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. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the

Body

Lampanyctodes hectoris
(1) - operculum (gill cover), (2) - lateral line, (3) - dorsal fin, (4) - adipose fin, (5) - caudal peduncle, (6) - caudal fin, (7) - anal fin, (8) - photophores, (9) - pelvic fins (paired), (10) - pectoral fins (paired)

Fish have a variety of different body plans. A body plan, or bauplan, is essentially the blueprint for the way the body of an organism is laid out 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). True eels ( Anguilliformes) are an order of Fish, which consists of four suborders 19 families 110 Genera and approximately 600 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 Anatomy of Fish is primarily governed by the physical characteristics of Water, which is much denser than air holds a relatively small amount of dissolved 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. A photophore is a light-emitting organ which appears as luminous spots on various marine animals including Fish and Cephalopods. 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. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have

The lateral line is a sense organ used to detect movement and vibration in the surrounding water. In Fish, 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 ampullae of Lorenzini are special sensing organs forming a network of jelly-filled canals found on Elasmobranchs ( Sharks and rays) and

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.

Head

Parts of the head

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. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain The jaw is either of the two opposable structures forming or near the entrance to the Mouth. The operculum of a bony fish is the hard bony flap covering and protecting the Gills In most fish the rear edge of the operculum roughly marks the division between A gill is an anatomical structure found in many aquatic organisms Cheeks ( Latin: buccae) constitute the area of the Face below the Eyes and between the Nose and the left or right Ear The operculum and preopercle may or may not have spines. The lower jaw defines a chin. The mandible (from Latin mandibula, "jawbone" or inferior maxillary bone forms the lower Jaw and holds the lower teeth in place In the Human anatomy, the chin is the lowermost part of the Face.

In lampreys, the mouth is formed into an oral disk. A lamprey (sometimes also called lamprey eel) is a Jawless fish with a toothed funnel-like sucking mouth 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. In fishes a suckermouth is a ventrally orientated (inferior mouth adapted for grazing on algae and small organisms that grow on submerged objects

Positions of the fish's mouths:
(a) - terminal,
(b) - superior,
(c) - subterminal, inferior

The head may have several fleshy structures known as barbels, which may be very long and resemble whiskers. A barbel on a Fish is a slender whiskerlike tactile organ near the Mouth. 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.

Fins

The fins are the most distinctive features of a fish. fin is a surface used to produce lift and Thrust or to steer while traveling in Water, air or other Fluid media

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. In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species 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. The caudal fin is what is connected to the end of each fin.

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. Catfish ( order Siluriformes) are a very diverse group of bony Fish. Triggerfish also use spines to lock themselves in crevices to prevent being pulled out. Triggerfishes are brightly colored Fish of the family Balistidae.

Types of fin

• dorsal fins are located on the back. A dorsal fin is a Fin located on the backs of some Fishes Whales Dolphins and Porpoises as well as the (extinct A fish can have up to three of them. The dorsal fins serve to protect the fish against rolling, and assists in sudden turns and stops.
  • In anglerfish, the anterior of the dorsal fin is modified into an illicium and esca, a biological equivalent to a fishing pole and a lure. Anglerfish are the members of the order Lophiiformes. They are bony fish named for their characteristic mode of Predation, wherein a fleshy
  • The bones that support the dorsal fin are called Pterygiophore. There are two to three of them: "proximal", "middle", and "distal". In spinous fins the distal is often fused to the middle, or not present at all.
• The caudal fin is the tail fin, located at the end of the caudal peduncle.
  

  types of caudal fin :
  (A) - Heterocercal, (B) - Protocercal,
  (C) - Homocercal, (D) - Diphycercal
  • The tail can be heterocercal, which means that the vertebrae extend into a larger lobe of the tail or that the tail is asymmetrical
    • Epicercal means that the upper lobe is longer (as in sharks)
    • Hypocercal means that the lower lobe is longer (as in flying fish)
  • Protocercal means that the caudal fin extends around the vertebral column, present in embryonic fish and hagfish. The Exocoetidae or flying fish are a marine Fish family comprising about 50 Species grouped in 7 to 9 genera. Hagfish are marine Craniates of the class Myxini, also known as Hyperotreti. This is not to be confused with a caudal fin that has fused with the dorsal and anal fins to form a contiguous fin.
  • Diphycercal refers to the special, three-lobed caudal fin of the coelacanth and lungfish where the vertebrae extend all the way to the end of the tail. Coelacanth (ˈsiːləkænθ adaptation of Modern Latin Cœlacanthus > cœl-us + acanth-us from Greek κοῖλ-ος + ἄκανθ-α) is the common name for Lungfish are freshwater fish belonging to the Subclass Dipnoi.
  • Most fish have a homocercal tail, where the vertebrae do not extend into a lobe and the fin is more or less symmetrical. This can be expressed in a variety of shapes.
    • The tail fin may be rounded at the end.
    • The tail fin may be truncated, or end in a more-or-less vertical edge (such as in salmon).
    • The fin may be forked, or end in two prongs.
    • The tail fin may be emarginate, or with a slight inward curve.
    • The tail fin may be lunate, or shaped like a crescent moon.
• The anal fin is located on the ventral surface behind the anus. In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species The anus is an opening at the opposite end of an Animal 's Digestive tract from the Mouth. This fin is used to stabilize the fish while swimming.
• The paired pectoral fins are located on each side, usually just behind the operculum, and are homologous to the forelimbs of tetrapods. In Evolutionary biology, homology has come to mean any similarity between characters that is due to their shared ancestry. Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals
  • A peculiar function of pectoral fins, highly developed in some fish, is the creation of the dynamic lifting force that assists some fish, such as sharks, in maintaining depth and also enables the "flight" for flying fish. The prevailing type of fish locomotion is Swimming in Water. In addition some fish can "walk" i Sharks ( Superorder Selachimorpha) are a type of Fish with a full cartilaginous Skeleton and a highly streamlined body Flight is the process by which an object achieves sustained movement either through the Air (or movement beyond Earth's atmosphere, in the case of The Exocoetidae or flying fish are a marine Fish family comprising about 50 Species grouped in 7 to 9 genera.
    

