Air Bladder
    Many fish species maintain their relative depth in the water column by adjusting the volume and pressure of gas in their air bladder in order to maintain a neutral buoyancy. To maintain equilibrium at increasing depths where the gas in the air bladder would be compressed, greater gas pressure is required in the air bladder. Conversely, at shallow depths less pressure is required as the gas in the air bladder expands. The air bladder occupies approximately 4 to 6% of the total volume of the fish. Quick vertical  movements without adjustment to the rates of secretion of gas into, or reabsorption of gas from, the air bladder. However the magnitude of these movements may be related to the depth of the fish. The rapid removal from deep water at a rate far in excess of the rate that the fish can actively remove gas from the air bladder. Often the result is an excessively inflated air bladder that may distend the abdomen, or force the air bladder
and gut lining to protrude out of the mouth. The probability of survival for a fish released with a distended air bladder is not high. The fish may reabsorb the excess gas in time. Some people claim they can release the air from the bladder by poking a hole in the fish with a needle but a tear in the gut wall would readily allow water to penetrate the  internal body cavity of the fish. This would most likely lead to the entry of water into the body cavity resulting in death of the fish.