Hatching enzymes Fish hatching enzymes are metallo proteinases belonging to the astacin family.
The eggs of the medaka are surrounded by an egg membrane, the chorion, which consists of a thinner outer and a thicker inner layer and that becomes very tough within few minutes after fertilization. The hatching enzyme is an embryo secreted enzyme, which digests the chorion, allowing the embryo to emerge at the time of hatching. This suggests that these enzymes belong to the astacin family, beeing distinct from sea urchin hatching enzyme, which is similar to collagenase.