 In early summer each year, around June and July, male freshwater pearl mussels release sperm into the water, where they are inhaled by female mussels.Inside the female, the fertilized eggs develop in a pouch on the gills for several weeks, until temperature or other environmental cues trigger the female to release the larvae into the surrounding water.Once the most abundant bivalve mollusc in ancient rivers around the world, numbers of the freshwater pearl mussel are now declining in all countries and this species is nearly extinct in many areas.