Critters of the Chesapeake BayFishes

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 FishesPropulsion 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 ShapesThere are four basic body shapes with all kinds of variation in between.

CompressedCompressed fish look like they have been smashed on both sides.

DepressedDepressed fish look like they were smashed from the top and bottom.

Terete or RoundThese fishes are round like a pipe. Most eels are in this group.

Fusiform or TeardropThis one we already mentioned. Typical of the faster fish species.

ScalesActually, not all fish have scales. Lampreys and freshwater catfish lack scales. The American eel actually has small scales. There are four basic types that well 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!

CirculationThe 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