WARD, A.B.; AZIZI, E: Kinematics of the Startle Response in Elongate Fishes and Amphibians

Escape responses in fishes have typically been described as C-starts which are characterized by two kinematic stages: a rapid unilateral bend occurs in stage one and a propulsive wave is passed in stage two. Our observations indicate that, when startled, elongate fishes and amphibians do not perform a typical C-start. Instead, their startle response is a production of multiple waves on the body that causes a rapid posterior retraction of the head. This accordian-like movement is likely a result of bilateral muscle activation. High-speed video was used to describe the kinematics of this head retraction behavior in five species of fishes: (Anguilla rostrata, Gymnothorax polyuranodon, Macrognathus circumcinctus, and Mastacembelus siamensis, Petromyzon marinus), two species of salamanders (Amphiuma tridactylum, Siren lacertina), and one species of caecilian (Typhlonectes natans). One key feature of the head retraction startle behavior is the lack of a propulsive phase (stage 2). Since propulsive waves are not passed down the body, no anterior movement of the head occurs. Whereas C-starts typically include a large lateral deflection of the head, relatively smaller changes in head angle occur during head retraction startle behavior. Preliminary results indicate that the maximum velocity of the head during head retraction startle behavior is within the range of velocities reported for C-starts in similarly sized fish. This descriptive kinematic study will serve as a first step for understanding the neural mechanism, motor pattern, biomechanics, and evolution of the aquatic startle response of elongate fishes and amphibians. This work was supported by NSF IBN 9875245.