Flow field, swimming velocity and boundary layer: parameters which affect the stimulus for the lateral line organ in blind fish.

The data presented support the hypothesis that the flow field supplies the stimulus to the lateral line organ (LLO) in blind cave fish (Anoptichthys jordani). Two basic predictions from the theoretical analysis of the flow field were confirmed: (i) individual blind cave fish prefer particular swimming velocities, (ii) the velocity preferred depends on the cross-sectional area (CSA) of the fish, i.e. the smaller the CSA the higher the swimming velocity. This relationship was found also in experimentally blinded fish of other species. Furthermore, when placed in unfamiliar surroundings, blind cave fish swim at higher velocities than in familiar surroundings for a certain habituation period. The boundary layer which surrounds the fish attenuates the amplitude of the hydrodynamic stimulus because of its damping properties. Computations of the current velocity distribution within the boundary layer indicate that the stimulus for freestanding neuromasts is considerable even during swimming in open water.