The External Anatomy of a Fish

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The External Anatomy of a Fish

By: Barbie Bischof

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If you're someone who's going to care for your own fish instead of having a service maintain your tank, you need to know a little bit about fish anatomy. Here are some of the basic - and not so basic - external fish parts.

Remember that unlike humans, whose basic form as a species is upright, fish range much more in shape, and even in which body parts they have. But, generally speaking, they're similar enough and easy to identify.

The Shapes of Fish

Fusiform. Bullet-shaped, the most common form.

Truncate. Shortened fusiform like a triggerfish or cowfish.

Serpentine. Eel or snake-like.

Attenuate. Long and thin like a needlefish.

Compressed. Disk-like to bullet-shaped and very thin, like an angelfish or butterfly fish, or very flat, like a flounder.

Fins

Perhaps the most familiar parts of a fish are its fins.

Fins are not much more than sheets of skin that hang from the fish and are supported by a structure of rays to offer a fish stability when jetting through the water. These rays are made from organic material that can be soft or hard. Throughout evolution, some fins have evolved into protective devices like spines, or into a bait decoy that lures the prey closer to a hungry mouth.
The Extras

Some fish have these various decorations and adaptations, many do not.

Cirri. Hair-like projections that extend from the forehead area (called the nape).

Fin-spine. A hard fin ray that provides not only support to the fin, but also a protective device.

Barbel. A whisker-like projection or projections located under the mouth of a fish.

Snout. The mouth-area of the fish.

Nape. The forehead-area before the dorsal fin begins.

Lateral line. A row of highly sensitive nerves aligned usually along the center of the body. These nerves help the fish detect water pressure changes and other environmental conditions.

Dorsal fins. These can be single or in pairs. These fins are on the top and toward the front of the body when seen from the side. Sometimes, there is a second dorsal fin behind it - if so, the plain dorsal fin gets promoted to first dorsal fin.

Pectoral fins. In some fish these fins, found on opposite sides of the fish behind the gill slit or close to them, have adapted to something more like arms.

Ventral fins. One or more fins located on the bottom of the fish when seen in profile.

Anal fin. A fin that is positioned very close to where the tail begins and opposite the second dorsal fin. Not all fish have this fin.

Finlets. Some fish, like tuna, have a small series of fins that run along behind a bigger dorsal fin.

Gill slits. The obvious slits that are the opening to the gills. They commonly denote where the head ends and the body begins.

Gill-plate cover. The "flap" of skin that covers the gills.

Scales. Fingernail-like plates that cover the skin of many fish. Some scales are bigger, and more obvious, than others.

The tail fin, also called the caudal fin, can be either a single fin or forked. If it is forked, the upper and lower parts of the fork are called the upper and lower lobes, respectively.

Border of tail. The lower and upper parts of a tail fin that make up part of the "fan" of the tail.

Margin of tail. The edge of the tail fin that lies on the end or outside of the tail fin "fan."

Base of tail. The boundary where the body of the fish ends and the tail fin begins.

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According to the fossil record, fish were among the first kind of animals to appear on the planet. The earliest known record is of a jawless fish that presumably roamed the seabed sucking up invertebrates....
Read More
2Do Fish Sleep?
It is believed that fish sleep, although it is a controversial subject; some fish keep very still, experiencing a quiet period (quiescence) that you might call sleep, when they become less aware of their...
Read More
3History of the Aquarium
As far back as 2500 B.C., the Sumerians, the ancient people of Mesopotamia, have been identified as the world's earliest fish keepers.
Read More
4How Do Fish Breathe?
Fish and humans resemble each other in many ways. We have digestive, circulatory and nervous systems similar to those of other vertebrates. And fish need oxygen just like we do. But when we spend time...
Read More
5References for the Saltwater Aquarium Hobbyist
The following is a list of books that were not only helpful in putting together the information on saltwater systems and species that you will find on the PetPlace.com database, but also could be a valuable...
Read More

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The External Anatomy of a Fish

The External Anatomy of a Fish

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