The pectoral fins are the two fins located on the sides of a fish (or marine mammal). These fins are primarily responsible for control of directional movement, up and down or side to side. Pectoral fins can come in all shapes and sizes which fill different functions for different fish. The pectoral fins of a Coelacanth (Latimeria chalumnae) have a wide range of motion and are capable of “sculling” like the oar of a boat. These specialized pectoral fins are useful for making small correction movements to maintain a Coelacanth’s position, hovering just off the ocean floor. The pectoral fins for Bluefin Tuna (Thunnus thynnus) are retractable; they fit into slots so that when they are retracted, they are flush with the side of the fish.
For a fast-moving fish in open oceans where it doesn’t often have to change direction quickly, this feature is highly efficient – it reduces drag and saves energy. Some flatfish, like the Hogchoker (Achirus fasciatus), lose their pectoral fins all together. Their highly derived body shape and life history eliminates the traditional role for pectoral fins. (fishionary.fisheries.org/pectoral-fins)
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