Fig. 4. Histograms presenting the numbers of responsive and non-responsive juvenile roach (2.5 cm) in the rarefaction and compression half of the test chamber, respectively. The frequency of the initial half-cycle of the acceleration was about 6.7 Hz, and the stimulus level was approximately 15 dB above response threshold in all trials. The fish mainly responded to the combination of linear acceleration and a pressure increase. Blocking of the lateral line system by adding 0.1 mmol l^–1 Co²⁺ to the water (Co²⁺ water) did not significantly change the observed response patterns. The escape responses (see Fig. 2) were therefore triggered by stimulation of the inner ear.