Fanshell


Description and biology

A medium–sized freshwater mussel, the fanshell measures about 3.2 inches (8.1 centimeters) long. Its shell is yellowish–green with fine green lines across the surface. The inside of the shell is gray–white. It feeds on plant material it removes from the water through a tube called a siphon. Muskrats are known predators of this mussel.

The reproductive cycle of the fanshell is complex. In the spring, a male releases sperm that is carried away by stream currents. A female takes in this sperm as she is feeding, and the eggs stored in her gills are fertilized. When the eggs hatch, the glochidia (pronounced glow–KID–ee–a; larval forms of the mussel) develop in the female’s gills.

After a while, the glochidia are released from the gills into the stream and they attach themselves to the gills of a passing fish (those glochidia that do not attach themselves to a host fish sink to the bottom of the stream and die).

The glochidia remain attached to the fish until they begin to develop a shell and are large enough to survive on their own. They detach from the fish and fall to the stream bottom, burying themselves until only their shell margins (edges) and feeding siphons are exposed.

Habitat and current distribution

Populations of breeding fanshells are found in only three locations: in Clinch River in Tennessee and Virginia, in Green River in Kentucky, and in Licking River in Kentucky. Additional populations are scattered throughout eight other rivers, but these fanshells are older and are no longer reproducing.

Like other North American freshwater mussels, fanshells need clean, undisturbed stream habitats. Any silt (mineral particles) or sediment (sand and stones) in the water can pose a serious threat. It can clog their siphons and ultimately kill them.

History and conservation measures

The fanshell was once found in 26 rivers running through 7 states. It has declined in number because of major, harmful changes to its habitat. The construction of dams on rivers and the mining of sand and gravel from river bottoms have combined to destroy much of the fanshell’s habitat.

Pollution has become another serious threat. In Clinch River, coal mining operations and toxic spills from a power plant have killed a considerable number of fish and mussels.

The fanshell will survive only if its remaining habitat is protected.

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