The caudal fin is a fin located on the tail of many aquatic animals: non-pinnipeds, fish, some marine mammals (cetaceans and sirens), as well as some extinct marine reptiles. Its shape is closely related to the type of movement.

According to the size ratio of the upper and lower blades, caudal fins can be epi-, hypo-, and isobathic (cercal). In the epibat (epicercal) type, the upper blade is longer (sharks, sturgeons); in the hypobat (hypocercal) type, the upper blade is shorter; in the isobat (isocercal) type, both blades are of the same length (herring, tuna).

Hypobate type of tail fin - belongs to fish with a lower tail fin blade longer than the upper one (flying fish, Czechoslovak).