Fish are aquatic vertebrates that are typically ectothermic (previously cold-blooded), covered with scales, and equipped with two sets of paired fins and several unpaired fins. Marine biology is the scientific study of living Organisms in the Ocean or other marine or Brackish bodies of water Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds In most biological nomenclature a scale ( Greek lepid, Latin squama) is a small rigid plate that grows out of an Animal fin is a surface used to produce lift and Thrust or to steer while traveling in Water, air or other Fluid media Fish are abundant in the sea and in fresh water, with species being known from mountain streams (e. g. , char and gudgeon) as well as in the deepest depths of the ocean (e. Salvelinus is a Genus of salmonid Fish, often called char or charr; many of the fish called " Trouts quot also Gudgeon is a common name for a number of small Freshwater fishes of the families Cyprinidae, Eleotridae or Ptereleotridae. g. , gulpers and anglerfish). Saccopharyngiformes is an order of unusual Ray-finned fish superficially similar to Eels but with many internal differences Anglerfish are the members of the order Lophiiformes. They are bony fish named for their characteristic mode of Predation, wherein a fleshy They are of tremendous importance as food for people around the world, either collected from the wild (see fishing) or farmed in much the same way as cattle or chickens (see aquaculture). For the computer security term see Phishing. Fishing is the activity of catching Fish. Cattle, colloquially referred to as cows, are domesticated Ungulates a member of the Subfamily Bovinae of the family The chicken ( Gallus gallus, sometimes G gallus domesticus) is a domesticated Fowl which is traditionally believed to have descended from Aquaculture is the farming of freshwater and saltwater organisms including Molluscs Crustaceans and aquatic plants Fish are also exploited for recreation, through angling and fishkeeping, and are commonly exhibited in public aquaria. Angling is a method of Fishing by means of an "angle" ( hook) Fishkeeping is a popular Hobby concerned with keeping Fish in the home Aquarium or garden Pond. An aquarium (plural aquariums or aquaria) is a Vivarium consisting of at least one transparent side in which Water -dwelling Plants Fish have an important role in many cultures through the ages, ranging as widely as deities and religious symbols to subjects of books and popular movies. See also List of deities A deity is a Postulated Preternatural or Supernatural Being, who is always

A giant grouper at the Georgia Aquarium, seen swimming among schools of other fish

The ornate lionfish as seen from a head on view

Definition

The term "fish" is most precisely used to describe any non-tetrapod chordate, (i. For other meanings see Grouper (disambiguation. Groupers are Fish of any of a number of genera in the subfamily Epinephelinae of The Georgia Aquarium, located in Atlanta, Georgia at Pemberton Place, is billed as the "world's largest aquarium" with more than 8 Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates e. , an animal with a backbone), that has gills throughout life and has limbs, if any, in the shape of fins. A gill is an anatomical structure found in many aquatic organisms ^[1] Unlike groupings such as birds or mammals, fish are not a single clade but a paraphyletic collection of taxa, including hagfishes, lampreys, sharks and rays, ray-finned fishes, coelacanths, and lungfishes. Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all A taxon (plural taxa) or taxonomic unit, is a name designating an organism or a group of Organisms In Biological nomenclature according to Hagfish are marine Craniates of the class Myxini, also known as Hyperotreti. A lamprey (sometimes also called lamprey eel) is a Jawless fish with a toothed funnel-like sucking mouth Chondrichthyes or cartilaginous fishes are jawed Fish with paired fins paired nostrils scales two-chambered hearts and skeletons made of Cartilage rather The Actinopterygii (the plural form of Actinopterygius) comprise the class of the ray-finned fishes. 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. ^[2][3]

A typical fish is ectothermic; has a streamlined body that allows it to swim rapidly; extracts oxygen from the water using gills or an accessory breathing organ to enable it to breath atmospheric oxygen; has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin, and a tail fin; has jaws; has skin that is usually covered with scales; and lays eggs that are fertilized internally or externally. Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds Fluid flow is described in general by a Vector field in three (for steady flows or four (for non-steady flows including time dimensions In most biological nomenclature a scale ( Greek lepid, Latin squama) is a small rigid plate that grows out of an Animal

Fish come in many shapes and sizes. This is a sea dragon, a close relative of the seahorse. The leafy sea dragon, Phycodurus eques, is a marine Fish related to the Seahorse. Seahorses are a Genus ( Hippocampus ') of fish belonging to the family Syngnathidae, which also includes Pipefish and Leafy Their leaf-like appendages enable them to blend in with floating seaweed

To each of these there are exceptions. Tuna, Swordfish, and some species of sharks show some warm-blooded adaptations, and are able to raise their body temperature significantly above that of the ambient water surrounding them. Tuna, are several Species of ocean-dwelling Fish in the family Scombridae, mostly in the genus Thunnus. Swordfish ( Xiphias gladius) are large highly migratory Predatory Fish characterized by a long flat bill. Sharks ( Superorder Selachimorpha) are a type of Fish with a full cartilaginous Skeleton and a highly streamlined body In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant ^[4] Streamlining and swimming performance varies from highly streamlined and rapid swimmers which are able to reach 10-20 body-lengths per second (such as tuna, salmon, and jacks) through to slow but more maneuverable species such as eels and rays that reach no more than 0. Carangidae is a family of fish which includes the jacks Pompanos Jack mackerels and scads True eels ( Anguilliformes) are an order of Fish, which consists of four suborders 19 families 110 Genera and approximately 600 Batoidea is a Superorder of cartilaginous fish containing more than 500 described species in thirteen families 5 body-lengths per second. ^[5] Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures. Lungfish have paired lungs similar to those of tetrapods, gouramis have a structure called the labyrinth organ that performs a similar function, while many catfish, such as Corydoras extract oxygen via the intestine or stomach. Lungfish are freshwater fish belonging to the Subclass Dipnoi. The gouramis or gouramies are a family, Osphronemidae, of freshwater Perciform Fishes The fish are native to The Anabantoidei is a suborder of perciform ray-finned Freshwater fishes distinguished by their possession of a Lung -like labyrinth Members of the South American Corydoras Genus are Freshwater Temperate and Tropical Catfish in the armored catfish ^[6] Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms as seahorses, pufferfish, anglerfish, and gulpers. Seahorses are a Genus ( Hippocampus ') of fish belonging to the family Syngnathidae, which also includes Pipefish and Leafy Tetraodontidae is a family of primarily marine and estuarine fish Anglerfish are the members of the order Lophiiformes. They are bony fish named for their characteristic mode of Predation, wherein a fleshy Saccopharyngiformes is an order of unusual Ray-finned fish superficially similar to Eels but with many internal differences Similarly, the surface of the skin may be naked (as in moray eels), or covered with scales of a variety of different types usually defined as placoid (typical of sharks and rays), cosmoid (fossil lungfishes and coelacanths), ganoid (various fossil fishes but also living gars and bichirs, cycloid, and ctenoid (these last two are found on most bony fish. Moray eels are large cosmopolitan Eels of the family Muraenidae. Denticles are body surface structures found on some fish and insects In most biological nomenclature a scale ( Greek lepid, Latin squama) is a small rigid plate that grows out of an Animal In most biological nomenclature a scale ( Greek lepid, Latin squama) is a small rigid plate that grows out of an Animal 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. A cycloid is the curve defined by the path of a point on the edge of circular wheel as the wheel rolls along a straight line Ctenoid means 'having the margin toothed like a comb' It is used to the scales of some fishes such as Perciforms that have such a toothed margin Osteichthyes (ˌɒstiːˈɪkθiːz also called bony fish, are a taxonomic Class of Fish that includes the ray-finned fish ( Actinopterygii ^[7] There are even fishes that spend most of their time out of water. Mudskippers feed and interact with one another on mudflats and are only underwater when hiding in their burrows. Mudskippers are members of the subfamily Oxudercinae ( tribe: Periophthalmini) within the family Gobiidae ( ^[8] The catfish Phreatobius cisternarum lives in underground, phreatic habitats, and a relative lives in waterlogged leaf litter. Catfish ( order Siluriformes) are a very diverse group of bony Fish. Phreatobius cisternarum is a Species of Catfish in the Genus Phreatobius. The term phreatic is used in Earth sciences to refer to matters relating to ground water below the static Water table (the word originates from the Greek Plant litter (sometimes called leaf litter or tree litter) is dead Plant material such as leaves, Bark, and Twigs ^[9][10]

Fish range in size from the 16 m (51 ft) whale shark to the 8 mm (just over ¼ of an inch) long stout infantfish. The whale shark, Rhincodon typus, is a slow filter feeding Shark that is the largest living Fish Species. Schindleria brevipinguis is a Species of marine Fish in family Schindleriidae of Perciformes.

