· There are about 30,000 different kinds of fish in the world.

Fish are alike in that they:

· Are vertebrates, or animals with backbones.
· Live in water
· Breathe mainly through their gills.
· Are cold-blooded. (Their body temperature is the same as the water around them).

Fins - Most fish have fins, but not always the same number or the same shape. Fins help fish swim and keep their balance.
Nostrils - They are not for breathing but for smelling.
Ears - Fish have ears?!? Yes, they are buried deep in their heads.
Gills - Most fish breathe by taking in water and closing their mouths. The water passes over their gills. The blood flowing through causes oxygen throughout the body. The water flows out the gill slits, which are covered by flaps.
Eyes - most fish have one eye on each side of their head, except the flounder which has two eyes on one side of its body.
Scales - most fish have scales.
Special scales - fish feel with a special organ called the lateral line, which runs down the sides of a fish. Special scales over the lateral line allow the fish to detect movement in the water nearby.

Saltwater and freshwater fish:

Three-fifths of all fish are saltwater fish. The others are freshwater fish. Fish live at different depths and at different temperatures.

Fish spend most of their time looking for their next meal while trying to not become a meal themselves. Very few fish die of old age.