The sensory basis of rheotaxis in the blind Mexican cave fish, Astyanax fasciatus

The sensory basis of rheotaxis (orientation to currents) was investigated i n the blind Mexican cave fish, Astyanax fasciatus. An unconditioned rheotac tic response to uniform velocity flows was exhibited, with a threshold of l ess than 3 cm s(-1). Disabling the entire lateral line or the superficial n euromast receptor class increased the rheotactic threshold to greater than 9 cm s(-1) A pharmacological block of the lateral line canal system alone h ad no effect. These results demonstrate that the superficial lateral line s ystem controls rheotaxis at low current velocities. The effect of pairing a n odor stimulant with the water current dropped the rheotactic threshold to less than 0.4 cm s(-1). This study provides a clear behavioral role for th e superficial neuromasts where none previously existed, and also establishe s a link between the mechanosensory lateral line and olfactory systems in t he olfactory search behavior of the cave fish.