BIERMAN, HS; SCHRIEFER, JE; HALE, ME; Univ. of Chicago; Univ. of Chicago; Univ. of Chicago: Head and tail retraction in startle behaviors of the bichir Erpetoichthys.

Startle response behaviors and motor patterns vary markedly among fish species and with the type of stimulus eliciting the response. The family Polypteridae (the bichirs) is an excellent group in which to explore startle response diversity because the group demonstrates a range of startle behaviors despite sharing basic features of the locomotor system (e.g. similar skin and fin morphology) among species. We examined the elongate polypterid species Erpetoichthys calabaricus for comparison to data from previously examined Polypterus species with less elongate morphology. We recorded high-speed video (250Hz) of the fish from ventral view. EMGs were recorded from 12 electrodes, six distributed along each side of the body. Kinematics and EMGs were synchronized to examine the relationship between motor pattern and movements. Fish were startled by lightly pinching the tip of the snout or the caudal fin. We found that Erpetoichthys does not perform C-start behavior. Instead it increases bending at pre-existing body bends when startled at the head as in other elongate species. Similarly, retraction also occurred in response to tail stimuli instead of either S-start or C-start responses. The retraction of head and tail (combined distance moved by tail tip and snout) was greater in response to tail stimuli than to head stimuli. Proportionately, the region on the body stimulated accounted for most of the total retraction. While retraction movement constituted the entire response to head stimuli, retraction was followed by propulsive movements when the tail was stimulated. These data indicate that retraction can function alone or as the first stage of a propulsive response and demonstrate that C-start and retraction behaviors can occur in closely related species.