subcarangiform

Subcarangiform locomotion is a mode of aquatic locomotion used by many ray-finned fishes (teleosts) in which propulsion is produced by undulatory waves that travel along the body, but are largely confined to the posterior portion of the body. The term describes a middle ground between anguilliform locomotion, in which the entire body undulates, and carangiform locomotion, where movement is restricted mainly to the tail region.

Kinematics and mechanics: In subcarangiform swimming, a lateral wave originates near the midbody or posterior trunk and propagates toward the tail. The anterior trunk remains relatively stiff, while the posterior body and caudal region flex with increasing amplitude toward the tail. The caudal fin is the principal source of thrust, though the dorsal and anal fins can contribute to stability and minor propulsion. The undulation frequency and wavelength adapt with swimming speed.

Functional implications: This mode offers a balance between flexibility and control, enabling efficient propulsion at moderate speeds and good maneuverability. It is versatile across ecological niches, from cruising to rapid bursts, and allows stable locomotion in a range of flow conditions.

Variation and context: Subcarangiform locomotion is one of several locomotor categories used to describe fish propulsion; others include anguilliform, carangiform, and ostraciform. Some species can transition along this spectrum with speed or environmental demands, showing more posterior undulation at higher speeds and more extensive body bending at lower speeds.