Many types of aquatic animals commonly referred to as "fish" are not fish in the sense given above; examples include shellfish, cuttlefish, starfish, crayfish and jellyfish. An aquatic animal is an Animal which lives in water for most or all of the time Shellfish is a Culinary and Fisheries term for those aquatic Invertebrate animals that are used as Food: various species of molluscs Cuttlefish are marine animals of the order Sepiida belonging to the Cephalopoda class (which also includes Squid, Octopuses Starfish (also called sea stars) are any Echinoderms belonging to the class Asteroidea. Crayfish, crawfish, crawdads, or crodgers are freshwater Crustaceans resembling small Lobsters to which they are closely Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the In earlier times, even biologists did not make a distinction - sixteenth century natural historians classified also seals, whales, amphibians, crocodiles, even hippopotamuses, as well as a host of aquatic invertebrates, as fish^[11]. Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising Whales are marine mammals which are neither Dolphins (ie members of the families Delphinidae or Platanistoidae) nor Porpoises Orcas Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and A crocodile is any Species belonging to the family Crocodylidae (sometimes classified instead as the Subfamily Crocodylinae) The hippopotamus ( Hippopotamus amphibius) from the Greek ἱπποπόταμος ( hippopotamos, ιππος hippos meaning "horse" In some contexts, especially in aquaculture, the true fish are referred to finfish to distinguish them from these other animals.

Classification

Fish are a paraphyletic group: that is, any clade containing all fish also contains the tetrapods, which are not fish. In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals For this reason, groups such as the "Class Pisces" seen in older reference works are no longer used in formal classifications.

Some palaeontologists consider that Conodonta are chordates, and so regard them as primitive fish. Pteraspidomorphi is an extinct subclass of early Jawless fish. There is much debate over whether the clade of Palaeozoic fish known as the Thelodonti (formerly coelolepids) represent a monophyletic grouping, or disparate For turtles see Anapsida. The Anaspida ("Without Shields" are stem Gnathostomes, and are classically regarded as Cephalaspidomorphs are a Taxon of jawless fishes named for the cephalaspids a group of osteostracans. Hyperoartia is a group of Jawless fishes that includes the modern Lampreys and their Fossil relatives the jawless fishes of the class A lamprey (sometimes also called lamprey eel) is a Jawless fish with a toothed funnel-like sucking mouth A lamprey (sometimes also called lamprey eel) is a Jawless fish with a toothed funnel-like sucking mouth Galeaspida ("Helmet shields" is an extinct taxon of jawless marine and freshwater Fish. The Pituriaspida (" Pituri Shield" are a small group of armored jawless fishes with tremendous nose-like Rostrums which lived in the marine deltaic The Class Osteostraci ("Bony Shields" was a group of bony-armored jawless fish termed " Ostracoderms quot that lived in what is now North America Gnathostomata is the group of Vertebrates with Jaws The group is traditionally a superclass, including the familiar classes of Fish, The Placodermi were a class of armoured Prehistoric fishes known from Fossils which lived from the late Silurian to the end of the Devonian Chondrichthyes or cartilaginous fishes are jawed Fish with paired fins paired nostrils scales two-chambered hearts and skeletons made of Cartilage rather Acanthodii (sometimes called spiny sharks) is a class of extinct Fishes having features of both bony fish ( Osteichthyes) and cartilaginous fish ( Osteichthyes (ˌɒstiːˈɪkθiːz also called bony fish, are a taxonomic Class of Fish that includes the ray-finned fish ( Actinopterygii The Actinopterygii (the plural form of Actinopterygius) comprise the class of the ray-finned fishes. Sarcopterygii (from Greek σαρξ sarx, flesh and πτερυξ pteryx, fin is traditionally the class of lobe-finned Fishes consisting Coelacanth (ˈsiːləkænθ adaptation of Modern Latin Cœlacanthus > cœl-us + acanth-us from Greek κοῖλ-ος + ἄκανθ-α) is the common name for 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. Lungfish are freshwater fish belonging to the Subclass Dipnoi. Conodonts are extinct chordates resembling eels classified in the class Conodonta. Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates For a fuller treatment of classification, see the vertebrate article. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes

The various fish groups taken together account for more than half of the known vertebrates. There are almost 28,000 known extant species of fish, of which almost 27,000 are bony fish, with the remainder being about 970 sharks, rays, and chimeras and about 108 hagfishes and lampreys. Extant is a term commonly used to refer to Taxa (such as Species, genera or families) that are still in existence (living Chondrichthyes or cartilaginous fishes are jawed Fish with paired fins paired nostrils scales two-chambered hearts and skeletons made of Cartilage rather ^[12] A third of all of these species are contained within the nine largest families; from largest to smallest, these families are Cyprinidae, Gobiidae, Cichlidae, Characidae, Loricariidae, Balitoridae, Serranidae, Labridae, and Scorpaenidae. The family Cyprinidae, from the Ancient Greek κυπρῖνος ( kuprīnos "carp" consists of the Carps gobies form the family Gobiidae, which is one of the largest families of Fish, with more than 2000 Species in more than 200 Genera Cichlids (ˈsɪklɪd are Fish from the family Cichlidae in the order Perciformes. The Characidae, characids or characins are a family of freshwater Subtropical and Tropical fish belonging to the Loricariidae is the largest family of Catfish (Order Siluriformes with almost 700 species and new species being described each year The hillstream loaches or river loaches are a family Balitoridae of small Eurasian Fish. Serranidae is a large family of Fishes belonging to the order Perciformes. The wrasses are a family, Labridae, of marine Fish, many of which are brightly colored The scorpionfish are a family ( Scorpaenidae) of mostly marine Fish that includes many of the world's most venomous species On the other hand, about 64 families are monotypic, containing only one species. Monotypic is an adjective that refers to a taxonomic group with only one type: In Botany, "monotypic" means that a Taxon has only It is predicted that the eventual number of total extant species will be at least 32,500. ^[13]

Anatomy

Main article: Fish anatomy

The anatomy of 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)

Digestive system

The advent of jaws allowed fish to eat a much wider variety of food, including plants and other organisms. 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 In fish, food is ingested through the mouth and then broken down in the esophagus. The esophagus or oesophagus (see American and British English spelling differences) sometimes known as the gullet, is an organ in When it enters the stomach, the food is further broken down and, in many fish, further processed in fingerlike pouches called pyloric caeca. The pyloric caeca secrete digestive enzymes and absorb nutrients from the digested food. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Organs such as the liver and pancreas add enzymes and various digestive chemicals as the food moves through the digestive tract. The liver is a vital organ in the human body and is present in Vertebrates and some other animals The pancreas is a Gland organ in the digestive and Endocrine system of Vertebrates. The intestine completes the process of digestion and nutrient absorption.

