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Fish gills are organs that allow fish to breathe underwater. Most fish exchange gases like oxygen and carbon dioxide using gills that are protected under gill covers (operculum) on both sides of the pharynx (throat). Gills are tissues that are like short threads, protein structures called filaments. These filaments have many functions including ...
In some fish, capillary blood flows in the opposite direction to the water, causing countercurrent exchange. The muscles on the sides of the pharynx push the oxygen-depleted water out the gill openings. In bony fish, the pumping of oxygen-poor water is aided by a bone that surrounds the gills called the operculum. [6]
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.
In fish and some molluscs, the efficiency of the gills is greatly enhanced by a countercurrent exchange mechanism in which the water passes over the gills in the opposite direction to the flow of blood through them. This mechanism is very efficient and as much as 90% of the dissolved oxygen in the water may be recovered.
The pulmonates have lost their gills [1] and adapted the mantle cavity into a pallial lung. The lung has a single opening on the right side, called the pneumostome, which either remains permanently open, or opens and closes as the animal breathes. The roof of the lung is highly vascularised, and it is through this surface that gas exchange occurs.
Aquatic animals generally conduct gas exchange in water by extracting dissolved oxygen via specialised respiratory organs called gills, through the skin or across enteral mucosae, although some are evolved from terrestrial ancestors that re-adapted to aquatic environments (e.g. marine reptiles and marine mammals), in which case they actually ...
Most vertebrates are aquatic and breathe with gills, where water comes in contact for exchanging dissolved oxygen before flowing out through a series of openings to the outside. Each gill is supported by a cartilaginous or bony gill arch, [1] which helps to maintain the gill's surface area.
They typically breathe by extracting oxygen from water through gills. Fish use fins to propel and stabilise themselves in the water. Over 33,000 species of fish have been described as of 2017, [ 1 ] of which about 20,000 are marine fish.