Fish blisters are swim bladders, one of the organs of fish, scleractinian fish, most of which have swim bladders. The swim bladder makes up about 5% of the body. Its shape can be ovoid, conical, heart-shaped, horseshoe-shaped and so on. The swim bladder is filled with gases mainly oxygen, nitrogen and carbon dioxide, with oxygen being the most abundant. Therefore, in an oxygen-deficient environment, the swim bladder can be used as an auxiliary respiratory organ to provide oxygen to the fish. Most bony fishes have swim bladders, long thin sacs located on the dorsal side of the body cavity. The swim bladder is usually divided into two chambers and contains oxygen, nitrogen and carbon dioxide. The swim bladder is connected to the esophagus by a swim bladder tube called the laryngeal swim bladder, which belongs to the swim bladder of lower bony fishes, such as carp. The swim bladder without a swim bladder tube is called a closed swim bladder, and belongs to the swim bladders of higher bony fishes, such as perch. From a functional point of view, except for a few fish (such as lungfish, finfish) swim bladder has a respiratory function, for most fish, swim bladder is a body specific gravity regulation organ, through the swim bladder gas changes to help regulate the body's floating and sinking.