The caudal fin is the tail fin, located at the end of the caudal peduncle.
The tail can be heterocercal, which means that the vertebrae extend into a larger lobe of the tail or that the tail is asymmetrical:
- Epicercal means that the upper lobe is longer (as in sharks)
- Hypocercal means that the lower lobe is longer (as in flying fish)
- Protocercal means that the caudal fin extends around the vertebral column, present in embryonic fish and hagfish. This is not to be confused with a caudal fin that has fused with the dorsal and anal fins to form a contiguous fin.
- Diphycercal refers to the special, three-lobed caudal fin of the coelacanth and lungfish where the vertebrae extend all the way to the end of the tail.
- Most fish have a homocercal tail, where the vertebrae do not extend into a lobe and the fin is more or less symmetrical. This can be expressed in a variety of shapes.
- The tail fin may be rounded at the end.
- The tail fin may be truncated, or end in a more-or-less vertical edge (such as in salmon).
- The fin may be forked, or end in two prongs.
- The tail fin may be emarginate, or with a slight inward curve.
- The tail fin may be lunate, or shaped like a crescent moon.