Comparative cytogenetics among allopatric populations of the fish, Hoplias malabaricus. Cytotypes with 2n = 42 chromosomes.

The available chromosomal data on Hoplias malabaricus make possible the identification of three major karyotypic forms in this fish group, all of them bearing 2n = 42 chromosomes, and named as Cytotypes A, B and E in previous studies. While Cytotype A and B share a general macrokaryotypic feature, Cytotype E is well differentiated concerning the morphology and size of some chromosome pairs. On the other hand, Cytotype B presents an exclusive XX/XY sex chromosome system. Six allopatric populations, belonging to Cytotype A, were subjected to cytogenetic analysis in the present study. Despite their basic karyotypic similarity, some differences in the chromosome formulae, as well as in the heterochromatin and Ag-NORs locations, were observed among populations indicating that they no more correspond to a unit, at least in the cytogenetical level.