fish maw
fish maw (zo?l.), the stomach of a fish; also, the air bladder, or sound... see fish | ||||
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Fish maw Definition from Encyclopedia Dictionaries & Glossaries
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Gas bladder
The gas bladder (also fish maw, less accurately swim bladder or air bladder) is an internal organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth, ascend, or descend without having to waste energy in swimming.
The gas bladder is a gas-filled sac located in the dorsal portion of the fish. It has flexible walls that contract or expand according to the ambient pressure. The walls of the bladder contain very few blood vessels and are lined with guanine crystals, which make them impermeable to gases. In physostomous gas bladders, a connection is retained between the gas bladder and the gut, allowing the fish to fill up the gas bladder by "gulping" air and filling the gas bladder through the pneumatic duct. In more derived varieties of fish, the bladder has a gas gland that can introduce gases (usually oxygen) to the bladder to increase its volume and thus increase buoyancy. To reduce buoyancy, gases are released from the bladder into the blood stream and then expelled into the water via the gills. In order to introduce gas into the bladder, the gas gland excretes lactic acid; the resulting acidity causes the hemoglobin of the blood to lose its oxygen, which then diffuses into the bladder while flowing through a complex structure known as the rete mirabile. Elsewhere, at a similar structure known as the oval window, the bladder is in contact with blood and the oxygen can diffuse back.
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