Japanese Freshwater Crab

Japanese Freshwater Crab key facts

Care level

Beginner-friendly

Lifespan

Several years up to about 10

Size

20-30mm carapace width

Diet

Algae, aquatic and terrestrial insects, worms and vegetables

Tank

Use a sand substrate with rocks and a dry area the crab can climb out onto. It hides under stones by day, so it needs spaces to creep into. It is territorial, so provide more refuges than crabs, and fit a lid because it escapes.

Water Temperature & Quality

It lives in clean upper-stream water and indexes the cleanest water class. It is considered fairly easy to keep provided the water stays cool and clean.

Tank Mates

Territorial, and squabbles are common when several are kept together. Freshly moulted individuals are at risk of cannibalism, so provide ample cover. Being omnivorous it will catch small fish and shrimp, so it is not a community animal.

Diet & Feeding

An omnivore taking algae, aquatic and terrestrial insects, snails and worms. In captivity worms and cabbage suit it well. Remove anything uneaten, which quickly fouls the water.

Breeding & Spawning

Mating runs from spring into early summer, and the female carries several dozen unusually large eggs of about 2mm on her pleopods, far fewer than other crabs lay. The larvae metamorphose inside the egg and hatch as crabs, and the young shelter under the mother for a while.

Health & Notes

It is an intermediate host for dangerous parasites including lung flukes, so it must be thoroughly cooked if eaten, and hands should be washed after handling. Local populations are genetically distinct, so never release collected crabs anywhere but where they were found.

About Japanese Freshwater Crab

A care guide for the sawagani (Japanese freshwater crab), a small native species with a 20–30mm carapace, dark brown shell, and vermilion legs. It favors clean, cool water and suits first-time keepers.

7 things to know before welcoming a Japanese Freshwater Crab

1. 1Clean Water Is Essential

   Sawagani are sensitive enough to serve as an indicator species for Japan's cleanest water grade, Water Quality Class I. They're easily affected by ammonia and other pollutants, so frequent water changes and reliable filtration are essential. Poor water quality can quickly affect their health.

2. 2Keep Water Cool

   As natives of mountain streams and rural waterways, sawagani need cool water and cleanliness to thrive. Be especially careful of temperature spikes in summer, and place the tank somewhere cool and out of direct sunlight.

3. 3Secure the Lid Well

   Crabs are strong climbers and can escape by scaling tank walls or squeezing through gaps around equipment. Use a tightly fitting lid and seal any gaps around cords or filter tubing to keep them safely inside.

4. 4Provide a Land Area

   Sawagani spend a good deal of time out of the water, not just submerged. Arrange driftwood or rocks so they can climb completely out of the water onto dry land.

5. 5They Grow by Molting

   As crustaceans, sawagani grow by repeatedly molting their shells. Right after molting, their new shell is soft and they're vulnerable, so provide hiding spots and keep them separated from other individuals during this time.

6. 6Best Kept Solitary

   Sawagani are territorial, and housing multiple crabs together can lead to fighting, with weaker individuals sometimes attacked. If keeping several, provide plenty of hiding spots, or ideally house them individually.

7. 7Easy Omnivorous Diet

   Sawagani are omnivores that will eat everything from prepared pellets to vegetable scraps and protein-rich foods. Leftover food can foul the water, so offer small amounts they can finish quickly.

Frequently asked questions about Japanese Freshwater Crab

Q.Does a sawagani ever need salt water?

A.No, the sawagani is a Japan-native species that spends its entire life in fresh water. You can keep it in a freshwater setup only, with no need for salt water at any stage.

Q.How big does a sawagani get?

A.Even as an adult, it stays small, with a carapace width of about 20 to 30mm — small enough to fit in the palm of your hand. This compact size makes it easy to keep in a limited amount of space.

Q.Can it be kept with fish or shrimp?

A.Not well. Sawagani are omnivores and will catch and eat small fish or shrimp, so they are not suited to community tanks. It is best to keep them separate from fish and shrimp.

Q.Can it escape from the tank?

A.Yes, crabs are capable climbers and can escape by scaling the tank walls or wiring. A tightly fitting, gap-free lid is the best way to prevent this.

Q.How long do sawagani live?

A.Their lifespan ranges from several years up to about a decade, making them a relatively long-term companion. Maintaining proper water quality and temperature is key to helping them live a full life.

Useful tools for Japanese Freshwater Crab care

Learn more about Japanese Freshwater Crab in the encyclopedia

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