Anatomy of a Fish

Fish are cold-blooded aquatic animals, found in abundance in various water bodies on the planet. In fact, there exist thousands of fish species in the world, each of which has adapted to a specific environment which they inhabit. Different varieties are found in different habitats, ranging from saltwater deep oceans to freshwater shallow streams. It is very important to know the fish anatomy to understand its ability to sustain itself in such diverse environment.

Body Shape
The body shape of a fish corresponds to the habitat it dwells in. Surface dwelling fish have a flat back, whereas bottom dwelling fish have flattened bellies. Fish living in slow moving waters have broad laterally compressed bodies, while fish living in fast-moving waters have slender bodies. These variations make it easier for them to swim in their respective habitat. An air filled bladder, known as the swim bladder, helps the fish to remain in a neutral state of buoyancy, wherein they neither float to the surface nor sink in the depths.

The Mouth
The mouth of the fish indicates the feeding habit of the species. Surface dwelling fish, which feed on insects present on the surface of the water, have an upturned mouth which makes it easier for them to swoop up on their prey. The mouth of a predatory fish is wider than that of an omnivorous fish. Bottom dwelling fish have an underslung mouth, often accompanied with whiskers, which act as radars, helping the fish to locate its prey in deep dark waters. The suction-cup like mouth of the species of fish which dwell at the bottom of the ocean helps them to feed on marine life, like algae and plants growing on the ocean floor.

The Fins
One of the most important organs of fish, the fins are utilized for movement, stability and as tactile organs. The tail fin, also known as caudal, is used as a propeller. Forked tail fins help the fish to swim faster; such a tail is generally noticed in fast swimming fish. Predatory fish have rounded caudal fins, which help the fish to get into action swiftly. At times, large elongated fins noticed in some female species are used to attract the male species. The single anal fin located on the underside of the body, helps the fish to be stable while swimming. In some species of fish, longer anal fins are also used as propellers along with caudal.

The paired pelvic fins, also known as the ventrals, are long and thread like in nature. They are multipurpose and act as the tactile organs of the fish, provide stability to its movement and also help a species, like the catfish, to carry the eggs while breeding. The paired pectoral fins, used by the fish for maneuvering, are located near the gill cover. Pectoral fins, armed with spines, are used as defense against lurking predators. The dorsal fin, located on the back, helps the fish to balance its body while swimming.

The Gills
The gills are the respiratory organs of the fish. They help the fish to extract oxygen dissolved in water, and excrete carbon dioxide. Though many aquatic animals do not require gills for respiration as their modified skin allows them to breathe through the entire body, it is observed that those species which use gills for respiration are more active than those who don't. Some species of fish swallow water and store it in the swim bladder, where the oxygen is extracted.

The Scales
Scales, rigid plates on the skin of a fish, work as a protective covering for the fish. Not all species of fish have scales, species like the catfish have bony plates as their protective covering. The fluid filled ducts located under the scales are designed to feel and pick up vibrations in water. This helps the fish to detect predators and find food. Because of this mechanism, many species of fish can move through the dark parts of the ocean which are too deep for the sunlight to penetrate.

The Color
Color plays an important role for the different species of fish. The color of the fish is determined by pigmentation, for fish which are dark in color, and by light reflection, for fish having a silvery appearance. Color helps in camouflaging, for predators as well as the prey. In some species, bright colors are used to attract members of opposite sex.

Over the period, fish species on the planet have adapted themselves to a wide range of conditions, which, in turn, has helped them survive the odds. It is this very adaptability that has helped fish survive for more than 450 million years now, while several other species which came after them, including the dinosaurs, have become extinct.