Reproduction of the LAWA Freshwater Mussel|
In the summer when mussels are ready to reproduce, the males merely release sperm into the water, and the females catch what they can. The sperm is siphoned by the female and used to fertilize her eggs internally. Obviously, if they aren't grouped fairly closely, reproduction is hard to achieve. After fertilization, the female then holds up to several thousand eggs at a time in her gills. There they can obtain oxygen and have a place to brood until they develop into glochidia-the larval stage of mussels.
In the late spring or early summer, the glochidia are expelled into the water where they have to fend for themselves. They need to attach themselves to the gills of a host fish within a couple days. Most freshwater mussels team up with only one type of fish. Our northwest species favor salmon and without salmon as hosts, mussels cannot successfully reproduce.
Once the larval mussels attach to the fish, the fish body reacts to cover them with cells-an unconscious action that forms a cyst, where the glochidia remain for two to five weeks (depending on the temperature). Hitchhiking on a fish is a baby mussel's only opportunity to travel and experience more of the world, and traveling this way results in a free ride to a new home. After the mussels change from the larval form and begin to resemble adults, they break out of the cyst and fall to the bottom of Lake Washington nearshorelands where they bury themselves in the bottom and begin to live an independent life. Only one in a million survive to the adult stage, but to offset these low odds, mussels lead a very long reproductive life and produce millions of eggs per year!