To elucidate the molecular mechanism of oocyte maturation in the kuruma prawn (Marsupenaeus japonicus), subtractive suppressionhybridization (SSH) was initially used to identify novel up-regulated genes during the final stages of oocyte maturation, followed byevaluation of the differential expression profile by macroarray and quantitative real-time RT–PCR analyses. The cathepsin C (dipeptidylpeptidase I) gene was thus found to exhibit a significantly higher expression around the onset of cortical rod (CR) formation (early CR stage,appearance of round CRs), progress to a higher mRNA level until the middle CR stage (elongation of CRs), then rapidly revert to a lowexpression level at the late CR stage (occurrence of germinal vesicle breakdown, GVBD), as also observed at the non-CR stage(previtellogenesis and vitellogenesis). In situ hybridization analyses revealed that the sites of the expression of cathepsin C transcripts in theovary were distributed in both oocyte and follicle cells, particularly at the early CR stage. A full-length cDNA sequence of this stage-specificgene was subsequently determined by rapid amplification of the cDNA 3V and 5V ends (3V and 5V RACE). The deduced amino acid sequenceof the 230-residue mature peptide shared 67–70% identity to the known cathepsin C in mammals. Western blot analysis showed thatexpression of procathepsin C protein was exclusively at CR stages. The storage site of procathepsin C protein was localized in CRs asrevealed by immunohistochemical analysis. This is the first report on the full-length cDNA sequence of cathepsin C and a demonstration ofits involvement in the final stages of oocyte maturation in crustacean species.