Facts on the Mating Habits of the Fanshell

The Fanshell mussel -- scientific name Cyprogenia stegaria -- and its relative, the Western Fanshell mussel or Cyprogenia aberti, are among several endangered North American mussels. Found primarily in rivers and streams of the Ozark Mountain region and the highlands of the Mississippi River area, these mussels face extinction due to factors such as toxic runoff and damming. The life cycle and mating habits of Fanshell mussels also play a role in their declining populations.

  1. Fanshell Mussels: An Endangered Species

    • Fanshell mussels, also called "pearly mussels" for their large green shells and pearly bodies, live in freshwater streams and riverbeds in the central United States. Because adult mussels live for years in the same place, they can be especially vulnerable to the accumulation of toxins from runoff and pollutant dumping. Because their reproductive cycle depends on the presence of host fish such as the slenderhead darter, a decline in the population of those fish limits opportunities for Fanshell mussel larvae to mature.

    Mating Behaviors

    • In order to fertilize a female's eggs, male fanshell mussels must be positioned upstream from her so that the flow carries sperm to the eggs. Fertilized eggs develop in the female's gill tubes into tiny larvae or glochidia, which are later discharged into the water to attach to the gills of a passing host fish. The host fish carries the larvae until they drop off and mature as adults in a new area. Because adult mussels never leave their location, this ensures the wider dispersal of the species.

    Lures and Host Fish

    • Each species of mussel depends on the presence of specific host fish to disperse their larvae. Fanshell mussel glochidae attach only to the slenderhead and fantail darters, as well as the logperch and banded sculpin. To attract a host fish, the female Fanshell fashions a lure resembling a worm from as many as 20,000 unfertilized eggs. When a host fish bites the lure, the larvae clinging to it attach themselves to the fish's gills, where they remain, traveling with the fish and feeding from it until mature enough to drop off in a new location.

    Saving the Fanshell Mussel

    • Because of the severe decline in the population of Fanshell and Western Fanshell mussels, these mollusks remain listed as endangered. Efforts to save them focus on keeping streams and rivers toxin-free and maintaining mussel and fish habitats wherever possible. The Center for Mollusk Conservation in Frankfurt, Kentucky, also provides an environment where pregnant mussels can connect with appropriate host fish to boost the survival rate of the species.