Fish require oxygen for survival just like other animals, but they filter it from water using specialized organs called gills. A fish draws in oxygen-rich water and passes it through its gills. The organs absorb the oxygen from the water, carrying it into the fish's bloodstream for use by its organs.Know More
Gills are made up of many small filaments that contain capillaries, which give the organs a large amount of surface area. This is necessary due to the lower oxygen content of water compared with atmospheric air. Any given volume of air contains more than 25 times as much oxygen as the same volume of freshwater. As a fish swims, it creates a constant current of water over its gills, allowing it to extract as much oxygen as possible. Some fish have the ability to create this pressurized stream of water using their internal organs, while others must remain constantly in motion to draw enough water through their gills to survive.
Not every species of fish relies on gills for oxygen. Some fish have rudimentary lung structures or absorb oxygen through their skin. These must occasionally surface to partake of the oxygen-rich air instead of filtering it from the water around them.Learn more about Biology
Tadpoles breathe through the gills by moving their throat through regular rhythmic movements, known as pulsing. They can also breathe through lungs, according to Natural History. When they metamorphose into frogs, they eventually lose their gills and start breathing through the lungs or through the skin.Full Answer >
According to the Australian Museum, crayfish breathe through their gills. Their feather-like gills, which are protected by the carapace, branch off from the base of their legs.Full Answer >
Snails can be divided into two categories when discussing manners of breathing: those with lungs and those with gills. Pulmonate (lung) snails assimilate oxygen through the thin wall ("lung") of their mantel cavity. Other snails breathe using gills.Full Answer >
Human beings require air because, like all other animals, they are aerobic organisms who require oxygen, which is a component of air. While oxygen is found in water, humans evolved to extract the oxygen from air, as birds, mammals and reptiles do, instead of from the water, as fish and some amphibians do. Additionally, air is necessary to keep the planet warm as it insulates the planet like a blanket.Full Answer >