The Tetraodontiformes are one of the main irradiation lineages of Teleosts representing a highly specialized
group. Among its families, Tetraodontidae has the lowest DNA/cell content of the vertebrates, and for this
reason has been used as a model group for genomic evolution studies. Seeking to widen the cytogenetic
database of this family, we performed a chromosomal analysis of the species Canthigaster figueiredoi using
conventional staining, Ag-NORs, C-banding, base-specific fluorochromes DAPI-CMA3, and in situ hybridization
with 18 S rDNA probe. This species has 2n=36 (10 m+6sm+20a; FN=52). Multiple Ag-NORs
(CMA3+) sites were detected on the four chromosome pairs. Heterochromatic blocks (CMA3
+) were present in the centromeric regions of most of the pairs, extending on the short arm of some chromosomes. A GCpositive polymorphic heterochromatic region was identified in some of the individuals, in one or both of the
homologs of the 6th pair. The presence of heteromorphic B microchromosomes was detected in the
karyotype of one female, exhibiting intra-individual variation of 0–3 Bs. The occurrence of heterochromatic
polymorphisms, multiple NORs, and B chromosomes in C. figueiredoi are very infrequent events in marine
fish. They are probably associated to the accentuated restructuring and genomic reduction suffered by this
family.