ABSTRACT
This chapter reviews the results obtained so far with fishes from the Neotropical region. According to available data on marine Neotropical fishes, the karyotypic formulae are known for most of the species analyzed. A general analysis of the available cytogenetic data clearly indicates that these studies are mainly concentrated in freshwater Neotropical fishes. This chapter reviews the results obtained so far with fishes from the Neotropical region. The order Characiformes represents a wide fish group distributed in the tropical and Neotropical regions. The order Siluriformes is worldwide distributed but a large number of families is endemic of the Neotropical regions. The studies have provided valuable information for the understanding of the relationship between groups, the occurrence of cryptic species and species complexes, the mechanism of sex determination and sex chromosome evolution, nucleolus organizer regions distribution, supernumerary chromosomes and the relationship of polyploidy and evolution.
