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 does air. Water is a tasteless, odorless substance that is essential to all known forms of life and is known as the universal solvent. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ...

Body

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

Nearly all fish have a streamlined body plan, which is divided into head, trunk, and tail, although the dividing points are not always externally visible. In fluid dynamics, a streamline is a line which is everywhere tangent to the velocity of the flow. ... This article is in need of attention from an expert on the subject. ...

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 lower jaw defines a chin. 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. Closeup of a blue-green human eye. ... It has been suggested that this article or section be merged with mandible. ... The operculum in fish is the hard bony flap covering and protecting the gills of Bony fish. ... gills of a Smooth Newt Gills inside of a tuna head In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. ... Look up Cheek in Wiktionary, the free dictionary The Cheeks are the fleshy area of the face below the eyes and between the nose and the left or right ear, the skin being suspended by the chin and the yaws. ... This article is about the human bone. ... Chin may refer to: In the human anatomy, the chin is the lowermost part of the face. ... This koi carp has two pairs of barbels, the second pair being quite small. ... A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. ... This article is about nares, the scientific term for a birds or a frogs([[for Mr. ...

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). In most biological nomenclature, a scale (Greek lepid, Latin squama) is a small rigid plate that grows out of an animals skin to provide protection. ... A scute (Latin scutum, shield) is a horny, chitinous, or bony external plate or scale, as on the shell of a turtle or the underside of a snake. ...

The lateral line is a sense organ used to detect movement and vibration in the surrounding water. It consists of a line of receptors running along each side of the fish. In fish, the lateral line is a sense organ used to detect movement in the surrounding water. ...

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 term peduncle has several meanings: In botany, a Peduncle (botany) is a flower stalk, or stem. ...

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 A photophore is a light-emitting organ which appears as luminous spots on various marine fishes. ... ... Common Clownfish (Amphiprion ocellaris) in their Magnificent Sea Anemone (Heteractis magnifica) home. ... Subgroups Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are microscopic, unicellular organisms. ...

Fins

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

Bigeye tuna Thunnus obesus showing finlets and keels.
Drawing by Dr Tony Ayling

• The dorsal fins are located on the back. A fish can have up to three of them. There are two types of dorsal fin rays, spiny and soft. A fin can contain only spiny rays, only soft rays, or a combination - if the latter the spiny rays are always anterior. These comments about fin rays also apply to the anal, pectoral, and pelvic fins.
• The caudal fin is the tail fin, located at the end of the caudal peduncle.
• The anal fin is located on the ventral surface behind the anus.
• The paired pectoral fins are located on each side, usually just behind the operculum, and are homologous to the forelimbs of tetrapods.
• The paired pelvic or ventral fins are located ventrally below the pectoral fins. They are homologous to the hindlimbs of tetrapods.
• 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.
• 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.
• The "horns" of manta rays and their relatives are called cephalic fins.
• Finlets are small, rayless, non-retractable, fins between the last dorsal and/or anal fin and the caudal fin. They are found on fast swimming fish such as tuna.

