shellfish are described separately, beginning
on p. 218.
Fish Anatomy
For about 400 million years, beginning well
before reptiles or birds or mammals had even
made an appearance, fish have had the same
basic body plan: a streamlined bullet shape
that minimizes the water’s resistance to their
movement. There are exceptions, but most
fish can be thought of as sheets of muscle
tissue anchored with connective tissue and the
backbone to a propulsive tail. The animals
push water behind them, developing thrust by
undulations of the whole body and flexing of
the tail.
Skin and Scales Fish skin consists of two
layers, a thin outer epidermis and a thicker
underlying dermis. A variety of gland cells in
the epidermis secrete protective chemicals,