The escape response to a touch stimulus is impaired in arnt2-/- larvae at 120 hpf. When touched on the head a representative WT larva instantly reacts by swimming rapidly away from the mounted probe (top). The same brisk escape response is observed in the WT larva when touched on the tail (results not shown). In contrast, a representative arnt2-/- larva at 120 hpf shows either a very weak response when touched on the tail (middle) or no response when touched on the head (bottom). The video images were recorded at 1 frame/0.07 s after the larva was touched. Results are representative of n=6 WT or arnt2-/- larvae.