D-Glutamate, a novel d-amino acid found in animal tissues, exclusively exists in the male reproductive tissues of the kuruma prawn, Marsupenaeus japonicus. Herein, changes in the d-glutamate content were determined in the male reproductive tissues of M. japonicus during acclimation to breeding seawater temperatures of 18-22°C and unilateral eyestalk ablation. The d-glutamate content in the testis increased with increasing seawater temperature and with unilateral eyestalk ablation. This suggests that both stimulations induced d-glutamate synthesis in the testis. Although the d-alanine content in the testis increased after unilateral eyestalk ablation, it did not change with elevated seawater temperature. Furthermore, we determined the d-glutamate distribution in the M. japonicus spermatophore. This indicates that d-glutamate is crucial in prawn fertilization.