The book depicts, the effect of cadmium on spermatogenesis at two different exposures (15 and 30 days) in mature male prawn Macrobrachium rosenbergii. Assessment of sperm count and sperm length as directly indicated with sperm quality. Interestingly, the sperm count and sperm length also decreased in treated groups when compared to control. Biochemical parameters are the best indicators of stress situations caused by cadmium. The amount of protein and lipid content decreased in the testis, hepatopancreas and hemolymph of treated groups compared to controls. The histology of gills, hepatopancreas and testis treated with cadmium at 30 days exposure show lamella hypotrophy, lamellar fusion, Cuticular layer also destroyed and irregular arrangement of epithelial cells is seen in treated gills. Hepatopancreas showed reduced tubule structure, abnormal lumen, and fusion of hepatocytes in treated groups. Testis showed reduction in the diameter of semniferous tubule and decrease in the number of sperms. The present investigation clearly showed that the cadmium possibly affect the neuro endocrine system which in turn affect the process of spermatogenesis in Macrobrachium rosenbergii.