Fish fins are typically composed of bony spines or rays protruding from the body, with skin covering them and joining them together. They either end up in a webbed fashion as seen in most bony fish, or a flipper as seen in cartilaginous fish like sharks.
Then there’s the fleshy, lobed, paired fins joined to the body by a single bone, found in this class of bony fish called Sarcopterygii.
The key function of fins is to help the fish balance and turn as it swims. Here are the different types of fins typically found on a fish:
Fins located at different parts of the fish serve different purposes:
Protects the fish against rolling, and assists in sudden turns and stops. Most fish have one dorsal fin, but some have up to three.
Ventral (pelvic) fins
Comes in a pair, assists with moving up or down through the water, turning sharply, and stopping quickly.
Caudal (tail) fin
The main propelling fin in most fish
Helps to maintain stable equilibrium
A pair of fins used for balancing and braking.
Scientists do not have a definitive answer for the purpose of the adipose fin. Some said it serves as a pre-caudal flow sensor.
Different fish, different fins
Not every fish has all the above fins. Depending on their body structure, nature has equipped them with different combinations of fins to help them swim efficiently.
Other uses for fins
While most fish use fins when swimming, there are some that use their fins for rather different purposes. Such as the flying fish which use their pectoral fins for gliding, and the frogfish and epaulette shark that use theirs for ‘walking’. In species like gobies and lumpsuckers, their pelvic fins are fused into a sucker disk which they use to attach themselves to objects.
The lumpsucker’s pelvic fins have evolved into adhesive discs on their undersides.
Epaulette sharks use their pectoral fins as prototype legs to ‘walk’ from one tide pool to another.
The next time you’re at S.E.A. Aquarium, don’t forget to take a closer look at their fins.