Trichodinids are the most common ectoparasites of both freshwater and marine fishes. Their generic identification is relatively easy, while the specific diagnosis is laborious due to the high intraspecific variability of some species. Four species of the genus Trichodina from the skin and fins of Oreochromis niloticus (Linnaeus, 1758) Egyptian black variety were identified by means of morphological methods and the use of digital correlation invariant to position, rotation and scale by species specific composite filters. Trichodina magna Van As Bassson, 1989 and Trichodina nigra Lom, 1961 represent new records of host and geographic location, while Trichodina centrostrigata Van As, Basson & Van As, 1998 and Trichodina heterodentata Duncan, 1977, have already been reported for O. niloticus in Mexico. The automatic identification of the four species studied was done through the developm...