An observation of the nucleolar organizer regions (NORs) by the modified stiver stainig methods in Channa maculatus

C. asiatica and C. argus was carried out. They all present only one pair of homologs bearing NORs. The silver-stained NORs were presented as two small dark dots located on the short arms of the subtelocentric chromosome pair (group C). We therefore suggest that chromosomal rearangements in this pair of homologs have not occurred during the process of evolution and in fishes there is generally one or at most

a few pairs of homologs involved in nucleolar organization.An excellent correlation can be found between the number of NORs in the metaphase and the maximum number of nucleoli found in the interphase nucleoli

but the nucleoli are larger than the NORs

this difference was due to the genetic activity of rDNA. Differences in the size of NORs in the homologs and nucleoli in the interphase in Channa asiatica showed a change in transcriptive activity of rDNA during the evolution.