Euryhaline organisms are able to adapt to a wide range of

salinities Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

. An example of a euryhaline

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

is the molly (''Poecilia sphenops'') which can live in

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estua ...

, or

salt water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, ...

. The green crab (''

Carcinus maenas ''Carcinus maenas'' is a common littoral crab. It is known by different names around the world. In the British Isles, it is generally referred to as the shore crab, or green shore crab. In North America and South Africa, it bears the name eur ...

'') is an example of a euryhaline invertebrate that can live in salt and brackish water. Euryhaline organisms are commonly found in habitats such as

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...

and

tide pools A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. Many of these pools exist as separate bodies of water only at low tide. Many tide pool habitats are home to especially adaptable animals that ...

where the salinity changes regularly. However, some organisms are euryhaline because their

life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring * Life-cycle hypothesis ...

involves migration between freshwater and marine environments, as is the case with

salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...

and

eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

s. The opposite of euryhaline organisms are stenohaline ones, which can only survive within a narrow range of salinities. Most freshwater organisms are stenohaline, and will die in seawater, and similarly most marine organisms are stenohaline, and cannot live in fresh water.

Osmoregulation

Osmoregulation Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration o ...

is the active process by which an organism maintains its level of water content. The osmotic pressure in the body is

homeostatic In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...

ally regulated in such a manner that it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis. Two major types of osmoregulation are osmoconformers and osmoregulators.

Osmoconformer Osmoconformers are marine organisms that maintain an internal environment which is isotonic to their external environment. This means that the osmotic pressure of the organism's cells is equal to the osmotic pressure of their surrounding environme ...

s match their body osmolarity to their environment actively or passively. Most marine invertebrates are osmoconformers, although their ionic composition may be different from that of seawater. Osmoregulators tightly regulate their body osmolarity, which always stays constant, and are more common in the animal kingdom. Osmoregulators actively control salt concentrations despite the salt concentrations in the environment. An example is freshwater fish. The gills actively uptake salt from the environment by the use of mitochondria-rich cells. Water will diffuse into the fish, so it excretes a very

hypotonic In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane-imp ...

(dilute) urine to expel all the excess water. A marine

has an internal osmotic concentration lower than that of the surrounding seawater, so it tends to lose water (to the more negative surroundings) and gain salt. It actively excretes

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

out from the

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

s. Most fish are stenohaline, which means they are restricted to either salt or fresh water and cannot survive in water with a different salt concentration than they are adapted to. However, some fish show a tremendous ability to effectively osmoregulate across a broad range of salinities; fish with this ability are known as euryhaline species, e.g.,

. Salmon has been observed to inhabit two utterly disparate environments — marine and fresh water — and it is inherent to adapt to both by bringing in behavioral and physiological modifications. Some marine fish, like sharks, have adopted a different, efficient mechanism to conserve water, i.e., osmoregulation. They retain urea in their blood in relatively higher concentration. Urea is damaging to living tissue so, to cope with this problem, some fish retain ''

trimethylamine oxide Trimethylamine ''N''-oxide (TMAO) is an organic compound with the formula (CH3)3NO. It is in the class of amine oxides. Although the anhydrous compound is known, trimethylamine ''N''-oxide is usually encountered as the dihydrate. Both the anhydro ...

''. This provides a better solution to urea's toxicity. Sharks, having slightly higher solute concentration (i.e., above 1000 mOsm which is sea solute concentration), do not drink water like marine fish.

Euryhaline fish

File:Poecilia sphenops.jpg, Short-finned molly File:Neogobius melanostomus1.jpg,

Round goby The round goby (''Neogobius melanostomus'') is a fish. Defined as a euryhaline bottom-dwelling goby of the family Gobiidae, it is native to Central Eurasia, including the Black Sea and the Caspian Sea. Round gobies have established large non-na ...

File:Dasyatis sabina florida.jpg, Atlantic stingray File:Myliobatis californica monterey bay aquarium.jpg,

Bat ray The bat ray (''Myliobatis californica'')Gill, T.N. (1865). "Note on the family of myliobatoids, and on a new species of ''Aetobatis''". ''Ann. Lyc. Nat. Hist. N. Y.'' 8, 135–138. is an eagle ray found in muddy or sandy sloughs, estuaries and ...

File:Dasyatis guttata.jpg, Longnose stingray File:Atherina boyeri, Gulf of Odessa, Black Sea.jpg,

Big-scale sand smelt The big-scale sand smelt (''Atherina boyeri'') is a species of fish in the family Atherinidae. It is a euryhaline amphidromous fish, up to 20 cm in length. Description It is a small pelagic fish species which occurs near the surface in th ...

