The archerfish is known to hunt land-based preys by squirting water on them and knocking them off into the water before feasting on them. Findings of a new research, however, found that the fish is more adept at creating and using water jets than previously believed and showed how the fish manipulate the water for its advantage.
In a new study published in the journal Current Biology on Sept. 4, Peggy Gerullis and Stefan Schuster, both from the Department of Animal Physiology at the University of Bayreuth in Germany, used high-speed camera to record specially trained archerfish targeting small spheres that are 20 to 60 cm. away so they could measure the force and velocity of the water jets produced and examine how the fishes influence the hydrodynamics of these jets.
Earlier research has found that the archerfish forms its mouth into a gun-barrel like shape before spitting out powerful streams of water. For the new study, the researchers found that the fish modulate these water jets so it could powerfully hit its target even over an extended range with precision, an ability that the researchers said is comparable to powerful throwing ability in humans.
"The time needed until water assembles at the jet tip is not fixed," the researchers wrote. "Rather, it is adjusted so that maximum focusing occurs just before impact. Surprisingly, the fish achieve this by modulating the dynamics of changes in the cross-section of their mouth opening."
Archerfish are highly accurate at shooting with the adult fish almost always hitting their target in their first attempt and the special ability to squirt water jets at their prey which include small lizards, spiders and insects, has made it popular in aquariums. Based on how the fish intentionally and actively affects the hydrodynamics of the water jet to successfully aim and catch its prey, the researchers said that the fish is using the water as a tool.
"It's analogous to a human throwing a stick," Schuster said. "If they just threw the stick, it wouldn't count as using a tool because they didn't change it. But if they sharpened it or removed branches, that would be a tool."
Schuster sees potentials in the mechanism used by the fish to precisely alter the hydrodynamic properties of water. He said that this mechanism could be applied in human-built nozzles and adjustable jets that have crucial uses in a number of industries.
