Cytogenetic analysis of the pufferfish Tetraodon fluviatilis (Osteichthyes)

Because of their compact genome, pufferfish (Tetraodontiformes) have been p roposed as a model for the study of the vertebrate genome. The genome of pu fferfish is peculiar as it has the structural complexity of the genomes of higher vertebrates, but has small introns and lacks large clusters of highl y repetitive sequences. Despite such interest, information about the geneti cs of pufferfish is still scanty. To fill this gap, we have performed a cyt ogenetic analysis of the pufferfish, Tetraodon fluviatilis, which can be ma intained in an aquarium for a long time and, unlike the pufferfish, Fugu ru bripes, it is not difficult to obtain. Karyotype analysis shows that T. flu viatilis has 2n = 42 with two metacentric chromosomes, four submetacentrics , two subtelocentrics and 34 acrocentrics. C-banding, followed by DAPI stai ning, showed that heterochromatin is essentially AT-rich and is located at centromeres. Staining of the same metaphase plates with CMA(3) showed the p resence of four heterochromatic regions located on two pairs of submetacent ric chromosomes. Silver staining and FISH with a 28S rDNA probe showed that these GC-rich regions are nucleolar organizing regions (NORs). Finally, re gardless of the technique used, no difference in the chromosome complement was found between males and females.