File:Monodactylus argenteus.JPG,

Moonyfish Monodactylidae is a family of perciform bony fish commonly referred to as monos, moonyfishes or fingerfishes. All are strongly laterally compressed with disc-shaped bodies and tall anal and dorsal fins. Unusually for fish, scales occur on their ...

es File:Ocean stage and spawning pink salmon.gif,

Pink salmon Pink salmon or humpback salmon (''Oncorhynchus gorbuscha'') is a species of anadromous fish in the salmon family. It is the smallest and most abundant of the Pacific salmon. The scientific species name is based on the Russian common name for ...

File:Barramundi.jpg,

Barramundi The barramundi (''Lates calcarifer'') or Asian sea bass, is a species of catadromous fish in the family Latidae of the order Perciformes. The species is widely distributed in the Indo-West Pacific, spanning the waters of the Middle East, Sout ...

File:Sawfish genova.jpg,

Green sawfish The longcomb sawfish, narrowsnout sawfish or green sawfish (''Pristis zijsron'') is a species of sawfish in the family Pristidae, found in tropical and subtropical waters of the Indo-West Pacific. It has declined drastically and is now considered ...

File:Aphanius iberus.png,

Spanish toothcarp The Spanish toothcarp (''Aphanius iberus''), also known as the Spanish pupfish or Iberian killifish, is a small, endemic species of fish in the family Cyprinodontidae. Its risk of extinction is one of the greatest of any Iberian vertebrate. Its ...

File:Atlantic threadfin ( Polydactylus octonemus ).jpg, Atlantic threadfin File:Male female mecularius.jpg,

Desert pupfish The desert pupfish (''Cyprinodon macularius'') is a rare species of bony fish in the family Cyprinodontidae. It is a small fish, typically less than 7.62 cm (3 in) in length. Males are generally larger than females, and have bright-blue ...

File:Mayan10a.jpg,

Mayan cichlid ''Mayaheros urophthalmus'', also known as the Mayan cichlid or Mexican mojarra is a species of cichlid. Taxonomy Previously, this species was a member of the genus ''Cichlasoma'' and the subgeneric section ''Nandopsis''. However, the genus ''Cic ...

File:Crevalle jack aquarium.jpg,

Crevalle jack The crevalle jack (''Caranx hippos''), also known as the common jack, black-tailed trevally, couvalli jack, black cavalli, jack crevale, or yellow cavalli is a common species of large marine fish classified within the jack family, Carangidae. The ...

s The level of

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

in intertidal zones can also be quite variable. Low salinities can be caused by rainwater or river inputs of freshwater. Estuarine species must be especially euryhaline, or able to tolerate a wide range of salinities. High salinities occur in locations with high evaporation rates, such as in

salt marsh A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is domin ...

es and high intertidal pools. Shading by plants, especially in the salt marsh, can slow evaporation and thus ameliorate salinity stress. In addition, salt marsh plants tolerate high salinities by several physiological mechanisms, including excreting salt through salt glands and preventing salt uptake into the roots. Despite having a regular freshwater presence, the Atlantic stingray is physiologically euryhaline and no population has evolved the specialized

osmoregulatory Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration o ...

mechanisms found in the river stingrays of the family

Potamotrygonidae River stingrays or freshwater stingrays are Neotropical freshwater fishes of the family Potamotrygonidae in the order Myliobatiformes, one of the four orders of batoids, cartilaginous fishes related to sharks. They are found in rivers in tropic ...

. This may be due to the relatively recent date of freshwater colonization (under one million years), and/or possibly incomplete genetic isolation of the freshwater populations, as they remain capable of surviving in

. Freshwater Atlantic stingrays have only 30-50% the concentration of

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...

and other

osmolyte Osmolytes are low-molecular weight organic compounds that influence the properties of biological fluids. Their primary role is to maintain the integrity of cells by affecting the viscosity, melting point, and ionic strength of the aqueous solution. ...

s in their blood compared to marine populations. However, the osmotic pressure between their internal fluids and external environment still causes water to

diffuse Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

into their bodies, and they must produce large quantities of dilute

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra. Cel ...

(at 10 times the rate of marine individuals) to compensate. ;Partial list * Atlantic stingray *

Bull shark The bull shark (''Carcharhinus leucas''), also known as the Zambezi shark (informally zambi) in Africa and Lake Nicaragua shark in Nicaragua, is a species of requiem shark commonly found worldwide in warm, shallow waters along coasts and in ri ...

Green chromide The green chromide (''Etroplus suratensis'') is a species of cichlid fish that is native to fresh and brackish water habitats in some parts in India such as Kerala, Goa, Chilika Lake in Odisha and Sri Lanka. The species was first described by ...

Herring Herring are forage fish, mostly belonging to the family of Clupeidae. Herring often move in large schools around fishing banks and near the coast, found particularly in shallow, temperate waters of the North Pacific and North Atlantic Oceans, i ...

Lamprey Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...

Mummichog The mummichog (''Fundulus heteroclitus'') is a small killifish found along the Atlantic coast of the United States and Canada. Also known as Atlantic killifish, mummies, gudgeons, and mud minnows, these fish inhabit brackish and coastal waters in ...

