Natural triploidy and B chromosomes in Astyanax scabripinnis (Characiformes, Characidae): a new occurrence
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Several cases of natural triploidy have already been described in fish, however this is the first report of a surviving triploid that also carries two different supernumerary chromosomes. Cytogenetic analysis of an Astyanax scabripinnis population revealed a standard karyotype of 2n = 50, with a chromosome formula consisting of: 6 metacentric + 16 submetacentric + 14 subtelocentric + 14 acrocentric chromosomes. In addition, specimens showed a polymorphism for the presence of up to two supernumerary chromosomes. Among the specimens analyzed one was a natural triploid (with 75 chromosomes) that also carried a small sized and a macro-supernumerary chromosome. The co-occurrence of spontaneous triploidy and two supernumerary chromosome indicates the viability of this karyotype constitution as well as this fish capacity of tolerating extra chromosomes in large numbers.