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Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs light more than air does.
Additional recommended knowledge
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 laterally compressed (thin) or vertically depressed (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.
The head includes the snout, from the eye to the forwardmost point of the upper jaw, the operculum or gill cover (absent in sharks), and the cheek, which extends from eye to preopercle. The operculum and preopercle may or may not have spines. The lower jaw defines a chin.
In lampreys, the mouth is formed into an oral disk. In most jawed fish, however, there are three general configurations. The mouth may be on the forward end of the head (terminal), may be upturned (superior), or may be turned downwards or on the bottom of the fish (subterminal or inferior). The mouth may be modified into a suckermouth adapted for clinging onto objects in fast-moving water.
The head may have several fleshy structures known as barbels, which may be very long and resemble whiskers. Many fish species also have a variety of protrusions or spines on the head. The nostrils or nares of almost all fishes do not connect to the oral cavity, but are pits of varying shape and depth.
Fish that feed on plankton and those with tube-shaped mouths (the Syngnathidae) may lack teeth. Some other fish have teeth, in a wide range of configurations. The teeth are classified according to the bones they sit on:
Some species, including salmonidae and osteoglossidae (meaning bony tongues), also have sharp teeth on dental plates on their tongue. Shark teeth are particularly unusual, having developed as modified scales.
Tooth form is generally optimized for dietary function. Predatory fish may have sharp conical teeth, called canine (dog) teeth to hold prey. They generally hold a struggling baitfish until it is weakened, and then swallow it. Pharyngeal teeth help to block prey from escaping the throat. Non-predatory fish may have very different shapes of teeth; corallivorous have grinding teeth, and Scaridae (parrot fish) have plates of fused teeth for breaking coral.
The fins are the most distinctive features of a fish.
Spines and rays
In bony fish, most fins may have spines or rays. A fin can contain only spiny rays, only soft rays, or a combination of both. If both are present, the spiny rays are always anterior. Spines are generally stiff and sharp. Rays are generally soft, flexible, segmented, and may be branched. This segmentation of rays is the main difference that separates them from spines; spines may be flexible in certain species, but they will never be segmented.
Spines have a variety of uses. In catfish, they are used as a form of defense; many catfish have the ability to lock their spines outwards. Triggerfish also use spines to lock themselves in crevices to prevent being pulled out.
Types of fins
For every fin, there are a number of fish species in which this particular fin has been lost during evolution.
In many species of fish, fins have been modified to allow internal fertilization.
A gonopodium is an anal fin that is modified into an intromittent organ in males of certain species of live-bearing fish in the families Anablepidae and Poeciliidae. It is movable and used to impregnate females during mating. The male's anal fin’s 3rd, 4th and 5th rays are formed into a tube like structure in which the sperm of the fish is ejected. In some species, the gonopodium may be as much as 50% of the total body length. Occasionally the fin is too long to be used, as in the "lyretail" breeds of Xiphophorus helleri. Hormone treated females may develop gonopodia. These are useless for breeding. One finds similar organs having the same characteristics in other types of fish, for example the andropodium in the Hemirhamphodon or in the Goodeidae.
When ready for mating, the gonopodium becomes “erect” and points forward, towards the female. The male shortly inserts the organ into the sex opening of the female, with hook-like adaptations that allow the fish to grip onto the female to insure impregnation. If a female remains stationary and her partner contacts her vent with his gonopodium, she is fertilized. The sperm is preserved in the female's oviduct. This allows females to, at any time, fertilize themselves without further assistance of males.
Male cartilaginous fish have claspers modified from pelvic fins. These are intromittent organs, used to channel semen into the female's cloaca during copulation.
The outer body of many fish is covered with scales. Some species are covered instead by scutes. Others have no outer covering on the skin; these are called naked fish. Most fish are covered in a protective layer of slime (mucus).
There are four types of fish scales.
Another, less common, type of scale is the scute, which is:
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fish_anatomy". A list of authors is available in Wikipedia.|