System of Multiple Sex Chromosomes in Eigenmannia trilineata Lopez & Castello, 1966 (Sternopygidae, Gymnotiformes) from Iguatemi River Basin, MS, Brazil

The genus Eigenmannia belongs to the family Sternopygidae, a monophyletic group of Neotropical electrogenic fish. Eigenmannia trilineata from Iguatemi River basin were analyzed using classical cytogenetic techniques. Chromosomes of this species of Eigenmannia presented a X1X1X2X2 : X1X2Y sex chromosome system, with 2n=31chromosomes for the males and 2n=32 for the females, where the Y is metacentric chromosome originated from Robertsonian translocation. The NORs are located interstitially on the long arm of chromosome pair 10. Constitutive heterochromatin is distributed in very conspicuous blocks at the juxtacentromeric regions acrocentrics chromosomes in the males and females, including the unique large metacentric neo-Y in the males also presented a juxtacentromeric block. The chromosomal data obtained may be useful for the taxonomy and phylogenetic studies in this fish group.