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Home , Spiracle (vertebrates)

How breath

• Respiration in or in that of any organism that lives in the water is very different from that of human beings. Organisms like fish, which live in water, need oxygen to breathe so that their cells can maintain their living state. To perform their respiratory function, fish have specialized organs that help them inhale oxygen dissolved in water. • Respiration in fish takes with the help of . Most fish possess gills on either side of their head. Gills are tissues made up of feathery structures called filaments that provide a large surface area for gas exchange. A large surface area is crucial for gas exchange in aquatic organisms as water contains very little amount of dissolved oxygen. The filaments in fish gills are arranged in rows in the gill arch. Each filament contains lamellae, which are discs supplied with capillaries. Blood enters and leaves the gills through these small blood vessels. Although gills in fish occupy only a small section of their body, the immense respiratory surface created by the filaments provides the whole organism with an efficient gas exchange. • Some fish, like and lampreys, possess multiple gill openings. However, bony fish like Rohu, have a single gill opening on each side.

Bony fish (, )

• . Greek for bone fish, Osteichthyes includes all bony fishes, and given the diversity of animals found in the world's oceans, it should come as no surprise that it is the largest of all vertebrate classes. There are nearly 28,000 members of Osteichthyes currently found on Earth, and numerous extinct species found in fossil form. • Examples -- tuna fish,Salmon fish,gold fish and Rehu etc. Salmon fish The Osteichthyes

• The Osteichthyes Respiratory System • Unlike humans, who live on land among oxygen-rich air, fish live in saltwater seas or bodies of freshwater. With the exception of some who are able to breathe at the surface, the majority of fish get the oxygen they need from the water they live in. Water contains dissolved molecules of oxygen that the fish are able to use for respiration, just as humans are able to use the oxygen in the air. The red, meat-looking structure shown here are the gills. They are used for gas exchange and are the primary organ of the bony fish respiratory system. Respiration in bony fish

• Most fish exchange gases using gills on either side of the pharynx (throat). Gills are tissues which consist of threadlike structures called filaments. These filaments have many functions and "are involved in ion and water transfer as well as oxygen, carbon dioxide, acid and ammonia exchange. Each filament contains a capillary network that provides a large surface area for exchanging oxygen and carbon dioxide. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. In some fish, capillary blood flows in the opposite direction to the water, causing countercurrent exchange. The gills push the oxygen-poor water out through openings in the sides of the pharynx. Gills in fishes and its function

• Gills usually consist of thin filaments of tissue, branches, or slender tufted processes that have a highly folded surface to increase surface area. The high surface area is crucial to the gas exchange of aquatic organisms as water contains only a small fraction of the dissolved oxygen that air does. A cubic meter of air contains about 250 grams of oxygen at STP. The concentration of oxygen in water is lower than air and it diffuses more slowly. In a litre of freshwater the oxygen content is 8 cm3 per litre compared to 210 in the same volume of air. Water is 777 times more dense than air and is 100 times more viscous Oxygen has a diffusion rate in air 10,000 times greater than in water. The use of sac-like lungs to remove oxygen from water would not be efficient enough to sustain life. Rather than using lungs "Gaseous exchange takes place across the surface of highly vascularised gills over which a one-way current of water is kept flowing by a specialised pumping mechanism. The density of the water prevents the gills from collapsing and lying on top of each other, which is what happens when a fish is taken out of water." Tuna gills in situ structure Cocurrent and countercurrent flow exchange systems • Cocurrent and countercurrent flow exchange systems Red represents a higher value (e.g. of temperature or the partial pressure of a gas) than blue so the property being transported in the channels flows from red to blue. In fish a countercurrent flow (lower diagram) of blood and water in the gills is used to extract oxygen from the environment.[ Fish gill respiration Bony fish

• In bony fish, the gills lie in a branchial chamber covered by a bony (branchia is an Ancient Greek word for gills). The great majority of bony fish species have five pairs of gills, although a few have lost some over the course of evolution. The operculum can be important in adjusting the pressure of water inside of the pharynx to allow proper ventilation of the gills, so that bony fish do not have to rely on ram ventilation (and hence near constant motion) to breathe. Valves inside the mouth keep the water from escaping.[7 Most bony fish have five gills • The gill arches of bony fish typically have no septum, so that the gills alone project from the arch, supported by individual gill rays. Some species retain gill rakers. Though all but the most primitive bony fish lack a spiracle, the associated with it often remains, being located at the base of the operculum. This is, however, often greatly reduced, consisting of a small mass of cells without any remaining gill-like structure. • Fish transfer oxygen from the sea water to their blood using a highly efficient mechanism called countercurrent exchange. Countercurrent exchange means the flow of water over the gills is in the opposite direction to the flow of blood through the capillaries in the lamellae. The effect of this is that the blood flowing in the capillaries always encounters water with a higher oxygen concentration, allowing diffusion to occur all the way along the lamellae. As a result the gills can extract over 80% of the oxygen available in the water. • The gill arches of bony fish typically have no septum, so that the gills alone project from the arch, supported by individual gill rays. Some species retain gill rakers. Though all but the most primitive bony fish lack a spiracle, the pseudobranch associated with it often remains, being located at the base of the operculum. This is, however, often greatly reduced, consisting of a small mass of cells without any remaining gill-like structure. Respiratory mechanism in bony fish

• Respiratory mechanism in bony fish The fish draws oxygen-rich water in through the mouth (left). It then pumps it over gills so oxygen enters the bloodstream, and allows oxygen- depleted water to exit through the gill slits (right)