Archerfish can knock insects off branches by shooting a stream of water from below. The insect is sitting above the surface, minding its own insect business. The fish aims, fires, and, with a little cooperation from gravity, dinner drops into the water.
That already sounds like a questionable design choice for a fish. The more surprising part is how carefully the shot is controlled. Archerfish adjust their water jets for targets at different distances, and controlled experiments have shown that they can learn to hit moving targets, too.
A fish with a built-in water pistol
Archerfish are members of the Toxotidae family, found in freshwater and brackish habitats across the Indo-West Pacific. Their unusual hunting method lets them target prey perched on plants above the water rather than waiting for everything edible to fall in on its own.
A fish takes aim from below the surface and sends a jet upward from its mouth. If the strike knocks the prey loose, the fish can move to seize it when it lands. It’s a hunting method that makes a remarkable amount of use of an animal’s most available building material: water.
This is not a story about fish randomly splashing in the right direction. Their shots can be accurately aimed and adjusted, even though the fish is viewing a target across the boundary between water and air. That boundary bends light, complicating the visual problem.
The trick is controlling the water before it hits
In a 2014 study in Current Biology, Peggy Gerullis and Stefan Schuster trained archerfish to shoot at targets at different heights. High-speed observations showed that the fish changed the timing of how they opened and closed their mouths. As a result, the water in a shot concentrated near the target, delivering a more effective impact.
Shots traveling farther required different timing from those heading to nearby targets. The fish weren’t just expelling water at a fixed setting and hoping for the best: they were actively shaping the jet.
The researchers described the control problem as surprisingly similar in one respect to accurate throwing: timing matters. That does not mean an archerfish thinks about projectile physics the way a person does. It means the measured behavior involves a sophisticated adjustment of a physical action.
The same researchers’ later work also showed archerfish can use water jets underwater to disturb substrate and expose buried food. Apparently, one surprising trick wasn’t enough.
They can even learn to hit a moving target
An earlier 2006 study, also published in Current Biology, found that archerfish could learn to strike rapidly moving targets. That requires accounting for where the target will be when the water arrives, not merely where it was when the fish started shooting.
The study reported another twist: fish that watched a trained group member could learn the moving-target task without practicing the shots themselves during observation. The finding came from a controlled experiment, so it shouldn’t be stretched into a claim that every archerfish learns every skill just by watching. But it makes the water-jet hunting behavior more than an odd party trick.
Researchers continue to investigate how flexible the fish’s aiming system is. In a 2024 study published in eLife, archerfish trained in a tank reduced their shooting errors after experimenters introduced airflow that displaced their jets. When the disturbance was removed, the fish briefly showed errors in the opposite direction, evidence consistent with motor adaptation.
The weirdest part may be the precision
An animal that lives in water uses water to catch food. That much sounds almost obvious. But the archerfish version demands accurate aim, split-second timing, and adjustments to the jet itself. For a fish looking up at an insect on a leaf, that’s a lot of engineering without an engineer.
Fish have other wonderfully improbable skills. Male pufferfish, for instance, build elaborate sand circles to attract mates. Archerfish have gone in a more direct direction: if lunch is out of reach, shoot it down.