The swim bladder has the following three major functions:

Firstly, it assists the fish in lifting and lowering in the water, and it is also used as a stabilizer to keep the center of gravity downward due to the center of the fish's body.

The contraction and expansion of the swim bladder controlled by the swim bladder muscle can make the air content in the body change and regulate the density of the body, and the buoyancy generated in the water will change accordingly to achieve the purpose of rising or sinking. When the fish dives, the swim bladder muscle will contract, the space becomes smaller and the air pressure becomes bigger to counteract the effect of water pressure. When the fish rises, the water pressure becomes less, the swim bladder muscles relax, the space becomes larger, and the air pressure becomes less. The swim bladder muscle controls the amount of pressure that the swim bladder can withstand and determines the different waters that different fish species live in. The swim bladder muscle is thicker and has more pressure. They live in deeper waters and are deep-water (sea) fish. On the contrary, they can only move in shallow water (sea).

The growth of the swim bladder follows the growth of the body of the fish until the body stops growing and so does the swim bladder. Its shape is determined by the shape of the fish body and the spatial structure of the abdominal cavity, so that the buoyancy force generated at various points of the fish body is counterbalanced by the gravity force generated in different parts. In the case of carp, the structure of the front and back parts of the swim bladder also evolved to accommodate the rapid turning of the fish's body. It is able to bend quickly in response to the rapid deformation of the fish's body to achieve a rapid balance of the body without causing the fish to tip over on its side.

Cartilaginous fish do not have swim bladders, so they cannot keep their bodies still, and can only rely on non-stop swimming to maintain up and down balance, and sharks are one of them. Deep-sea fish have high pressure in their swim bladders, and once they are out of the water, the compressed gas is released, bursting the swim bladder. Shallow-water fish once sick or dead, the fish body on both sides of the balance line, the buoyancy generated by the swim bladder and the body of the fish produced by the center point of gravity is different, resulting in the fish body occurs on the side of the upturned fish belly up.

Secondly, the fish's abdominal cavity produces enough space to protect its internal organs and avoid excessive water pressure and damage to internal organs.

Third, the swim bladder can be used as an auxiliary respiratory organ in lungfish and total finfish.

Fourth, the swim bladder can be used as a ****ing chamber to produce or receive sound.

Fifth, the swim bladder can be used as an auxiliary respiratory organ to provide oxygen to the fish in an oxygen-deficient environment. After obtaining the swim bladder, dissect it, remove the blood vessels and mucous membranes, wash it, flatten it and dry it in the sun; or wash it and use it fresh. It is a very good medicinal herbs and ingredients, there are yellow fish belly, back to the fish belly, eel fish belly, etc. The dried swim bladder is mostly pressed into long rounded thin slices, light yellow, horny, slightly glossy. Yellowtail swim bladder is small, sturgeon and locust fish swim bladder is large. It is tough and not easy to be torn, and is fibrous at the fracture; it is easy to be swollen in water, and is almost completely dissolved when boiled, and the thick solution condenses into jelly glue after cooling, which is very viscous. Gas slightly fishy, light flavor. After dissolution, condensed into a jelly glue, known as swim bladder glue. Commodities collectively referred to as fish maw. Sturgeon, sturgeon swim bladder known as yellow lip belly or yellow sturgeon glue. There are cut into lines called line fish glue.

Mainly produced in China's coastal and Nanyang Islands and other places, produced in Guangdong, "wide belly" quality is the best, Fujian, Zhejiang, produced in the area of the "Mao Changduo" soft second to the wide belly, but also known as the best product. Broad tripe, hair often tripe transparent color, no black bloodstain, large body hair strong. Yellow fish maw divided into three kinds, the body thick piece of large known as "mention piece", the body thin piece of small known as "hanging piece", mention piece and hanging piece to color yellowish bright for the best, good hair, there is also a "hitch piece ", the Department of several small fish maw hitched together to become a large sun-dried, muddy and unknown color, quality, hair rise is insufficient. Back to the nature of the fish maw is relatively hard, yellowish color for the best. Wormy, gray and black color for the second best. Fish maw before eating, must be soaked in advance, the method of oil and water method of two kinds of hair, thick fish maw two hair method can be, and thin fish maw, hair easy to rot, or oil hair is better.

1. oil hair: yellow fish maw, turtle fish maw and other small fish maw should use oil hair. First use warm water to wash and drain the fish maw, and then put into the warm oil pot to fry, the oil should be kept at a low temperature in order to ensure the quality of frying, frying do not fry burnt yellow, outside of the caramelized impermeable, when the fish maw frying to the hand of a folded break, the broken surface, such as spongy, can be fished out, but pay attention to fish maw due to the thickness of the thickness is not the same, will not be at the same time frying, the hair of a good to be the first to be fished out, so as to avoid overcooking. Yellow lip belly, hair often belly, sturgeon belly and other large and thick, oil hair, first fish belly in a low-temperature frying pan in the Chinese fire simmering for 1-2 hours, see the fish belly soft, and then use a more vigorous fire to raise the oil temperature, and constantly turning, until the fish belly bloated big enough to date. But the fire can not be too strong, otherwise, it is easy to cause the outside of the scorched inside impermeable;

2. water hair: first soak the fish maw in water for a few hours, and scrubbed, put into the stewing pot, add cold water to boil off the fire, to be cooled down and burned again, burned two or three times a day, two days after taking out, soak in water to be used.

Soak the fish maw, do not contact the water with boiled shrimp, crab, so as not to stain the odor.