Respiratory system

Most fish exchange gases by using gills that are located on either side of the pharynx. A gill is an anatomical structure found in many aquatic organisms The pharynx (plural pharynges) is the part of the Neck and Throat situated immediately Posterior to (behind the Mouth and Nasal Gills are made up of threadlike structures called filaments. Each filament contains a network of capillaries that allow a large surface area for the exchange of oxygen and carbon dioxide. Capillaries are the smallest of a body's Blood vessels measuring 5-10 μm in diameter which connect Arterioles and Venules and enable the interchange Surface area is the measure of how much exposed Area an object has Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gill filaments. The blood in the capillaries flows in the opposite direction to the water, causing counter current exchange. Countercurrent exchange is a mechanism used to transfer some property of a Fluid from one flowing current of fluid to another across a Semipermeable membrane or thermally-conductive They then push the oxygen-poor water out through openings in the sides of the pharynx. Some fishes, like sharks and lampreys, possess multiple gill openings. Sharks ( Superorder Selachimorpha) are a type of Fish with a full cartilaginous Skeleton and a highly streamlined body A lamprey (sometimes also called lamprey eel) is a Jawless fish with a toothed funnel-like sucking mouth However, most fishes have a single gill opening on each side of the body. This opening is hidden beneath a protective bony cover called an operculum. 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

Juvenile bichirs have external gills, a very primitive feature that they hold in common with larval amphibians. The bichirs are a family Polypteridae, of archaic-looking ray-finned fishes, the sole family in the order Polypteriformes. Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and

Swim bladder of a Rudd (Scardinius erythrophthalmus)

Many fish can breathe air. The mechanisms for doing so are varied. The skin of anguillid eels may be used to absorb oxygen. The buccal cavity of the electric eel may be used to breathe air. The electric eel, Electrophorus electricus, is a species of Fish. Catfishes of the families Loricariidae, Callichthyidae, and Scoloplacidae are able to absorb air through their digestive tracts. Loricariidae is the largest family of Catfish (Order Siluriformes with almost 700 species and new species being described each year Callichthyidae is a family of Catfishes ( order Siluriformes called armored catfishes due to the two rows of bony plates (or scutes running Scoloplax is the only Genus in the Catfish ( order Siluriformes family Scoloplacidae, the spiny dwarf catfishes ^[14] Lungfish and bichirs have paired lungs similar to those of tetrapods and must rise to the surface of the water to gulp fresh air in through the mouth and pass spent air out through the gills. Lungfish are freshwater fish belonging to the Subclass Dipnoi. The bichirs are a family Polypteridae, of archaic-looking ray-finned fishes, the sole family in the order Polypteriformes. Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals Gar and bowfin have a vascularised swim bladder that is used in the same way. 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 Bowfins are an order ( Amiiformes) of primitive Ray-finned fish. Loaches, trahiras, and many catfish breathe by passing air through the gut. The Erythrinidae, also known as Trahiras, are a family of freshwater Fishes found in the rivers of South America. Catfish ( order Siluriformes) are a very diverse group of bony Fish. Mudskippers breathe by absorbing oxygen across the skin (similar to what frogs do). A number of fishes have evolved so-called accessory breathing organs that are used to extract oxygen from the air. Labyrinth fish (such as gouramis and bettas) have a labyrinth organ above the gills that performs this function. The gouramis or gouramies are a family, Osphronemidae, of freshwater Perciform Fishes The fish are native to Betta is a large Genus of small often colorful Freshwater Ray-finned fishes in the Gourami family (Osphronemidae The Anabantoidei is a suborder of perciform ray-finned Freshwater fishes distinguished by their possession of a Lung -like labyrinth A few other fish have structures more or less resembling labyrinth organs in form and function, most notably snakeheads, pikeheads, and the Clariidae family of catfish. Channidae is a family of Freshwater fish commonly known as snakeheads, and is native to Africa and Asia. Airbreathing catfishes are Fishes comprising the family Clariidae of order Siluriformes.

Being able to breathe air is primarily of use to fish that inhabit shallow, seasonally variable waters where the oxygen concentration in the water may decline at certain times of the year. At such times, fishes dependent solely on the oxygen in the water, such as perch and cichlids, will quickly suffocate, but air-breathing fish can survive for much longer, in some cases in water that is little more than wet mud. At the most extreme, some of these air-breathing fish are able to survive in damp burrows for weeks after the water has otherwise completely dried up, entering a state of aestivation until the water returns. Estivation or aestivation (from Latin aestas, summer also known as "summer sleep" is a state of Dormancy somewhat similar

Tuna gills inside of the head. The fish head is oriented snout-downwards, with the view looking towards the mouth.

Fish can be divided into obligate air breathers and facultative air breathers. Obligate air breathers, such as the African lungfish, must breathe air periodically or they will suffocate. Facultative air breathers, such as the catfish Hypostomus plecostomus, will only breathe air if they need to and will otherwise rely solely on their gills for oxygen if conditions are favourable. Most air breathing fish are not obligate air breathers, as there is an energetic cost in rising to the surface and a fitness cost of being exposed to surface predators. ^[14]

Circulatory system

Fish have a closed circulatory system with a heart that pumps the blood in a single loop throughout the body. This is an article about the rock music band "Circulatory System" The heart is a muscular organ in all Vertebrates responsible for pumping Blood through the Blood vessels by repeated rhythmic Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products The blood goes from the heart to gills, from the gills to the rest of the body, and then back to the heart. In most fish, the heart consists of four parts: the sinus venosus, the atrium, the ventricle, and the bulbus arteriosus. This article is on an embryological structure For the heart defect of the same name please see atrial septal defect. In Anatomy, the atrium (plural atria) refers to a chamber or space In the Heart, a ventricle is a heart chamber which collects Blood from an atrium (another heart chamber that is smaller than a ventricle and Despite consisting of four parts, the fish heart is still a two-chambered heart. ^[15] The sinus venosus is a thin-walled sac that collects blood from the fish's veins before allowing it to flow to the atrium, which is a large muscular chamber. In the Circulatory system, a vein is a Blood vessel that carries Blood back toward the Heart (as opposed to Artery, a blood vessel The atrium serves as a one-way compartment for blood to flow into the ventricle. The ventricle is a thick-walled, muscular chamber and it does the actual pumping for the heart. It pumps blood to a large tube called the bulbus arteriosus. At the front end, the bulbus arteriosus connects to a large blood vessel called the aorta, through which blood flows to the fish's gills.

Excretory system

As with many aquatic animals, most fish release their nitrogenous wastes as ammonia. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Some of the wastes diffuse through the gills into the surrounding water. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement Others are removed by the kidneys, excretory organs that filter wastes from the blood. The kidneys are complicated organs that have numerous biological roles In Chemistry and common usage a filter is a device (usually a membrane or layer that is designed Kidneys help fishes control the amount of ammonia in their bodies. Saltwater fish tend to lose water because of osmosis. Osmosis is the Diffusion of a solvent (frequently water through a semi-permeable membrane, from a solution of low solute concentration (high water potential In saltwater fish, the kidneys concentrate wastes and return as much water as possible back to the body. The reverse happens in freshwater fish, they tend to gain water continuously. Fresh water fish are Fish that spend some or all of their lives in Fresh water, such as Rivers and Lakes with a Salinity of less The kidneys of freshwater fish are specially adapted to pump out large amounts of dilute urine. Some fish have specially adapted kidneys that change their function, allowing them to move from freshwater to saltwater.

Sensory and nervous system

Dorsal view of the brain of the rainbow trout. The rainbow trout ( Oncorhynchus mykiss) is a species of Salmonid native to tributaries of the Pacific Ocean in Asia and North America

Central nervous system

Fish typically have quite small brains relative to body size when compared with other vertebrates, typically one-fifteenth the mass of the brain from a similarly sized bird or mammal. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain ^[16] However, some fish have relatively large brains, most notably mormyrids and sharks, which have brains of about as massive relative to body weight as birds and marsupials. The family Mormyridae, sometimes called elephantfish, are freshwater fishes native to Africa in the order Osteoglossiformes. Sharks ( Superorder Selachimorpha) are a type of Fish with a full cartilaginous Skeleton and a highly streamlined body Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Marsupials are an Infraclass of Mammals characterized by a distinctive pouch (called the marsupium) in which females carry their young through ^[17]

The brain is divided into several regions. At the front are the olfactory lobes, a pair of structure the receive and process signals from the nostrils via the two olfactory nerves. The olfactory bulb is a structure of the Vertebrate Forebrain involved in Olfaction, the perception of Odors. The olfactory nerve, or cranial nerve I, is the first of twelve Cranial nerves The specialized Olfactory receptor neurons of the olfactory nerve are located ^[16] The olfactory lobes are very large in fishes that hunt primarily by smell, such as hagfish, sharks, and catfish. Behind the olfactory lobes is the two-lobed telencephalon, the equivalent structure to the cerebrum in higher vertebrates. The telencephalon (tɛlɛnˈsɛfəlɒn cerebrum, or forebrain is the most Anterior or especially in humans most Dorsal region of the The telencephalon (tɛlɛnˈsɛfəlɒn cerebrum, or forebrain is the most Anterior or especially in humans most Dorsal region of the In fishes the telencephalon is concerned mostly with olfaction. Olfaction (also known as olfactics or smell) refers to the Sense of smell. ^[16] Together these structures form the forebrain.

