I can't take the pressure!
Why don't fish get crushed from the pressure deep in the ocean?
Because the pressure inside their bodies is about equal to the water pressure outside their bodies. This is precisely the reason why each individual species of fish is limited to a very specific range of depths. Should the fish venture too deep, the pressures of the overhead water will indeed crush him. Should he venture too shallow, his internal body pressure will exceed that of its surroundings and he will (quite literally) explode. I should add that it would be possible for a fish to move into a depth range that is outside his normal sphere. The fish would have to do so very gradually, however, to give his body time to equalize the pressure difference.