Swim bladder is an organ used by fish to adjust sinking and floating, also known as fish bubble, which contains gas. Bony fish, most of which have swim bladders.
The volume of the swim bladder accounts for about 5% of the body. Its shapes are oval, conical, heart-shaped, horseshoe shaped and so on.
The gas filled in the swim bladder is mainly oxygen, nitrogen and carbon dioxide, and the content of oxygen is the most. Therefore, in anoxic environment, swim bladder can be used as an auxiliary respiratory organ to provide oxygen for fish.
Most teleosts have swim bladders, long thin sacs located at the back of the body cavity. The swim bladders are generally divided into two chambers, containing oxygen, nitrogen and carbon dioxide.
The swim bladder has a swim bladder tube connected with the esophagus, which is called the laryngeal swim bladder. It belongs to the swim bladder of lower bony fish, such as carp. The swim bladder without swim bladder tube is called closed swim bladder. It belongs to the swim bladder of higher bony fish, such as bass.
From a functional point of view, except for a few fish (such as lung fish and fin fish), the swim bladder is a regulating organ of body specific gravity for most fish, which can help regulate the rise and fall of the body by changing the gas in the swim bladder. In laryngeal swim bladder fish, the gas in the swim bladder is mainly regulated by swallowing or discharging gas directly from the mouth through the swim bladder tube. The gas regulation in the swim bladder of closed swim bladder fish depends on the gas released by the red gland on the inner wall of the swim bladder and the gas absorbed by the oval chamber on the back of the swim bladder.