Fishes often exhibit stable body undulating in body and caudal fin (BCF) mode during cyclic swimming, but can perform remarkable maneuverability with significantly different swimming modes in case of C-start. Aiming at unveiling the mechanisms of swimming hydrodynamics and maneuverability of C-start, we have developed an integrated computational framework to model a free-swimming larval zebrafish (Danio rerio) by coupling the equations of 3DoF (Degrees of Freedom) motion and Navier-Stokes (NS) equations. Unsteady hydrodynamics is resolved by integrating models of realistic fin-body morphology and body-undulatory kinematics with an in-house NS solver. The instantaneous forces and moments on the body provided by the NS-solutions serve as input for 3DoF equations of motion. In this study, with a specific focus on a C- start as well as a subsequent transient phase till the cyclic swimming phase, we construct a larval zebrafish model, which can mimics realistic body motions and deformations based on measurements. Validation of the simulation is discussed by comparing model predictions with experimental measurements, which indicates that the present integrated model is capable to accurately predict free-swimming dynamics and hydrodynamics. The model successfully simulated a swimming bout of C-start and cyclic swimming: a wake topology of double row vortex ring structures is observed behind the fish; and a strong jet is visible at the center of the vortex ring, pushing water backward as the fish accelerates.

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