When the fish swims, the tail fin swings left and right to push the fish forward. When the fish is not moving, the pectoral fin opens to both sides of the fish. When the fish moves forward, it swings back and forth. When the fish turns, one side of the pectoral fin swings. The ventral fin swings slightly to both sides to keep the fish stable, and the dorsal fin is used to keep balance. How do the fins of various parts move when a fish swims? Usually, when swimming slowly, the pectoral fin of the fish can paddle like a boat paddle, while when swimming at high speed, the fish will stick the pectoral fin close to the body, and can slow down and brake at critical moments.
The dorsal fin can keep the fish sideways. Without it, the fish will roll over. There are also some fish with long body, whose dorsal fin can provide power, such as hairtail, sea eel, hippocampus, etc.
The caudal fin of fish can determine the direction of movement and provide power. Fish without caudal fin can only swim in one direction in a lifetime. Different fish have different shapes of caudal fins, some have only one leaf, some have upper and lower leaves. （YuYouDongShiGeBuWeiDeQiShiZenMeDongDe）