Fish Use 'Sixth Sense' to Detect Water Flows

Fish apparently use a "sixth sense" to detect water flows, solving a long-standing mystery of how these aquatic creatures respond to their environment, according to a new study.

It is well known that fish do things like avoid obstacles, use less energy by slaloming between vortices, or whirlpools, and tracking changes in water flow left by prey, all while coming off as carefree swimmers. But how do they respond to changes in their environment this way without even being able to rely on their eyesight?

"We identified a unique layout of flow sensors on the surface of fish that is nearly universal across species, and our research asks why this is so," study author Leif Ristroph, from New York University, said in a statement. "The network of these sensors is like a 'hydrodynamic antenna' that allows them to retrieve signals about the flow of water and use this information in different behaviors."

The findings were published in the journal Physical Review Letters.

To get to the bottom of this "sixth sense," researchers focused on a fish's "lateral line" - a system of sensory organs known to detect both movement and vibration in the water that surrounds them. They also looked at canals that they posses which open to the environment via numerous pores. They subjected a fish model of a rainbow trout to several real-life aquatic conditions, including changes in water flow that altered water pressure or mimicked the presence of "prey."

Their results showed that the locations of the canal system was key to their sensory abilities, found on the body wherever strong variations in pressure occur, such as on the head.

"You can't put pressure sensors on a live fish and have it behave normally," said co-author James Liao. "This was a creative way to use engineering and physics techniques to answer biological questions you can't answer otherwise."

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