Cytogenetic studies involving conventional air drying techniques, Giemsa staining,constitutive heterochromatin analysis and silver staining were carried out onT. spegazzinifrom three hydrographic basins of the northwest of Argentina. In spite of colour and subtle morphological differencies the three populations showed the same karyologycal formulae, 54 biarmed chromosomes, 42 M and 12 SM pairs, NF = 108, with a very conspicuous first metacentric pair. The NORs were located at the terminal region on the short arm on a single submetacentric medium sized pair. The C banding analysis showed the presence of small blocks in pericentromeric position in an single metacentric large chromosome pair (3° o 4°). The species showed a conservative karyotype, with plesiomorphic condition for chromosome number and NOR bands.