Connecting the forebrain to the midbrain is the diencephalon (in the adjacent diagram, this structure is below the optic lobes and consequently not visible). The diencephalon (or interbrain is the region of the Brain that includes the Thalamus, Hypothalamus, Epithalamus, Prethalamus or The diencephalon performs a number of functions associated with hormones and homeostasis. Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit ^[16] The pineal body lies just above the diencephalon. The pineal gland (also called the pineal body, epiphysis cerebri, or epiphysis) is a small endocrine gland in the vertebrate Brain This structure performs many different functions including detecting light, maintaining circadian rhythms, and controlling colour changes. ^[16]

The midbrain or mesencephalon contains the two optic lobes. In biological anatomy the mesencephalon (or midbrain) comprises the Tectum (or corpora quadrigemini Tegmentum, the ventricular mesocoelia (or "iter" In biological anatomy the mesencephalon (or midbrain) comprises the Tectum (or corpora quadrigemini Tegmentum, the ventricular mesocoelia (or "iter" These are very large in species that hunt by sight, such as rainbow trout and cichlids. The rainbow trout ( Oncorhynchus mykiss) is a species of Salmonid native to tributaries of the Pacific Ocean in Asia and North America Cichlids (ˈsɪklɪd are Fish from the family Cichlidae in the order Perciformes. ^[16]

The hindbrain or metencephalon is particularly involved in swimming and balance. The metencephalon is a developmental categorization of portions of the Central nervous system. ^[16] The cerebellum is a single-lobed structure that is usually very large, typically the biggest part of the brain. ^[16] Hagfish and lampreys have relatively small cerebellums, but at the other extreme the cerebellums of mormyrids are massively developed and apparently involved in their electrical sense. A lamprey (sometimes also called lamprey eel) is a Jawless fish with a toothed funnel-like sucking mouth The family Mormyridae, sometimes called elephantfish, are freshwater fishes native to Africa in the order Osteoglossiformes. 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 ^[16]

The brain stem or myelencephalon is the most posterior part of the brain. The myelencephalon is a developmental categorization of a portion of the Central nervous system. ^[16] As well as controlling the functions of some of the muscles and body organs, in bony fish at least the brain stem is also concerned with respiration and osmoregulation. Osmoregulation is the active regulation of the Osmotic pressure of bodily fluids to maintain the Homeostasis of the body's Water content that is it keeps ^[16]

Sense organs

Most fish possess highly developed sense organs. Nearly all daylight fish have well-developed eyes that have color vision that is at least as good as a human's. Many fish also have specialized cells known as chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears in their heads, many fish may not hear sounds very well. However, most fishes have sensitive receptors that form the lateral line system. In Fish, the lateral line is a Sense organ used to detect movement and vibration in the surrounding water The lateral line system allows for many fish to detect gentle currents and vibrations, as well as to sense the motion of other nearby fish and prey. ^[18] Some fishes such as catfishes and sharks, have organs that detect low levels electric current. ^[19] Other fish, like the electric eel, can produce their own electricity.

Pain reception in fish

In 2003, Scottish scientists at the University of Edinburgh performing research on rainbow trout concluded that fish exhibit behaviors often associated with pain. A scientist, in the broadest sense refers to any person that engages in a systematic activity to acquire Knowledge or an individual that engages in such practices The University of Edinburgh (Oilthigh Dhùn Èideann founded in 1582 is a renowned centre for teaching and research in Edinburgh, Scotland, UK. Pain, in the sense of physical pain, is a typical sensory experience that may be described as the unpleasant awareness of a noxious stimulus or bodily harm ^[20] Professor James D. Rose of the University of Wyoming critiqued the study, claiming it was flawed. The University of Wyoming is a Land-grant university located in Laramie, Wyoming, situated on Wyoming's high Laramie Plains, at an elevation ^[21] Rose had published his own study a year earlier arguing that fish cannot feel pain as they lack the appropriate neocortex in the brain. The neocortex ( Latin for "new Bark " or "new Rind " is a part of the Brain of Mammals It is the outer layer of ^[22]

Muscular system

Main article: Fish locomotion

Most fish move by contracting paired sets of muscles on either side of the backbone alternately. The prevailing type of fish locomotion is Swimming in Water. In addition some fish can "walk" i These contractions form S-shaped curves that move down the body of the fish. As each curve reaches the back fin, backward force is created. This backward force, in conjunction with the fins, moves the fish forward. The fish's fins are used like an airplane's stabilizers. Fins also increase the surface area of the tail, allowing for an extra boost in speed. The streamlined body of the fish decreases the amount of friction as they move through water. Since body tissue is more dense than water, fish must compensate for the difference or they will sink. Many bony fishes have an internal organ called a swim bladder that adjust their buoyancy through manipulation of gases. gas bladder (also fish maw, less accurately swim bladder or air bladder) is an internal organ that contributes to the ability of a Fish

Reproductive system

Further information: Spawning

Organs

Organs: 1. Spawning is the production or depositing of large quantities of eggs in water In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument Liver, 2. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Gas bladder, 3. gas bladder (also fish maw, less accurately swim bladder or air bladder) is an internal organ that contributes to the ability of a Fish Roe, 4. Roe or hard roe is the fully ripe internal ovaries or egg masses of Fish and certain marine Animals such as Shrimp, Scallop Duodenum, 5. In Anatomy of the Digestive system, the duodenum is a hollow jointed tube about 25-30 cm (10-12 in long connecting the Stomach to the Jejunum Stomach, 6. In Human anatomy, the stomach is a J-shaped hollow muscular organ of the Gastrointestinal tract involved in the second phase of Digestion, following Intestine

Fish reproductive organs include testes and ovaries. In Anatomy, the intestine is the segment of the alimentary canal extending from the Stomach to the Anus and in humans and other mammals consists The testicle (from Latin testiculus, diminutive of testis, meaning "witness" virility plural testes) is the male "Ovaria" redirects here This is also a proposed section and a Synonym of Solanum. In most fish species, gonads are paired organs of similar size, which can be partially or totally fused. ^[23] There may also be a range of secondary reproductive organs that help in increasing a fish's fitness.

In terms of spermatogonia distribution, the structure of teleosts testes has two types: in the most common, spermatogonia occur all along the seminiferous tubules, while in Atherinomorph fishes they are confined to the distal portion of these structures. A spermatogonium (plural spermatogonia) is an intermediary male Gametogonium (a kind of Germ cell) in the production of Spermatozoa. Fishes can present cystic or semi-cystic spermatogenesis in relation to the phase of release of germ cells in cysts to the seminiferous tubules lumen. Spermatogenesis is the process by which male Spermatogonia develop into mature Spermatozoa. ^[23]

Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian. In the first type, the oocytes are released directly into the coelomic cavity and then enter the ostium, then through the oviduct and are eliminated. The coelom (pronounced "seal-um" is a fluid filled cavity formed within the Mesoderm. Secondary gymnovarian ovaries shed ova into the coelom and then they go directly into the oviduct. The coelom (pronounced "seal-um" is a fluid filled cavity formed within the Mesoderm. In the third type, the oocytes are conveyed to the exterior through the oviduct. Oviduct is also another name for Fallopian tube In Oviparous Animals (those that lay eggs, the passage from the ovaries ^[24] Gymnovaries are the primitive condition found in lungfishes, sturgeons, and bowfins. Cystovaries are the condition that characterizes most of the teleosts, where the ovary lumen has continuity with the oviduct. ^[23] Secondary gymnovaries are found in salmonids and a few other teleosts.

