Active wall following by Mexican blind cavefish (Astyanax mexicanus)

When introduced into a novel environment that limits or prevents vision, a variety of species including Mexican blind cavefish (Astyanax mexicanus) exhibit wall-following behaviors. It is often assumed that wall following serves an exploratory function, but this assertion remains untested against alternative artifactual explanations. Here, we test whether wall following by cavefish is a purposeful behavior in which fish actively maintain a close relationship with the wall, or an artifactual consequence of being enclosed in a small concave arena, in which fish turn slightly to avoid the wall whenever it impedes forward movement. Wall-following abilities of fish were tested in a large, goggle-shaped arena, where forward motion along the convex wall was unimpeded. In this circumstance, cavefish continued to follow the wall at frequencies significantly above chance levels. Lateral line inactivation significantly reduced the ability of fish to follow convex, but not concave or straight, walls. Wall-following abilities of normal fish decreased with decreasing radius of wall convex curvature. Our results demonstrate that cavefish actively follow walls of varying contours. Radius-of-curvature effects coupled with the difficulties posed by convex walls to lateral line-deprived fish suggest a partially complementary use of tactile and lateral line information to regulate distance from the wall.