If you haven’t the infinite ammo of the late Hunter S. Thompson or the lightning-fast trigger finger (and impressive spray radius) of a recent Vice President, it actually takes considerable skill to shoot a fish in a barrel (exact difficulty proportional to size of barrel and fish depth and inversely proportional to size of fish). Some of this trickiness is due to refraction, or the change in speed and thus direction of light waves as they move from air to water.
Wait a minute!? Isn’t the speed of light constant?
Yes. But only in a vacuum.
If you shoot light through glass, it travels only 0.67 times its original speed and if you shoot light through water it travels only 0.75 times its speed in a vacuum (in beer, light travel 0.74 times as fast, though one would imagine this to differ slightly from, say, porter to pilsner...hmmm, research needed).
And the more you slam on the brakes, the more light changes direction. You can see this when you stick a straw in a glass.
Refraction is also responsible for rainbows: as white sunlight refracts through atmospheric water, each frequency contained within this white light adopts a slightly different speed and thus refracts slightly more or less, spreading out into the immediately recognizable ROY-G-BIV spectrum.
Thus, as seen in the diagram, if you are trying to shoot a fish at position R, it—in fact—appears at position L and you will need to aim lower than it appears in order to hit it.
Note: shooting fish drastically decreases the chance of successful catch and release.
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