AbstractA molecular marker for germ cells of the giant freshwater prawn, Macrobrachium rosenbergii, was studied. A vasa‐like gene, Mrvlg, from the ovary was isolated and characterized by a reverse transcriptase‐polymerase chain reaction (RT‐PCR) method. A full‐length sequence was obtained by the rapid amplification of cDNA end (RACE) method. Analysis of the nucleotide sequence revealed that Mrvlg comprises 2,686 bps with an open reading frame of 2,130 bps encoding 710 amino acids. The deduced amino acid sequence contains four arginine–glycine–glycine motifs and eight conserved motifs belonging to the DEAD‐box protein family. The MrVLG sequence shows high similarity to Vasa homologue of zebrafish (73%). In the adult tissues, the Mrvlg transcripts were specifically detected in the germ cells. In situ hybridization analysis showed that Mrvlg RNA was detected in the cytoplasm of oogonia, previtellogenic, and vitellogenic oocytes and was also detected in the nucleoplasm of mature oocytes. In the testis, the Mrvlg transcript was detected in the cytoplasm of spermatogonia and primary spermatocytes but was detected in the nuclei of secondary spermatocytes and sperm. Sequence similarity and specific localization in the germ cells suggest that Mrvlg is the prawn vasa homologue of the Drosophila gene and can be used as a molecular marker for prawn germ cells. Mol. Reprod. Dev. 74: 835–842, 2007. © 2006 Wiley‐Liss, Inc.