Crayfish-plague
Guides
Astacidae
Astacid Crayfishes, Freshwater Crayfish
Astacidae is a family of freshwater crayfish comprising four extant genera: Astacus, Austropotamobius, Pontastacus, and Pacifastacus. Members are native to Europe, western Asia, and western North America. The family is distinguished by a gonopore positioned on the coxa of the third pair of walking legs in males (fifth pair in females), a trait shared with all Astacoidea. Several species, particularly Pacifastacus leniusculus (signal crayfish), have become invasive outside their native ranges, carrying crayfish plague (Aphanomyces astaci) that threatens native European populations.
Pacifastacus
Pacific Crayfish
Pacifastacus is a genus of freshwater crayfish endemic to western North America, comprising six species including the widespread signal crayfish (P. leniusculus) and two extinct species. The genus has gained significant conservation attention due to the invasive spread of P. leniusculus in Europe and Japan, where it transmits crayfish plague and displaces native species. Within its native range, several Pacifastacus species face population declines from habitat degradation and competition from invasive crayfishes.
Pacifastacus leniusculus
Signal Crayfish
The signal crayfish is a large North American freshwater crayfish introduced to Europe in the 1960s to replace declining native fisheries. It has become one of the most ecologically impactful invasive decapods in Europe, outcompeting native crayfish and serving as a carrier of crayfish plague (Aphanomyces astaci). The species establishes self-sustaining populations rapidly, with six age cohorts documented within a few years of introduction. It shows sex- and size-specific coloration patterns, with males displaying more saturated and brighter ventral claw surfaces than females, suggesting a role in intraspecific communication.
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