be either soft or hard or erect and are controlled by small muscles that have the ability to extend or fold the fins. There are generally seven fins in total. There is three single fins, the caudal fin (tail), dorsal fin (the back) and anal fin (under the back of fish near the tail). There are two types of matching fins called the pelvic (ventral on the underbelly) and the pectoral fin (under the gills). Some fish have an extra small fin on its back next to the tail called a adipose fin. The picture below shows the fins mentioned.

Some fish require fewer fins and the ones that do have will vary in shape and size between species. Fins control direction, position. The tail or Caudal fin is the engine of a fish; the dorsal and anal fin stabilizes the fish; pelvic fins are used for turning; and the pectoral fins can lift the fish and gesture to rivals.
Like the body shape of fish the size and shape of a fish fins is an indication of the environment that they live in. Larger fins and a wide tail are normally found on larger fish as these are needed to maintain a correct position in the water. Fast moving fish have smaller more streamline fins and a large crescent shaped tail to provide plenty of power. Some fish use their fins as the only source of propulsion and make no other body movement.
Other uses for fish fins are defence (white fin lionfish has venomous spins) mating and even used for a type of walking or dragging.