not a species from Argentina:
Imparfinis cochabambae (Fowler, 1940)

published in:
Almirón, A., J. Casciotta, J. Bechara, F. Ruíz Díaz, C. Bruno, S. D’Ambrosio, P. Solimano & P. Soneira ( 2007):
Imparfinid mishky (Siluriformes, Heptapteridae) a new species from the ríos Paraná and Uruguay basins in Argentina.
Revue suisse de Zoologie 114 (4): 817-824

abstract (from publication):
Imparfinis mishky sp.n. is described from the río Paraná and Uruguay basins in Argentina. Imparfinis mishky sp.n. is distinguished from other species of the genus by the following combination of characters: pectoral-fin spine with smooth anterior and posterior margins; caudal fin deeply forked with dorsal lobe longer than ventral lobe; adipose fin not reaching caudal fin; body with six dark saddles across the dorsum, and without a mid-lateral band. It was found inhabiting well oxygenated, neutral pH, flowing waters, with sandy or cobble covered bottom.

remarks (from publication):
p. 817: Some years ago several specimens similar to Imparfinis cochabambae (Fowler, 1940) were collected in the ríos Paraná and Uruguay basins. The study of these specimens showed that they belong to a new species described below. The genus Imparfinis includes eighteen species (Bockmann & Guazelli, 2003). Two of these species have been recorded from La Plata basin in Argentina: Imparfinis cochabambae from a single specimen taken from the río Paraná basin, and I. hollandi Haseman, 1911, which was described from and is apparently restricted to the río Iguazú basin.
p. 823: Only two species belonging to the genus Imparfinis were previously recorded from freshwater in Argentina: Imparfinis hollandi and I. cochabambae (cited by Castello et al., 1978 as Pimelodella cochabambae). …
The single specimen examined by Castello et al (1978) that was identified as Pimelodella cochabambae (MACN-Ict 6971) appears to be neither I. mishky nor I. cochabambae
Thus, although we were unable to assign this specimen to any named species of Imparfinis, it appears not to be I. cochabambae. Therefore, following Bockmann & Guazzelli (2003), the presence of I. cochabambae in freshwater environments of Argentina has not been established.