This study provides new insight into the chromosomal diversification in Loricariinae. We analyzed nine species from different Brazilian hydrographic basins, using conventional and molecular cytogenetic methods, aiming to understand the karyotypic diversification, and contribute with cytotaxonomic markers in this group considered one of the most diverse of Loricariidae. Our results evidenced a high karyotypic variability in diploid number (2n) ranging from 2n = 54 (Loricariichthys platymetopon and Loricariichthys anus), 2n = 60 (Rineloricaria reisi and Rineloricaria parva), 2n = 62 (Proloricaria prolixa), 2n = 64 (Loricaria cataphracta complex species), 2n = 66 (Sturisoma barbatum), and 2n = 68 (Pyxiloricaria menezesi). Different patterns of 18S and 5S ribosomal DNA (rDNA) were also identified, while slight divergences in heterochromatin distribution were observed. This high variability is probably related with independent events of Robertsonian translocations, pericentric inversions, and different mechanisms of rDNA sites dispersion (nonreciprocal translocation and transposable element [TEs] co-localization). In addition, our study provides a set of efficient chromosomal markers for the characterization of all analyzed species, and certainly, in future analyzes, will contribute as a useful cytotaxonomic tool in groups where the traditional taxonomy based on morphological data are not sufficient to clarify their relationship.

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