Abstract
The genus Pseudacanthicus comprises five valid species distributed in the Amazon, Guyana and Suriname basins: P. serratus, P. fordii, P. histrix, P. spinosus and P. leopardus. A new species of Pseudacanthicus from the Tocantins river basin is described. The new species is distinguished from its congeners by the following combination of characters: presence of dark blotches anostomosing to form continuous zigzag bands alongside longitudinal keels; absence of blotches on ventral surface of body; faint blotches on head; all fins with orange to red color on unbranched ray and sometimes on subsequent branched rays; and sphenotic and sixth infraorbital not in contact. Brief comments on the phylogeny of the genus, ornamental fisheries activities, threats and conservation of the new species are also provided.