Spit to kill? How the archerfish shoots prey with fearsome accuracy

If you’re a tasty-looking insect, spider or even a lizard, being in “spitting distance” of an archerfish makes you a dangerously perfect target. At first, these water-shooting fish may not look as remarkable as flying fish (or walking fish), but they harbor a fearsome skill – the ability to shoot jets of water from their mouths and hit insects, high above the water, with incredible precision.

Now, a new study in Current Biology reveals that the archerfish is an even more talented water-wielder than scientists thought – it can manipulate the liquid jet in precise and subtle ways, to accurately shoot down targets at different distances. When it comes to ingenious tool use, then, the archerfish might join animals like humans, chimpanzees and perhaps even the crocodile.

Scientists have known for a while about the archerfish’s uncanny ability to shoot down unsuspecting targets from beneath the water’s surface – and they know that the jet has to be very powerful and remarkably accurate. As the jet travels up, the water amasses at the tip – acting like a balled-up fist at the end of a liquid arm, sucker-punching an unsuspecting insect so hard that it falls into the water. The stunned prey is now easy pickings for the archerfish, which swims over and gobbles it up.

But what if the fish really has to reach a much more distant target? To find out if the animals could control the subtleties of the jet, researchers at the University of Bayreuth in Germany took specially trained archerfish (known formally as Toxotes jaculatrix) and placed targets at 20 cm, 40 cm and even 60 cm above the water. After studying 313 different jets, they found a remarkable pattern: The fish were altering the hydrodynamics of the jets for far-off targets – changing the flow’s movement and shape so that the water would start to bunch up into its fist-like tip only in the moments right before making impact.

“Jets that have to travel farther also live longer,” the study authors wrote. “Furthermore, the time needed until water assembles at the jet tip is not fixed. Rather, it is adjusted so that maximum focusing occurs just before impact.”

How were the fish doing this? The researchers watched their body movements – but the fish kept quite still. Then they watched their mouths.

“Surprisingly, the fish achieve this by modulating the dynamics of changes in the cross-section of their mouth opening,” the study authors wrote, “a mechanism that seems to not have been applied yet in human-built nozzles.”

Human jet technology is used in a range of fields, from materials science to medical devices, but the jets are typically controlled by adding abrasives or releasing water in precise pulses, the authors wrote. Building an ‘active nozzle’ that works like the archerfish’s mouth could prove a very useful strategy in building better jet tech.

The archerfish’s precision adjustments are akin to what humans do when throwing a ball accurately, the scientists said – a task that requires a lot of brainpower, and might be part of what drove our brains to grow larger, the researchers said. In other words, it could mean these fish are pretty smart, too – which might mean it’s time to test their brainpower, not just their athletic skill.

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