Hydrodynamic imaging by blind Mexican cave fish (Astyanax fasciatus)

Abstract

Blind Mexican cave fish (Astyanax fasciatus) lack a functioning visual system, and are known to use self-generated water motion to sense their surroundings; an ability termed hydrodynamic imaging. Nearby objects distort the flow field created by the motion of the fish. These flow distortions are sensed by the mechanosensory lateral line. Little is known about the fluid mechanics involved in hydrodynamic imaging. We used automated image analysis to measure the swimming kinematics of the fish when introduced into a novel environment. In a separate experiment the flow fields around freely swimming fish were experimentally measured using Particle Image Velocimetry (PIV) in the same situations. We also created a series of computational fluid dynamic (CFD) models. In the kinematics experiments, the fish altered their swimming when following walls and their ability to detect surfaces was reduced when they were beating their tails. The fish reacted to avoid head-on collisions with a wall at a remarkably short mean distance of 0.09 ± 0.01 body lengths (BL). This agreed with the PIV and CFD results, where the stimulus to the lateral line was estimated to be sufficient for the fish to be able to detect the wall at 0.10 BL, but decreased rapidly at increasing distances. The combined results of these three methods showed that hydrodynamic imaging is a short range sensory ability and that the fish change their swimming kinematics depending on their surroundings.