A General Look

External Anatomy

There are about 25,000 different

species of fishes. This is more than any

other vertebrate group.

They come in all shapes and sizes.

The largest is the whale shark.

The abundance of fish life is a reflection of the abundance of plankton.

Fish show almost infinite variety when it comes to color. They have

special skin cells called chromatophores.

These chromatophores can expand or contract to change

the color of the fish.

There are also many patterns. Many open water fish like this

tuna show countershading.

They tend to be dark on top and light on the bottom.

Why do you think they have this pattern?

Some fishes have a coloration pattern that allows them to blend

in to their environment.

Some fish have very colorful warning coloration.

This is often used if they are poisonous, dangerous, or taste

bad.

Many mid-depth fish are often red while lots of the deep water fish are

black and may have luminescent organs.

Movement In Fishes

Propulsion in most fishes is

from the caudal fin and flexing the hind part of

the body.

The faster swimming fish

also have a teardrop or

fusiform body shape to help them move through the

water.

The dorsal and anal fins serve

primarily as rudders.

The pectoral and pelvic fins are

used for balancing ,

turning, braking and going

backwards.

Body Shapes

There are four basic body shapes with all kinds of variation in

between.

Compressed

Compressed fish look like they

have been smashed on both sides.

Depressed

Depressed fish look like they

were smashed from the top and bottom.

Terete or Round

These fishes are round like a

pipe. Most eels are in this

group.

Fusiform or Teardrop

This one we already

mentioned. Typical of the

faster fish species.

Scales

Actually, not all fish have scales. Lampreys and freshwater catfish

lack scales. The American eel actually has small scales.

There are four basic types that we’ll look at today.

Sharks and their relatives have placoid scales.

They feel a lot like sand paper.

Gar fish, reedfishes, and

parts of sturgeons have a scale type known as rhombic

or ganoid.

Ganoine gives them the “pearly”

look.

Most bony fishes have

one or both of the next two

types.

The bony –ridge scales: cycloid and ctenoid.

Cycloid are round and lack a “comb”

like edge.

Ctenoid have the comb like edge. Scales can be over 7 inches!

Circulation

The heart of a fish is simple when

compared to our heart.

They have a two cambered heart that follows a heart-gills-

body-heart path.

Oxygen is then taken out of the water by the gills

Internal Anatomy