A Discovery of Nucleolar Organizer Regions (NORs) Polymorphism and Karyological Analysis of Smith's Barb, Puntioplites proctozysron (Cypriniformes, Cyprinidae) in Thailand

Abstract

A discovery of nucleolar organizer regions (NORs) polymorphism and karyological analysis in the Smith's barb, Puntioplites proctozysron (Bleeker, 1865) from Nong Khai province, in the northeast of Thailand, were studied. Blood samples were taken from 4 male and 4 female fish. After standard whole blood lymphocytes had been cultured at 27°C for 96 hours in the presence of colchicine, metaphase spreads were performed on microscopic slides and air-dried. Conventional and Ag-NOR staining techniques were applied to stain the chromosome. The results showed that the diploid chromosomes number of P. proctozysron was 2n=50 and the fundamental numbers (NF) of both sexes were 82. The types of autosomes were 4 large metacentric, 8 large submetacentric, 2 large acrocentric, 2 large telocentric, 2 medium metacentric, 6 medium submetacentric, 10 medium acrocentric, 14 medium telocentric and 2 small telocentric chromosomes. No strange size chromosomes related to sex were observed. In addition, the short arm near telomere of chromosome pair 4 showed clearly observable nucleolar organizer regions (NORs). This is the first report on polymorphism of NORs in P. proctozysron. The result showed that a heteromorphism in 1 female had a different size of NORs of chromosome pair 4 (4a4b), while 3 females and 4 males had an equal size of both chromosome pair 4 with a homomorphism (4a4a). The karyotype formula for P. proctozysron is as follows:
2n (diploid) 50=L₄^m+L₈^sm+L₂^a+L₂^t+M₂^m+M₆^sm+M₁₀^a+M₁₄^t+S₂^t