Mexican blind cavefish (Astyanax mexicanus) have convergently evolved eye loss and heightened sensitivity of the lateral line system. Blind cavefish exhibit dramatic changes in lateral line-mediated behavior when compared to sighted surface fish. For the first time, we investigate the neurophysiological mechanisms of enhanced sensitivity and active-flow sensing. Electrophysiological recordings of posterior lateral line afferent neurons reveal that spontaneous activity is elevated in blind cavefish which suggest a lower threshold for lateral line signal transduction. In surface fish, like many fishes, there is an efferent system that cancels out self-generated flow stimuli during locomotion to stay receptive to biologically relevant stimuli. In contrast, cavefish do not have a fully functional efferent system because they rely on self-generate flow to navigate their environment. Afferent recordings reveal cavefish lateral line sensitivity is not modulated by efferent neurons during swimming. Targeted ablation of hindbrain efferent neurons in surface fish results in lateral line signaling similar to cavefish. Cavefish may either have functionally diminished efferent neurons or have evolved post-synaptic differences compared to surface fish. Our results suggest decreased functionality of efferent neurons. to enable active-flow sensing. has converged across three separate populations of cavefish.