NUCLEOLUS ORGANIZER REGIONS AS A MARKER O F ONCORHYNCHUS-MASOU (BREVOORT) MASU SALMON POPULATIONS

Variation in the number of nucleolus organizer regions (NORs) was anal yzed in masu salmon fry belonging to two geographically distant popula tions of the rivers Belaya (southern Sakhalin) and Edinka (northern Pr imor'e). Differences between populations in average number of NORs wer e detected. The number of NORs per cell varied from 1.59 to 2.73 in fi sh from the river Belaya and from 1.36 to 2.30 in fish from the river Edinka; the average number of NORs was 1.96 in females and 2.22 in mal es from the river Belaya and 1.67 in females and 1.76 in males from th e river Edinka. Data obtained in the study suggest the possibility of employing Ag-NOR staining for karyological differentiation between mas u salmon populations.