Three species of Ergasilus Nordmann, 1832 are reported from the gills of Salminus spp. in Brazil. Ergasilus salmini Thatcher & Brazil-Sato, 2008 from Salminus brasiliensis Cuvier is redescribed, based on examination of paratypes. The study revealed morphological differences from the original description, especially in the morphology of the cephalothorax and the ornamentation of antenna, antennule and legs. Ergasilus lacusauratus n. sp. described from S. brasiliensis in lake Lagoa Dourada (Paraná) differs from the only known species from this host group, E. salmini, in the shape and size of the cephalothorax and the general morphology of the egg-sacs. Ergasilus sinefalcatus n. sp. from S. franciscanus Lima & Britsky in River São Francisco (Minas Gerais) closely resembles E. pitalicus, E. coatiarus and E. leporinidis in the lack of a pectinate seta on the first exopodal segment, a feature common in species of Ergasilus in the Neotropics. Ergasilus sinefalcatus n. sp. differs from these species in the presence of a spiniform process on the coxae of legs 2, 3 and 4, an ornament never reported from freshwater species of Ergasilus in South America.