Sex Chromosomes in Stephanolepis hispidus (Monacanthidae, Tetraodontiformes)

Abstract

Several systems of sex chromosomes were described in fishes. Some of them are characterized by male heterogamety (XY/XX, X₁X₁X₂X₂/X₁X₂Y, XX/XY₁Y₂), others by female heterogamety (ZZ/ZW, ZZ/ZW₁W₂). In Tetraodontiformes, few multiple sex systems were reported. In the present work, specimens of Stephanolepis hispidus collected along the Bahia and Rio de Janeiro shore were cytogenetically analyzed. All individuals presented a diploid number of 2n=33/34 (NF=34), with 32 acrocentric chromosomes and a large submetacentric unpaired element in males and 34 acrocentric in females. An odder diploid number and the presence of 3 heteromorphic unpaired chromosome observed in the males, were characterized as a multiple sex chromosomal system of the type X₁X₁X₂X₂/X₁X₂Y. Ag-NOR marks were identified on a single chromosomal pair at interstitial position. Heterochromatic blocks were visualized at pericentromeric and centromeric regions. The presence of large chromosomes and a reduced diploid number indicates a chromosomal evolutionary pattern determined by centric fusions, similar to that observed in Balistidae species.