**4. Conclusion**

As noted above, Cd exhibits biochemical and physiological toxicity for crabs and shrimps, affecting on activity of antioxidant enzymes, affecting metabolic enzymes, affecting Na+- K+-ATPase, etc. In some cases, Cd had a stimulating action at low concentration and inhibiting activity at high concentration.

Cd showed noticeable effects on the reproduction of crabs and shrimps. 1. Female crabs exposed to 0.50 mg/L Cd showed significantly (*P <* 0.05) lower the gonadal somatic index, oocyte diameter values and the ovary vitellin than controls. These proved certain concentration of Cd inhibited ovary development in *E. sinensis*. 2. Cd stimulated the secretion of GIH, increased progesterone level and decreased estradiol level in haemolymp. 3. The vesicles of the endoplamic reticulum became swelled and dissolved; ribosomes on the endoplamic reticulum gradually fell off by Cd toxicity. 4. Cd restrained the proliferation of isolated spermatogenic cells from *M. nipponense* at dose of 50, 500, 1 000 ng/mL after 24 h exposure.
