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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 ...
When underwater, the animal is essentially holding its breath and has to routinely return to the surface to breathe in new air. Therefore, all amniote animals, even those that spend more time in water than out, are susceptible to drowning if they cannot reach the surface to breath.
The operculum can be important in adjusting the pressure of water inside of the pharynx to allow proper ventilation of the gills, so 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. [9]
Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney. [4] Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, diadromous fish have the ability to migrate between fresh and saline ...
Fish from multiple groups can live out of the water for extended time periods. Amphibious fish such as the mudskipper can live and move about on land for up to several days, or live in stagnant or otherwise oxygen depleted water. Many such fish can breathe air via a variety of mechanisms. The skin of anguillid eels may absorb oxygen directly.
Fish typically breathe by extracting oxygen from water through gills and have a skin protected by scales and mucous. They use fins to propel and stabilise themselves in the water, and usually have a two-chambered heart and eyes well adapted to seeing underwater, as well as other sensory systems .
The majority of marine gastropods breathe through a single gill, supplied with oxygen by a current of water through the mantle cavity. This current is U-shaped, so that it also flushes waste products away from the anus , which is located above the animal's head, and would otherwise cause a problem with fouling.
The diet of the arapaima consists of fish, crustaceans, fruits, seeds, insects, and small land animals that walk near the shore. [18] The fish is an air breather, using its labyrinth organ, which is rich in blood vessels and opens into the fish's mouth, [19] an advantage in oxygen-deprived water that is often found in the Amazon River.