Fish Anatomy is Complex and Compact
© Anthony C. Terceira

Although everybody knows what a fish looks like, few people really bother to examine them closely. They are highly complex containing most of the same organs as other mammals.

The body is cover with skin and bony type plates or scales. Each scale overlaps the one that is behind it, not only to offer protection, but also to help the streamlining and the fish speed through the water. Most fish have seven fins.

The pectoral fins compare with the forelegs of animals; the ventral fins are much like the hind legs. The dorsal fin is sometimes split into to main portions" the foremost is called the anterior dorsal, and the hindmost call the posterior dorsal. A few fish have a small 'fatty' fin called the
adipose fin, which is behind the dorsal fin

Dorsal Fin:
This fin is large and usually stands up because of the hard bony rays it contain. This fin can be raised or lowered for display in courtship or as a gesture used to frighten other fish. The rear portion can be moved to the left or right and helps to steer the fish when speeding along.

Pectoral Fins:
These fins are used for movement, by paddling, when the fish is moving up, down, forward or backward.

Ventral Fin:
In fish these fins act as stabilizers. Many modern ships have adopted this principle to prevent or reduce their rolling.

Anal Fin:
In live bearing fishes, the anal fin changes shape in adult fish and becomes the gonopodium. It also helps to keep the fish upright and is an aid in steering.

Tail Fin (Caudal):
The tail or caudal fin is the main means of propulsion. One stroke of this powerful fin can drive a fish several times its own length through the water at amazingly high speed.

Mouth & Teeth:
All fish have mouths and many have sharp teeth just inside with which to bite or tear off animal or vegetable food. There are other fish, which have bony plates in the throat to grind food small enough to be swallowed.

Most fish have two eyes. Some have four such as mudskippers, which live in shallow water and often climb out onto mud banks. The lower pair of eyes scans the surrounding air for suitable insects. Fish do not have eyelids.

The bony plates known as gill plates protect gills. The soft membranes underneath contain blood vessels that extract the dissolved oxygen from the water entering the fish's mouth and afterwards are expelled through the gill plate slits.

Lateral Line:
Along each side of a fish can be seen a very thin line. This starts just behind the gill plates and may rise a short distance to drop mid-way along its length and then finish in a more or less
straight line trough to the tail. It is only in certain light that the line is visible. It then looks as if the fish has been scrapped with a needle. The line is made up of canals that contain sense organs developed in the skin. Vibrations in the water are picked up by the cells and passed through to the "swim bladder" which acts as an auxiliary hearing organ. Some of the scientists think that fish can recognize their own species from the wavelength picked up by the lateral line.

The Vent:
The vent is situated just in front of the anal fin and waste products of food are excreted here. In the same area is the 'cloaca' which is the urinary and genital duct.

Internal Organs:
Fish have a heart, liver, kidneys, intestines, testes, ova, etc.. An organ unique to fish is the swim bladder. It enables them to rise and sink or stay balanced in mid-water without any effort. Fish are able to fill or discharge 'gas' in the swim bladder; therefore, fish do not have to battle with their fins all the time in order to maintain certain levels in the water. The swim bladder might be compared to the ballast tanks of a submarine.

This is a brief insight into the very complex and compact creatures known as fish. Now that we know a little more about the anatomy of fishes perhaps we will be able to appreciate and enjoy them more than we already do.

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