Oogonia development in teleosts fish varies according to the group, and the determination of oogenesis dynamics allows the understanding of maturation and fertilization processes. Changes in the nucleus, ooplasm, and the surrounding layers characterize the oocyte maturation process. ^[23]

Postovulatory follicles are structures formed after oocyte release; they do not have endocrine function, present a wide irregular lumen, and are rapidly reabosrbed in a process involving the apoptosis of follicular cells. The endocrine system is an integrated system of small organs that involve the release of extracellular signaling molecules known as Hormones The endocrine system is instrumental A degenerative process called follicular atresia reabsorbs vitellogenic oocytes not spawned. This process can also occur, but less frequently, in oocytes in other development stages. ^[23]

Some fish are hermaphrodites, having testes and ovaries either at different phases in their life cycle or, like hamlets, can be simultaneously male and female. A hermaphrodite is an organism having both male and female reproductive organs A hamlet is a Fish of the genus Hypoplectrus. It is a Grouping fish that is found mainly in Coral reefs in the Caribbean Sea

Reproductive method

Over 97% of all known fishes are oviparous,^[25] that is, the eggs develop outside the mother's body. Oviparous animals are animals that lay eggs, with little or no other Embryonic development within the mother Examples of oviparous fishes include salmon, goldfish, cichlids, tuna, and eels. Salmon is the common name for several species of Fish of the family Salmonidae. The goldfish, Carassius auratus, was one of the earliest Fish to be domesticated, and is still one of the most commonly kept aquarium fish and Cichlids (ˈsɪklɪd are Fish from the family Cichlidae in the order Perciformes. Tuna, are several Species of ocean-dwelling Fish in the family Scombridae, mostly in the genus Thunnus. True eels ( Anguilliformes) are an order of Fish, which consists of four suborders 19 families 110 Genera and approximately 600 In the majority of these species, fertilisation takes place outside the mother's body, with the male and female fish shedding their gametes into the surrounding water. A gamete (from Ancient Greek γαμέτης; translated gamete = wife gametes = husband is a cell that fuses with another gamete However, a few oviparous fishes practise internal fertilisation, with the male using some sort of intromittent organ to deliver sperm into the genital opening of the female, most notably the oviparous sharks, such as the horn shark, and oviparous rays, such as skates. Ichthyology uses several terms that are unique to the science The horn shark, Heterodontus francisci, is a Bullhead shark. It can reach a size of 121 cm (4 ft) and weigh 10 kg (22 lb Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays In these cases, the male is equipped with a pair of modified pelvic fins known as claspers. The pelvis (pl pelvises or pelves) or pelvic girdle is the irregular bony structure located at the base of the spine (properly known In Biology, a clasper or valva (plural valvae) is a body part of certain male animals used in mating

The newly-hatched young of oviparous fish are called larvae. A larva ( Latin; plural larvae) is a juvenile form of Animal with indirect development, undergoing Metamorphosis (for example They are usually poorly formed, carry a large yolk sac (from which they gain their nutrition) and are very different in appearance to juvenile and adult specimens of their species. The yolk sac is the first element seen in the Gestational sac during Pregnancy, usually at 5 weeks Gestation. The larval period in oviparous fish is relatively short however (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to resemble juveniles of their species. Metamorphosis is a Biological process by which an Animal physically develops after Birth or hatching involving a conspicuous and relatively During this transition larvae use up their yolk sac and must switch from yolk sac nutrition to feeding on zooplankton prey, a process which is dependent on zooplankton prey densities and causes many mortalities in larvae. Zooplankton are the Heterotrophic (sometimes detritivorous) type of Plankton.

Ovoviviparous fish are ones in which the eggs develop inside the mother's body after internal fertilization but receive little or no nutrition from the mother, depending instead on the yolk. Ovoviviparous Animals develop within eggs that remain within the mother's body up until they hatch or are about to hatch Nutrition (also called nourishment or aliment) is the provision to cells and Organisms of the materials necessary (in the form of food to support An egg yolk is the part of an egg which serves as the Food source for the developing Embryo inside Each embryo develops in its own egg. Familiar examples of ovoviviparous fishes include guppies, angel sharks, and coelacanths. The guppy (la '''''Poecilia reticulata''''' also known as the millionfish, is one of the most popular freshwater aquarium fish species in the world The angel sharks are an unusual genus of Sharks with flattened bodies and broad Pectoral fins that give them a strong resemblance to skates and Coelacanth (ˈsiːləkænθ adaptation of Modern Latin Cœlacanthus > cœl-us + acanth-us from Greek κοῖλ-ος + ἄκανθ-α) is the common name for

Some species of fish are viviparous. A viviparous Animal is an animal employing vivipary: the embryo develops inside the body of the mother as opposed to outside in an egg ( Ovipary In such species the mother retains the eggs, as in ovoviviparous fishes, but the embryos receive nutrition from the mother in a variety of different ways. Typically, viviparous fishes have a structure analogous to the placenta seen in mammals connecting the mother's blood supply with the that of the embryo. The placenta is an Ephemeral organ present in placental Vertebrates, such as Eutherial Mammals and Sharks during Gestation See also Evolution of mammals Eutheria ("true beast" are a group of Mammals consisting of Placental mammals plus all extinct Mammals Examples of viviparous fishes of this type include the surf-perches, splitfins, and lemon shark. The surfperches are a family Embiotocidae, of Perciform fishes Splitfins, are a family Goodeidae, of Teleost Fish endemic to Mexico and some areas of the United States. The lemon shark, Negaprion brevirostris, is a Shark belonging to the family Carcharhinidae that can grow long (3 m The embryos of some viviparous fishes exhibit a behaviour known as oophagy where the developing embryos eat eggs produced by the mother. Oophagy (egg eating is the practice of Embryos feeding on eggs produced by the Ovary while still inside the mother's Uterus. This has been observed primarily among sharks, such as the shortfin mako and porbeagle, but is known for a few bony fish as well, such as the halfbeak Nomorhamphus ebrardtii. The shortfin mako shark, Isurus oxyrinchus ("sharp nose" is a large Shark of the Lamnidae family The porbeagle, Lamna nasus, is a Pelagic predatory Shark of the family Lamnidae. The halfbeaks ( family Hemiramphidae) are a geographically widespread and numerically abundant family of Epipelagic Fish inhabiting ^[26] Intrauterine cannibalism is an even more unusual mode of vivipary, where the largest embryos in the uterus will eat their weaker and smaller siblings. Cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food This behaviour is also most commonly found among sharks, such as the grey nurse shark, but has also been reported for Nomorhamphus ebrardtii. The grey nurse shark (Australia spotted ragged-tooth shark (Africa or sand tiger shark (US and UK Carcharias taurus, is a large Shark ^[26]

Aquarists commonly refer to ovoviviparous and viviparous fishes as livebearers. Fishkeeping is a popular Hobby concerned with keeping Fish in the home Aquarium or garden Pond. Live-bearing aquarium fish, often simply called livebearers, are Fish that retain the eggs inside the body and give birth to live free-swimming young

