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signal crayfish
The signal crayfish, ''Pacifastacus leniusculus'', is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the Scandinavian ''Astacus astacus'' fisheries, which were being damaged by crayfish plague, but the imports turned out to be a carrier of that disease. The signal crayfish is now considered an invasive species across Europe and Japan, ousting native species there.
==Description and ecology==
Members of this species are typically long, although sizes up to are possible.〔 They are bluish-brown to reddish-brown in colour with robust, large, smooth claws. They have a white to pale blue-green patch near the claw hinge, like the white flags that signalmen used for directing trains—hence the name.
The life cycle of the signal crayfish is typical for the family Astacidae. Around 200–400 eggs are laid after mating in the autumn, and are carried under the female's tail until they are ready to hatch the following spring.〔 The eggs hatch into juveniles, which pass through three moults before leaving their mother. Sexual maturity is reached after two to three years, and the life span can be up to 20 years.〔
The signal crayfish is an omnivore, with most of its dietary intake being detritus.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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