How fish feel the flow

Hair-like sensors are suspected to aid fish navigation in complex environments. Laboratory experiments and computational simulations reveal how these sensors can detect water flow to direct the swimming responses of fish. See Letter p.445 Imagine you are a very small fish in the ocean being carried along in a uniform flow in darkness. How do you sense that you are in a flow at all? From your frame of reference you would be stationary. Even so, fish — even very small ones — consistently orientate themselves against the current. So how do they detect the current to begin with? Florian Engert and colleagues show that larval zebra fishes use their mechanosensory lateral line to detect tiny vortices in the water flow, as well as how these vortices evolve with time. This enables them to deduce flow direction.