To
us, the environment in which fish dwell often seems col dark, and mysterious. But there are advantages to living in water,
nd they have played an important role in making fish what they are
One is that water isn't subject to sudden temperature changes
Therefore it makes an excellent habitat for a cold-blooded animal
Another advantage is the water's ability to easily support body
weight. Protoplasm has approximately the same density as water, so
a fish in water is almost weightless. This "weightlessness"in turn
means two things: first, a fish can get along with a light weight and
simple bone structure, and second, limitations to a fish's size are
practically removed.
Yet there is one basic difficulty to living in water-the fact that
it's incompressible. For a fish to move through water, it must actually
shove it aside. Most car
this by wiggling back and forth in
