Relationship between hatching rate and the outer egg membranes of the in vitro artificially fertilized eggs of the Japanese mitten crab Eriocheir japonica

This study shows that by removing the outer membranes of the in vitro artificially fertilized eggs of the Japanese mitten crab Eriocheir japonica, the normal zoea hatching rate of the eggs can be raised from 10% up to over 90%. This finding suggests that the normal zoea hatching rate is strongly influenced by the outer egg membranes of the in vitro artificially fertilized eggs. In addition, observations by transmission electron microscopy indicate that the outer egg membranes of the in vitro artificially fertilized eggs are 1.5 to 3 times thicker than those of the naturally spawned eggs. Discussion focuses on the role these thick outer egg membranes play in the normal zoea hatching rate of in vitro artificially fertilized eggs.