1. Adjusting density Most bony fish have swim bladders, and for them, the biggest role of swim bladders is to adjust the density of fish. Gas can be stored inside the swim bladder, the more gas, the smaller the overall density of the fish, so that it can better float up, the same, after the gas is discharged, the density of the fish increases, convenient for it to dive.
Another very important role of the swim bladder is to protect the organs in the fish. Especially for the fish living in the deep sea, because the water pressure is very high, the internal organs are easily damaged. The swim bladder creates enough space in the fish's body, and the organs will not be affected by the water pressure.
Fish need to use gills to breathe, but there are also some fish that can use swim bladders to assist breathing, such as African lungfish. The swim bladder of this fish is special, there are many small air chambers around the central cavity, which can store a certain amount of gas, when the water dries up, you can get oxygen through this lung-like swim bladder.
Fish can also make a sound, but the organs that make the sound are not the same. Some fish can make a sound through the swim bladder. Many of the fish that make sounds are male, and in the breeding season, they attract females by making sounds, so as to mate and reproduce.
