HETEROCHROMATIN DIFFERENTIATION IN THE CHARACID FISH ASTYANAX-SCABRIPINNIS

Chromosomes of a small characid fish, Astyanax scabripinnis, were subm itted to several types of chromosome banding. Three different types of C-band positive heterochromatin were detected: i) minute centromeric and pericentromeric blocks in most of the chromosomes in the complemen t; ii) clearly visible blocks on the short arm of pair No. 18, corresp onding to Ag-NOR sites, and conspicuous fluorescent chromomycin A(3) ( CMA(3)(+)) and mitramycin A (MM(+)), and iii) heterochromatic regions strongly stained with Giemsa after C-banding, which were distamycin A/ 4'-6-diamidine-2-phenylindole (DA/DAPI) and MM/DAPI-, which showed no differentiation by silver nitrate, CMA(3), MM, or DAPI without counter staining. The equilocal distribution of these DA/DAPI(-) heterochromat ins suggests a common origin for these chromosome segments in A. scabr ipinnis.