Scientists Resolve the Mystery behind the Spitting of Archer fish

A species of fish that has a killer aim uses physics to chase for its prey, according to scientists. Archerfish lurk under the surface of water before spitting to hit unsuspecting insects that have landed nearby, which when hit, fall to their death to provide the fish with food.

Research has shown that the animal is able to impulsively take into account light refraction and other physics principles such as the Plateau–Rayleigh instability to be one of the most accurate hunters in the natural world.

The aptly named archerfish employs a unique process to hunt land based insects and small animals – it aims, spits, and stuns. It prowls under the surface of the water, waiting for unsuspecting insects to land nearby. Then, it spits out water jets at a great force, instantly killing the prey. The entire process takes just one-tenth of a second. The archerfish, a species made up of 7 fish that belong to the genus Toxotes, is able to spurt water at its prey with unbelievable speed and accuracy. Cleverer still is the fish’s aim, as the tiny creature takes into account the way light bends as it enters water.

An archerfish can bring down insects as far as three meters above the water’s surface. Once it selects the prey, it alternates its eyes so that the prey’s image falls on a particular part of the eye. Then it presses its tongue against the groove on the roof of its mouth to form a narrow channel, and contracts its gill covers to issue a powerful jet of water through the channel. The power of this shot can be altered for prey of diverse sizes. The jet can be up to five meters long.

Surprisingly, research has showed that the force of the water that hits the insects is much higher than the force at which it leaves the archerfish. Which means the water gains speed, instead of losing it. This is reverse to how a ball or bullet behaves when it is fired.

For years, scientists believed the archerfish had specific internal muscles or organs that helped it spit very hard. But thanks to research done by physicists from the University of Milan, we now know that this isn’t the case. In fact, the fish’s forceful strike is formed externally, using water dynamics.