Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

is the short-finned 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 salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but 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 estuary ...

, or salt water. The green crab ('' Carcinus maenas'') 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 environm ...

and tide pools where the salinity changes regularly. However, some organisms are euryhaline because their life cycle involves migration between freshwater and marine environments, as is the case with

salmon Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...

and eels. 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 is the active process by which an organism maintains its level of water content. The

osmotic pressure Osmotic pressure is the minimum pressure which needs to be applied to a Solution (chemistry), solution to prevent the inward flow of its pure solvent across a semipermeable membrane. It is also defined as the measure of the tendency of a soluti ...

in the body is homeostatically 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. Osmoconformers 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 memb ...

(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 In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

out from the

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, 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 r ...

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''. 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 euryhaline bottom-dwelling species of fish of the family (biology), family Gobiidae. It is native to Central Eurasia, including the Black Sea and the Caspian Sea. Round gobies have established larg ...

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

File:Monodactylus argenteus.JPG, Moonyfishes File:Ocean stage and spawning pink salmon.gif, Pink salmon File:Barramundi.jpg, Barramundi File:Sawfish genova.jpg, Green sawfish File:Aphanius iberus.png, Spanish toothcarp 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 teleost, 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 br ...

File:Mayan10a.jpg, Mayan cichlid File:Crevalle jack aquarium.jpg, Crevalle jacks The level of

salinity Salinity () is the saltiness or amount of salt (chemistry), 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 dimensio ...

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, saltmarsh or salting, 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. I ...

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 mechanisms found in the river stingrays of the family Potamotrygonidae. 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 salt water. Freshwater Atlantic stingrays have only 30-50% the concentration of

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

and other osmolytes in their blood compared to marine populations. However, the

between their internal fluids and external environment still causes water to diffuse into their bodies, and they must produce large quantities of dilute

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

(at 10 times the rate of marine individuals) to compensate. ;Partial list * Atlantic stingray * Bull shark * Green chromide * Herring *

Lamprey Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...

* Mummichog * Molly * Guppy * Puffer fish *

Salmon Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...

Shad The Alosidae, or the shads, are a family (biology), family of clupeiform fishes. The family currently comprises four genera worldwide, and about 32 species. The shads are Pelagic fish, pelagic (open water) schooling fish, of which many are anadr ...

* Striped bass * Sturgeon * Tilapia * Trout * Barramundi * Mangrove jack * White perch * Killifish *

File:Rachycentron canadum.png, Cobia File:Mugil cephalus.jpg, Flathead mullet File:Shark fish chondrichthyes.jpg, Bull shark

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 Ocean, Pacific and Indian Oceans. Common names include narrowleaf seagrass in English language, English and ''a'shab bahriya'' in Ara ...

'' 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 File:Gammarus roeselii.jpg, Amphipods of the family Gammaridae File:Irrawaddy dolphin-Orcaella brevirostris by 2eight.jpg, Irrawaddy dolphin File:Hemigrapsus sanguineus.jpg, Asian shore crab File:Carcinus maenas.jpg, Shore crab 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, Sumatra in Indonesia, the Philippines and more rarely as far west as Orissa in India. It has also been introduced to Guam, most lik ...

File:Diamondback turtle adult female.jpg, Diamondback terrapin

References

{{Animalosmo Aquatic ecology

Osmoregulation

Euryhaline fish

Other euryhaline organisms

See also

References