Japanese Freshwater Crab

Japanese endemic species inhabiting mountain streams

Scientific name	Geothelphusa dehaani
English name	Japanese Freshwater Crab
Japanese name	沢蟹
Class	Malacostraca
Order	Decapoda
Family	Potamidae
Genus	Geothelphusa
Species	dehaani
Full length	20-30mm (carapace)
Distribution	Distributed south of Aomori Prefecture.

Japanese Freshwater Crab Characteristics and Morphology

The entire body is reddish dark brown. There are individual and regional differences in body color, with some being lighter brown or blue.
The chelae are milky white, lacking the brownish tint. The surface of the carapace is smooth and reddish dark brown. The legs are strongly reddish.

Male

Males have significantly larger chelae.
The sternal flap (fundoshi) is narrow.

Female

The sternal flap (fundoshi) is wide and roundish.

Japanese Freshwater Crab Ecology

Habitat

Found in clean mountain streams. They mainly inhabit under rocks in the upper to middle reaches of rivers. They cannot live unless the water quality is reasonably clean.

Food

Omnivorous, feeding on insects, earthworms, and plants.

Life Cycle

They breed during the summer and are thought to live for about 10 years.

Japanese Freshwater Crab Photos

Japanese Freshwater Crab Photos are introduced.
Tap the photo to open the detail page.

Japanese Freshwater Crab Behavior

They may venture into the forests near rivers on rainy days or when humidity is high.

Japanese Freshwater Crab Information

How to Eat Geothelphusa dehaani

They can be eaten as tsukudani (simmered in soy sauce) or deep-fried. The author also tried them deep-fried as a child. If fried until crispy, they are quite delicious. If not fried enough, a fishy odor remains.

Japanese Freshwater Crab Found Locations

Minamiasakawa-machi, Hachiōji

This individual was photographed along a forest road near a stream in Minamiasakawa-machi, Hachiōji. It quickly hid under the grass. When I approached the camera for photography, it raised its claws high to threaten me. They can be commonly found in the city if the river is not muddy. Individuals climbing trees have also been found in parks with water features.

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