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In fish, the long bony cover for the gill (the operculum) can be used for pushing water. Some fish pump water using the operculum. Without an operculum, other methods, such as ram ventilation, are required. Some species of sharks use this system. When they swim, water flows into the mouth and across the gills.
The physiology of underwater diving is the physiological adaptations to diving of air-breathing vertebrates that have returned to the ocean from terrestrial lineages. They are a diverse group that include sea snakes, sea turtles, the marine iguana, saltwater crocodiles, penguins, pinnipeds, cetaceans, sea otters, manatees and dugongs.
Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline. Fish dependent solely on dissolved oxygen, such as perch and cichlids , quickly suffocate, while air-breathers survive for much longer, in some cases in water that is little more than wet mud.
Another important adaptation that aids breathing while out of water is their enlarged gill chambers, where they retain a bubble of air. These chambers close tightly when the fish is above water, due to a ventromedial valve of the gill slit, keeping the gills moist, and allowing them to function while exposed to air.
This is achieved in different groups of fish by a variety of mechanisms of propulsion, most often by wave-like lateral flexions of the fish's body and tail in the water, and in various specialised fish by motions of the fins. The major forms of locomotion in fish are: Anguilliform, in which a wave passes evenly along a long slender body;
These structures, make the density of their bodies very close to that of the surrounding water. Some hydrozoans, such as siphonophores, has gas-filled floats; the Nautilus, Sepia, and Spirula ( Cephalopods ) have chambers of gas within their shells; and most teleost fish and many lantern fish (Myctophidae) are equipped with swim bladders .
A fish's hypoxia tolerance can be represented in different ways. A commonly used representation is the critical O 2 tension (P crit), which is the lowest water O 2 tension (P O 2) at which a fish can maintain a stable O 2 consumption rate (M O 2). [2] A fish with a lower P crit is therefore thought to be more hypoxia-tolerant than a fish with a ...
These two versions of the enzyme allow for faster catalytic function and metabolism depending on if the fish is in northern, colder waters or southern, warmer waters. [27] Based on genetic studies, the enzymes serum esterase (SERE) and malate dehydrogenase (MDH ) also appear to play an important role in mummichog temperature control.