The arrangement of 6 repetitive DNA sequences in the mitotic and meiotic sex chromosomes of 2 Erythrinidae fish, namely <i>Hoplias malabaricus</i> and <i>Erythrinus</i><i>erythrinus</i>, both with a multiple X₁X₁X₂X₂/X₁X₂Y sex chromosome system, was analyzed using fluorescence in situ hybridization. The distribution patterns of the repetitive sequences were distinct for each species. While some DNA repeats were species-specific, others were present in the sex chromosomes of both species at different locations. These data, together with the different morphological types of sex chromosomes and the distinct chromosomal rearrangements associated with the formation of the neo-Y chromosomes, support the plasticity of sex chromosome differentiation in the Erythrinidae family. Our present data highlight that the sex chromosomes in fish species may follow diverse differentiation patterns, even in the same type of sex chromosome system present in cofamiliar species.