RESUMEN
Beginning with a description of the conventional Giemsa-stained karyotype of the tench (Tinca tinca L.), the structure and variability of the chromosomal heterochromatic regions in this cyprinid species were analyzed by means of C-, silver-, and restriction endonuclease banding. Silver staining revealed active nucleolus organizer regions (NORs) on the secondary constriction of chromosome pair 3. Constitutive heterochromatin was associated with NOR regions detected by C-banding. Restriction endonuclease digestion with AluI, TaqI, and HaeIII induced specific banding patterns that allowed identification of homologous chromosome pairs and revealed features about the sequence composition of several chromosomal heterochromatic regions and of the NOR-associated heterochromatin.