Here we go........again :, you guys talkin bout swimbladders have the slightest idea on how the swimbladder works, from where the gas inside it comes and to where it goes ? you are just speculating on what the swimbladder does.
The swimbladder's main function is that of a hydrostatic organ. Neutral buoyancy, the ability of an organism to use little or no energy to stay at particular levels of water, is achieved through the expanding and shrinking of the swimbladder due to varying gas pressures.
When a fish dives, it 's swimbladder is compressed as a result of the increase in pressure at greater water depths. So in order for the fish to return to its former, higher level in the water, the swimbladder must be reinflated. Therefore, the most essential function of the swimbladder is the regulation of gases coming in and out of the fish's body. Thus it is necessary for fishes to be efficient controllers of their buoyancy.
DEFLATION:
On the posterior wall of a closed swimbladder lies a network of capillary beds. Next to these capillaries is a muscular valve, the oval, which has the job of controlling gases exiting the swimbladder. Within the oval there are two types of muscles-- circular and radial. When the circular muscles are relaxed, the radial muscles are contracted in order to stretch the swimbladder out, which in turn creates a greater capillary surface area for diffusion. Gases from within the bladder diffuse out to the blood through these capillaries. When sufficient levels of gases have been removed to create a new level of buoyancy, the circular muscles contract. Now the oval is no longer in contact with the bladder and so the gases are not able to diffuse from one area to another. A fish "knows" its buoyancy through the responses of nerve endings to the stretching and shrinking of the bladder wall. So with any change of pressure within the swimbladder as a result of diving or surfacing, a message can be relayed to the brain to initiate the deflation or inflation of the swimbladder so that the fish can maintain neutral buoyancy. The movement of gases from the bladder through the oval is a slow process however, taking over several hours to adjust to just a small pressure change.
INFLATION
The swimbladder has an interesting way of retaining gases. The inner lining of the swimbladder consists of numerous gland cells collectively called the gas gland. When the gas volume within the swimbladder is low this gland reacts by releasing lactic acid into the blood, acidifying it. With acidification, the blood releases oxygen where it accumulates in the rete mirabile.The rete mirabile ("wonderful net") is a bundle of close-lying arterial and venous capillaries that diffuse gases between one another as blood is carried through them, in and out of the gas gland. The rete mirabile, much like the oval, requires a large surface area for optimal contact between the arterial and venous capillaries.The diffusion of oxygen out through the bladder wall is blocked by a thin layer of crystalline guanine, thus also maintaining the volume of the swimbladder.
In order to restore gases to a deflated, closed swimbladder, the rete mirabile and the gas glands must create a combined pressure greater than that pressure within the swimbladder. Oxygen, having been forced off hemoglobin by lactic acid, is retained in the venous capillaries of the rete. Because of the rete's parallel arrangement of venous and arterial capillaries, a countercurrent multiplier effect occur. This is when gases are able to diffuse from a higher oxygen volume in the venous to the lower oxygen volume in the arterial capillaries, therefore keeping more oxygenated blood within the loop of the rete. When the pressure in the rete exceeds that of the swimbladder, oxygen diffuses out of the rete and into the bladder. The idea of multiplication comes into effect when we look at the varying lengths of capillaries that make up the rete. The longer the capillaries are, there is a greater surface area for gas exchange. So, with longer capillaries, a greater oxygen pressure can be created.This can be most important to those fish who spend the majority of their time at great depths. With an increase in swimbladder pressure as a result of the greater water depth, the fish would have a harder time keeping gases from being lost from the system. Therefore, those fish found in deep waters, where the pressure is greatest, generally have longer capillaries that make up their rete so that there is a greater surface area for gas exchange.