A First Karyotype Analysis and Chromosomal Characteristic of Nucleolar Organizer Regions (NORs) of Common Sheathfish, Micronema apogon (Siluriformes, Siluridae) in Thailand

Abstract

A first karyotype analysis and chromosomal characteristic of nucleolar organizer regions (NORs) of the common sheathfish, Micronema apogon (Bleeker 1985), from the Chao Praya, Chi, and Song karm basins (3 populations), Thailand, were studied. Kidney cell samples were taken from 10 male and 10 female fish. The mitotic chromosome preparations were conducted by taken directly from kidney, spleen and/or gill cells. Conventional and Ag-NOR staining techniques were applied to stain the chromosomes. The results showed that diploid chromosomes number of M. apogon was 2n=64, and the fundamental numbers (NF) were 108 in both sexes. The chromosome types consist of 10 large metacentric, 12 large submetacentric, 4 large acrocentric, 2 large telocentric, 8 medium metacentric, 8 medium submetacentric, 2 medium acrocentric, 8 medium telocentric and 10 small telocentric chromosomes. No strange size chromosomes related to sex were observed. In chromosome pair 3, the region adjacent to the telomere of the short arm showed clearly observable secondary constriction/NORs. The karyotype formula for M. apogon could be deduced as:
2n (diploid) 64=L₁₀^m+L₁₂^sm+L₄^a+L₂^t+M₈^m+M₈^sm+M₂^a+M₈^t+S₁₀^t