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Abstract
Among the great marine fish diversity, the Order Tetraodontiformes is remarkable by presenting post-Perciformes modern features, representing one of the major branches of the teleosteans radiation. Patterns of chromosomal evolution in this group are not fully understood. In the present work, cytogenetical analyses were carried out in the species Balistes vetula (2n=44; FN=44) and Melichthys niger (2n=40 and FN=40) (Balistidae), Chilomycterus antennatus (2n=52; 6M+46st/a, FN=58) (Diodontidae) and Sphoeroides testudineus (2n=46; 18m+4sm+6st+18a, FN=74) (Tetraodontidae), collected along the Brazilian coast and Saint Pauls Rocks. All species presented Ag-NORs sites on a single chromosomal pair. Heterochromatic regions in this group are reduced and located at centromeric position over most of chromosomal pairs. The evolutionary patterns of chromosomal changes were diverse in the distinct Tetraodontiformes families. In Balistidae, the evolution process seems to be determined by in tandem or centric fusions, followed by pericentric inversions. The higher chromosomal number in Diodontidae indicates that centric fissions and pericentric inversions played an important role in the karyotypi-cal definition of this group. The Tetraodontidae S. testudineus displayed small chromosomes with a modal number shared with other species previously analyzed from this family. Such great karyotypical diversity is compatible with a scenario of several modifications established by the adaptative irradiation of this group.