* Molly *

Guppy The guppy (), also known as millionfish and rainbow fish, is one of the world's most widely distributed tropical fish and one of the most popular freshwater aquarium fish species. It is a member of the family Poeciliidae and, like almost all ...

Puffer fish Tetraodontidae is a family of primarily marine and estuarine fish of the order Tetraodontiformes. The family includes many familiar species variously called pufferfish, puffers, balloonfish, blowfish, blowies, bubblefish, globefish, swellfish ...

Salmon Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...

* Shad *

Striped bass The striped bass (''Morone saxatilis''), also called the Atlantic striped bass, striper, linesider, rock, or rockfish, is an anadromous perciform fish of the family Moronidae found primarily along the Atlantic coast of North America. It has al ...

Sturgeon Sturgeon is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretace ...

Tilapia Tilapia ( ) is the common name for nearly a hundred species of cichlid fish from the coelotilapine, coptodonine, heterotilapine, oreochromine, pelmatolapiine, and tilapiine tribes (formerly all were "Tilapiini"), with the economically most ...

Trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salmoni ...

Mangrove jack The mangrove red snapper (''Lutjanus argentimaculatus''), also known as mangrove jack, grey snapper, creek red bream, Stuart evader, dog bream, purple sea perch, red bream, red perch, red reef bream, river roman, or rock barramundi, is a species ...

White perch The white perch (''Morone americana'') is not a true perch but is a fish of the temperate bass family, Moronidae, notable as a food and game fish in eastern North America. In some places it is referred to as "Silver Bass". The name "White per ...

Killifish A killifish is any of various oviparous (egg-laying) cyprinodontiform fish (including families Aplocheilidae, Cyprinodontidae, Fundulidae, Profundulidae and Valenciidae). All together, there are 1,270 species of killifish, the biggest family ...

File:Rachycentron canadum.png,

Cobia The cobia (''Rachycentron canadum'') is a species of carangiform marine fish, the only extant representative of the genus ''Rachycentron'' and the family Rachycentridae. Other common names include black kingfish, black salmon, ling, lemonfis ...

File:Mugil cephalus.jpg,

Flathead mullet The flathead grey mullet (''Mugil cephalus'') is an important food fish species in the mullet family Mugilidae. It is found in coastal tropical and subtropical waters worldwide. Its length is typically . It is known with numerous English name ...

File:Shark fish chondrichthyes.jpg,

Other euryhaline organisms

File:Seagrass Halodule uninervis (5777808662).jpg, the seagrass ''

Halodule uninervis ''Halodule uninervis'' is a species of seagrass in the family Cymodoceaceae. It is native to the western Pacific and Indian Oceans. Common names include narrowleaf seagrass in English and ''a'shab bahriya'' in Arabic.Guiry, M. D. & G. M. Guiry. 2 ...

'' File:S. droe.JPG, Green sea urchin File:Phyllorhiza punctata (White-spotted jellyfish) edit.jpg, White-spotted jellyfish File:Cerastoderma glaucum MHNT 1.jpg, Lagoon cockle File:New Zealand Mud snails.jpg,

New Zealand mud snail The New Zealand mud snail (''Potamopyrgus antipodarum'') is a species of very small freshwater snail with a gill and an operculum. This aquatic gastropod mollusk is in the family Tateidae. It is native to New Zealand, where it is found throug ...

File:Gammarus roeselii.jpg, Amphipods of the family

Gammaridae Gammaridae is a family of amphipods. In North America they are included among the folk taxonomic category of " scuds", and otherwise gammarids is usually used as a common name. They have a wide distribution, centered on Eurasia, and are eury ...

File:Irrawaddy dolphin size.svg,

Irrawaddy dolphin The Irrawaddy dolphin (''Orcaella brevirostris'') is a euryhaline species of oceanic dolphin found in scattered subpopulations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia. It closely resembles the ...

(compared with an average human) File:Hemigrapsus sanguineus.jpg, Asian shore crab File:Carcinus maenas.jpg,

Shore crab ''Carcinus maenas'' is a common littoral crab. It is known by different names around the world. In the British Isles, it is generally referred to as the shore crab, or green shore crab. In North America and South Africa, it bears the name eur ...

File:Fejer cancri 050422 011 tdp.jpg,

Crab-eating frog The crab-eating frog (''Fejervarya cancrivora'') is a frog native to south-eastern Asia including Taiwan, China, the Philippines and more rarely as far west as Orissa in India. It has also been introduced to Guam, and was most likely introduced f ...

File:Diamondback turtle adult female.jpg,

Diamondback terrapin The diamondback terrapin or simply terrapin (''Malaclemys terrapin'') is a species of turtle native to the brackish coastal tidal marshes of the Northeastern and southern United States, and in Bermuda. It belongs to the monotypic genus ''Mal ...

References

{{Animalosmo Aquatic ecology

Osmoregulation

Euryhaline fish

Other euryhaline organisms

See also

References