Regression analysis of log10 upper and lower caudal lobe area (whole ‘uncropped’ caudals) against log10 standard length for ten prey species of the piranha showed significant differences in both slope and intercept for only one species (Astyanax fasciatus) although intercepts alone were significantly different for two others (A. bimaculatus and Poecilia vivipara). Caudal lobe — standard length regression statistics were used to generate estimates of caudal lobe loss in cropped prey species and these clearly demonstrated highly significant differential cropping incidences in several species and size categories. Particularly in the Astyanax species, the upper caudal lobe was subject to low cropping loss and the lower caudal lobe to high cropping loss. Differential cropping of caudal fin lobes suggests that piranha initiate their attack from below and behind prey fishes.