For every fin, there are a number of fish species in which this particular fin has been lost during evolution. Image File history File links Download high resolution version (576x640, 9 KB) Thunnus obesus (Bigeye tuna) cropped diagram File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Fish anatomy ... Image File history File links Download high resolution version (576x640, 9 KB) Thunnus obesus (Bigeye tuna) cropped diagram File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Fish anatomy ... Binomial name Thunnus obesus (Lowe, 1839) The Bigeye Tuna (Thunnus obesus) is an important food fish, a type of tuna of the family Scombridae. ... Dorsal Fin of the Orca A dorsal fin is a fin located on the backs of fishes, whales, dolphins and porpoises. ... It has been suggested that Human Anatomical Terms be merged into this article or section. ... It has been suggested that Human Anatomical Terms be merged into this article or section. ... Female Human Anatomy Male Human Anatomy Anal redirects here. ... In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ... Groups See text. ... In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ... Groups See text. ... Genera (see text) Salmonidae is a family of ray-finned fish, the only family of order Salmoniformes. ... Genera Subfamily Alestiinae - African tetras  Alestes (or Brycinus)  Hydrocynus  Micralestes  Phenacogrammus  Rhabdalestes  and 13 other genera Subfamily Characidiinae  8 genera Subfamily Characinae  Acestrorhynchus - Pike characins  Aphyocharax  Boehlkea  Chalceus  Charax  Cynodo  Exodon  Hasemania  Hydrolycus  Nematobrycon  Petitella  Priocharax  Rhaphiodon  Roeboides  Thayeria  ... Subfamily Crenuchinae  Crenuchus  Poecilocharax Subfamily Glandulocaudinae  16 genera Subfamily Iguanodectinae  Iguanodectes... Families Akysidae Amblycipitidae Amphiliidae Ariidae Aspredinidae Astroblepidae Auchenipteridae Bagridae Callichthyidae Cetopsidae Chacidae Clariidae Claroteidae Cranoglanididae Diplomystidae Doradidae Erethistidae Hypophthalmidae Ictaluridae Lacantuniidae Loricariidae Malapteruridae Mochokidae Nematogenyidae Pangasiidae Parakysidae Pimelodidae Plotosidae Schilbeidae Scoloplacidae Siluridae Sisoridae Trichomycteridae Catfish (order Siluriformes) are a diverse group of fish. ... Binomial name Manta birostris Dondorff, 1798 The manta ray, or giant manta (Manta birostris), is the largest of the rays, with the largest known specimen having been nearly 76 meters (250 ft) across its pectoral fins (or wings) and weighed in at 3,000 kg (6,600 lb). ... Species See text Tuna, sometimes called tunafish, are several species of ocean-dwelling fish in the family Scombridae, mostly in the genus Thunnus. ...

Scales

types of caudal fin :
(A) - Heterocercal, (B) - Protocercal,
(C) - Homocercal, (D) - Diphycercal

Positions of the fish's mouths:
(a) - final,
(b) - upper,
(c) - bottom

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. They are typical of sharks and rays.
2. Ganoid scales are flat, basal-looking scales that cover a fish body with little overlapping. They are typical of gar.
3. Cycloid scales are small oval-shaped scales with growth rings. Bowfin and remora have cycloid scales.
4. Ctenoid scales are similar to the Cycloid scales, with growth rings. They are distinguished by the spines that cover one edge. Halibut have this type of scale.

Another, less common, type of scale is the scute, which is: Denticles or placoid scales are small outgrowths which cover the skin of many cartilaginous fish including sharks. ... Parts of a tooth, including dentin Dentin (BE: dentine) is the substance between the enamel (substance in the crown) or cementum (substance in the root) of a tooth and the pulp chamber. ... 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 parts of the tooth. ... Orders see text Sharks are a group (superorder Selachimorpha) of fish, with a full cartilaginous skeleton, a streamlined body plan with between 5 and 7 gill slits along the sides (most often) or side of the head (the first modified slit is behind the eye and called a spiracle), dermal... Radiation has a variety of different meanings. ... Species Atractosteus spatula Atractosteus tristoechus Atractosteus tropicus Lepisosteus oculatus Lepisosteus osseus Lepisosteus platostomus Lepisosteus platyrhincus In American English the name gar (or garpike) is strictly applied to members of the Lepisosteidae, a family including seven living species of fish in two genera that inhabit fresh, brackish, and occasionally marine, waters... Binomial name Amia calva Linnaeus, 1766 The bowfins are an order (Amiiformes) of primitive ray-finned fish. ... Genera 10 species in 5 genera: Echeneis Phtheiricthys Remora Remorina Rhombochirus Remoras or suckerfish are elongate brown fish (order Perciformes, family Echeneidae) 30-90 cm long (1-3 feet) whose distinctive dorsal fin takes the form of a modified oval sucker-like organ with slat-like structures that open and... A large halibut with a fisher to its right A halibut is a type of flatfish from the family of the righteye flounders (Pleuronectidae). ...

• 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 (eg pineconefish) are completely or partially covered in scutes. Genera Cleidopus Monocentris Pineconefish 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. It is often absent in fast swimming fishes such as the Tuna and Mackerel families.
• The gills, located under the operculum, are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. They are not usually visible, but can be seen in some species eg the frilled shark.
• Gill rakers are bony, finger-like projections of the gill arch filaments which function in retaining food organisms.