One: 1 The elevation of the fish does not depend on the swim bladder, which can only control the specific gravity of the fish so that the fish stays in a certain layer of water. The pectoral and ventral fins in the even fins control the balance, while the dorsal and anal fins in the odd fins keep the balance. The caudal fin is used to control direction, and the fish consumes the least amount of energy while in the water, in a stationary or semi-stationary state. The swim bladder then plays a role in keeping the fish balanced when it is at rest. The dorsal and ventral fins ensure that the fish is in a vertical line. The lines on the sides are the balance detectors, and the spine is the center of gravity balance point that runs the length of the body to form a flat horizontal line. When the fish is at rest or semi-still in the water, the pectoral fins are the main source of up and down movement. The swim bladder keeps the body balanced and does not cause the fish to sink because it is at rest. The buoyancy produced by the swim bladder exactly counteracts the force of gravity, thus allowing the fish to freely control its body at a certain water level when it is at rest.

2The 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's body and the spatial structure of the abdominal cavity, so that buoyancy is generated at various points of the fish's body to counteract the gravity 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 can bend quickly with the rapid deformation of the fish body to achieve rapid body balance without causing the fish to turn sideways.

3The size of the swim bladder varies with the age of the fish. The air pressure inside the same fish is the same. When the fish dives, the swim bladder muscle will contract, the space becomes smaller and the air pressure becomes bigger to offset the water pressure. When the fish surfaces, the water pressure becomes less, the swim bladder muscle relaxes, the space becomes larger, and the air pressure becomes less. Therefore, the swim bladder muscle controls the amount of pressure on the swim bladder and determines the different waters where different fish species live. 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 be active in shallow water (sea).

4Chondrichthyes do not have swim bladders, so they can't keep their bodies still and have to keep swimming to keep their balance. Deep-sea fish have high pressure in their swim bladders, and once out of the water, the compressed gas is released, bursting the swim bladder. Once the shallow water fish is sick or dead, the equilibrium line on both sides of the fish body, the sensitivity decreases or fails, the buoyancy produced by the swim bladder is different from the center of gravity produced by the fish body, resulting in the fish body flipping upwards and the belly of the fish is facing upwards.