Cytogenetic analysis of Opistognathus macrognathus by conventional Giemsa staining, AgNO3-impregnation
to highlight Nucleolus Organizer Regions (NOR), and C-banding revealed a diploid modal chromosome complement of 2n=40
comprising 2 metacentric, 6 submetacentric, 4 subtelocentric, and 28 acrocentric elements. Sequential silver nitrate impregnation
of selected metaphase spreads carried out to identify congruity of NOR-bearing chromosomes with the same chromosomes
previously stained with Giemsa allowed the identification of a pair of active NOR-bearing chromosomes having positive
signals at the terminal end of the short arm of the largest subtelocentric pair (number 5). C-banding showed small heterochromatic
blocks in the centromeric regions of almost all chromosomes. These results prove that karyotypes differing from the 2n=48
acrocentric arrangement are not uncommon to marine fishes.