Immune system

Types of immune organs vary between different types of fish. ^[27] In the jawless fish (lampreys and hagfishes), true lymphoid organs are absent. Agnatha ( Greek, "no jaws" is a Paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata Instead, these fish rely on regions of lymphoid tissue within other organs to produce their immune cells. The lymphatic system in Vertebrates is a network of conduits that carry a clear fluid called Lymph. For example, erythrocytes, macrophages and plasma cells are produced in the anterior kidney (or pronephros) and some areas of the gut (where granulocytes mature) resemble primitive bone marrow in hagfish. Red blood cells are the most common type of Blood cell and the Vertebrate body's principal means of delivering Oxygen to the body tissues via the Blood Macrophages ( Greek: "big eaters" from makros "large" + phagein "eat" ( Mø) are cells within the tissues that Plasma cells (also called plasma B cells or plasmocytes) are cells of the Immune system that secrete large amounts of antibodies. Pronephros the most primitive of the three excretory organs that develop in Vertebrates corresponding to the first stage of Kidney development Granulocytes are a category of White blood cells characterised by Bone marrow is the flexible tissue found in the hollow interior of Bones In adults marrow in large bones produces new Blood cells It constitutes 4% of Cartilaginous fish (sharks and rays) have a more advanced immune system than the jawless fish. Chondrichthyes or cartilaginous fishes are jawed Fish with paired fins paired nostrils scales two-chambered hearts and skeletons made of Cartilage rather They have three specialized organs that are unique to chondrichthyes; the epigonal organs (lymphoid tissue similar to bone marrow of mammals) that surround the gonads, the Leydig’s organ within the walls of their esophagus, and a spiral valve in their intestine. All these organs house typical immune cells (granulocytes, lymphocytes and plasma cells). They also possess an identifiable thymus and a well-developed spleen (their most important immune organ) where various lymphocytes, plasma cells and macrophages develop and are stored. In Human anatomy, the thymus is an organ located in the upper Anterior portion of the chest cavity just behind the Sternum. The spleen is an organ found in all Vertebrate animals In humans the spleen is located in the abdomen of the body where it functions in the destruction of redundant Red A lymphocyte is a type of White blood cell in the Vertebrate Immune system. Chondrostean fish (sturgeons, paddlefish and birchirs) possess a major site for the production of granulocytes within a mass that is associated with the meninges (membranes surrounding the central nervous system) and their heart is frequently covered with tissue that contains lymphocytes, reticular cells and a small number of macrophages. The Actinopterygii (the plural form of Actinopterygius) comprise the class of the ray-finned fishes. The meninges (singular meninx) is the system of membranes which envelops the Central nervous system. A reticular cell produces Reticular fibers and surrounds the fibers with its Cytoplasm, which isolates the fiber from other components of the tissues or The chondrostean kidney is an important hemopoietic organ; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Like chondrostean fish, the major immune tissues of bony fish (or teleostei) include the kidney (especially the anterior kidney), where many different immune cells are housed. Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes ^[28] In addition, teleost fish possess a thymus, spleen and scattered immune areas within mucosal tissues (e. g. in the skin, gills, gut and gonads). Much like the mammalian immune system, teleost erythrocytes, neutrophils and granulocytes are believed to reside in the spleen whereas lymphocytes are the major cell type found in the thymus. ^[29][30] Recently, a lymphatic system similar to that described in mammals was described in one species of teleost fish, the zebrafish. Although not confirmed as yet, this system presumably will be where naive (unstimulated) T cells will accumulate while waiting to encounter an antigen. T cells belong to a group of White blood cells known as Lymphocytes, and play a central role in Cell-mediated immunity. An antigen (from antibody-generating) or immunogen is a substance that prompts the generation of Antibodies and can cause an immune response ^[31]

Evolution

The early fossil record on fish is not very clear. It appears it was not a sufficiently successful animal early in its evolution to leave many fossils. However, this would eventually change over time as it became a dominant form of sea life and eventually branched to create land vertebrates. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes

The proliferation was apparently due to the formation of the hinged jaw because jawless fish left very few descendants. The jaw is either of the two opposable structures forming or near the entrance to the Mouth. ^[32] Lampreys may be a rough representative of pre-jawed fish. A lamprey (sometimes also called lamprey eel) is a Jawless fish with a toothed funnel-like sucking mouth The first jaws are found in Placodermi fossils. The Placodermi were a class of armoured Prehistoric fishes known from Fossils which lived from the late Silurian to the end of the Devonian It is unclear if the advantage of a hinged jaw is greater biting force, respiratory-related, or a combination.

Some speculate that fish may have evolved from a creature similar to a coral-like Sea squirt, whose larvae resemble primitive fish in some key ways. Tunicate, also known as urochordata, tunicata (and by the common names of urochordates, sea squirts, and sea pork) is the The first ancestors of fish may have kept the larval form into adulthood (as some sea squirts do today), although maybe the reverse of this is case. Neoteny (niːˈɒtɨniː also called juvenilization, is the retention by adults in a species of traits previously seen only in juveniles ( pedomorphosis/paedomorphosis Candidates for early fish include Agnatha such as Haikouichthys, Myllokunmingia, Pikaia, and Conodonts. Agnatha ( Greek, "no jaws" is a Paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata Haikouichthys is an extinct Genus of craniate believed to have lived c Myllokunmingia is a primitive probably agnathid jawless Fish from the Lower Cambrian Maotianshan shales of China, thought to be Pikaia gracilens is an extinct animal known from the Middle Cambrian Fossil found near Mount Pika in the Burgess Shale of British Columbia Conodonts are extinct chordates resembling eels classified in the class Conodonta.

Homeothermy

A 3 to 4 m great white shark off Isla Guadalupe

Although most fish are exclusively aquatic and ectothermic, there are exceptions to both cases. The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform Guadalupe Island, or Isla Guadalupe ( is a volcanic island located 241 kilometers (150 Statute miles off the west coast of Mexico 's Baja Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds

Fish from a number of different groups have evolved the capacity to live out of the water for extended periods of time. Of these amphibious fish, some such as the mudskipper can live and move about on land for up to several days. Amphibious fish are Fish with the ability to leave their usual aquatic environments water for prolonged periods of time Mudskippers are members of the subfamily Oxudercinae ( tribe: Periophthalmini) within the family Gobiidae (

Also, certain species of fish maintain elevated body temperatures to varying degrees. Endothermic teleosts (bony fishes) are all in the suborder Scombroidei and include the billfishes, tunas, and one species of "primitive" mackerel (Gasterochisma melampus). In Biology, a warm-blooded Animal species is one whose members maintain thermal Homeostasis; that is they keep their body temperature at a roughly constant Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes All sharks in the family Lamnidae – shortfin mako, long fin mako, white, porbeagle, and salmon shark – are known to have the capacity for endothermy, and evidence suggests the trait exists in family Alopiidae (thresher sharks). Lamnidae is a family of Sharks commonly known as mackerel sharks or white sharks. Thresher sharks are large Lamniform Sharks of the family Alopiidae. The degree of endothermy varies from the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 °C above ambient water temperatures. The Celsius Temperature scale was previously known as the centigrade scale. See also gigantothermy. Gigantothermy is a phenomenon with significance in Biology and Paleontology, whereby large bulky ectothermic (cold-blooded animals are more easily able Endothermy, though metabolically costly, is thought to provide advantages such as increased contractile force of muscles, higher rates of central nervous system processing, and higher rates of digestion. The nervous system is a Network of specialized cells that communicate information about an animal's surroundings and itself Digestion is the breaking down of chemicals in the body into a form that can be absorbed

Diseases

Like other animals, fish can suffer from a wide variety of diseases and parasites. To prevent disease they have a variety of non-specific defences and specific defences. Non-specific defences include the skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually Should pathogens breach these defences, fish can develop an inflammatory response that increases the flow of blood to the infected region and delivers the white blood cells that will attempt to destroy the pathogens. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious Inflammation ( Latin, inflamatio, to set on fire is the complex biological response of vascular tissues to harmful stimuli such as Pathogens Specific defences are specialised responses to particular pathogens recognised by the fish's body, in other words, an immune response. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor ^[33] In recent years, vaccines have become widely used in aquaculture and also with ornamental fish, for example the vaccines for furunculosis in farmed salmon and koi herpes virus in koi. A vaccine is a biological preparation which is used to establish or improve immunity to a particular disease Boil or furuncle is a skin disease caused by the infection of Hair follicles resulting in the localized accumulation of Pus and dead tissue Salmon is the common name for several species of Fish of the family Salmonidae. (kɔɪ or more specifically (niɕikigoi literally " brocaded carp" are ornamental domesticated varieties of the Common carp Cyprinus carpio. ^[34][35]

Some fish will also take advantage of cleaner fish for removal of external parasites. Cleaner fish are Fishes that provide a service to other fish species by removing dead Skin and Parasites This is an example of Mutualism, an The best known of these are the Bluestreak cleaner wrasses of the genus Labroides found on coral reefs in the Indian Ocean and Pacific Ocean. The bluestreak cleaner wrasse ( Labroides dimidiatus) is a species of Wrasse found on Coral reefs in the Indian Ocean and much of the Pacific The Indian Ocean is the third largest of the world's Oceanic divisions covering about 20% of the water on the Earth 's surface The Pacific Ocean is the largest of the Earth 's Oceanic divisions These small fish maintain so-called "cleaning stations" where other fish, known as hosts, will congregate and perform specific movements to attract the attention of the cleaner fish. ^[36] Cleaning behaviours have been observed in a number of other fish groups, including an interesting case between two cichlids of the same genus, Etroplus maculatus, the cleaner fish, and the much larger Etroplus suratensis, the host. ^[37]

