Cytogenetic studies of species of
Rhamdia branneri, R. voulezi and
Rhamdia sp., endemic of the River Iguacu basin, were carried out. Karyotypic analysis resulted in diploid number of 2
n =58 for the 3 species. A variation between 58 to 62 chromosomes was observed in
Rhamdia branneri, while in
Rhamdia voulezi and
Rhamdia sp. the number of chromosomes ranged from 58 to 60. These variations were attributed to the presence of B chromosomes. Although the diploid number and karyotypic formulae were similar, differences in number and type of B chromosomes were observed. While in
R. branneri and
R. voulezi were found metacentric B chromosomes, in
Rhamdia sp. was observed an acrocentric B microchromosome. A submetacentric B chromosome found in
R. branneri, was also considered as species-specific marker. The results from C banding analysis and chromomycin A
3 showed that in
R. branneri the metacentric B chromosome was heterochromatic partially and CMA
+3 in telomeric regions, while those in
R. voulezi and
Rhamdia sp. (metacentric and acrocentric, respectively) were euchromatic and CMA
-3. The submetacentric B chromosome of
R. branneri showed C
+ band and CMA
-3 in subterminal region of the long arm. These differences may be considered as a cytotaxonomical characteristic. Silver differential coloration also showed differences :
R. voulezi had simple NOR and
R. branneri and
Rhamdia sp. had a system of multiple NOR.
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