Fish Fins


January 14, 2018 by katerinazapfe, posted in Animals, Fins, Fish, Future Frogmen, Marine Science

Far from the heavily stylized, square-tailed fish that we learn in our younger years, fish actually display a plethora of odd shapes. Fins are one of the main drivers behind locomotion in water, whether it be expansive open ocean, sandy bottoms, or rocky reef crevices. But first, lets step back. Fish don’t possess just a few fins, they have seven: one dorsal (down the back), two pectoral (one on each side), two pelvic (both mid bottom), one anal (back bottom), and of course the caudal (tail) fin. Each fin contributes to a fish’s ability to successfully survive and navigate its environment. Considering the myriad of ocean environments and challenges, fin morphology has diversified into quite a spread to match.

Locomotion in water is a challenge. We as humans enjoy the ocean and do our best with specially designed swimming enhancements, but ask any snorkeler or diver and they will agree hands down that fish seem to effortlessly glide, almost fly through the water. In fact, swimming can be likened to flight, with studies showing strong parallels between optimum aspect ratios and incidence angles for efficient forward motion. A fish’s fins not only move it forward, but help keep it from sinking or floating in the process. C shaped caudal fins are optimized for bursts of speed and are characteristic of open water predators like marlin, tuna, swordfish and sailfish. Deeply forked tails, such as pompano or permit fish (image: top right) are useful for more relaxed, but still faster swimming speeds. Rounded fins allow for very short bursts and are excellent for maneuverability. Schooling fish, like Sergeant major (image: top left) use their pectorals while in groups, but can dart quickly when needed thanks to a rounded fork caudal shape. Rounded fins like those of the pinkbar goby (image: top right) help the fish burrow in the sand and are suited for a slower, bottom-dwelling lifestyle.

Fin shape can also help a fish be competitive in complex habitats, such as reef rubble. Many reef fish sport rounded fins necessary for quick turns, diving for shelter and hovering in currents. This ability to turn both quickly and sharply allows for evasive maneuvers and effectively takes advantage of any available cover. Wrasse and butterflyfish (image: bottom left) often use this method. Some fish have taken crevice hiding even further. Triggerfish are named for their ‘trigger’ or spine just before the dorsal fin that flips up when the fish finds a hide. This spine is raised and wedges the head end of the fish in a crevice, making it impossible to remove the fish. Such fin adaptations serve as defense mechanisms for dire situations.

Other significant fin alterations include the famous flying fish, which ‘flies’ upon large pectoral fins in an effort to leave the water for extended glides when danger is near, and the so-ugly-it’s-cute frogfish which waddles across the seafloor on pectorals modified to tripod the fish off the bottom. Its fin rays even resemble fingers!

Another common use for dramatic fin modifications, often rivaling locomotion in impressiveness, is signaling. High dorsal fins, filaments, embellishments and dramatic color all help signal (or remain inconspicuous) to both mates, rivals, and predators. Warning colorations and mating displays can be worn as needed when located on a fin surface, since many fish can raise their soft-spined dorsal section or flair their pectoral fins, flashing a color signal at will. In such a competitive ocean environment, taking advantage of fin modifications has repeatedly honed fish species’ fitness, creating both beautiful and strange morphologies across the marine fish tree of diversity.


Richard Hyman