Going Up

• Swim bladders are located in the center of a fish's body in order to help the fish's balance and swimming ability. According to the book "Goldfish", some fancy goldfish like the lionhead are poor swimmers because their swim bladder is located too far forward. When the fish wants to go up, a pneumatic duct opens to let in oxygen to swell the bladder up like a little balloon. By gulping, the fish can help fill up the bladder. Some fish, like the rudd, have two swim bladders.
  
  

Going Down

• When the fish wants to swim lower, they deflate their swim bladders. The gas is absorbed into their gas glands, which are located on either side of the swim bladder. The fish's body can also use the gas glands to help inflate the swim bladder. Fish can also expel excess gas from their mouths in something similar to a belch. Also, if fish are caught in oxygen-poor water, they can use some of the oxygen in the gas glands or swim bladder to help them breathe. According to the Encyclopedia Britannica, some of fish species like sharks use oil instead of gas to inflate or deflate an area in the liver, since oil is lighter than water.
  
  

Going the Wrong Way

• If a fish is swimming sideways, is unable to rise to the surface or is clearly having trouble swimming, chances are it is due to swim bladder disorder. If a fish is constipated, this could press the digestive organs against the swim bladder, not allowing it to inflate properly. According to HealthyBetta.com, a fish that has swim a bladder disorder should go on a fast for a day and not be fed so much in the future. Also, splitting the feedings to two or three a day is better on the swim bladder than one large feed per day.