Fish gill

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Most gas exchange fish use gills on both sides of the pharynx (throat). Gills are short-threadlike tissue, a protein structure called a filament. This filament has many functions including ion and water transfer, as well as the exchange of oxygen, carbon dioxide, acids and ammonia. Each filament contains a capillary network that provides a large surface area for the exchange of oxygen and carbon dioxide. Gas exchange fish by pulling oxygen-rich water through their mouth and pumping it over the gills. In some fish, capillary flow flows in the opposite direction with water, causing a reverse flow. Gill pushes oxygen-poor water out through the hole on the pharynx side. Some fish, such as sharks and lampreys, have several gill openings. However, bony fish have one gill hole on each side. This opening is hidden under the cover of a protective bone called the operculum.

Young Bichirs have external gills, a very primitive feature they share with larval amphibians.

Previously, gill evolution was thought to have occurred through two divergent lines: gills formed from endoderm, as seen in jawless fish species, or forms by ectoderm, as seen in jawed fish. However, recent studies of gill formation of small skates ( Leucoraja erinacea ) have shown potential evidence supporting the claim that the gills of all fish species today have actually evolved from the same ancestors.

Video Fish gill

Breathe with gills

Air breathing fish can be divided into mandatory air breath and facultative breath air. Remnants of compulsory air, such as African lungfish, are required to breathe air regularly or they suffocate. Facultative air respirators, such as catfish Hypostomus plecostomus , only breathe the air if they need to and can instead rely on their gills for oxygen. Much of the air breath is a facultative air breath that avoids energetic costs rising to the surface and exposure of fitness exposure surfaces.

All basal vertebrates breathe with gills. The gills are brought right behind the head, limiting the posterior margin of a series of openings from the esophagus to the outside. Each gill is supported by cartilage gill arch or bone. Vertebrate gills usually develop in the pharyngeal wall, along a series of gill openings to the outside. Most species use reverse-exchange systems to increase the diffusion of substances inside and outside the gills, with blood and water flowing in opposite directions.

These gills consist of comb-like filaments, lamellae gills, which help increase the surface area for oxygen exchange. When the fish breathes, it pulls in its mouth full of water regularly. Then he pulled both sides of his throat together, forcing the water through the opening of the gills, so that it passed through the gills outward. The bony fish has three pairs of arches, the cartiline fish has five to seven pairs, while the primitive fish without jaws has seven pairs. The vertebrate ancestor no doubt has more arches, as some of his relatives have more than 50 pairs of gills.

Gills usually consist of thin filaments of tissue, branches, or tufted process that has a highly folded surface to increase the surface area. High surface areas are essential for the exchange of gases from aquatic organisms since water contains only a small fraction of the dissolved oxygen carried by air. One cubic meter of air contains about 250 grams of oxygen in STP. The oxygen concentration in the water is lower than air and diffuses more slowly. In one liter of fresh water, the oxygen content is 8 cm ³ per liter compared to 210 in the same air volume. Water is 777 times denser than air and 100 times more viscous. Oxygen has a rate of diffusion in the air 10,000 times greater than in water. The use of lungs like a bag to expel oxygen from water will not be efficient enough to sustain life. Instead of using the lungs "Gas exchange takes place across the vascularized surface of the gull where a one-way flow of water is stored by a special pumping mechanism.The water density prevents the gills from collapsing and lying on top of each other, which occurs when a fish taken from water. "

High vertebrates do not develop gills, gill arch forms during fetal development, and laid the foundations of important structures such as the jaw, thyroid gland, larynx, columella (corresponding to stapes in mammals) and in malleus and incus mammals. Fish gill slits may be the evolutionary ancestors of the tonsils, thymus glands, and Eustachian tubes, as well as many other structures that originate from the embryonic branchial pouch.

Maps Fish gill

bony fish

In bony fish, the gill located in the branchial space covered by the bone operculum ( branchia is the Ancient Greek word for the gills). The majority of species of bony fish have five pairs of gills, though some have lost some during evolution. The operculum can be important in adjusting the water pressure within the pharynx to allow proper gill ventilation, so the bony fish does not have to rely on the ram ventilation (and hence near constant movement) to breathe. The valve in the mouth keeps the water out.

Gill arches of bony fish usually do not have a septum, so the project's own gills from the arch, supported by individual gill rays. Some species maintain gill filters. Although all but the most primitive boned fish have no spiracles, the pseudobranch associated with them often remains, located at the base of the operculum. This, however, is often greatly reduced, consisting of a small number of cells without structures like the remaining gills.

Marine teleost also uses gills to remove electrolytes. Large gill surface area tends to create problems for fish trying to regulate the osmolarity of their internal fluids. Saltwater is less dilute than this internal fluid, so the marine fish lose a lot of water osmotically through its gills. To get back the water, they drank a large amount of sea water and took salt out. However, fresh water is thinner than the fish's internal fluid, so freshwater fish get the water osmotically through its gills.

In some primitive bony fish and amphibians, the larvae bear an external gill, branched from the gill arch. This is reduced in adulthood, their function is taken over by the gills right in fish and lungs in most amphibians. Some amphibians maintain the external larval gill in adulthood, the complex internal gill system as seen in fish appears to be lost forever in the early evolution of tetrapods.

