Fish fins are found on the exterior of the body of the fish, and usually function as limbs or supports to aid the fish in terms of buoyancy and movement.

Fish have between five and seven fins which can be paired or unpaired. Paired fins are found away from the lateral line (central line) of the fish, whereas unpaired fins are usually found along this line.

Each of the fins has a different name and purpose, although they all work together to enable movement. In addition, the function of the fins can change depending on the species of fish.

  • Pectoral fins. These are paired fins.
  • Pelvic fins. These are paired fins.
  • Dorsal fin. This is an unpaired fin.
  • Anal fin. This is an unpaired fin.
  • Caudal fin. This is an unpaired fin.

Pectoral fins

This pair of fins is also known as the arm fins, as the placement is remarkably like the arms, upper body limbs, on a human. The primary function of the pectoral fins is to act as a brake and enable fast changes in the direction a fish is travelling and the speed at which they are travelling.
The pectoral fins also help fish to maintain the depth at which they are swimming enabling the fish to stay submerged at their required depth. The pectoral fins also function as an aid to assist flight in flying fish, due to the unique structure of these fins.

Pelvic fins

Pelvic fins also known as belly fins are located below the pectoral fins and their function is to aid the fish in swimming up and down. They also allow for sharp turns to be taken with ease as well as assisting the fish with braking.
This pair of fins helps to stabilise the fish’s movement allowing them to manoeuvre easily around obstacles.

Dorsal fins

The dorsal fin is also known as the spinal fin, due to its location along the spine of the fish.
A fish may possess up to three dorsal fins which may run in line with each other, either connected or unconnected along the spine.
The main purpose of the dorsal fin or fins is to assist with and maintain buoyancy within the water. This prevents and protects the fish from rolling over and allows the fish to remain the right way up.
An additional function of the dorsal fin is to assist the fish in sudden sharp turns and braking.

Anal fins

The anal fin is also known as the cloacal fin and is located behind the anus of the fish, hence the name. the primary function of the anal fin is to stabilize the swimming of the fish and to assist the fish in moving forwards, this is also known as propulsion.

Caudal fins

This fin is also known as the tail fin and is located at the end of the fish’s spine or body. There are four types of caudal fin, and they are categorised by their visual appearance.

  • Heterocercal: – this is where the spine of the fish continues along the top of the tail making the upper portion of the tail longer than the lower part of the tail, this results in the tail being asymmetrical in appearance.
  • Protocercal: – this is where the spine ends at the tip of the tail resulting in the tail being a pointed end.
  • Homocercal: – this is a symmetrical shaped tail, this type of tail can be either rounded, pointed or semi-circled in shape. This is all dependent on the species of fish.
  • Diphycercal: – the spine for this tail ends at the tip of the tail. However, this tail is symmetrical and expanded, so the tail fin fans out.

The tail fin allows for the fish to move forwards and helps with the direction which the fish wants to travel.