    Bigeye tuna Thunnus obesus showing finlets and keels. The bigeye tuna, Thunnus obesus, is an important food Fish and highly sought after recreational game fish
    Drawing by Dr Tony Ayling
  • In many fish, the pectoral fins aid in walking, especially in the lobe-like fins of some anglerfish and in the mudskipper. Walking fish, sometimes called ambulatory fish, is a general term that refers to fish that are able to travel over Land for extended periods of time Mudskippers are members of the subfamily Oxudercinae ( tribe: Periophthalmini) within the family Gobiidae (
  • Certain rays of the pectoral fins may be adapted into finger-like projections, such as in sea robins and flying gurnards. Sea robins are bottom-feeding Scorpaeniform Fishes in the family Triglidae. The flying gurnards are a family, Dactylopteridae, of marine Fish notable for their greatly enlarged Pectoral fins They have also
    • The "horns" of manta rays and their relatives are called cephalic fins; this is actually a modification of the anterior portion of the pectoral fin. The manta ray ( Manta birostris) is the largest of the rays, with the largest known specimen having been more than 7
• The paired pelvic or ventral fins are located ventrally below the pectoral fins. They are homologous to the hindlimbs of tetrapods. In Evolutionary biology, homology has come to mean any similarity between characters that is due to their shared ancestry. Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals The pelvic fin assists the fish in going up or down through the water, turning sharply, and stopping quickly.
  • In gobies, the pelvic fins are often fused into a single sucker disk. gobies form the family Gobiidae, which is one of the largest families of Fish, with more than 2000 Species in more than 200 Genera This can be used to attach to objects.
• The adipose fin is a soft, fleshy fin found on the back behind the dorsal fin and just forward of the caudal fin. It is absent in many fish families, but is found in Salmonidae, characins and catfishes. Salmonidae is a family of Ray-finned fish, the only living family of the order Salmoniformes. The Characidae, characids or characins are a family of freshwater Subtropical and Tropical fish belonging to the Catfish ( order Siluriformes) are a very diverse group of bony Fish.
• Some types of fast-swimming fish have a horizontal caudal keel just forward of the tail fin. This is a lateral ridge on the caudal peduncle, usually composed of scutes (see below), that provides stability and support to the caudal fin. There may be a single paired keel, one on each side, or two pairs above and below.
• Finlets are small fins, generally behind the dorsal and anal fins (in bichirs, there are only finlets on the dorsal surface and no dorsal fin). The bichirs are a family Polypteridae, of archaic-looking ray-finned fishes, the sole family in the order Polypteriformes. In some fish such as tuna or sauries, they are rayless, non-retractable, and found between the last dorsal and/or anal fin and the caudal fin. Tuna, are several Species of ocean-dwelling Fish in the family Scombridae, mostly in the genus Thunnus. Sauries are fish of the family Scomberesocidae. There are two genera, each containing two species

For every fin, there are a number of fish species in which this particular fin has been lost during evolution.

Internal fertilization

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. An intromittent organ is a general term for an external organ of a Male organism that is specialized to deliver Sperm during copulation. Anablepidae is a family of Freshwater and Brackish water fishes living on river estuaries from southern Mexico to southern South America. Poeciliidae is a family of fresh-water Fish which are live-bearing aquarium fish (they give birth to live young 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. For the genus of butterflies commonly known as swordtails see Graphium. 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. Hemirhamphodon is a Genus of Halfbeak found in peaty and lowland forest streams in Southeast Asia. Splitfins, are a family Goodeidae, of Teleost Fish endemic to Mexico and some areas of the United States.

