Fauna
Invertebrate

Japanese Freshwater Crab

Geothelphusa dehaani

Also known as Sawagani, Sawa Crab, Japanese Mountain Crab

Sawagani spend their lives entirely in cold, oxygen-rich mountain streams, bypassing the free-swimming marine larval stage typical of most crabs. Females carry relatively large, nutrient-rich eggs under their abdomens until miniature juveniles hatch fully formed. Coloration ranges strikingly across regional populations, presenting shades of porcelain blue, rusty red, or mottled olive brown.

NocturnalFreshwaterEndemic
Japanese Freshwater Crab reference1 / 7
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Least ConcernConservation statusIUCN Red List categoriesLCNTVUENCREWEXLeast ConcernRed List categories, explained →
Key facts
Diet & preyAquatic larvae, Fallen leaves, Freshwater snails
Predators
  • Herons
  • Raccoon dogs
  • Giant salamanders
ThreatsWater pollution, stream channelization, deforestation, localized overcollecting
HabitatsClean mountain streams, cold headwater brooks, damp forest floors
Life span3–5 years
Classification
  1. FamilyPotamidae
  2. SpeciesGeothelphusa dehaani
Range & activity
Range data is not available yet.
Safe observation
Interaction riskLow
  1. Low
  2. Moderate
  3. High
  4. Very high
Why interaction risk is low
Safe to observe at a normal distance along shaded stream banks.
Responsible observation
  • Stream Scouting: Look beneath submerged rocks and along mossy banks during humid nights when crabs emerge to forage.
  • Habitat Ethics: Carefully return turned stones to their original positions to protect delicate aquatic microhabitats.
Related species
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