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Cartiline Fish

Sharks and rays usually have five pairs of gill slits that open directly to the outside of the body, although some more primitive sharks have six or seven pairs. The adjacent crevices are separated by the gill arches of the ribs from which the project of such long piece of septum is supported by a further piece of cartilage called gill rays. Individual gill Lamellae is located on both sides of the septum. The base of the arch can also support the gill rib, a small projection element that helps filter food from water.

The smaller opening, the spiracle, is located behind the first gill slit. It contains a small pseudobranch that resembles gills in the structure, but only receives blood that has been given oxygen by the correct gills. Spiracles are considered homologous by opening the ears in higher vertebrates.

Most sharks rely on ram vents, forcing water into the mouth and through the gills by swiming forward quickly. In slow-moving or under-lived species, especially between roller-skates and rays, spiracles can be enlarged, and fish breathe by sucking water through this hole, not through the mouth.

Chimaeras differ from other cartilagenous fish, losing both spiracles and the fifth gill slits. The rest of the gap is covered by the operculum, developed from the gill arch septum in front of the first gills.

The nature of respiratory sharing through gills in bony fish and cartilaginous fish is a well-known example of symplesiomorphy. Bony fish are more closely related to terrestrial vertebrates, which evolved from clones of bony fish that breathed through their skin or lungs, rather than sharks, rays, and other cartilaginous fish. Respirations of their gills are divided by "fish" because they are present in their common ancestors and lost in other living vertebrates. But on the basis of this distributed nature, we can not conclude that bony fish are more closely related to sharks and rays than to land vertebrates.

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Lamps and hagfish

Lamprey and hagfish do not have such gill slits. Instead, the gills are contained in a round bag, with a circular opening outward. Like the higher gills of the fish, each bag contains two gills. In some cases, openings can be combined together, effectively forming the operculum. Lamprey has seven pairs of bags, while hagfishe may have six to fourteen, depending on the species. In hagfish, the pouch is connected internally with pharynx. In adult lamprey, separate respiratory tubes develop under the precise pharynx, separating food and water from respiration by closing the valve at its anterior end.

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Breathe without gills

Although most fish breathe primarily using gills, some fish can at least breathe using a mechanism that does not require gills. In some species skin respiration is responsible for 5 to 40 percent of total respiration, depending on the temperature. Skin respiration is more important in air-breathing species, such as mudskipper and reedfish, and in these species can account for nearly half of total respiration.

Fish from different groups can live out of water for a long time. Amphibian fish like mudskipper can live and move on land for a few days, or live in stagnant water or run out of oxygen. Many such fish can breathe air through various mechanisms. Anguillid eel skin can absorb oxygen directly. Electric buccal cavity eel can breathe air. Catfish from the Loricariidae family, Callichthyidae, and Scoloplacidae absorb the air through their digestive tract. Lungfish, with the exception of Australian lungfish, and bichir have lung pairs that are similar to tetrapods and should appear to swallow fresh air through the mouth and secrete air released through the gills. Garin and bowfin have bladder swimming with vascularization that works in the same way. Loaches, trahiras, and many catfish breathe by passing air through the intestine. Mudskippers breathe by absorbing oxygen in the skin (similar to frogs). A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. Labyrinth fish (like gouramis and bettas) have labyrinth organs over gills that perform this function. Some other fish have structures resembling labyrinth organs in form and function, especially snakehead, pikeheads, and the family of catfish Clariidae.

Air respiration is mainly used for fish that inhabit the shallow waters of seasonal variables where water oxygen concentrations can decrease seasonally. Fish depend only on dissolved oxygen, such as tengger and cichlids, rapidly suffocating, while air-breath lasts longer, in some cases in water that is little more than wet mud. At the most extreme, some air-breathing fish can survive in a moist burrow for weeks without water, entering aestivation state until the water returns.

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Parasites on the gills

Fish gills are the preferred habitat of many ectoparasites (parasites attached to the gills but live from it); the most common are monogeneans and certain groups of parasitic copepods, which can be very numerous. Other ectoparasites found in gills are leeches and, in seawater, gnathiid isopod larvae. Endoparasites (parasites that live in the gills) include the dried-up immature dried-up trematosoid trematoda, some trichosomoidid nematodes of the Huffmanela genus, including Huffmanela ossicola living in the gill bone, and the dwarfed. parasite derivatives Paravortex . Various protists and Myxosporea are also parasites in the gills, where they form cysts.

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See also

• Water respiration
• Lung books
• Gill raker
• Gill slit
• Lung
• Artificial gills (humans)

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References

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Further reference

• Evans, D H; Piermarini, P M; Choe, K P (2005). "Multifunctional fish gills: dominant sites of gas exchange, osmoregulation, acid-base regulation, and excretion of nitrogenous waste". Physiological Reviews . 85 (1): 97-177. doi: 10.1152/physrev.00050.2003. PMIDÃ, 15618479. < span>

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External links

• Fish Dissected - Gills exposed Australian Museum . Updated: June 11, 2010. Accessed on January 16, 2012.

Source of the article : Wikipedia