To investigate the characters of repetitive DNA sequence in the sex chromosomes of the spiny eel （Mastacembelus aculeatus）, the X chromosomal library was screened and a family of repetitive sequence, consisting of Ma 1-Ma 6, was isolated. The fluorescence in situ hybridization （FISH） result confirmed that Ma 1- Ma 5 dispersed over sex chromosomes and all autosomes, whereas, Ma 6 is sex chromosome-specific and distributed only on the C-band positive regions of X chromosome, and Ma 6 maybe the main components of the heterochromatic regions of X chromosome. This study provides additional information about the evolution of sex chromosomes in lower vertebrates such as fish.
