Cytogenetic analysis of the pufferfish Tetraodon fluviatilis (Osteichthyes).

Because of their compact genome, pufferfish (Tetraodontiformes) have been proposed as a model for the study of the vertebrate genome. The genome of pufferfish is peculiar as it has the structural complexity of the genomes of higher vertebrates, but has small introns and lacks large clusters of highly repetitive sequences. Despite such interest, information about the genetics of pufferfish is still scanty. To fill this gap, we have performed a cytogenetic analysis of the pufferfish, Tetraodon fluviatilis, which can be maintained in an aquarium for a long time and, unlike the pufferfish, Fugu rubripes, it is not difficult to obtain. Karyotype analysis shows that T. fluviatilis has 2n = 42 with two metacentric chromosomes, four submetacentrics, two subtelocentrics and 34 acrocentrics. C-banding, followed by DAPI staining, showed that heterochromatin is essentially AT-rich and is located at centromeres. Staining of the same metaphase plates with CMA3 showed the presence of four heterochromatic regions located on two pairs of submetacentric chromosomes. Silver staining and FISH with a 28S rDNA probe showed that these GC-rich regions are nucleolar organizing regions (NORs). Finally, regardless of the technique used, no difference in the chromosome complement was found between males and females.