Cytogenetic characterization of hybrids offspring between Colossoma macropomum (Cuvier, 1818) and Piaractus brachypomus (Cuvier, 1817) from Caicara del Orinoco, Venezuela

Conventional karyotype and nucleolar organizer regions (NORs) of C. macropomum x R brachypomus hybrids and parental species are reported. A modal diploid number of 54 chromosomes and a fundamental number (NF) of 108 were found for C. macropomum, R brachypomus and their hybrids. R brachypomus shows a pair of silver stained chromosomes, while cells with three and four Ag-NOR bearing chromosomes were observed in C macropomum. The hybrids consistently presented cells with a single metacentric Ag-NOR bearing chromosome and cells with three Ag-NOR bearing chromosomes. The FISH technique was employed to localize 18S rDNA in the chromosomes of the parentals and the hybrids. In R brachypomus the FIX signals appeared in the SM pair as when stained with silver salts. In C macropomum the signals were evidenced in six chromosomes. In the hybrids, as expected, the FITC dots were observed in four chromosomes. All the techniques employed in the present work represent good tools to identify the parentals and distinguish them of the hybrids.