structures in the pectoral fins, the scientists learned, resembled those that are crucial to sense of touch in mammals.
"Like us, fish are able to feel the environment around them with their fins," said UC graduate mentor Melina Hale. "Touch sensation may allow fish to live in dim environments, using touch to navigate when vision is limited."
"It raises a lot of exciting questions," she added, "on how sensory cells shape the brain's perception of environmental features, and may provide insight into the evolution of sensation in vertebrates."
Furthermore, the researchers think this sense of touch is quite common among sea-floor fish. "We suggest that touch-sensitive fins may be widespread in fishes that maintain a close association with the bottom substrate," they wrote.
Currently, the team is experimenting with other species of fish, to see if the same touch-sensitivity is present. "We predicted that touch-sensitive fins would be very useful for bottom-dwelling fish," Hardy said, "but you can imagine its utility in nocturnal or deep-sea environments as well."
The researchers think the new findings could also aid in the design of future undersea robots that toil in dark environments.
"For example," offered Hale, "you can envision fish-inspired sensory membranes that can be used to scan surfaces in underwater environments where light may be obscured."
This week came distressing news from marine biologists, who reported that there were
spotted handfish left in a survey of the fish's only known habitat in waters off Tasmania. Spotted handfish (shown above) are small, bottom-dwelling fish that would rather 'walk' on their pectoral and pelvic fins than swim. Their distinctive mode of locomotion alone is worth hoping they can be saved (there is talk now of ramping up a captive breeding program). The critically endangered fish aren't the only ones that enjoy a nice walk, though. Let's sample a few of the other species of fish that like to feel the ground beneath their fins.
Here's a literal fish out of water. Mudskippers are the broad name given to more than three-dozen species of fish that are amphibious, using their fins to motor (or wriggle, really) around on land. Different sizes of mudskipper will venture on land to varying degrees, with the largest ones spending up to 90 percent of their time on land, on the uppermost part of mud flats that only become submerged at high tide. In water, they breathe through gills, like any other fish, but on land they draw oxygen from outsized gill chambers they fill with water before coming ashore. They can also breathe through their skin, but they have to stay wet or very moist to pull that off. They're found in freshwater tidal mud flats in tropic, subtropic and temperate areas of the Indo-Pacific region and Atlantic coast of Africa.
Frogfish won't venture onto land any time soon, but they do move across the sea bottom on their fins. They don't generally move much, however, preferring to wait idly until suitable prey comes into view. They dine on crustaceans, other fish, and even --
-- other frogfish.
Epaulette sharks, a species of longtailed carpet shark, are night owls that hang out in shallow waters such as tidal pools and coral reefs. Often times, in lieu of swimming, they will do a kind of walk, using their fins to push themselves along the sea floor.
Flying gurnards, despite their enlarged pectoral fins, can't actually go airborne or even glide for just a bit, but they
use their pelvic fins to "walk" along the bottom while they search out meals of crustaceans and small fish. They live in tropical to warm temperate waters on either side of the Atlantic, from southernmost South America to New England.
Flattened in shape, bottom-dwelling
, sometimes called batfish, can also stroll along the sea floor, using an awkward gait. This red batfish will rest on the sea floor and scoot along just skimming the bottom.
The "walking" species of catfish is, like the mudskipper, able to move across dry land, using its fins for balance and moving in a wriggling, snakelike motion. So long as it stays moist it can keep up its Earth-bound ways. It lives in swamps, ponds, and rivers and can take advantage of its over-land skills when such places dry up. It's native to Southeast Asia.
This little guy is a mangrove rivulus, an amphibious fish that lives in the Atlantic waters from Florida all the way down to Brazil. It's only about 3 inches long (75 millimeters) and it can live for a bit more than two
out of water! It manages this trick by breathing through its skin, while it hides out in tidy places such as fallen logs. And it gets even cooler. On land this little fish fashions long jumps by doing a kind of backflip, tossing its head back over its body in the direction of its tail.