Cytogenetic characterization of B chromosomes in two populations of Iheringichthys labrosus (Pisces, Pimelodidae) from the Capivara Reservoir (Parana, Brazil)

摘要

This study presents karyotype findings for Iheringichthys labrosus from two different municipalities near the Capivara Reservoir in Brazil. The 25 individuals studied showed a chromosome number of 2n=56, with a chromosome formula of 26 metacentrics M + 12 submetacentrics (SM) + 6 subtelocentrics (ST) + 12 acrocentrics (A). Eighteen of these specimens studied showed the presence of a B microchromosome, with inter and intraindividual variation. By use of the C-banding technique, this B microchromosome was found to be completely heterochromatic and the other chromosomes of the complement showed the presence of heterochromatin preferentially at the telomeres. The fluorochrome chromomycin A(3) (CMA(3)) produced fluorescent staining in some chromosomes of the normal complement, but not in the B chromosome. Meiotic analysis demonstrated in metaphase I the presence of 28 bivalents and one small univalent probably corresponding to the B microchromosome.