Science Snippet: Archer Fish

One of several animals that survive by calculating distance and direction is the Archer fish (genus Toxotes). These small fish live in Thailand and Southeast Asia. They spend their time just beneath the water’s surface looking up for insects perched on overlying vegetation. When a fish sees an insect, it corrects for the visual distortion when looking up through water and uses its mouth to spit out two globs of water, one after the other, knocking the prey into the water. To spit, the fish forms its water-filled mouth into a “gun barrel” shape, then snaps its gills closed, forcing the water out of its mouth along a groove in its tongue. The rear glob travels faster (about 32 ft./second) than the first, catching up with it and the double glob strikes the prey with great force, knocking it into the water. Not only does the fish’s brain calculate the correct trajectory of the globs, but once the insect hits the water the fish streaks over to its prey in a straight line (also calculated by its brain) and gobbles it up. All this happens within a tenth of a second. In summary, three calculations are required by the fish’s brain: 1) correcting for visual distortion through the air/water interface, 2) calculating the distance to the target and accounting for the trajectory of the glob of spit, and 3) determining the quickest path to the floundering prey. (voices.nationalgeographic.com, Sept 4, 2014; Rossel et al, 2002, J. of Experimental Biology, Nov. 1; other sources)