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Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. Within the gill filaments, capillary blood flows in the opposite direction to the water, causing counter-current exchange. The gills push the oxygen-poor water out through openings in the sides of the pharynx.
Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. In species like the spiny dogfish and other sharks and rays, a spiracle exists near the top of the head that pumps water into the gills when the animal is not in motion. [5]
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.
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.
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.
This allows them, like lungfish, to "breath" in two ways: they can extract oxygen from the water when breathing through their gills, but can also break the water's surface to breathe or gulp air through the pneumatic duct. [35] [36] When performing low-level physical activity, bowfin obtain more than half of their oxygen from breathing air. [37]
Secondary gills are also present in the unrelated genus Patella, in which they are found as folds within the mantle cavity. Some smaller gastropods have neither true gills nor cerata. The genus Lepeta uses the whole of the mantle cavity as a respiratory surface, while many sea butterflies respire through their general body surface.
The major means of respiration in teleosts, as in most other fish, is the transfer of gases over the surface of the gills as water is drawn in through the mouth and pumped out through the gills. Apart from the swim bladder , which contains a small amount of air, the body does not have oxygen reserves, and respiration needs to be continuous over ...