Projections such as cteni increase friction at low speeds so a trade-off occurs. For the sake of greater burst speed, efficiency at low speed is reduced. Mucus Small amounts of long-chain, high molecular mass polymers added to water can cause a substantial reduction in frictional drag under turbulent flow conditions. Appendage drag Fins are necessary for maneuvering, generating lift and generating thrust. However, anything sticking out will create its own drag.
Most fast fish can fold their paired fins flat against the body surface.
Dorsal and anal fins may have slots into which they fold when not in use. Still, when in use , they create turbulent drag. A narrow, crescent-shaped fin ending in a point will shed a narrower vortex and thus create less drag than a broader fin. The caudal fin is responsible for most thrust. It is inefficient in the area of turbulence shed by the body, so extending it out and incising the center will provide maximum eficiency at high speeds.