Body
Fish have a variety of different body plans. Their body is divided into head, trunk, and tail, although the divisions are not always externally visible. The body is often fusiform, a streamlined body plan often found in fast-moving fish. They may also be filiform (eel-shaped) or vermiform (worm-shaped). Also, fish are often either compressed (laterally thin) or depressed (dorso-ventrally flat).
The caudal peduncle is the narrow part of the fish's body to which the caudal or tail fin is attached. The hypural joint is the joint between the caudal fin and the last of the vertebrae. The hypural is often fan-shaped.
Photophores are light-emitting organs which appears as luminous spots on some fishes. The light can be produced from compounds during the digestion of prey, from specialized mitochondrial cells in the organism called photocytes, or associated with symbiotic bacteria, and are used for attracting food or confusing predators.
The lateral line is a sense organ used to detect movement and vibration in the surrounding water. In most species, it consists of a line of receptors running along each side of the fish.
The ampullae of Lorenzini allow sharks to sense electrical discharges.
The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish often can be determined by the shape of its papilla.
Read more about this topic: Fish Anatomy
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—Marcus Minucius Felix (2nd or 3rd cent. A.D.)
“Sang a bone upon the shore;
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—William Butler Yeats (1865–1939)