B microchromosomes in the family Curimatidae (Characiformes): mitotic and meiotic behavior

In the present work, six curimatid species were analyzed: Cyphocharax voga (Hensel, 1870), C. spilotus (Vari, 1987), C. saladensis (Meinken, 1933), C. modestus (Fernández-Yépez, 1948), Steindachnerina biornata (Braga & Azpelicueta, 1987) and S. insculpta (Fernández-Yépez, 1948) collected from two hydrographic basins. All samples presented 2n=54 meta-submetacentric (m-sm) chromosomes and FN equal to 108, and 1 or 2 B microchromosomes in the mitotic and meiotic cells of the six sampled populations showing inter-and intraindividual variation. The analysis of the meiotic cells in C. saladensis, C. spilotus, and C. voga showed a modal number of 54 chromosomes in the spermatogonial metaphases and 27 bivalents in the pachytene, diplotene, diakinesis and in metaphase I stages, and 27 chromosomes in metaphase II; in C. modestus, S. biornata, and S. insculpta, spermatogonial metaphases with 54 chromosomes and pachytene and metaphase I with 27 bivalents were observed. The B microchromosome was observed as univalent in the spermatogonial metaphase of C. spilotus, in the pachytene stage in the other species, with the exception of C. saladensis, and S. biornata in metaphase I. New occurrences of the B microchromosome in C. voga, C. saladensis and S. biornata were observed, confirming that the presence of this type of chromosome is a striking characteristic of this group of fish.