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Swim bladder
The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ in bony fish that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift via swimming, which expends more energy. Also, the dorsal position of the swim bladder means that the expansion of the bladder moves the center of mass downwards, allowing it to act as a stabilizing apparatus. Additionally, the swim bladder functions as a resonating chamber to produce or receive sound.
The swim bladder is evolutionarily homologous to the lungs of tetrapods and lungfish, and some ray-finned fish such as bowfins have also evolved similar respiratory functions in their swim bladders. Charles Darwin remarked upon this in On the Origin of Species, and reasoned that the lung in air-breathing vertebrates had derived from a more primitive swim bladder as a specialized form of enteral respiration.
Some species, such as mostly bottom dwellers like the weather fish and redlip blenny, have secondarily lost the swim bladder during the embryonic stage. Other fish, like the opah and the pomfret, use their pectoral fins to swim and balance the weight of the head to keep a horizontal position. The normally bottom-dwelling sea robin can use their pectoral fins to produce lift while swimming like cartilaginous fish do.
The gas/tissue interface at the swim bladder produces a strong reflection of sound, which is used by sonar equipment to find fish.
Cartilaginous fish such as sharks and rays do not have swim bladders, as they belong to a completely different evolutionary clade. Without swim bladders to modular buoyancy, most cartilaginous fish can only control depth by actively swimming, which produce dynamic lift; others store up lipids with specific density less than that of seawater to produce a neutral or near-neutral buoyancy, which cannot be readily changed with depth.
The swim bladder normally consists of two gas-filled sacs located in the dorsal portion of the fish, although in a few primitive species, there is only a single sac. 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. By adjusting the gas pressurising organ using the gas gland or oval window, the fish can obtain neutral buoyancy and ascend and descend to a large range of depths. Due to the dorsal position it gives the fish lateral stability.
In physostomous swim bladders, a connection is retained between the swim bladder and the gut, the pneumatic duct, allowing the fish to fill up the swim bladder by "gulping" air. Excess gas can be removed in a similar manner.
In more derived varieties of fish (the physoclisti), the connection to the digestive tract is lost. In early life stages, these fish must rise to the surface to fill up their swim bladders; in later stages, the pneumatic duct disappears, and the gas gland has to introduce gas (usually oxygen) to the bladder to increase its volume and thus increase buoyancy. This process begins with the acidification of the blood in the rete mirabile when the gas gland excretes lactic acid and produces carbon dioxide, the latter of which acidifies the blood via the bicarbonate buffer system. The resulting acidity causes the hemoglobin of the blood to lose its oxygen (Root effect) which then diffuses partly into the swim bladder. Before returning to the body, the blood re-enters the rete mirabile, and as a result, virtually all the excess carbon dioxide and oxygen produced in the gas gland diffuses back to the arteries supplying the gas gland via a countercurrent multiplication loop. Thus a very high gas pressure of oxygen can be obtained, which can even account for the presence of gas in the swim bladders of deep sea fish like the eel, requiring a pressure of hundreds of bars. Elsewhere, at a similar structure known as the 'oval window', the bladder is in contact with blood and the oxygen can diffuse back out again. Together with oxygen, other gases are salted out[clarification needed] in the swim bladder which accounts for the high pressures of other gases as well.
Hub AI
Swim bladder AI simulator
(@Swim bladder_simulator)
Swim bladder
The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ in bony fish that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift via swimming, which expends more energy. Also, the dorsal position of the swim bladder means that the expansion of the bladder moves the center of mass downwards, allowing it to act as a stabilizing apparatus. Additionally, the swim bladder functions as a resonating chamber to produce or receive sound.
The swim bladder is evolutionarily homologous to the lungs of tetrapods and lungfish, and some ray-finned fish such as bowfins have also evolved similar respiratory functions in their swim bladders. Charles Darwin remarked upon this in On the Origin of Species, and reasoned that the lung in air-breathing vertebrates had derived from a more primitive swim bladder as a specialized form of enteral respiration.
Some species, such as mostly bottom dwellers like the weather fish and redlip blenny, have secondarily lost the swim bladder during the embryonic stage. Other fish, like the opah and the pomfret, use their pectoral fins to swim and balance the weight of the head to keep a horizontal position. The normally bottom-dwelling sea robin can use their pectoral fins to produce lift while swimming like cartilaginous fish do.
The gas/tissue interface at the swim bladder produces a strong reflection of sound, which is used by sonar equipment to find fish.
Cartilaginous fish such as sharks and rays do not have swim bladders, as they belong to a completely different evolutionary clade. Without swim bladders to modular buoyancy, most cartilaginous fish can only control depth by actively swimming, which produce dynamic lift; others store up lipids with specific density less than that of seawater to produce a neutral or near-neutral buoyancy, which cannot be readily changed with depth.
The swim bladder normally consists of two gas-filled sacs located in the dorsal portion of the fish, although in a few primitive species, there is only a single sac. 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. By adjusting the gas pressurising organ using the gas gland or oval window, the fish can obtain neutral buoyancy and ascend and descend to a large range of depths. Due to the dorsal position it gives the fish lateral stability.
In physostomous swim bladders, a connection is retained between the swim bladder and the gut, the pneumatic duct, allowing the fish to fill up the swim bladder by "gulping" air. Excess gas can be removed in a similar manner.
In more derived varieties of fish (the physoclisti), the connection to the digestive tract is lost. In early life stages, these fish must rise to the surface to fill up their swim bladders; in later stages, the pneumatic duct disappears, and the gas gland has to introduce gas (usually oxygen) to the bladder to increase its volume and thus increase buoyancy. This process begins with the acidification of the blood in the rete mirabile when the gas gland excretes lactic acid and produces carbon dioxide, the latter of which acidifies the blood via the bicarbonate buffer system. The resulting acidity causes the hemoglobin of the blood to lose its oxygen (Root effect) which then diffuses partly into the swim bladder. Before returning to the body, the blood re-enters the rete mirabile, and as a result, virtually all the excess carbon dioxide and oxygen produced in the gas gland diffuses back to the arteries supplying the gas gland via a countercurrent multiplication loop. Thus a very high gas pressure of oxygen can be obtained, which can even account for the presence of gas in the swim bladders of deep sea fish like the eel, requiring a pressure of hundreds of bars. Elsewhere, at a similar structure known as the 'oval window', the bladder is in contact with blood and the oxygen can diffuse back out again. Together with oxygen, other gases are salted out[clarification needed] in the swim bladder which accounts for the high pressures of other gases as well.