Ward, A.B. and E. Azizi
Escape responses in fishes have typically been described as C-starts that 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 retraction of the head. High-speed video was used to describe the kinematics of this head retraction startle behavior in five species of fishes: (Anguilla rostrata, Gymnothorax polyuranodon, Macrognathus siamensis, Mastacembelus armatus, and Petromyzon marinus), three species of amphibians (Amphiuma tridactylum, Siren intermedia, and Typhlonectes natans). One key feature of the head retraction behavior is the lack of a propulsive phase (stage 2). In addition, whereas C-starts include a large lateral deflection of the head, relatively smaller changes in head angle occur during head retraction. Phylogenetic analysis of escape behaviors in aquatic vertebrates suggests that head retraction has evolved independently numerous times. This study will serve as a first step for understanding the neural mechanisms, motor patterns, biomechanics, and evolution of the aquatic startle response of elongate fishes and amphibians.
Ecology & Evolutionary Biology - Brown University