The breeding of black-lipped pearl oysters (Pinctada margaritifera) on hanging nets requires about 4 years and a lot of care and attention : two years of growth until the grafting plus another two years for the mother-of-pearl to enclose the ball and produce a pearl. The same oyster can be grafted several times over a decade but the success rate remains low : only 5% of the grafted oysters produce quality round pearls.