A new species of the genus Trichomycterus is described from the rio Uruguai drainage, Rio Grande do Sol State, Brazil, with a single paratype from the rio Paranapanema basin, São Paulo State. Both rivers are tributaries within the rio Paraná watershed.

Trichomycterus perkos is named from the Greek ‘perkos’ (περκὸς), meaning ‘spotted or streaked with black marks’ in allusion to its colour pattern comprising dark stripes in smaller individuals and a combination of dark stripes and spots in larger specimens.

The genus is diverse, representing almost 60% of the 250+ species currently recognised in the family Trichomycteridae, but poorly-diagnosed and probably polyphyletic. Most members are small and inhabit fast-flowing water, and T. perkosis diagnosed by the following combination of characters: large-sized specimens (more than 65.8 mm SL), presumably adults, are distinguished from congeners in having a distinctive coloration with melanophores arranged in two distinct skin layers, forming (1) a freckled pattern, with minute light brown spots scattered on the superficial tegumentar layer of the dorsum and caudal peduncle, and (2) a striped pattern, with three – sagittal, midlateral, and ventrolateral– wide, irregularly bordered, and sometimes interrupted dark brown stripes running along an inner skin layer of the trunk and caudal peduncle. Smaller individuals (less than 43.3 mm SL), presumably juveniles, lack the superficial freckled pattern, but already exhibit the three wide dark stripes found in the adults.

The new species also differs from congeners in various morphological characters.

For further information see the paper: Datovo, A., M. Carvalho, and J. Ferrer. 2012. A new species of the catfish genus Trichomycterus from the La Plata River basin, southern Brazil, with comments on its putative phylogenetic position (Siluriformes: Trichomycteridae). Zootaxa 3327: 33-44, of which the abstract is available here.