BullFish: Software for an automated stepwise analysis of positional and postural kinematics of zebrafish locomotion.

Zebrafish are a tractable vertebrate model for studying locomotor behavior across development. We applied BullFish, an automated tracking and gait-analysis tool that quantifies macro- and micro-parameters-speed, orientation, tail- and trunk-bend angles, body curvature, stroke symmetry, and postural changes-across ages, sizes, and arbitrary arena shapes. In targeted experiments using a dopaminergic lesion model (6-OHDA) and a fin-amputation model, BullFish binned instantaneous swimming speed and extracted kinematic metrics within each bin (tail-beat frequency and amplitude, burst duration, inter-bout interval, and turn velocity). Dopaminergic loss spared low-speed metrics but reduced high-speed tail-beat frequency and amplitude, shortened burst durations, and decreased high-acceleration bouts-implicating deficits in rapid propulsion. Fin amputation preserved high-speed bursts but altered low-speed control with fewer fine postural corrections-consistent with impaired low-force maneuvering and stability. BullFish also corrected common tracking errors from other tools and delivered consistent, stage-spanning locomotor phenotypes to improve behavioral interpretation in neurobiology and injury studies.