The lateral line system is not necessary for rheotaxis in the Mexican blind cavefish (Astyanax fasciatus).

Fish resist being swept downstream by swimming against a current. Mexican blind cavefish (Astyanax fasciatus) exhibit this innate behavior, rheotaxis, without the aid of vision, but it has been debated whether this ability requires sensing flow with the lateral line system. We tested the role of the lateral line by comparing swimming in a flow chamber in a group of cavefish with a compromised lateral line with a control group. Consistent with previous studies, we found that cavefish orient toward flow and more frequently swim upstream at a higher flow speed. We found that these responses to flow were indistinguishable between fish with compromised and functioning lateral line systems. Rheotaxis was also unaltered by exposing fish to varying degrees of turbulence. These results suggest that the sensing of flow is unnecessary for rheotaxis in cavefish. It appears that tactile stimuli provide a sufficient means of executing this behavior in fish and that rheotaxis may not be a major function of the lateral line system.