Meeting Abstract
The typical orientation of a neutrally buoyant fish is with the venter down and the head pointed anteriorly along the longitudinal surge axis. However various advanced teleosts will reorient the body vertically for feeding, concealment or prehension. This change in body orientation requires active movement of the fins to generate the forces necessary to overcome the stabilizing torque resulting from the relative positions of the center of gravity (CG) and center of buoyancy (CB). Furthermore, maintenance of a vertical body orientation will impact the swimming performance. The shrimpfish (Aeoliscus punctulatus) maintains a vertical orientation with the head pointed downward. This posture is the stable orientation for the shrimpfish as CB is located posterior of CG along the longitudinal axis of the body. The shrimpfish swims with dorsum of the body moving anteriorly. The body has a fusiform design with a rounded leading edge at the dorsum and tapering trailing edge at the venter. The median fins (dorsal, caudal, anal) are positioned along the venter of the body and are beat or used as a passive rudder to effect movement of the body in concert with active movements of pectoral fins. Burst swimming and turning maneuvers by rolling were recorded at 500 frames/s. Maximum burst speed and turning rate were measured at 2.3 body lengths/s and 957.5 deg/s, respectively. Although such swimming performance is below that of fish with a typical orientation, modification of the design of the body and position of the fins allows the shrimpfish to effectively swim in the head-down orientation.
