The Archer Fish’s Arrows

The archer fish hunts by shooting a jet of water at insects in the leaves above and knocking them into the water. How the fish achieve this feat has been a matter of contention.  A study of high-speed video of the archer’s shot shows that fluid dynamics are key.  The fish releases a pulsed liquid jet, imparting greater velocity to the tail of the jet than the head.  As a result, the tail tends to catch up to the head and increase the jet’s mass on impact while decreasing the duration of impact.  Simultaneously, the jet tends to break down into droplets via the Rayleigh-Plateau instability caused by surface tension.  Surface tension’s power to hold the water in droplets combined with the inertial effects of the pulsed jet create a ball of fluid that strikes the archer’s prey with more than five times the power than vertebrate muscles alone can impart. For more on archer fish, check out this video and the original research paper by A. Vailati et a. (Photo credits: Scott Linstead and BBC; submitted by Stuart R)

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