Fig. 3. Characteristics of the pacemaker frequency as a function of fish length. (A) Raster of the first-order intervals emitted by a resting fish of 37 mm length. Note the regularity of electric organ discharge (EOD) interval, interrupted by accelerations, followed by slower relaxations up to the basal EOD interval (arrows). (B) Histogram of the inter-EOD intervals represented in A. Note the skew of the histogram that results from the accelerations indicated by the arrows in A. (C) Box plot comparing the individual means of the EOD intervals exhibited by fish of different lengths. The first category, fish shorter than 30 mm, discharged their EO at a rate significantly lower than the others. (D) Box plot comparing the variance of the EOD intervals exhibited by fish of different lengths. The EOD was significantly more regular for the two categories above 60 mm. (E) First-order frequency polygon of the inter-EOD interval normalized to the mean interval obtained from 45 fish ranging from 12 to 226 mm, showing the constancy of the distribution.