1. swim bladder: Similar to a balloon, the buoyancy can be adjusted by controlling the air volume.

2. Fishtail: By swinging from side to side, the reaction force of water can be obtained. The fishtail can also control the direction.

3. Sideline: Induce the magnetic field and determine the direction.

4. Streamlined shape: reduce water resistance.

5. Fish gills: It can filter oxygen in water.

6. Fish scales: there is synovial fluid on it, which has small resistance and plays a protective role.