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. Chondrichthyes or cartilaginous fishes are jawed Fish with paired fins paired nostrils scales two-chambered hearts and skeletons made of Cartilage rather These are intromittent organs, used to channel semen into the female's cloaca during copulation. In zoological anatomy a cloaca is the posterior opening that serves as the only such opening for the intestinal and urinary tracts of certain animal species

Skin

The outer body of many fish is covered with scales. In most biological nomenclature a scale ( Greek lepid, Latin squama) is a small rigid plate that grows out of an Animal 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.

1. Placoid scales, also called dermal denticles, are similar to teeth in that they are made of dentin covered by enamel. Denticles are body surface structures found on some fish and insects Dentin ( BE: dentine) is a calcified tissue of the body and along with enamel, Cementum, and pulp is one of the four Tooth enamel is the hardest and most highly mineralized substance of the body and with Dentin, Cementum, and dental pulp is one of the four major They are typical of sharks and rays. Sharks ( Superorder Selachimorpha) are a type of Fish with a full cartilaginous Skeleton and a highly streamlined body Batoidea is a Superorder of cartilaginous fish containing more than 500 described species in thirteen families
2. Ganoid scales are flat, basal-looking scales that cover a fish body with little overlapping. They are typical of gar and bichirs. In American English the name gar (or garpike) is strictly applied to members of the Lepisosteus, a family including seven living species of fish in two The bichirs are a family Polypteridae, of archaic-looking ray-finned fishes, the sole family in the order Polypteriformes.
3. Cycloid scales are small oval-shaped scales with growth rings. Bowfin and remora have cycloid scales. Bowfins are an order ( Amiiformes) of primitive Ray-finned fish. Remoras or suckerfish are elongate brown Fish in order Perciformes and family Echeneidae.
4. Ctenoid scales are similar to the cycloid scales, with growth rings. They are distinguished by spines that cover one edge. Halibut have this type of scale. A halibut is a type of Flatfish

Another, less common, type of scale is the scute, which is:

• an external shield-like bony plate, or
• a modified, thickened scale that often is keeled or spiny, or
• a projecting, modified (rough and strongly ridged) scale, usually associated with the lateral line, or on the caudal peduncle forming caudal keels, or along the ventral profile. Some fish, such as pineconefish, are completely or partially covered in scutes. Pinecone fishes are small and unusual Beryciform marine Fish of the family Monocentridae.

Internal organs

• The gas bladder, or swim bladder, is an internal organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth, ascend, or descend without having to waste energy in swimming. gas bladder (also fish maw, less accurately swim bladder or air bladder) is an internal organ that contributes to the ability of a Fish It is often absent in fast swimming fishes such as the tuna and mackerel families.
• Certain groups of fish have modifications to allow them to hear, such as the Weberian apparatus of Ostariophysians. The Weberian apparatus is made up of a set of bones known as Weberian ossicles, a chain of small bones that connect the auditory system to the Gas bladder of Ostariophysi is the second-largest Superorder of Fish. Members of this superorder are called ostariophysans.
• The gills, located under the operculum, are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. A gill is an anatomical structure found in many aquatic organisms The operculum of a bony fish is the hard bony flap covering and protecting the Gills In most fish the rear edge of the operculum roughly marks the division between They are not usually visible, but can be seen in some species, such as the frilled shark. The frilled shark, Chlamydoselachus anguineus, is a primitive Shark species of the family Chlamydoselachidae in the order
• The labyrinth organ of Anabantoidei and Clariidae is used to allow the fish to extract oxygen from the air. The Anabantoidei is a suborder of perciform ray-finned Freshwater fishes distinguished by their possession of a Lung -like labyrinth Airbreathing catfishes are Fishes comprising the family Clariidae of order Siluriformes.
• Gill rakers are bony, finger-like projections of the gill arch filaments which function in filter-feeders in retaining food organisms.
• Electric fish are able to produce electric fields by modified muscles in their body. An electric fish is a fish that can generate Electric fields It is said to be electrogenic; a fish that has the ability to detect electric fields is said to be
• Many fish species are hermaphrodites. A hermaphrodite is an organism having both male and female reproductive organs Synchronous hermaphrodites possess both ovaries and testes at the same time. "Ovaria" redirects here This is also a proposed section and a Synonym of Solanum. The testicle (from Latin testiculus, diminutive of testis, meaning "witness" virility plural testes) is the male Sequential hermaphrodites have both types of tissue in their gonads, with one type being predominant while the fish belongs to the corresponding gender. The gonad is the organ that makes Gametes The gonads in males are the Testes and the gonads in Females are the Ovaries. ^[1]

See also

• Fish development
• Ichthyology terms
• Fish measurement

fish hear by water vibrations

References

1. ^ Gilbert, Scott F. The development of Fishes is unique in some specific aspects compared to the development of other animals Ichthyology uses several terms that are unique to the science Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. (1994). Developmental Biology, 4th edition, Sunderland, Massachusetts: Sinauer Associates, Inc. , p. 781. ISBN 0878932496.