Cytogenetic characterization of the North American white sturgeon Acipenser transmontanus (Pisces, Acipenseridae)

Sola L. Cordisco C. Bressanello S. Cataudella S.

Chromosome number of A. transmontanus was found to be around 240 (range 226-288) and about half of the chromosomes are microchromosomes (range 116-199). After C-banding some (one to seven) small size macrochromosomes have been found entirely heterochromatic, so that they can probably be considered as B-chromosomes, i.e., supernumerary chromosomes. However, after Ag-staining, at least one of these, a small metacentric, was found to carry NORs on the telomeric region of both arms. Up to five AgNORs per cell were observed on small size macrochromosomes and on microchromosomes. NORs were never observed CMA3-positive. The heterochromatin shows a centromeric and subcentromeric distribution, and no corresponding AT- or Go-rich DNA fluorescent signals can be detected except for one CMA3-positive heterochromatic band on the subcentromeric region of one chromosome pair, numbered 33. This region was never observed Ay-positive. Ag- and CMA3-staining reactions of NORs lead to hypothesise a different organisation of ribosomal cistrons in A. transmontanus compared to Teleosts.