Fish Anatomy




Caudal Fin

Single tail fin

Main propelling fin for most fish

Dorsal Fin

Single fin on top of the back

Vertical stability in swimming

Adipose Fin

Single lobe shaped fin behind the dorsal fin on lower back

Aids in stability

Pectoral Fin

Paired fins on either side of the body near the head

Locomotion and side to side movement

Pelvic Fin

Paired belly fins

Steering, braking, and balancing

Anal Fin

Single fin near the anus

Lends stability in swimming


Paired on either side of head

Sight organs

Olfactory Pit

Paired openings on front of snout

Smell organs

Gill Cover

Paired openings on either side of head behind cheeks

Protect gills

Lateral Line

Horizontal line on both sides

Series of sensory pores that sense vibrations in the water


Paired flaps on sides of mouth

Form a round enclosure to reduce the risk of prey escaping


The fins of most fish consist of stiff rays covered by skin. Most fins are jointed and separate near the edge of the fin. However, certain fish have rays that are bony, stiff and unjointed called spines. Some species have both types of fins. For example, Bass have a spiny dorsal near the front and a soft dorsal near the rear that are connected. The number of rays in the fin is used in classification of the species.


The skin of fish consists of two layers. The Epidermis (outer) and the Dermis. The Epidermis consists of cells arranged one above the other. Just like humans, these cells are constantly shed and replaced. Interspaced between the skin cells are slime cells which produce mucoid secretions that form the very important protective covering known as "slime".


The dermis of the skin consists of connective tissue, collagen, and blood vessels. The scales lie in pockets in the dermis and extend out from the connective tissue. Scales are covered by the epithelial layer mentioned above. Scales overlap to form a protective flexible armor capable of withstanding trauma.


Respiration is carried out by means of gills located under gill covers on either side of the head. There are several slit-like openings. Gills are attached to the connective tissue called gill arches. Gills consist of a delicate system of blood vessels covered by a very thin epithelium through which the gaseous exchange takes place.

Lateral Line

The lateral line consists of a series of scales, each modified by a pore, which connects to a system of canals containing sensory cells and nerve fibers. It runs in a horizontal line from the gill covers to the tail fin. The lateral line has been shown to be a very important sensory organ in fish. It can detect minute electrical currents, vibrations (in and through the water), and it serves as a kind of echo location process that helps the fish identify its surroundings.


Cells in the dermis produce the many exotic colors and patterns seen in fish. These cells are named for the pigment they contain. Some fish can change color rapidly due to movement of melanin grains within each cell. When dispersed, they absorb more light and the area of the fish darkens. When tightened the fish looks pale.

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