A finlet is a small, detached ray or fin found in certain fishes, such as mackerels and tunas. These small, non-retractable fins are located on the dorsal and ventral sides of the fish's body, typically between the main dorsal or anal fin and the caudal (tail) fin. Finlets are generally rayless and serve hydrodynamic functions, potentially reducing drag and modulating flow around the fish's body to enhance swimming efficiency. They do not produce thrust but help in reducing drag and improving maneuverability in fast-swimming fish like scombrids (mackerels, tunas, and bonitos).
Finlets are specialized fins that contribute to the impressive locomotion capabilities of these fishes by affecting the water flow and possibly assisting in controlling turbulence near the tail region.