Importance to humans

Economic importance

Main article: Fish (food)

Main article: Industrial fishing

Main article: Aquaculture

Main article: Fish farming

Recreation

Main article: Fishkeeping

Main article: Recreational fishing

Main article: Angling

Conservation

A Whale shark, the world's largest fish, is classified as Vulnerable. The fishing industry includes any industry or activity concerned with taking culturing processing preserving storing transporting marketing or selling fish or fish products Aquaculture is the farming of freshwater and saltwater organisms including Molluscs Crustaceans and aquatic plants Fish farming is the principal form of Aquaculture, while other methods may fall under Mariculture. Fishkeeping is a popular Hobby concerned with keeping Fish in the home Aquarium or garden Pond. Recreational fishing, also called sport fishing, is Fishing for Pleasure or Competition. Angling is a method of Fishing by means of an "angle" ( hook) The whale shark, Rhincodon typus, is a slow filter feeding Shark that is the largest living Fish Species. A vulnerable species is a Species which is likely to become endangered unless the circumstances threatening its survival and reproduction improve

As of 2006, the IUCN Red List describes 1,173 species of fish as being threatened with extinction. The IUCN Red List of Threatened Species (also known as the IUCN Red List or Red Data List) created in 1963 is the world's most comprehensive inventory of the global ^[38] Included on this list are species such as Atlantic cod,^[39] Devil's Hole pupfish,^[40] coelacanths,^[41] and great white sharks. The Atlantic cod, Gadus morhua, is a well-known Demersal food fish belonging to the family Gadidae. The Devil's Hole pupfish, Cyprinodon diabolis, is a Species of fish native to Devil's Hole, a geothermal ( Aquifer -fed pool Coelacanth (ˈsiːləkænθ adaptation of Modern Latin Cœlacanthus > cœl-us + acanth-us from Greek κοῖλ-ος + ἄκανθ-α) is the common name for The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform ^[42] Because fish live underwater they are much more difficult to study than terrestrial animals and plants, and information about fish populations is often lacking. However, freshwater fish seem particularly threatened because they often live in relatively small areas. For example, the Devil's Hole pupfish occupies only a single 3 m by 6 m pool. The Devil's Hole pupfish, Cyprinodon diabolis, is a Species of fish native to Devil's Hole, a geothermal ( Aquifer -fed pool ^[43]

Overfishing

Main article: Overfishing

In the case of edible fishes such as cod and tuna a major threat is overfishing. Overfishing occurs when Fishing activities reduce fish stocks below an acceptable level Tuna, are several Species of ocean-dwelling Fish in the family Scombridae, mostly in the genus Thunnus. ^[44][45] Where overfishing persists, it eventually causes the collapse of the fish population (known as a "stock") because the population cannot breed fast enough to replace the individuals removed by fishing. One well-studied example of the collapse of a fishery is the Pacific sardine Sadinops sagax caerulues fishery off the coast of California. The South American pilchard, Sardinops sagax, is a Sardine of the Family Clupeidae, the only member of the Genus Sardinops From a peak in 1937 of 790,000 tonnes the amount of fish landed steadily declined to a mere 24,000 tonnes in 1968, at which point the fishery stopped as no longer economically viable. This article is about the tonne or metric ton For other tons see Ton. Such commercial extinction does not mean that the fish itself goes extinct, merely that it can no longer sustain a profitable fishery. ^[46] The main tension between fisheries science and the fishing industry is the need to balance conservation with preserving the livelihoods of fishermen. In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments have a vested interest in finding a balance between conserving fish stocks while maintaining an economic level of commercial fishing. Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. Newfoundland and Labrador (ˈnuːfɨn(dlənd ən(d ˈlæbrəˌdɔr (Terre-Neuve-et-Labrador is a province of Canada, the tenth and latest to join the Confederation Alaska ( Аляска Alyaska) is a state in the United States of America, in the northwest of the North American continent ^[47][48] On the other hand, scientists and conservations push for increasingly stringent protection for fish stocks, warning that many stocks could be wiped out within fifty years. ^[49][50]

Habitat destruction

See also: Environmental effects of fishing

A key stress on both freshwater and marine ecosystems is habitat degradation including water pollution, the building of dams, removal of water for use by humans, and the introduction of exotic species. The environmental effects of fishing can be divided into issues that involve the availability of fish to be caught such as Overfishing, Sustainable fisheries, and Pollution is the introduction of contaminants into an environment that causes instability disorder harm or discomfort to the physical systems or living organisms they are in A dam is a barrier that divides waters. Dams generally serve the primary purpose of retaining water while other structures such as Floodgates, Levees Introduced species|Weed Invasive species is a phrase with several definitions ^[51] An example of a fish that has become endangered because of habitat change is the pallid sturgeon, a North American freshwater fish that living in rivers that have all been changed by human activity in a variety of different ways. The pallid sturgeon ( Scaphirhynchus albus) is an Endangered species of ray-finned fish endemic to the waters of the Missouri and lower ^[52]

Exotic species

Introduction of exotic species has occurred in a variety of places and for many different reasons. Introduced species|Weed Invasive species is a phrase with several definitions One of the best studied (and most severe) examples was the introduction of Nile perch into Lake Victoria. The Nile perch ( Lates niloticus) is a Species of Freshwater Fish in family Latidae of order Perciformes Lake Victoria or Victoria Nyanza (also known as Ukerewe and Nalubaale) is one of the Great Lakes of Africa. Since the 1960s the Nile perch gradually exterminated the 500 species of cichlid fishes found only in this lake and nowhere else. Cichlids (ˈsɪklɪd are Fish from the family Cichlidae in the order Perciformes. Some species survive now only in captive breeding programmes, but others are probably extinct. ^[53] Carp, snakeheads,^[54] tilapia, European perch, brown trout, rainbow trout, and sea lampreys are other examples of fish that have caused problems by being introduced into alien environments. Carp is a common name for various Freshwater Fish of the family Cyprinidae, a very large Channidae is a family of Freshwater fish commonly known as snakeheads, and is native to Africa and Asia. Tilapia (təˌlɑpiə is the common name for nearly a hundred Species of Cichlid Fishes from the Tilapiine cichlid tribe Perca is the genus of fish referred to as perch or sometimes yellow perch, a group of freshwater Fish belonging to the family Percidae The brown trout ( Salmo trutta morpha fario and S trutta morpha lacustris) and the sea trout ( S The rainbow trout ( Oncorhynchus mykiss) is a species of Salmonid native to tributaries of the Pacific Ocean in Asia and North America The sea lamprey ( Petromyzon marinus) is a Parasitic Lamprey (a kind of Jawless fish) found on the Atlantic coasts of

Aquarium collecting

Main article: Fishkeeping#Conservation_and_Science

Culture

Incarnation of Vishnu as a Mermaid

In the Book of Jonah a "great fish" swallowed Jonah the Prophet. Fishkeeping is a popular Hobby concerned with keeping Fish in the home Aquarium or garden Pond. Avatar or Avatara (अवतार IAST Avatāra) is often inaccurately translated into English as incarnation For other meanings see Vishnu (disambiguation. Vishnu ( IAST viṣṇu Devanagari विष्णु (honorific In the Hebrew Bible, the Book of Jonah is the fifth book in a series of books called the Minor Prophets According to the Hebrew Bible ( Tanakh / Old Testament) and Qur'an, Jonah (; Arabic: يونس, Yunus or In Religion, a prophet (or prophetess) is a person who has encountered the Supernatural or the divine and serves as an intermediary Legends of half-human, half-fish mermaids have featured in stories like those of Hans Christian Andersen and movies like Splash. A mermaid is a Mythological aquatic creature that is half human half aquatic creature (e Hans Christian Andersen (ˈhanˀs ˈkʰʁæʂd̥jan ˈɑnɐsn̩ in Danish or simply H Splash is a 1984 Fantasy film and Romantic comedy film directed by Ron Howard and written by Lowell Ganz and

