Everyone is familiar with the basic five senses of sight, hearing, smell, taste and touch, but NYU Shanghai Professor of Physics and Mathematics Jun Zhang is part of a research team that studies how fish navigate their underwater environments with a sixth sense.
It has been known for many years that fish detect their fluid environment using pressure-sensitive receptors that are distributed along their bodies. Yet, two fundamental questions have puzzled scientists over more than a century of research: Why are these receptors arranged in very similar layouts (lateral line systems) across 30,000 species, and what fluid information is retrieved during swimming?
Zhang reports, “Our recent study, which was published in Physical Review Letters, has addressed both questions. We found that when a fish is misaligned to an oncoming flow, the pressure difference across its body, due to the motion of the flows, is well correlated to the density of the flow-detecting sensors. In other words, as a result of natural evolution in their fluid environment, these sensors are optimally located or configured to retrieve flow signals. Our finding strongly suggests that the lateral line systems of fish operate like ‘hydrodynamical antennas’ that help swimming fish to orient themselves in their natural habitat.”
This theory was tested with a rainbow trout model, replicating the location of the fish’s canals and using illuminated flow markers to detect surrounding water speed. With replicated aquatic conditions such as changes in water flow altering water pressure and the suggested presence of ‘prey,’ they examined the canal locations in relation to the strongest changes in water pressure. Like an antenna, the fish’s canal system proved sensitive to pressure changes.
Other authors of this study include Leif Ristroph, an assistant professor at New York University's Courant Institute of Mathematical Sciences, and James Liao, an assistant professor at the University of Florida's Whitney Laboratory for Marine Bioscience.
"You can't put pressure sensors on a live fish and have it behave normally," Liao says. "This was a creative way to use engineering and physics techniques to answer biological questions you can't answer otherwise."