TankBud

Sawagani

Geothelphusa dehaani

Also known as Japanese freshwater crab, Japanese dwarf warrior crab, Sawagani crab

FreshwaterCrab

Sawagani (Geothelphusa dehaani)
Apple2000 · CC BY 3.0

Care at a glance

Temperature
41–75°F
5–24°C
pH
6.5–8.0
Adult size
1.2 in
3 cm
Minimum tank
11 gal
40 L
Temperament
Mostly peaceful
Social behavior
Solitary
Own kind
One male per tank
Tankmates
With caution
Swim level
Bottom
Diet
Omnivore
Difficulty
Medium
Breeding
Egg carrier · Medium
Rarity
Very rare
Family
Potamidae
Origin
Japan, from Aomori in northern Honshu to the northern Ryukyu Islands

Overview

The Sawagani is a nocturnal freshwater crab from Japanese streams that hides by day. It needs a cool-water tank and is a step up from the easiest crabs.

Did you know

The Sawagani is also a bar snack. In Japan the little crabs are deep fried whole and served crunchy at izakaya. The same clean-stream crab is used as a sign that a river's water is still in good shape.

Caring for the Sawagani

Give a Sawagani a tank of at least 11 gal (40 L), with sand and a pile of rocks to hide under. It is amphibious, so add a rock or piece of wood that breaks the surface for it to climb out on. The lid must be tight, because it climbs out of the tank and wanders if it can.

Above all else, keep the water cool and clean. A Sawagani weakens above the mid 20s C, and 30°C kills it. It is a crab for an unheated room, a fan or a chiller, at 41 to 75°F (5 to 24°C). It is not fussy about pH within 6.5 to 8.0, but it needs strong filtration and plenty of oxygen.

The Sawagani is an omnivore. In the wild it eats insects, worms, snails and leaf litter, so feed it sinking pellets, frozen bloodworm, blanched vegetables and dead leaves. Leave cuttlebone in the water for the molt.

It will catch dwarf shrimp and small fish resting on the bottom, and crabs fight. Keep one, or one male with a female or two in a large, rock-filled tank.

It develops directly. The female carries about 50 large eggs under her abdomen in summer, and they hatch as tiny finished crabs. There is no larval stage and no need for the sea.

Good to know

The Sawagani, Geothelphusa dehaani, is also called the Japanese freshwater crab, and it belongs to the family Potamidae. It comes in three color forms, red brown, dark purple and gray blue. They only partly line up with the genetic populations found in a 2025 genome-wide SNP study. It is thought to live about ten years and hibernates under water through the winter. A 2024 revision by Naruse and Ng split two new species out of it. Trade animals labeled dehaani are really a species complex. The IUCN lists it as Least Concern.

In the wild

Sawagani live in Japan, from Aomori in northern Honshu to the northern Ryukyu Islands. They hide under rocks in the clean, cool upper and middle reaches of streams. Their streams stay around 20°C even in high summer. On rainy days they walk out onto the wet forest floor.

Common questions

What size tank does a Sawagani need?

A Sawagani needs at least 11 gal (40 L). It spends most of its time in the bottom.

What temperature and pH does a Sawagani need?

A Sawagani is comfortable at 41–75°F (5–24°C) with a pH of 6.5–8.0.

What does a Sawagani eat?

A Sawagani is an omnivore that eats insects, worms, snails and leaf litter in the wild. In a tank, feed it sinking pellets, frozen bloodworm, blanched vegetables and dead leaves.

How big does a Sawagani get?

An adult Sawagani reaches about 1.2 in (3 cm).

How does a Sawagani breed?

A female Sawagani carries about 50 large eggs under her abdomen in summer. They hatch as tiny finished crabs, with no larval stage and no need for the sea.

Related species