Biology
The Neuroethology of Prey Capture in Archerfish and Their Ballistic Trajectories
Quick fact
Archerfish can adjust their spit to account for the bending of light at the water surface, and they predict the falling trajectory of prey so precisely that they often move to the exact spot where the insect will land without seeing it fall.
Why this is interesting
You've probably seen archerfish spit water at insects above the surface—but how do they hit a target that looks shifted due to refraction, and how do they know where to be when the prey falls?
Read the full explanation
Understanding The Neuroethology of Prey Capture in Archerfish and Their Ballistic Trajectories
Archerfish live in murky waters and hunt insects perched on overhanging vegetation. When they see a bug, they shoot a jet of water from their mouth to knock it into the water. But the bug appears in a different position due to refraction at the water-air interface. The fish must compute the true location from the apparent one. They also have to adjust for the distance and angle to the target. Archerfish learn to do this through trial and error, and they can even learn to hit targets that are moving or that are beyond their normal range.
A deeper explanation
The key to the archerfish's success lies in its ability to predict the ballistic trajectory of the falling insect. When the water jet strikes the prey, the fish doesn't just wait—it plans its next move. It calculates where the insect will land based on its initial speed and direction, and then swims to that location, sometimes arriving before the prey hits the water. This predictive behavior is controlled by a network of neurons in the fish's brain that integrate visual information about the prey's motion with motor commands for swimming. Studies have shown that archerfish can even learn the relationship between the initial position of the prey and its landing point, allowing them to improve their accuracy over time. This combination of refraction correction and trajectory prediction makes archerfish a fascinating model for studying how brains compute precise motor actions.