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Adaptations of Fish Fins

Fish use fins principally for movement through water. Fins are also used for resting on and for display purposes. The highly modified dorsal fin of a triggerfish is used to lock the fish into a crevasse when it rests at night. The caudal or tail fin of a fish is typically the largest and is used for forward movement. The dorsal or top fins and the anal fins underneath the fish are used for lateral stability. Pectoral fins, which are positioned behind the operculum or gill covers, are used for hovering and turning. The powerful, open water species have relatively small pelvic fins, while bottom dwellers normally possess much larger pelvic fins.

Modified Fin Rays
- These fish from the Indo-West Pacific possess a hard, modified dorsal fin, which can be raised and lowered at will. The fish raises this trigger mechanism to prevent itself from being swallowed by a much larger predator. The triggerfish also uses the modified fin to lock itself into a cave or similar safe place when it rests or sleeps. When the trigger is raised, an expanding ventral flap supported by a large movable pelvic bone is lowered to help wedge the fish tightly into place. Triggerfish swim by undulating their soft dorsal and ventral fins and use their pectoral or side fins for precision manoeuvres. Unlike many other species of coral fish, members in this family can reverse with ease.
Venom Glands for Protection
- The hard fin rays of select species have venom glands at their base. Venom glands are typically associated with the dorsal, pelvic and anal fins in these species. The venom produced by the stonefish can be fatal in humans. It is denatured by heat, and the victim's life can be saved by immersing the affected hand or foot into extremely hot water. Water should be at least 113 degrees F and immersion should last from 30 to 90 minutes. The lionfish and scorpionfish also possess venom glands at the base of their hollow fin rays, but venom from these species is rarely fatal to humans.
Fins for Flying
- Flying fish possess extremely long pectoral fins, which are an adaptation that allows these species to glide over the ocean surface for a distance of 492 feet. Flying fish can remain airborne for up to 20 seconds.
Fins for Resting and Walking
- Hawkfish use their pectoral fins to rest or perch on coral rubble or similar reef structures, while mudskippers use their pectoral fins to support themselves and to move about on the wet mud flats of mangrove swamps.
Fins for Tasting and for Catching Prey
- The bottom-dwelling threadfins have modified pectoral fins, which include touch receptors and taste buds with which they source nourishment. The anglerfish possesses a lure at the tip of its dorsal fin, which is used to attract potential prey.

Animals & Science