Scything through the water, fish keep track of passing currents with a sensory organ known as the lateral line. Composed of mechanosensory cells that detect water speed and pressure gradients, the lateral line helps fish negotiate a path through their watery domain. Jacob Engelmann and his colleagues wondered whether these sensory organs could also detect vortices generated in water by obstacles and other creatures. Using a combination of particle image velocimetry and neurophysiological methods, Engelmann, Boris Chagnaud and Horst Bleckmann visualised vortices passing along the fish's side while recording neural responses from the lateral line and found that the mechanosensory cells responded to the direction that the water swirled in the vortex. The lateral line seems to detect vortices(p. 327).
Given that every flick of a fin generates spinning vortices, Engelmann explains that several groups have suggested that `detection of vortex rings may be of importance for prey detection' for fish with a taste for other fish. Having shown that the lateral line is capable of detecting these gentle swirling movements, it is possible that fish may hunt by vortex detection.