(A) Inset: Head of a larval zebrafish. Image of RS labeling is overlaid in approximate location. Schematic of RS neurons in the mid and hindbrain labeled by spinal backfill with large nMLF neurons (red) and control ablation neurons (blue) (either a subset of RoM neurons from the 2nd and 3rd rhombomeres or the Mauthner cells). Scale bar 50 μm. (B) Maximum intensity z-projection of image stacks taken of the nMLF before and 4 hours post-ablation. Targeted cells are indicated by red dot. Scale bar 25 μm. (C) Histogram of the probabilities of various kinematic parameters of swimming occurring before (grey; 17 larvae; 1506 bouts), and after (red; same larvae; 806 bouts) ablation of the nMLF. From left to right: the bout duration (ms), the maximum TBF (Hz), the bout distance (mm), and the bout speed (mm/s). The cumulative distribution functions pre and post-ablation are plotted in the upper right. The distributions of the two histograms are significantly different in all cases (KS test, p<0.05 (single asterisk) or p<0.01 (double asterisk)). (D) Histogram of swimming speed before (grey; 10 larvae; 1364 bouts), and after (blue; same larvae; 1012 bouts) ablation of control neurons for the same kinematic parameters. The cumulative distribution functions pre and post-ablation are plotted in the upper right and are not significantly different in any case.