Fig. 1. The shadow response is elicited by shading 1.5 d.p.f. surface fish (A–D), Pachón cavefish (E–H), and Tinaja cavefish (I–L) larvae. Each frame shows an individual assay chamber. Video recordings were made through the side of the chambers at 0.05 s intervals for a total of 5 s. Examples of frames are shown at 0 s (A,E,I), 1.0 s (B,F,J), and 5.0 s (C,G,K). (D,H,L) Merged frames of all images from 0 to 5.0 s. Before shading (0 s), larvae were located at the bottom of the assay chambers. During shading (1.0 to 5.0 s) most larvae swam upwards until they reached the surface of the water. Scale bar, 1 cm.