1. How dose fish manage gas exchange in swim bladder ?

2. The structure and mechanism by which gases enter and are released from the gas bladder differ in the major groups of teleosts.The pneumatic duct is a connection between the gas bladder and the gut.Physostomous fishes retain the connection in adult,whereas physoclistous fishes lose the connection in adult,if it’s present at all during development.In physostomous fishes,gas can be taken in and emitted through the pneumatic duct.More primitive soft-rayed teleost have the primitive physostomous condition;whereas more advanced spiny-rayed fishes are physoclistous,lacking a pneumatic duct.

3. How about physoclistous?
The gas in the swim bladder is dependent on the red glands in the inner wall of the bladder to release the gas and the oval in the back of the bladder. Red glands concentrate a lot of capillaries, and the red gland's epithelial cells can isolate the oxygen, carbon dioxide and other gases in the blood. The oval walls are covered with capillaries, and the gas permeates the blood vessels.

4. Another,more complex mechanism,which involves two distinct regions of the gas bladder,has evolved to allow gas exchange in these fishes. The anteroventral secre- tory region contains the gas gland and the rete mirabile. The gas gland secretes lactic acid into the beginning of the capillary loop.This acidifies and reduces the solubility of all dissolved gases.A change of 1 pH unit releases 50％ of the oxygen bound to hemoglobin.This raises the partial pressure of blood oxygen by the Root and Bohr effects.

5. The rete mirabile,or wonder net, is not actually a net but a looping bundle of arterial and venous capillaries associated with the gas gland that functions as a countercurrent multiplier.
The posterodorsal resorptive region of the gas bladder is called the oval.It develops from the distal end of the degenerating pneumatic duct and consists of a thin,highly vascularized area.

7. What is Root and Bohr effects?
The Bohr effect is a physiological phenomenon first described in by the Danish physiologist Christian Bohr, stating that hemoglobin's oxygen binding affinity (see Oxygen–haemoglobin dissociation curve) is inversely related both to acidity and to the concentration of carbon dioxide. Since carbon dioxide reacts with water to form carbonic acid, an increase in CO2 results in a decrease in blood pH, resulting in hemoglobin proteins releasing their load of oxygen. Conversely, a decrease in carbon dioxide provokes an increase in pH, which results in hemoglobin picking up more oxygen.

8. The Root effect is a physiological phenomenon that occurs in fish hemoglobin, named after its discoverer R. W. Root. It is the phenomenon where an increased proton or carbon dioxide concentration (lower pH) lowers hemoglobin's affinity and carrying capacity for oxygen. The Root effect is to be distinguished from the Bohr effect where only the affinity to oxygen is reduced. Hemoglobins showing the Root effect show a loss of cooperativity at low pH. This results in the Hb-O2 dissociation curve being shifted downward and not just to the right. At low pH, hemoglobins showing the Root effect don't become fully oxygenated even at oxygen tensions up to 20kPa. This effect allows hemoglobin in fish with swim bladders to unload oxygen into the swim bladder against a high oxygen gradient. The effect is also noted in the choroid rete, the network of blood vessels which carries oxygen to the retina. In the absence of the Root effect, retia will result in the diffusion of some oxygen directly from the arterial blood to the venous blood, making such systems less effective for the concentration of oxygen. It has also been hypothesized that the loss of affinity is used to provide more oxygen to red muscle during acidotic stress.

9. List of References https://en.wikipedia.org/wiki/Swim_bladder