This study evaluated the ectoparasite distribution on the gill archs of pond-reared pacu (Piaractus mesopotamicusHolmberg, 1887), hybrid patinga (P. mesopotamicusfemale x P. brachypomus(Cuvier, 1817) male), hybrid tambacu (Colossoma macropomum(Cuvier, 1816) female x P. mesopotamicus male) and hybrid surubim (Pseudoplatystoma reticulatumfemale x P. corruscansSpix & Agassiz, 1829 male). Atotal of 300 fish were examined from fish farms in West-Central Brazil for parasitological assessment of the gill arches I, II, III and IV, from the outer to inner arch, respectively. Only the monogenean Mymarothecium boegeriCohen & Kohn, 2005 and Anacanthorus penilabiatusBoeger, Husak & Martins, 1995 from the hybrid patinga showed the greatest (p<0.05) mean intensities on the gill arch I when compared to gill arch IV. Microhabitat preference was not observed in the other fish examined. Cope...