Another fish that is equipped marvelously for overcoming the light refraction property of water is the archer fish. Almost everyone has noticed that an object under water appears to be closer to the viewer from above the water, or that a pole stuck into the water at an angle looks bent. If one should aim an arrow or a gun at a small object in the water one would need to make quite a complex calculation to hit the object. The archer fish has this problem in reverse. He sees an insect on a hanging branch. He quickly projects his head, or just his mouth, out of the water and shoots down the insect as by “antiaircraft” with a stream of water. In order to do this, he must take aim as he is coming to the surface of the water, compensating for the water’s refraction as he does so. Is this ability for instant mathematical computation built into the archer fish by design, or did a complex pattern of many factors just happen to imprint itself in some early archer fish’s bodily mechanism and thereafter stay with all his descendants?

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How does the archer fish compensate for water refraction so that he accurately “shoots down” insects?