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 Japanese Marsh Crab Factoids

Origin

Widespread in Japan -- one of two Japanese freshwater crabs.

Maximum Size

Usually under an inch

Longevity

Probably 1.5 to 2 years

Housing

About a square foot

Security

All crabs like nooks and crannies

Temperature

Room temp fine

Attitude

Active climbers.  Fairly slow moving.

Foods

Beach-combing scavengers.  Not picky.

Reproduction Female gives birth to fully developed young -- not zygotes.
Other Info Served in some sushi restaurants

Water

Plain water with maybe a "pinch" of salt.  They like clean water.

Threats Climbing out and drying up.  Shore birds in the wild.

LA
He's facing away from you while looking directly at you.  Eery looking eyeballs.

Origins.  Apparently these tiny (under an inch) crabs grow all over the islands of Japan.  We got ours out of Chicago.  They called them Mandarin crabs, an obvious misnomer for a crab from Nippon.  They also called them Geosesarma aristocrateseosis, anothe misnomer.  Anyways (as the kids say), when we see a new critter on our availability lists, we have to have one or six to see exactly what they are and what they do.

Japan Info.  Japanese marsh crabs are called sawagani in Japan -- sawa = marsh plus gani=crab.  They are popular in sushi restaurants (lightly fried in oil).  We couldn't sell them at the Iowa State Fair because they're too small to fit on a stick.  A U.S. Geological Survey found a colony in Las Vegas, NV.  They attributed their introduction to a local sushi restaurant.

Reproduction Info.  Most female crabs produce incredible numbers of tiny nauplii that float among the other tiny critters that inhabit the plankton layer of the ocean.  Japanese marsh crabs change sex during their lifetime.  Females then give birth to fully developed baby crabs. 

LA
Here's looking at you, kid.

Attitude.  Most crabs of any size assume a pugilistic stance -- fists (or in their cases, pincers) up and ready to fend off all adversaries.  These little Japanese marsh crabs usually face the other way and retreat if at all possible.  Meanwhile, they're looking right at you.

LA
Pictured here for size.  Facing away and looking right at you.

LA
He managed to shag his way out fairly quickly.

Climbers.  When our "mandarin crabs" first arrived, I put them in a small aquarium mostly full of water and continued putting away several other boxes of fish.  Looking at them 20 minutes later, I saw one was clinging to the top lip of his aquarium -- several inches above the water level.  He had climbed up the aquarium sealer that held the sides together.  At this point, I decided they were land crabs (like most other freshwater crabs) and changed their crabitat.

LA
We started them on Tetra's color crisps, mostly because they sink.  They very delicately dined upon them.

LA
Next day, they turned up their non-existent noses at this recently deceased goldfish.

LA
Patriot Crabs, on the other hand, relish deceased goldfish.

Japanese Marsh Crab Foods.  Most crabs do not subscribe to the Epicurean Gazette.  They pretty much eat whatever they can find..  Probably any fish food will suffice.  HBH makes a Crab Bites food, but most crabs will eat anything.  Since these little guys don't eat much, be careful not to overfeed your Japanese marsh crabs.  The next day they ate small cichlid pellets.

LA
Careful how you grab red claw crabs.  They'll grab you back (hard) if they can reach you.

Compare and Contrast.  Japanese marsh crabs look like a mini-version of the red claw (often called red Thai crabs).  You could probably treat them the same.  Don't mix them tho.  The larger red claws consider Japanese food delicious.  An aside: red claws are considerably cheaper and much easier to find.  Speaking of delicious, deep-fried Japanese marsh crabs are considered delicious by some gourmets -- not so much in Des Moines.

LA
Here's one Japanese marsh crab facing forward.  Just a trace of water here.

Water Conditions.  Any critter with an exoskeleton will prefer harder water -- not a problem in Des Moines.  Aged tap water works great.  We like to add a bit of salt to most crustacean tanks.  You need not worry much about pH.  Hard water prefers to stay on the alkaline side.  Just make sure you keep their water clean.


LA
They're so little they're hard to turn over.

LA
Much easier to turn over when they die.  Females have wider tails.

Sexing Japanese Marsh Crabs.  You're not likely to breed your Japanese marsh crabs.  Go to Mini-Crabs for a way to sex crabs.  By the way, crabs are similar in needs and actions to shrimp.  Both are little scavengers.  Crabs differ mostly in the way their tails fold under.  Shrimp sport long flexible tails that enable them to swim backwards rapidly -- much like our crayfish.  Just remember that your male Japanese marsh crab will turn into a female Japanese marsh crab.

LA
You can pick one of these little guys up with one finger.

How to Pick up a Japanese Marsh Crab.  Fear not these little guys.  One might pinch you, but they'd rather avoid you than clamp on.  They rarely pinch.  And they're not big enough to hurt or run away fast.

LA
Cool eyes.

Not Hiders.  Most crabs flinch (kind of duck down or rare up to fight) when approached by humans.  Japanese marsh crabs mostly ignore human activity.  They accept hand feeding from day one.  Just move slowly.

LA
No substrate at all works also.  About a half-inch of water here.  This container also has a snap-on lid.

Substrate.  White sand has some disadvantages, but it really shows off your crabs.  In any event, they pretty much disappear over red, orange, or brown.  Bare habitats work fine and clean more easily.

LA
They like these little sponges made for hermit crabs.  They'll climb on anything.

Container.  Keep well covered.  Japenese marsh crabs insist on climbing out.  They also like access to air every so often.  Within 15 minutes of housing a brace of them in a foot high tank, one of them had made his way to the top and was hanging on the lip of the tank.  He had climbed up the sealer in the corner.  They will bail on you.

LA
Cute little devils with weird eyes.

LA

LA
Just a little larger than a dime.

LA

Last Words.  Crabby people will like these guys.  Just remember, they are very small  LA


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