Biochemical and morphological changes in the chorion of the carp cyprinus carpio oocyte following the cortical reaction

Summary Following oviposition and/or fertilization in fieshwater, the soft vitelline membrane surrounding the carp oocyte elevates and becomes tough (fertilization envelope). We have studied the biochemical (protease digestion) and morphological (analysis scanning electron microscopy) changes associated with this transformation. The vitelline envelope is easily digested by most proteolytic enzymes; following elevation, the chorion becomes very resistant to proteolyse. This chorion is much thinner and smoother than the vitelline membrane, but retains a characteristic porous appearance. These results are compared with previous observations obtained by transmission electron microscopy and are discussed in relation to the blockage to polyspermy.