Generally, fish have five fins, pectoral, pelvic, anal, caudal and dorsal, but some fish have six fins, and in addition to the five mentioned above, there are lipid fins. Of course, some fish have some fin degeneration, so it looks like a missing piece. For fish, the main function of fins is to keep balance and swim.

1. Providing power: The reason why fish can swim in water depends on fins. Most fish use caudal fins to provide power, but some use dorsal fins, such as seahorses. If the fish only swims slowly, the pectoral fins can also act like oars and provide power for it.

2. Change direction: The tail fin of a fish can not only provide power, but also change the swimming direction so that it can turn in the water. If the tail fin is lost, the fish can only swim in one direction. In addition to the caudal fin, if a fish moves upstream and downstream, it also needs pelvic fins to control it.

3. Keep balance: For fish, most fins keep their body balanced so that they don't roll over or shake. No matter which fin is lost, the fish will become unstable and sway from side to side when swimming.