Freshwater Pearl Mussel

• The oldest documented individual, in a river in northern Sweden, was 280 years old, which makes it one of the longest-lived animals on the planet.
• It is listed as Endangered globally and Critically Endangered in Europe.
• A female can release several million glochidia, of which a minute fraction survive.
• Most European natural freshwater pearls come from this species, and the historical harvest contributed to its decline.
• It can live for more than 250 years, which makes it one of the longest-lived freshwater invertebrates in the world.
• Its life cycle depends on salmon and trout. The larvae, called glochidia, have to attach themselves to the gills of a salmonid and spend several months there before dropping to the riverbed and burying themselves. Without the fish, there is no mussel.
• That chains its conservation to that of salmon rivers: the disappearance of salmonids cuts off its reproduction even if the adults remain alive, which is why there are entire populations of old individuals that have gone decades without recruiting young.
• It filters enormous quantities of water and its presence improves the quality of the watercourse, so it acts as an engineer of the river ecosystem.
• Its pearls were highly prized and were exploited for centuries in Scotland, Scandinavia and Spain; historical harvesting is one of the causes of its decline, together with pollution and the regulation of rivers.
• Its European population has fallen by more than 90% in the last century, and it is protected under the Habitats Directive.

Skeleton type

Invertebrate - external calcareous shell (mollusc)

Habitat & environment

Clean, cold, lime-poor rivers and streams with a gravel bed

Sexual maturity

12-20 years

Gestation / incubation

9-12 months (glochidium stage on the host fish)

Litter / clutch size

Up to 4 million glochidia per female and season

Sources consulted: Lista Roja de la UICN; Geist (2010), Hydrobiologia; Directiva Hábitats de la UE; Ministerio para la Transición Ecológica de España