Chromosome characterization of Trichomycterus spegazzini (Siluriformes, Trichomycteridae) from three hydrographic basins of the Northwest of Argentina

Cytogenetic studies involving conventional air drying techniques, Giemsa st aining, constitutive heterochromatin analysis and silver staining were carr ied out on T. spegazzini from three hydrographic basins of the northwest of Argentina. In spite of colour and subtle morphological differencies the th ree populations showed the same karyologycal formulae, 54 biarmed chromosom es, 42 M and 12 SM pairs, NF = 108, with a very conspicuous first metacentr ic 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 metacent ric large chromosome pair (3 degrees o 4 degrees). The species showed a con servative karyotype, with plesiomorphic condition for chromosome number and NOR bands.