A biodiversity approach in the neotropical Erythrinidae fish, Hoplias malabaricus. Karyotypic survey, geographic distribution of cytotypes and cytotaxonomic considerations

Hoplias malabaricus, a widely distributed neotropical freshwater fish, show s a conspicuous karyotypic diversification. An overview of this diversity i s presented here comprising several Brazilian populations, and some others from Argentina, Uruguay and Surinam. Seven general cytotypes are clearly id entified on the basis of their diploid number (2n=39 to 2n=42), chromosomal morphology and sex chromosome systems, which can be clustered into two maj or karyotypic groups. This clustering suggests that karyotype structure wou ld be more informative than the diploid number regarding cytotype relations hips in this fish group. While some cytotypes show a wide geographical dist ribution, some others appear to be endemic to specific hydrographic basins. Sympatric cytotypes can occur without detection of hybrid forms; this situ ation points to a lack of gene flow, a fact that is also reinforced by stud ies with genomic markers. The karyotypic data support the view that the nom inal taxon H. malabaricus corresponds to a species complex comprising disti nct evolutionary units, each with well-established chromosomal differences.