Respiration in fish or in any entity living in the water differs from that of human beings. Organisms such as fish, living in water, need oxygen to breathe for cells to sustain. Fish possess specialized structures to carry out the respiratory function, helping them inhale oxygen dissolved in water.
Respiration in Fish
Respiration in fish takes place with the help of gills. Most fish possess gills on either side of their head. Gills are tissues made up of feathery structures called gill filaments providing a large surface area for exchange of gases. 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 organized in rows in the gill arch. Each filament comprises lamellae, which are discs supplied with capillaries. Blood moves in and out of the gills through these small blood vessels. Though gills in fish occupy only a small section of their body, the extensive respiratory surface produced by the filaments renders the whole organism with efficient gas exchange.
Fish take in oxygen-rich water via their mouths and pump it over their gills. When water moves over the gill filaments, the blood within the capillary network takes up the dissolved oxygen. Then, the circulatory system supplies oxygen to all tissues of the body and finally to the cells while taking up carbon dioxide that is eliminated through the gills from the body. It exits the body of the fish once the water moves past the gills through the openings provided in the sides of the throat or through the operculum, a flap, usually found in bony fish, that covers and protects the fish gills.
Several fish, such as lampreys and sharks, have multiple gill openings. Rohu, a bony fish, has a single gill opening on either side.
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