Replies

Easy evolutionary explanation here:

The bug evolved from goo, right? So the fish evolved in one part of the lake and the bug evolved in the other part of the lake. The fish started to eat little amoebae to stay alive. Of course, this was after its eyes, gills, and digestive system had evolved so it could eat the little amoebae. (What it ate before then, I do not know.) One day 5,750,536,211 years ago, the fish and the bug met in the middle of the lake. The fish looked at its first meal with delight. The bug by that time had evolved into one of those bugs you see skittering around the surface of the lake, right? So when the fish lunged for its first real meal, the bug began skittering. But it skittered so fast due to fear that there was actually aerodynamic lift (probably the first instance of evolutionary Bernoulli's principle). As surprising as it might seem, the bug became airborne! It flew to the shore of the lake where it gave birth to other flying bugs. These bugs then stupidly flew too close to the surface of the lake, and Darwinian survival of the species continued. The ones who could fly higher - out of the reach of the fish - are ancestors of those we see today.

At least that's my explanation. :)

Wikipedia says the following:

Archerfish are remarkably accurate in their shooting, adult fish almost always hitting the target on the first shot. They can bring down an insect six feet above the water's surface. This is partially due to their good eyesight, but also because of their ability to compensate for the refraction which occurs when light travels through water. They do this by swimming directly under the prey, where the distortion is the least.

When their prey is spotted, the archerfish sticks its snout just above the surface and squirts a jet of water at its victim. It is able to do this because of the narrow groove it has at the top of its mouth. It presses its tongue against this groove to form a narrow channel, then contracts its gill covers to force a powerful jet of water through the channel.

The resulting jet of water can be up to 2-3 m long, but their accuracy only allows them to shoot insects 1-1.5 m away. If the first shot does not knock the victim into the water, the archerfish will keep trying. Young archerfish start shooting when about 2.5 cm long, but are inaccurate at first and must learn from experience.