Among the deities said to take the form of a fish are Ika-Roa of the Polynesians, Dagon of various ancient Semitic peoples, and Matsya of the Dravidas of India. In Māori mythology, Ikaroa is the long fish that gave birth to all the stars in the Milky Way or the Mother Goddess of the all the stars - ornaments of Polynesia (from Greek: πολύς many, νῆσος island) is a Subregion of Oceania, comprising a large grouping of over Dagon was a major northwest Semitic god reportedly of grain and agriculture In Linguistics and Ethnology, Semitic (from the Biblical " Shem " Hebrew שם translated as "name" Arabic: ساميّ This article concerns the Hindu avatar For the ancient kingdom see Matsya Rajya. Dravidian peoples refers to the peoples that natively speak languages belonging to the Dravidian language family. The astrological symbol Pisces is based on a constellation of the same name, but there is also a second fish constellation in the night sky, Piscis Austrinus. Astrology (from Greek grc ἄστρον astron, "constellation star" and grc -λογία -logia) is a group of Systems Pisces is the twelfth Astrological sign in the Zodiac, which originates from the Pisces constellation. Pisces (ˈpaɪsiːz Fish (plural symbol, Unicode ♓ is a Zodiac Constellation which lies between Aquarius to the west and Aries Piscis Austrinus (ˈpaɪsɪs ɒsˈtraɪnəs or Piscis Australis (/ɒsˈtreɪlɪs/ Southern Fish) was one of the 48 Constellations

Fish have been used figuratively in many different ways, for example the ichthys used by early Christians to identify themselves, through to the fish as a symbol of fertility among Bengalis. Ichthys or Ichthus Greek: grc ἰχθύς capitalized grc ΙΧΘΥΣ also transliterated and Latinized as ichthys, A Christian is a person who adheres to Christianity, a monotheistic Religion centered on the life and teachings of Jesus of Nazareth ^[55] Fish have also featured prominently in art and literature, as in movies such as Finding Nemo and books such as The Old Man and the Sea. Finding Nemo is a 2003 computer-animated American Family film. The Old Man and the Sea is a Novella (just over 100 pages in length by Ernest Hemingway, written in Cuba in 1951 and published in Large fish, particularly sharks, have frequently been the subject of horror movies and thrillers, most notably the novel Jaws, which spawned a series of films of the same name that in turn inspired similar films or parodies such as Shark Tale, Snakehead Terror, and Piranha. Horror films are Movies that strive to elicit Fear, Horror and terror responses from viewers The thriller is a broad Genre of Literature, Film, Gaming and Television. Peter Bradford Benchley ( May 8, 1940 -11 February 2006 was an American author best known for writing the novel Jaws and co-writing the Jaws is a 1975 thriller / horror Film directed by Steven Spielberg and based on Peter Benchley 's best-selling Shark Tale is a 2004 CGI comedy produced by DreamWorks Animation. Snakehead Terror is a science fiction / horror film released in 2004 Piranha is a 1978 comedy Horror film about a swarm of killer Piranha.

The golden fish (Sanskrit: Matsya), represents in the semiotic of Ashtamangala,(buddhist symbolism) the state of fearless suspension in samsara, thus perceived as the harmless ocean, referred to as 'buddha-eyes' or ' rigpa-sight] '. Semiotics, semiotic studies, or semiology is the study of sign processes (semiosis or signification and communication signs and Symbols both Ashtamangala are a Sacred suite of Eight Auspicious Signs endemic to a number of Indian religions. Buddhism is a family of beliefs and practices An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. The fishes symbolises the auspiciousness of all living beings in a state of fearlessness without danger of drowning in the Samsaric Ocean of Suffering, and migrating from teaching to teaching freely and spontaneously just as fish swim.

In the following quotation, the two golden fishes are linked with the Ganges and Yamuna, and nadi, prana and carp:

The two fishes originally represented the two main sacred rivers of India - the Ganges and Yamuna. The Ganges (ˈgænʤiːz also Ganga, Devanāgarī: hi गंगा in most Indian languages) is the major river in the Indian subcontinent For the goddess of the river who is sometimes called Yamuna see Yami The Yamuna (Sanskrit यमुना Prana (प्राण) is the Sanskrit for " Breath " (from the root prā "to fill" cognate to Latin plenus "full" These rivers are associated with the lunar and solar channels which originate in the nostrils and carry the alternating rhythms of breath & prana. They have religious significance in Hindu, Jain and Buddhist traditions but also in Christianity who is first signified by the sign of the fish, and especially referring to feeding the multitude in the desert. Christianity ( Greek Χριστιανισμός from the word Xριστός ( Christ)is a monotheistic Religion centered on the life and teachings Ichthys or Ichthus Greek: grc ἰχθύς capitalized grc ΙΧΘΥΣ also transliterated and Latinized as ichthys, Feeding the multitude (also known as The miracle of the loaves and fish) is the name of two Miracles attributed to Jesus, the first of which is reported In the dhamma of Buddha the fish symbolize happiness as they have complete freedom of movement in the water. Dhamma ( Pāli: धम्म or Dharma (धर्म in Buddhism has two primary meanings the teachings of the Buddha which lead to enlightenment They represent fertility and abundance. Often drawn in the form of carp which are regarded in the Orient as sacred on account of their elegant beauty, size and life-span. [3]

Terminology

Fish or fishes

Though often used interchangeably, these words actually mean different things. Fish is used either as singular noun or to describe a group of specimens from a single species. Fishes describes a group containing more than one species. ^[56] Hence, as plurals, these words could be used thus:

• My aquarium contains three different fishes: guppies, platies, and swordtails.
• The North Atlantic stock of Gadus morhua is estimated to contain several million fish.

Shoal or school

These squirrelfish are shoaling, not schooling: though swimming as a group, their speed and direction is not synchronised.

These jacks are schooling because their swimming is synchronised.

A random assemblage of fishes merely using some localised resource such as food or nesting sites is known simply as an aggregation. When fish come together in an interactive, social grouping, then they may be forming either a shoal or a school depending on the degree of organisation. A shoal is a loosely organised group where each fish swims and forages independently but is attracted to other members of the group and adjusts its behaviour, such as swimming speed, so that it remains close to the other members of the group. Schools of fish are much more tightly organised, synchronising their swimming so that all fish move at the same speed and in the same direction. Shoaling and schooling behaviour is believed to provide a variety of advantages. ^[57]

Examples:

• Cichlids congregating at lekking sites form an aggregation. A lek is a gathering of Males of certain animal species for the purposes of competitive Mating display
• Many minnows and characins form shoals.
• Anchovies, herrings, and silversides are classic examples of schooling fishes.

While school and shoal have different meanings within biology, they are often treated as synonyms by non-specialists, with speakers of British English using "shoal" to describe any grouping of fish, while speakers of American English often using "school" just as loosely. This article deals with the general meaning of the term "synonym" British English or UK English ( BrE, BE, en-GB) is the broad term used to distinguish the forms of the English language used in the Phonology North American English regional phonology In many ways compared to English English, North American English is conservative in its Phonology.

Further information: swarming

See also

References

External links

• United Nation - Fisheries and Aquaculture Department: Fish and seafood utilization
• FishBase online - Comprehensive database with information on over 29,000 fish species
• ANGFA - Illustrated database of freshwater fishes of Australia and New Guinea
• Ecology Asia - Photos and facts on freshwater fishes of Southeast Asia
• Fischinfos.de - Illustrated database of the freshwater fishes of Germany (in German)
• The Native Fish Conservancy - Conservation and study of North American freshwater fishes
• University of Washington Libraries Digital Collections - Digital collection of freshwater and marine fish images
• Fish Olympics - Child-oriented edutainment at the Liverpool Museum
• Philippines Fishes - Database with thousands of Philippine Fishes photographed in natural habitat