Fish Shoot Prey with Precise Water Guns

Archerfish, the snipers of the animal world, never waste a shot.

Archerfish hunt by firing precisely aimed streams of water [image] into the air to knock down prey as big as small lizards and gulp them down once they fall into the water. Investigators had thought these shots were all-or-none blasts of fixed force, but now scientists find archerfish to be more sophisticated, adjusting how much water they use based on the size of their targets.

To measure the force of each blast, animal physiologist Stefan Schuster and his colleagues at the University of Erlangen-Nürnberg in Germany recorded how fast archerfish shots were, using high-speed video, capturing images at 5,000 frames per second. Normally, televisions and movies display pictures at 24 frames per second.

At the same time, the researchers measured how much mass each blast expelled by having the fish fire into bowls filled with an absorptive material known as viscose, making sure no droplet was reflected. Based on the mass and speed at which water was fired over time, Schuster and his colleagues could determine the force of each shot.

"A major source of fun in the lab was when the fish did not shoot but jumped up to the bowl and took a mouthful of the material meant to absorb the shot," Schuster told LiveScience.

Among critters such as flies and lizards, the amount of force each uses to cling to a surface is closely proportional to its size. The researchers discovered that for any given size of prey, the archerfish instinctively tune their attacks such that prey are hit with about ten times the force animals their size could use to hold on.

The archerfish tune their attacks because firing each shot requires a significant amount of energy. Otherwise "it would be best and simplest for the fish to fire maximum power all-or-none shots to any target," Schuster explained.

Schuster and his colleagues report their findings in the Oct.10 issue of the journal Current Biology.