Swimming and turning behaviors of larval zebrafish have been described kinematically, but prey capture behaviors are less well characterized. High-speed digital imaging was used to record the axial kinematics of larval zebrafish as they preyed upon paramecia and also during other types of swimming. In all types of swim bouts, a series of traveling waves of bending is observed and these bends propagate along the trunk in the rostral to caudal direction. The prey capture swim bouts appeared to be more complex than other swim patterns examined. In the capture swim bouts, the initial bends were of low amplitude and were most prominent at far-caudal locations during each individual traveling wave of bending. Later bends in the bout (occurring just prior to prey capture) appeared to originate more rostrally and were of larger amplitude. These changes in bending pattern during capture swims were accompanied by a marked increase in tail-beat frequency. Associated with these axial kinematics were changes in heading and an abrupt increase in velocity close to the moment of prey capture. These changing patterns of bending suggest precise, bend-to-bend, neural control over both the timing and the rostral-caudal locus of bending. This degree of ‘fine axial motor control’ has not previously been described in the teleost behavioral literature and is notable because it occurs in larval zebrafish, where descending control signals are funneled through the roughly three-hundred neurons that project from brain into spinal cord. These findings will necessitate a significant increase in the complexity of current models of descending motor control in fishes.

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Larval zebrafish exhibit a variety of complex undulatory swimming patterns. This repertoire is controlled by the 300 neurons projecting from brain into spinal cord. Understanding how descending control signals shape the output of spinal circuits, however, is nontrivial. We have therefore developed a segmental oscillator model (using NEURON) to investigate this system. We found that adjusting the strength of NMDA and glycinergic synapses enabled the generation of oscillation (tail-beat) frequencies over the range exhibited in different larval swim patterns. In addition, we developed a kinematic model to visualize the more complex axial bending patterns used during prey capture.