A tiny Asian fish that can "shoot" its prey from the water, hitting a target as much as six feet above the surface with a powerful steam of water spit from its mouth, can fine-tune that jet like a precision tool, a study has found.
A zebra-striped archerfish in Thailand can knock land-based prey targets -- spiders, insects and sometimes small lizards -- from their perch into the water by gathering water between the roof of its mouth and its tongue, creating a tubular gun-barrel shape that allows it to spit a strong, accurate stream.
That's been known for some time, but in a new study published in Current Biology, researchers report discovering the fish can modulate those water jets, focusing them for the most power at a point just before impact.
That makes archerfish the first tool-using creature known to be able to change hydrodynamic properties in an expelled water jet, they say.
The ability to accurately throw something -- even a jet of water -- suggests a certain level of brainpower, the researchers add.
"One of the last strongholds of human uniqueness is our ability to powerfully throw stones or spears at distant targets," says researcher Stefan Schuster, an animal physiologist at the University of Bayreuth in Germany.
Such an impressive ability requires precise movement control, he says, something that in humans made our brains grow larger to create sufficient neurons to support such precision.
"It is remarkable that the same line of reasoning could also be applied to archerfish," he says.
In an experiment, archerfish in a lab were trained to take aim at a target that was moved from 8 inches away to 16 inches, and then to 24 inches.
The fish showed the ability to modify the stream of water they spat at targets to form a thick slug, almost like a bullet, just before their stream hit a target.
The fish were controlling the jets by changing the timing of how their mouths opened and closed, the researchers found, creating what amounts to an "active nozzle" out of which they shot their water streams.
Adjustable water jets are used by humans in fields from manufacturing to medicine, Schuster points out, the properties of which are normally modulated the changing the pressure.
The archerfish have apparently found a different -- and for them much more effective -- method, he says.
"We are not aware of someone actually using a dynamically adjustable valve," as the fish do, he says.
It's an evolutionary development that serves the fish well, he notes.
"The predominant impression from our field work in Thailand over several years is that there is very little to actually shoot at, so it's important for the fish to be efficient."
