THE JOURNAL OF EXPERIMENTAL BIOLOGY
The neural basis of behavioral choice in vertebrates emains largely unknown. Zebrafish larvae have a defined comotor repertoire as well as a simple nervous system and are therefore an attractive vertebrate system in which study this process. Here we describe a high-throughput system for quantifying the kinematics of motor events in zebrafish larvae in order to measure the initiation requency of different maneuvers. We use this system to analyze responses to photic stimuli and find that larvae respond to changes in illumination with both acute responses and extended behavioral programs. Reductions in illumination elicit large angle turns, distinct from startle responses, which orient larvae toward the source of light. In continuing darkness, larvae are transiently hyperactive before adopting a quiescent state. Indeed, locomotor activity is controlled by the state of light or dark adaptation similar to masking phenomena in higher vertebrates where light directly regulates motor activity. We propose that regulation of motor activity by photic stimuli in zebrafish larvae serves a behavioral goal of maximizing exposure to well lit environments optimal for feeding.